UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

For the fiscal year ended December 31, 2025

or

Commission File Number 001-38942

ARCTURUS THERAPEUTICS HOLDINGS INC.

(Exact name of Registrant as specified in its Charter)

(858) 900-2660

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐ No ☒

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the Registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. Yes ☒ No ☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. ☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ☐

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

The aggregate market value of the common equity held by non-affiliates of the Registrant, based on the closing price of the common stock on The Nasdaq Stock Market on June 30, 2025 was $323.5 million.

As of February 27, 2026, the registrant had 28,423,069 shares of voting common stock outstanding.

Table of Contents

Special Note Regarding Forward-Looking Statements

This Annual Report on Form 10-K, or this Annual Report, and the documents incorporated by reference herein may contain “forward-looking statements” within the meaning of the federal securities laws made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Our actual results could differ materially from those anticipated in these forward-looking statements as a result of various factors, including those set forth below under Part I, Item 1.A, “Risk Factors” in this Annual Report. Except as required by law, we assume no obligation to update these forward-looking statements, whether as a result of new information, future events or otherwise. These statements, which represent our current expectations or beliefs concerning various future events, may contain words such as “may,” “will,” “expect,” “anticipate,” “intend,” “plan,” “believe,” “estimate” or other words indicating future results, though not all forward-looking statements necessarily contain these identifying words. Such statements may include, but are not limited to, statements concerning the following:

These and other forward-looking statements are only current predictions and are subject to known and unknown risks, uncertainties, and other factors that may cause our or our industry’s actual results, levels of activity, performance or achievements to be materially different from those anticipated by the forward-looking statements. In addition, historic results of scientific research, preclinical and clinical trials do not guarantee that future research or trials will suggest the same conclusions, nor that historic results referred to herein will be interpreted the same in light of additional research, preclinical and clinical trial results. The forward-looking statements contained in this Annual Report are subject to risks and uncertainties, including those discussed in our other filings with the United States Securities and Exchange Commission (the “SEC”). Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. Although we currently believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance, or achievements.

References to Arcturus

In this Annual Report on Form 10-K, unless otherwise stated or the context otherwise indicates, references to the “Company,” “Arcturus,” “we,” “our” and “us” mean Arcturus Therapeutics Holdings Inc. and its consolidated subsidiaries from and after the effective time of the Redomiciliation (as defined below in Part I, Item 1. "Business" - "Available Information") and, prior to that time, to our predecessor, Arcturus Therapeutics Ltd.

Trademarks and Tradenames

The Arcturus logo and other trademarks of Arcturus appearing in this Annual Report on Form 10-K are the property of Arcturus. All other trademarks, service marks and trade names in this Annual Report on Form 10-K are the property of their respective owners. Solely for convenience, trademarks and trade names referred to in this report may appear without the ® or ™ symbols.

Market Data, Forecasts, and Other Information

Unless otherwise indicated, information in this Annual Report on Form 10-K concerning economic conditions, our industry, and our markets, including our general expectations and competitive position, market opportunity and market size, is based on a variety of sources, including information from independent industry analysts and publications, as well as our own estimates and research. In addition, certain information included references to third-party publications regarding our business, results of operations, products, and product candidates.

Our estimates are derived from industry and general publications, studies and surveys conducted by third-parties, as well as data from our own internal research. These publications, studies and surveys generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information, and we have not independently verified industry data from such third-party sources. While we believe our internal research is reliable and that our internal estimates are reasonable, such research has not been verified by any independent source and our internal estimates are based on our good faith beliefs as of the respective dates of such estimates. This Annual Report on Form 10-K includes references to and citations of third-party publications. Such publications and related materials are provided for informational purposes only. Neither these publications nor the information contained therein is incorporated by reference into, or deemed to form a part of, this Annual Report on Form 10-K, and we do not adopt or endorse the statements made in such materials.

PART I

Item 1. Business

Overview

We are a messenger RNA medicines company focused on the development of liver and respiratory rare disease therapeutics. We have ongoing Phase 2 clinical studies for our RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF).

We developed the world’s first approved self-amplifying messenger RNA (sa-mRNA) vaccine, KOSTAIVE® (“KOSTAIVE”), which we have partnered with Seqirus, Inc. (“CSL Seqirus”), a part of CSL Limited. KOSTAIVE has achieved approval in Japan, the European Union and the United Kingdom as a vaccine against COVID-19, and sales of KOSTAIVE began in Japan in October 2024.

We have several key platform technologies that we leverage to develop and advance a pipeline of mRNA-based therapeutics for rare genetic disorders with significant unmet medical needs and vaccines for infectious diseases. Current mRNA medicines have two critical components: the messenger RNA (“mRNA”) constructs and the lipid nanoparticles (“LNP”) which help deliver the mRNA to disease-relevant target tissues. We have extensive expertise in the design and optimization of mRNA constructs, including with respect to a type of mRNA technology known as self-amplifying mRNA (sa-mRNA). Our proprietary self-amplifying mRNA technology platform, or STARR® (“STARR”), has been demonstrated to induce a robust, longer-lasting and broader humoral immune response at lower dose levels than conventional mRNA-based vaccines. Our proprietary LNP delivery system, LUNAR® (“LUNAR”), is intended to address the major hurdle in RNA drug development, namely the effective and safe delivery of RNA to disease-relevant target tissues. LUNAR may enable multiple nucleic acid medicines. We also have significant expertise and valuable know-how in the development and scalability of complex and robust manufacturing processes required to deliver the next generation of nucleic acid medicines.

Our internal pipeline includes RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF), both rare diseases. In our vaccine program, we have partnered with CSL Seqirus, one of the world’s leading influenza vaccine providers, on the development and commercialization of mRNA vaccines for COVID-19, influenza and three other infectious diseases. In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing declining COVID-19 disease burden and more onerous U.S. regulatory requirements.

In our CF program, we enrolled and completed dosing in the three initially planned cohorts of our Phase 2 multiple ascending dose study of ARCT-032, confirming the safety and tolerability of ARCT-032 dosed daily for four weeks. This study was initiated in December 2024 and was designed to identify a safe and effective dose regimen in those with Class I (null) CFTR mutations and people with CF who do not benefit from CFTR modulators. In the study, six CF adults with Class I CFTR mutations inhaled 10 mg doses of ARCT-032 daily over 28 days. Interim results released in October 2025 demonstrated that the treatment was generally safe and well tolerated. Treatment-related adverse events (AEs) that were identified in the single-dose Phase 1 study were also observed in some participants for the first few doses but ceased with continued dosing. Bronchospasm has not been reported in this study thus far, neither with nor without albuterol pretreatment. One serious adverse event (SAE) occurred in a participant after the end of the dosing period. The safety review committee found no convincing evidence that the SAE is related to ARCT-032 and approved the study to proceed. We intend to initiate a 12-week safety and preliminary efficacy study in up to 20 CF participants in the first half of 2026, after the third cohort completes treatment. ARCT-032 has received Orphan Drug Designation by the U.S. Food and Drug Administration (the “FDA”) and Orphan Medicinal Product Designation by the European Medicines Agency (the “EMA”) for the treatment of CF, and Rare Pediatric Disease Designation from the FDA.

KOSTAIVE is the brand name approved in Japan and Europe for ARCT-154, which is the version of the sa-mRNA COVID vaccine encoding the ancestral strain of SARS-CoV-2, and also for updated variant-specific versions of this vaccine. We may use KOSTAIVE or the specific internally generated name, such as ARCT-154, ARCT-2301 and ARCT-2303, to identify a version of the vaccine.

In our OTC program, we have continued to conduct a Phase 2 double-blind multiple-dose study of ARCT-810. Five patients with OTC deficiency have now completed dosing, and a sixth patient has initiated dosing. A type C meeting with the FDA to discuss our plans for a proposed future pediatric study under the RDEP (Rare Disease

Evidence Principles) is scheduled for the first half of 2026. ARCT-810 has received Orphan Drug Designation from the FDA and Orphan Medicinal Product Designation from the EMA for treatment of OTC deficiency, as well as Fast Track Designation and Rare Pediatric Disease Designation from the FDA.

Commercial sales of KOSTAIVE began in October 2024 in Japan by Meiji Seika Pharma, Ltd. (“Meiji”), CSL Seqirus’ exclusive partner in Japan, marking the first commercial sales of an Arcturus-developed product. In September 2025, Meiji launched a new presentation of KOSTAIVE in Japan. The product is a 2-dose vial lyophilized presentation incorporating the updated XEC variant strain. Approval for offshore manufacturing of the 2-dose vial lyophilized presentation was granted by Japan in August 2025, followed by approval for onshore manufacturing in January 2026. KOSTAIVE was approved by the European Commission (EC) in February 2025 and by the United Kingdom in January 2026, providing further validation of our platform by additional significant regulatory authorities.

In December 2024, we initiated dosing of an sa-mRNA vaccine candidate against pandemic avian influenza (bird flu) in a Phase 1 trial funded by the Biomedical Advanced Research and Development Authority (“BARDA”). The study results were received in the second half of 2025, indicating a favorable tolerability and safety profile and the ability to induce a robust and durable humoral immune response in young and older adults.

We also improved our platform technologies and advanced our early-stage research activities and manufacturing process development and operations. We conducted exploratory platform development activities, including the evaluation of genome editing, and new targeting approaches, where our LUNAR and STARR platforms could be useful for identification and development of additional products for our portfolio.

Nucleic Acid Medicines and an Introduction to Arcturus’ Platform Technologies

Nucleic Acid Medicines

Nucleic acid medicines have the potential to treat diseases caused by genetic mutations, including diseases that cannot be treated by conventional drugs, such as small molecules and biologics. Some of these medicines function by providing the means for producing a deficient yet vital protein in vivo. Within a cell, DNA carries the blueprint, in the form of genes, which encode critical proteins necessary for life. Each gene’s code is transcribed into a nucleic acid molecule called mRNA, which informs the cell’s own machinery how to organize amino acid building blocks to make one or more proteins needed for normal biological function.

Nucleic acid therapeutics represent a significant advancement in targeted medicines and several of these therapeutics are being developed by public and private companies. The general objectives of these therapies include:

Brief Introduction to our LUNAR and STARR Technology Platforms

LUNAR®

A key challenge for nucleic acid medicines is the safe and effective delivery of the nucleic acid molecule into cells. In addition to enabling uptake of the medicine into cells, the nucleic acid delivery vehicle seeks to protect the nucleic acid from degradation prior to cell entry and to release the nucleic acid payload inside the cell. Arcturus has developed a novel lipid-mediated delivery system called LUNAR. LUNAR is comprised of a mixture of biodegradable synthetic lipids and naturally occurring lipids. Lipids are molecules that contain hydrocarbons and make up the building blocks of the structure and function of living cells. Examples of lipids include fats, oils, waxes and phospholipids. LUNAR is designed to address technical challenges facing the delivery of nucleic acid medicines into cells. We continue to expand our library of proprietary synthetic lipids, known as ATX, to over 300 to date. Our

preclinical studies have shown that formulations can be customized for the indication and target cell type of interest, and we have also demonstrated that our proprietary formulation process is scalable and reproducible. Our LUNAR platform is described in more detail below.

STARR®

Our STARR technology is our proprietary self-amplifying mRNA (or sa-mRNA) technology platform. When combined with a delivery system, such as our lipid-mediated delivery system LUNAR, the STARR technology has the potential to generate a protective immune response or drive therapeutic protein expression to prevent against or treat a variety of diseases. Self-amplifying RNA-based prophylactic vaccines developed with STARR trigger rapid and prolonged antigen expression in host cells, which may provide protective immunity against infectious pathogens. We have shown in clinical trials that combining LUNAR and STARR technologies can reduce dose requirements, deliver a superior immune response, and sustain protein expression compared with conventional RNA-based vaccines, potentially enabling faster production of larger volumes of vaccine doses.

Our Pipeline

Therapeutics

Vaccines

(i) Commercialized in Japan; approved by the European Commission and the United Kingdom

Rare Disease Program

The Orphan Drug Act of 1983 (the “Orphan Drug Act”) defines a rare disease as a disease affecting fewer than 200,000 individuals in the United States. According to the National Institutes of Health (“NIH”), there are approximately 10,000 such diseases that, together, affect nearly 30 million people in the United States. The European Union (the “EU”) defines a rare disease as having a prevalence of fewer than five in 10,000 people. Collectively, these disorders affect between 6% and 7% of the population in the developed world.

There is a pressing need for new medicines for rare diseases as few of the 10,000 known rare diseases have approved treatments. Biopharmaceutical industry researchers are making great progress in the fight against some rare diseases as innovative science has opened new opportunities. More than 770 medicines have been approved by the FDA since the enactment of the Orphan Drug Act and more than 800 medicines are currently in clinical development. Despite recent progress, there is more work to be done to overcome the scientific, operational, and financial challenges that arise.

We believe our technology should provide an excellent platform to address genetically inherited rare diseases. Specifically, we are focusing on developing medicines to treat people with rare respiratory and liver diseases who currently have limited or no treatment options.

Rare Disease Program - LUNAR-CF (Cystic Fibrosis)

The LUNAR-CF program addresses cystic fibrosis (CF) lung disease, a progressive disorder caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. ARCT-032, our lead development candidate for the treatment of CF, uses our LUNAR platform to deliver a codon-optimized CFTR mRNA into airway epithelial cells. This allows airway cells to produce functional human CFTR protein using native translational machinery and protein trafficking pathways which could result in the treatment of the underlying defect

that causes CF lung disease, regardless of the specific mutation. The Cystic Fibrosis Foundation (the “CFF”) has partnered with us to support the development of this therapy. ARCT-032 represents the first LUNAR-based mRNA therapeutic delivered by the inhaled route, offering direct delivery to the affected airways to restore functional CFTR.

There are close to 40,000 children and adults living with CF in the United States (and an estimated 105,000 people have been diagnosed with CF across 94 countries). CF can affect people of every racial and ethnic group. Approximately 800 people are newly diagnosed with CF each year in the United States. CF is caused by more than 2,000 known mutations in the CFTR gene. These mutations have been grouped into several different classes based on the mechanism by which they cause reduction in the production and/or function of the CFTR protein. When CFTR is absent or defective, the airway surfaces become dehydrated and coated with a layer of thick mucus that clogs the airways, causing difficulty breathing and often resulting in chronic infections, exaggerated inflammation, structural airway damage, and other serious complications in the lungs. CF is a multi-system disease that may also affect the pancreas, intestines, liver, sinuses, reproductive tract, and sweat glands. The median predicted survival of CF patients has dramatically improved since the introduction of highly effective CFTR modulators, and is approximately 65 years for those born between 2020-2024 in the United States. However, for those people with CF who are not eligible or otherwise cannot take modulators, the predicted survival remains much lower, and the cause of most of the mortality and morbidity is due to the lung disease.

Current non-curative therapies for CF lung disease are directed towards treating symptoms and preventing the progression of the disease. These treatments include aerosolized mucolytics, antibiotics, and airway clearance techniques that are time-consuming and represent a significant treatment burden for people with CF. Many CF patients ultimately suffer from a critical decline in lung function and require lung transplants.

The FDA has approved several CFTR modulator therapies (Kalydeco®, Orkambi®, Symdeko®, Trikafta®, and Alyftrek®) that assist certain classes of abnormal CFTR protein to reach the cell membrane and/or increase functional ion channel activity. The CFTR modulators, while effective in many patients, are mutation-specific and therefore are not effective in all persons with CF. Other treatments are required to target Class I mutations (no CFTR produced; approximately 10% of CF cases worldwide), and people who are intolerant or have poor response to CFTR modulator therapies. We are initially focusing ARCT-032 on these groups of patients, as they currently have the highest unmet need for CF therapies.

ARCT-032 has received Orphan Drug Designation by the FDA and Orphan Medicinal Product Designation by the EMA. The FDA also granted Rare Pediatric Disease Designation for ARCT-032. The Rare Pediatric Disease Designation is designed to recognize rare pediatric diseases in which the serious or life-threatening manifestations primarily affect patients from birth to 18 years of age. With this designation, if ARCT-032 achieves approval for a pediatric indication in the original rare pediatric disease product application in the United States, Arcturus (or the sponsor of ARCT-032) is eligible to receive a voucher for priority review of a subsequent marketing application for a different product.

In 2023, we successfully completed a safety and tolerability Phase 1 single ascending dose study of ARCT-032 (LUNAR-CF), our mRNA therapeutic candidate for CF. Thirty-two healthy participants (eight subjects in each of four dose cohorts) received a single inhaled dose of ARCT-032. Subsequently, seven CF adults received two administrations of ARCT-032 separated by two days in a Phase 1b study extension.

In the Phase 1/1b clinical study, ARCT-032 was generally safe and well tolerated in both the healthy volunteers and the participants with CF. Of the seven total CF participants in the Phase 1b study, six were being treated with CFTR modulators while one subject had Class I mutations that do not benefit from modulator therapy. No serious or severe adverse events (SAEs) were observed, and the safety profile was similar between healthy volunteers and CF participants. Mild, transient events of elevated temperature or feeling hot accompanied by other nonspecific symptoms were observed at dose levels that are higher than those planned for the Phase 2 study. In the CF subjects, lung function measured over eight days did not demonstrate a discernable pattern or safety concern after two doses of ARCT-032. Preliminary findings from the study were presented at the European CF Society Conference in June 2024 in Glasgow, Scotland, and at the North American CF Conference in September 2024 in Boston, MA.

In December 2024, we initiated dosing in our ARCT-032 Phase 2 multiple ascending dose study designed to identify a safe and effective dose in Class I (null) and other CF participants who do not benefit from CFTR modulators. This study is supported by safety and tolerability data collected in healthy volunteers (N = 32) and the

two-administration Phase 1b study in CF adults. The initial three dose cohorts are fully enrolled, with each participant in the Phase 2 CF study (NCT06747858) receiving daily treatments of ARCT-032 over a period of 28 days.

On October 21, 2025, we announced interim results from the ongoing Phase 2 clinical trial of ARCT-032 for CF. In the second cohort of the study, six Class I CF adults received inhaled 10 mg doses of ARCT-032 daily over 28 days. High-resolution computed tomography (HRCT) lung scans analyzed using FDA 510(k)-cleared AI technology, revealed reductions in mucus burden in four of six Class I CF participants. The treatment was generally safe and well tolerated. Bronchospasm was not reported in these participants, either with or without pretreatment with a bronchodilator. Treatment related AEs that were identified in the single-dose Phase 1 study were also observed in some participants for the first few doses but ceased with continued dosing. One SAE occurred in a participant after the end of the dosing period. The safety review committee found no convincing evidence that the SAE was related to ARCT-032 and approved the study to proceed. The third cohort is ongoing and has enrolled four subjects to determine if there is a different response at 15 mg daily over 28 days and if ARCT-032 continues to be generally safe and well tolerated. A fourth cohort is planned to begin enrollment of up to 20 adults with CF to explore safety, tolerability, and efficacy of ARCT-032 administered for 12 weeks.

In December 2025, we published our preclinical data of the ARCT-032 study. This study demonstrates that LUNAR lipid nanoparticles effectively deliver human CFTR mRNA to airway epithelia, restoring chloride channel function and mucociliary clearance in primary human cystic fibrosis cells and a ferret model of the disease.

Rare Disease Program – ARCT-810 (LUNAR-OTC)

The LUNAR-OTC development program addresses ornithine transcarbamylase (OTC) deficiency, a rare, life-threatening, genetic disease caused by mutations in the OTC gene that lead to dysfunctional or deficient OTC.

OTC deficiency is the most common of the urea cycle disorders, a group of inherited metabolic disorders that are associated with reduced ability to eliminate ammonia from the body. There are over 5,000 people with OTC deficiency in the United States, and the prevalence is approximately one in 14,000 to one in 77,000 people worldwide. Ammonia is a toxic waste product produced from the breakdown of protein. OTC is a critical enzyme in the urea cycle, which takes place in liver cells and converts ammonia to harmless urea which is eliminated by the kidneys. In patients with OTC deficiency, ammonia accumulates in the blood and is toxic to the brain and liver. Symptoms of high ammonia levels include vomiting, headaches, coma and death. OTC deficiency can cause developmental problems, seizures and death in newborn babies. As an X-linked disorder, OTC deficiency tends to be more severe in males, though female carriers are often affected. Patients with less severe symptoms may present later in life, as adults. Currently no cure exists for OTC deficiency apart from liver transplant; however, this treatment comes with significant risks and complications such as organ rejection, and transplant recipients must take immunosuppressant drugs for the rest of their lives. Current standard of care for OTC deficiency is a low-protein diet, dietary supplements, and nitrogen scavengers to try to prevent accumulation of ammonia. Life-threatening episodes of high ammonia levels can still occur, requiring treatment with dialysis or hemofiltration. These treatments do not address the underlying cause of disease, and there remains a high unmet need for an effective treatment.

Our LUNAR-OTC development candidate, ARCT-810, uses our LUNAR platform to deliver normal OTC mRNA into liver cells which then produce normal functioning OTC with possible disease-modifying effects. Our LUNAR-OTC approach has the potential to treat the underlying defect that causes the debilitating symptoms of OTC deficiency, rather than mitigating symptoms by sequestering ammonia. We have retained worldwide development and commercialization rights to ARCT-810.

LUNAR-OTC has received Orphan Drug Designation from the FDA and Orphan Medicinal Product Designation from the EMA for treatment of OTC deficiency. ARCT-810 was also granted Fast Track Designation in and Rare Pediatric Disease Designation (RPDD). Fast Track Designation is designated to facilitate development and expedite review of new therapeutics intended to treat serious or life-threatening conditions that demonstrate the potential to address important unmet medical needs. Rare Pediatric Disease Designation is designed to recognize rare pediatric diseases in which the serious or life-threatening manifestations primarily affect patients from birth to 18 years of age. Due to such designation, if ARCT-810 achieves approval for a pediatric indication in the original rare pediatric disease product application in the United States, Arcturus (or the sponsor of ARCT-810) is eligible to receive a voucher for priority review of a subsequent marketing application for a different product.

Preclinical data in OTC-deficient murine models demonstrated that dosing of LUNAR-OTC results in robust OTC protein expression and activity, thereby improving ureagenesis, reducing plasma ammonia, and increasing survival.

A Phase 1 double-blind, placebo-controlled, dose-escalation study of ARCT-810 in healthy volunteers, completed in November 2020, and demonstrated favorable safety, tolerability and PK profiles.

A single ascending dose, placebo-controlled Phase 1b study in 16 stable mild OTC-deficient adults was completed in the United States in September 2023. The trial assessed safety, tolerability, and pharmacokinetics of a single dose of ARCT-810, and exploratory biomarkers of drug activity. ARCT-810 was generally safe and well tolerated at doses ranging from 0.1- 0.5mg/kg and no serious or severe adverse events were observed. Sporadic infusion-related reactions (IRRs) were managed with symptomatic treatment and appeared to be less frequent with slower infusion rates. In plasma, ARCT-810 mRNA could be detected for up to four weeks, while ionizable lipid was no longer measurable after 48 hours, indicating rapid degradation of the lipid nanoparticle that was utilized to deliver ARCT-810 mRNA. Study results were presented at the Society for Inherited Metabolic Disorders meeting in Charlotte, North Carolina in April 2024 and at the annual symposium for the Society for the Study of Inborn Errors of Metabolism in Porto, Portugal in August 2024.

A Phase 2 double-blind study of ARCT-810 in stable OTC-deficient adolescents and adults in the European Union and the United Kingdom completed dosing of eight subjects in August 2024 at the 0.3 mg/kg dose level. The participants in this group were randomized 3:1 to receive six doses of ARCT-810 or placebo administered every 14 days. Study results were presented at the 6th International Symposium on Urea Cycle Disorders, Kyoto, Japan and International Congress of Inborn Errors of Metabolism, Kyoto, Japan in September, 2025.

In the second quarter of 2024, we expanded the Phase 2 clinical program of ARCT-810 to the U.S. with an open-label, multiple-dose study to evaluate pharmacodynamics and safety in adult and adolescent patients requiring clinical management for OTC-deficiency. The first OTC deficient participant receiving 0.5 mg/kg ARCT-810 initiated dosing in December 2024 in the United States. Each participant is expected to receive five intravenous infusions administered over two months.

On June 30, 2025, we announced positive multiple dosing data of ARCT-810 from two Phase 2 studies: (i) a completed placebo-controlled study in Europe that randomized eight participants to ARCT-810 0.3 mg/kg or placebo; and (ii) an open-label multiple ascending dose study in the U.S., with interim data from the initial three completed participants. Both studies evaluate safety and pharmacodynamics in adult and adolescent patients requiring clinical management for OTC-deficiency. We continue to enroll participants in the U.S. study. Each participant in the U.S. study is expected to receive five intravenous infusions administered over two months.

A Linear Mixed-Effects Model (LMM) was applied as an exploratory analysis to the Phase 2 glutamine and ureagenesis data. LMM is suitable for analyses of small, rare disease trial datasets. In the Phase 2 randomized European study, glutamine levels in patients who received multiple doses of ARCT-810 significantly (p-value = 0.016; LMM) decreased during the dosing period. In the Phase 2 open-label U.S. study, interim analysis of the first three participants showed a sustained and significant (p-value = 0.004; LMM) decrease in glutamine from baseline, reaching normal levels after the first three doses. In the combined analysis of both Phase 2 studies, significantly (p-value = 0.0055; LMM) decreased glutamine levels were observed. The ongoing U.S. Phase 2 open-label study uses a modified and improved 15N-ureagenesis assay (Allegri et al., 2025). The assay measures relative ureagenesis function (RUF) against a normal range established from healthy controls. The assay is not impacted by ammonia scavengers, has low intraindividual variability, and can distinguish between symptomatic and asymptomatic OTC deficient patients. In the first three participants in the ongoing Phase 2 open-label study, RUF statistically (p-value = 0.026, LMM) increased at all post treatment evaluations from a baseline of 29.0% (SD; 9.1%) to 43.7% (SD; 21.7%) at 28 days post-fifth dose. These results suggest a progressive increase of functional OTC enzymes in the liver with continued administrations of ARCT-810. Two of the three participants achieved RUF > 50% indicating a clinically meaningful improvement in urea cycle flux.

A type C meeting with the FDA to discuss our plans for a proposed future pediatric study under the RDEP (Rare Disease Evidence Principles) is scheduled for the first half of 2026.

Vaccine Programs

According to the National Foundation for Infectious Diseases, over 50,000 people die each year due to vaccine-preventable diseases and related complications in the United States alone (Centers for Medicare and

Medicaid Services, 2018; Walter et al., 2016). Influenza and pneumonia cases approach this number of deaths each year and more than one million individuals in the United States have died of COVID since the beginning of the COVID-19 pandemic (Centers for Disease Control and Prevention). The Department of Health and Human Services estimated that 330,000 lives were saved in the United States due to COVID-19 vaccination in 2021 alone. Outbreaks of new infectious diseases, and the rise of variants to existing viruses, create demand for new and novel approaches to producing vaccines in a more cost-effective and quicker manner.

The COVID-19 pandemic highlighted the efficacy, safety, and rapidity in which nucleic acid medicines can be used to vaccinate vulnerable populations, and our vaccine program has continued to progress. In 2020, we initiated development of our first self-amplifying mRNA vaccine candidate to protect against COVID-19. In December 2022, we entered into a Collaboration and License Agreement (“CSL Collaboration Agreement”) with CSL Seqirus, a part of CSL Limited and one of the world’s leading influenza vaccine providers, for the global exclusive rights to research, develop, manufacture and commercialize self-amplifying mRNA vaccines against COVID-19, influenza and up to three other infectious diseases and global non-exclusive rights to pandemic pathogens. The CSL Collaboration Agreement combines CSL Seqirus’ established global vaccine commercial and manufacturing infrastructure with Arcturus’ manufacturing expertise and innovative STARR self-amplifying mRNA vaccine and LUNAR delivery platform technologies. For a more comprehensive discussion of the CSL Collaboration Agreement, please see Item 1 “Business” – “Revenue and Collaboration Arrangements and Other Material Agreements” – “CSL Seqirus.”

In November 2023, ARCT-154 (KOSTAIVE) became the world’s first approved self-amplifying RNA vaccine following Japan’s approval of ARCT-154 for primary immunization and as a booster dose against COVID-19. In September 2024, Japan’s Ministry of Health, Labor and Welfare (MHLW) granted approval and authorization for an updated version of KOSTAIVE, targeted to protect against the JN.1 lineage of Omicron subvariants for adults 18 years of age and older. CSL Seqirus’ exclusive partner in Japan, Meiji, began distributing the updated vaccine in Japan in October 2024, marking the world’s first commercially available sa-mRNA COVID-19 vaccine for adults 18 and older. The approval was based on manufacturing data demonstrating the quality and consistency of the vaccine product, non-clinical immunogenicity data against JN.1 lineage of Omicron subvariants of KOSTAIVE (JN.1), and clinical evidence supporting the safety and immunogenicity of KOSTAIVE (bivalent, BA.4/5 and ancestral strain).

In our influenza vaccine franchise, a Phase 1 clinical trial of our seasonal influenza candidate was conducted in 2024-2025 under our collaboration with CSL Seqirus, and a BARDA-funded Phase 1 clinical trial of our H5N1 pandemic flu candidate was initiated in December 2024 and is ongoing.

KOSTAIVE® and COVID-19 Vaccine Program

Coronaviruses are a family of viruses that can lead to respiratory illness. Three viruses in this family have emerged in the past twenty years: Severe Acute Respiratory Syndrome (SARS-CoV), Middle East Respiratory Syndrome (MERS-CoV), and Severe Acute Respiratory Syndrome 2 (SARS-CoV-2), the virus responsible for the COVID-19 pandemic. Throughout the pandemic, there have been surges of infections as protective health measures have waxed and waned. Uncontrolled viral spread has led to billions of cases worldwide and the selection of viral variants that are more contagious, pathogenic, or both. Since late 2021, infections have been dominated by subvariants of the Omicron strain, which continue to displace previous circulating strains by evading immunity and spreading more efficiently, resulting in an increased risk of breakthrough infection among the vaccinated. Vaccines that induce robust and durable immunity against current and emerging variants of concern (“VOCs”) can help to reduce the infection and disease burden for both the public and the health care systems globally.

Our COVID-19 vaccine candidate, KOSTAIVE, is based on our STARR (self-amplifying mRNA) technology platform and our LUNAR platform. It was designed to elicit immune responses against the SARS-CoV-2 spike protein, the critical component that enables viral entry.

KOSTAIVE is the brand name approved in Japan and Europe for ARCT-154, the version of the sa-mRNA COVID-19 vaccine encoding the ancestral strain of SARS-CoV-2, as well as for updated variant-specific versions of this vaccine. We may use KOSTAIVE or internally generated names, such as ARCT-154, ARCT-2301, and ARCT-2303, to identify vaccines targeting specific SARS-CoV-2 variants.

The licensure of KOSTAIVE in Japan in 2023, followed by the approval of an updated version of KOSTAIVE (JN.1 Omicron subvariant) and initiation of commercial sales in Japan in 2024 are significant milestones in the advancement of our vaccine franchise. The approval of KOSTAIVE by the EMA in January 2025 and by the United

Kingdom (the UK Medicines and Healthcare Products Regulatory Agency (MHRA)) in January 2026 provided further validation of our platform by other major regulatory authorities.

On September 5, 2025, the week prior to the planned Biologics License Application (“BLA”) submission related to KOSTAIVE, the U.S. Food and Drug Administration (the “FDA”) requested that the submission of the BLA filing be delayed due to the FDA’s expectation of providing additional advice. On October 14, 2025, the FDA informed us that, although the FDA had previously agreed that our proposed data package could support a single-dose indication, upon further consideration it found that additional data from a clinical endpoint efficacy study will be needed to align with the current COVID-19 vaccine regulatory framework requirements published in The New England Journal of Medicine in May 2025. On September 26, 2025, Meiji Holdings Co., Ltd. announced that its subsidiary, Meiji, launched a new composition of KOSTAIVE®, a self-amplifying mRNA vaccine against COVID-19. The product targets the SARS-CoV-2 Omicron sub lineage JN.1 variant XEC. In non-clinical studies, it induced neutralizing antibodies not only against Omicron JN.1 and XEC, but also against LP.8.1 and the currently circulating variants XFG and NB.1.8.1. The formulation is lyophilized and supplied as a two-dose vial, with one vial per carton.

In 2025, several important manuscripts related to our studies were published, which are summarized below.

Commercialization of KOSTAIVE in Japan

Meiji has launched in Japan the two-dose vial of KOSTAIVE updated for the JN.1 variant XEC, following receipt of approval, in August 2025, from Japan’s Pharmaceuticals and Medical Devices Agency (PMDA). KOSTAIVE first received marketing authorization approval in Japan in 2023 for use as a primary immunization and booster in Japan for adults 18 years and older. The updated versions were approved and commercialized in the 2024-2025 and 2025-2026 seasons.

In January 2025, CSL Seqirus’ partner Meiji received approval for a partial amendment to the manufacturing and marketing approval of KOSTAIVE to include manufacturing sites in Japan. With this approval, Meiji and ARCALIS, Inc., Arcturus’ manufacturing joint venture in Japan, have been added as manufacturing sites. As a result, KOSTAIVE, with active pharmaceutical ingredients manufactured at such sites, may be shipped for commercial use in Japan.

Approval of KOSTAIVE (ARCT-154) in Europe

In February 2025, the European Commission granted marketing authorization for KOSTAIVE (ARCT-154) for individuals 18 years of age and older. The European Commission approval follows a positive opinion adopted by the Committee for Medicinal Products for Human Use (CHMP) of the EMA on December 12, 2024. The centralized marketing authorization of KOSTAIVE provided by the EC is valid in all 27 European Union (EU) member states and 3 additional European Economic Area (EEA) countries summarized here: Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, The Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain and Sweden.

KOSTAIVE BLA Submission

On September 5, 2025, the week prior to the planned Biologics License Application (“BLA”) submission related to KOSTAIVE, the FDA requested that the submission of the BLA filing be delayed due to the FDA’s expectation of providing additional advice. On October 14, 2025, the FDA informed us that, although the FDA had previously agreed that our proposed data package could support a single-dose indication, upon further consideration it finds that additional data from a clinical endpoint efficacy study will be needed to align with the current COVID-19 vaccine regulatory framework requirements published in The New England Journal of Medicine in May 2025. The FDA's sudden changes to regulatory requirements for COVID-19 vaccines have indefinitely delayed the U.S. BLA filing for KOSTAIVE.

Approval of KOSTAIVE (ARCT-154) in United Kingdom

In January 2026, the UK Medicines and Healthcare products Regulatory Agency (MHRA) under the International Recognition Procedure (IRP) granted marketing authorization for KOSTAIVE for individuals 18 years and older.

Clinical Studies of KOSTAIVE (COVID-19 vaccine)

In connection with the development of KOSTAIVE, we have conducted seven clinical studies, including four pivotal studies described below.

Pivotal Phase 1/2/3 Efficacy, Safety, and Immunogenicity Study of KOSTAIVE (ARCT-154) in Vietnam (NCT05012943)

This randomized, observer-blinded, placebo-controlled, and active-controlled study enrolled more than 19,000 adult individuals across multiple sites in Vietnam and demonstrated that a 2-dose vaccination series with

ARCT-154 induced protection in the seronegative population against heterologous SARS-CoV-2 variants (mainly Delta) with vaccine efficacy of 56.6% (48.7–63.3) for COVID-19 of any severity and 95.3% (80.5–98.9) for severe COVID-19. The vaccine was immunogenic against the ancestral SARS-CoV-2 strain and induced a cross-neutralizing immune response against new emergent variants. The vaccine was well tolerated, and safety analysis did not identify specific safety concerns. The study results served as the basis for vaccine licensure in Japan, the European Union, and the UK.

The results were broadly published and presented in multiple international forums.

The study was conducted in collaboration with Vinbiocare Biotechnology Joint Stock Company (“Vinbiocare”), a member of the Vingroup Joint Stock Company (Vingroup) group, and was sponsored by Vinbiocare.

Pivotal Phase 3 Non-Inferiority Study of KOSTAIVE (ARCT-154) in Japan (jRCT 2071220080).

This Meiji-sponsored, randomized, multicenter, observer-blind, active-controlled study evaluating the safety and immunogenicity of a booster dose of ARCT-154 and assessing its non-inferiority to COMIRNATY® (Monovalent, Original strain). The study demonstrated immunological non-inferiority of KOSTAIVE versus COMIRNATY for the ancestral SARS-CoV-2 strain and immunological superiority for the epidemiologically dominant Omicron BA.4/5 variant. KOSTAIVE also demonstrated a more durable humoral immune response up to 12 months post-booster dose. Overall, the study results support the favorable benefit/risk profile of the ARCT-154 vaccine when administered as a booster dose in adults who previously received other mRNA COVID-19 vaccines.

The study results were publicly disclosed in April 2024.

Pivotal Phase 3 Study of Bivalent Version of KOSTAIVE (ARCT-2301) in Japan (jRCT2031230340)

This Meiji-sponsored study of a bivalent version of KOSTAIVE (ancestral strain and Omicron BA.4/5) to further support immunogenicity and safety data for the self-amplifying mRNA platform and facilitate the timely release of future seasonal updates of our COVID-19 vaccine against evolving variants of concern. As with the monovalent vaccine, the bivalent sa-mRNA formulation demonstrated superior immunogenicity compared with the conventional bivalent mRNA vaccine COMIRNATY, with a higher immune response persisting up to six months after a booster dose, and broader variant coverage, supporting the robustness of the sa-mRNA vaccine platform for future vaccine strain updates.

The study results were published in March 2025.

Pivotal Phase 3 Co-administration Study of KOSTAIVE (ARCT-2303) and Seasonal Influenza Vaccines (NCT06279871).

This CSL- and Arcturus-funded randomized, observer-blind, placebo-controlled, phase 3 study aimed to generate additional immunogenicity and safety data in multiple ethnicities to support regulatory filings in the U.S. and globally. The study also assessed the co-administration of the ARCT-2303 vaccine with the age-appropriate seasonal influenza vaccines. The study results demonstrated robust immunogenicity of the XBB1.5-containing vaccine and support the concomitant administration of KOSTAIVE with licensed non-adjuvanted and adjuvanted influenza vaccines in both young and older adults. The safety and reactogenicity of co-administered vaccines were comparable to those of standalone administration. No safety concerns were raised based on the study results.

COVID-19 Vaccine Product Format

The product format of KOSTAIVE that began commercialization in Japan in October 2024 is a lyophilized product presentation. The stability and cold chain characteristics of KOSTAIVE in a lyophilized format compares favorably to frozen liquid format, and our ongoing development of proprietary manufacturing technology has led to significant increases in refrigerated and ambient temperature shelf-lives for both lyophilized and liquid drug products.

Seasonal Flu Collaboration Program

LUNAR-FLU (Seasonal Influenza)

Influenza is estimated to cause one billion infections globally every year and hundreds of thousands of deaths, especially in the elderly and individuals with underlying medical conditions. In many regions, influenza is seasonal, with infections peaking during November through April in the Northern Hemisphere and May through September in

the Southern Hemisphere. Year-round surveillance by the World Health Organization (“WHO”) in collaboration with various national health agencies informs WHO recommendations on the strains of influenza most likely to spread during the upcoming influenza season. National health agencies (such as the FDA) then make the final decision of which strains should be covered by vaccines licensed in their country.

Our LUNAR-FLU (seasonal) program, partnered with CSL Seqirus, has the objective of producing a safe and effective seasonal influenza vaccine candidate with significant advantages over the traditional egg-based inactivated quadrivalent vaccine. Inaccurate predictions of circulating influenza strains as well as mutations due to adaptation in egg-grown vaccines can substantially reduce efficacy on a year-to-year basis. We believe the ability of mRNA platforms to nimbly adapt to new viral strains should help improve efficacy. In addition, we do not expect mRNA vaccines to face the challenge from mutations common to egg-grown vaccines.

LUNAR-FLU has been designed to leverage our expertise in both our LUNAR lipid delivery platform and STARR self-amplifying mRNA technology. These technologies have been shown to deliver effective protection against COVID-19 and has been optimized to elicit robust immunogenicity with acceptable reactogenicity at a lower dose than conventional mRNA vaccines, with the objective of creating a highly effective influenza vaccine for use in general and high-risk populations. We conducted a Phase 1 study of ARCT-2138, a sa-mRNA seasonal influenza vaccine candidate encoding haemagglutinin (HA) and neuraminidase (NA) of four seasonal influenza strains as recommended by the World Health Organization (WHO). Overall, the study showed the potential of a self-amplifying mRNA vaccine, encoding eight antigens, to induce an immune response in both young and older adults with a dose as low as 2 μg, and was tolerable across a dose range of 2 to 20 μg.

Pandemic Avian Influenza Program (H5N1 Influenza)

Our LUNAR-H5N1 program continues to progress under the award from BARDA that we obtained in 2022 to advance through Phase 1 a vaccine to protect against disease caused by H5N1 highly-pathogenic avian influenza. H5N1 influenza is a significant concern in animal health. To date, H5N1 flu has affected over 10,000 wild birds, nearly a thousand dairy cows, and over 130 million poultry. Elevated H5N1 infections in animals have led to increasing numbers of human infections including two confirmed severe cases in the United States and one death. Most of the confirmed human infections are due to exposure of U.S. dairy and poultry workers to infected dairy cows and poultry. We are working diligently with our partners, BARDA and CSL Seqirus, to clinically validate our low-dose STARR mRNA technology for H5N1 to assist towards pandemic preparedness.

In April 2025, the FDA granted Fast Track Designation for ARCT-2304. This designation recognizes the potential of ARCT-2304 as an innovative approach to address unmet medical needs for the prevention of disease caused by pandemic influenza A virus H5N1, a significant global health risk. Fast Track Designation from the FDA is granted to vaccines intended to prevent serious conditions caused by infectious diseases. The designation is designed to expedite the development and review process, providing several benefits, including enhanced communication with the FDA, eligibility for priority review, and the possibility of a rolling review.

Our Phase 1 study of ARCT-2304, an sa-mRNA pandemic influenza A/H5N1 vaccine candidate, released interim results in September 2025. The study objectives were to evaluate the safety and tolerability of the vaccine and to characterize the immune response across three dose levels in 132 young adults (18-59 years of age) and 80 older adults (60-80 years of age). ARCT-2304 induced a humoral immune response after a single dose (as measured by microneutralization and enzyme-linked lectin anti-neuraminidase assays) in all tested dose levels. Administering a second dose of ARCT-2304 further increases immune responses. The magnitude of the anti-HA response was higher after an 8-week interval than after a 4-week interval in both young and older adults. ARCT-2304 in dose levels 5 and 12 µg (2 doses administered 4 or 8 weeks apart) and 1.5 µg (2 doses administered 8 weeks apart) induces a hemagglutinin-specific immune response similar to or higher than that after the MF59-adjuvanted pandemic vaccine (in both young and older adults). Immunogenicity monitoring up to eight months after the first vaccination confirmed high antibody persistence and substantial durability of vaccine-induced immunity. No safety or tolerability concerns were raised from available data.

Platform Technologies and R&D Programs

We have four key proprietary platform technologies:

LUNAR (Lipid-Mediated Delivery) Platform

Our LUNAR lipid-mediated delivery technology includes a diverse, growing library of over 300 proprietary lipids that we are rationally designing to be versatile, while maximizing efficacy and improving tolerability of a diverse selection of nucleic acids, refining the LNPs to target specific cell types, and determining the most favorable routes of administration. A key feature of our LUNAR lipids is their biodegradability, decreasing the undesired effects caused by lipid accumulation that are associated with tolerability issues present in other lipid-mediated RNA medicine delivery platforms. Our team continues to advance our LUNAR lipid formulated nucleic acid platform in a scalable and highly reproducible manner, reducing the costs of goods for the therapies in our pipeline.

In addition to our LUNAR lipid-mediated delivery technology, we believe we have created innovative, proprietary advancements in producing mRNA medicines, including improvements that increase purity, scalability, efficiency in production times, and adaptability to different mRNA modification strategies. We strive to use these proprietary innovations to benefit each mRNA medicine in our pipeline.

We continue to invest in and improve our LUNAR lipid-mediated delivery of mRNA with continuous improvements in our mRNA and sa-mRNA platforms in conjunction with improvements in our next generation proprietary lipids to improve targeting, efficacy and safety profiles for both our vaccine and therapeutic protein platforms. This investment has led to key innovations ensuring that our LUNAR formulated drug product candidates have optimal characteristics for therapeutic use, which we believe sets us apart from other nucleic acid therapeutics and lipid-mediated delivery platforms. As such, we consider ourselves a leader in the research and development of mRNA therapeutics for multiple indications.

We continue to conduct exploratory platform development activities, including the evaluation of genome editing, and new targeting approaches, where our LUNAR and STARR platforms could potentially be useful for identification and development of additional products for our portfolio.

Key Attributes of Our LUNAR Lipid-Mediated Delivery Technology

We have designed our LUNAR lipid-mediated delivery platform to address major challenges with nucleic acid medicine delivery, including transfection efficiency, adverse immune reactions and liver damage.

LUNAR is a multi-component, lipid-mediated drug delivery system that utilizes our proprietary lipids, called ATX lipids. Each of our ATX lipids contains an ionizable head group and a biodegradable lipid backbone. The head group is a key chemical component of the ATX lipid, making it pH-sensitive and providing it distinct advantages as a component of our LUNAR lipid formulation. At acidic pH, ATX lipids are positively charged, facilitating interaction with the negatively charged nucleic acid, thereby enabling LUNAR particle formation. At physiological pH (e.g., pH 7.4), the ATX lipids within the LUNAR formulations are neutrally charged, reducing the toxicity often seen with permanently positively charged lipid-mediated delivery technology. Upon uptake into a cell by endocytosis (a process that forms a cellular structure called an endosome around the LUNAR formulated nucleic acid therapeutic), the head group again becomes positively charged due to the low pH of the endosome, disrupting the endosome and the LUNAR particle, resulting in release of the nucleic acid therapeutic into the cell where it is translated to produce a therapeutic protein.

The disruption of the LUNAR particle also releases the components of the formulation into the cell, where the ATX lipid is degraded by enzymes called esterases in the cell allowing for the lipids to be cleared from the cell. We designed the ATX lipid to be rapidly biodegradable by engineering chemical structural components, called esters, into the ATX backbone that are sensitive to esterases. This degradation prevents ATX lipids from accumulating inside the cell and causing toxicity.

Biodegradable, highly optimized for each cell type

LUNAR-platform development

The development of our LUNAR platform is focused on continuous innovation and advancement in the following areas:

Through the above efforts, our versatile LUNAR platform continues to drive internal and partner programs.

ATX Lipid Design and In Vivo Screening Process

As mentioned above, we have generated a growing library of more than 300 proprietary ATX lipids. ATX lipids are rationally designed to fit different applications and vary depending on the target cell type and route of administration. We perform extensive formulation screening for each nucleic acid therapeutic candidate to determine the optimal ATX lipid to be used and the appropriate excipient composition (LUNAR composition) for the nucleic acid therapeutic candidate, the desired route of administration, and target cell type.

The design of ATX lipids is an iterative process based on in vivo protein expression and tolerability results from previous ATX lipid candidates. To date, we have developed seven generations of ATX lipids. New ATX lipids are chemically synthesized and used to package mRNAs expressing a secreted protein. The ATX lipid formulated RNAs must meet specific chemical and biophysical acceptance criteria before being tested for biological activity. RNA formulations meeting all acceptance criteria are first screened for protein expression in mice. Active candidates are further verified by evaluating protein expression in non-human primates. Active candidates are then tested for tolerability and preliminary tissue clearance rates following administration. Active ATX lipid candidates demonstrating high levels of protein expression and equivalent or improved tissue clearance rates are then assigned to a specific disease target for development of therapeutic applications. The following results are from an in vivo mRNA expression study which identified three new highly active LUNAR lipids with regard to protein expression in non-human primates compared to the positive control.

Expression of Human EPO in Mice 6 hours After IV Administration (Figure 1)

Mouse Liver Clearance of LUNAR Lipids 48 hours After IV Administration (Figure 2)

Expression of Human EPO in Non-Human Primates 6 Hours After IV Administration (Figure 3)

Figure 1: mice were injected intravenously with 4 different ATX lipid formulations containing mRNA expressing human erythropoietin (hEPO). The ATX lipids that were screened were C9G, C9H, C9I and B2G at 0.1 mg/kg and 0.3 mg/kg RNA doses. ATX lipid B2G formulation is a positive control to which expressions from the other formulations are compared. Mice were bled 6 hours after injection and assayed for hEPO, a secreted protein.

Figure 2: shows the clearance of the ATX lipids from the mouse liver 48 hours after administration of 0.1mg/kg and 0.3 mg/kg RNA doses. C9G, C9H and C9I yielded much higher expression levels of hEPO than B2G, the positive control for both doses tested. It also shows that the residual amount of C9G and C9I were below the limit of detection and the residual amount of C9H was at least 10-fold less than the remaining amount of B2G at the 0.1 mg/kg RNA dose and at least two-fold less than the residual amount of B2G at the higher RNA dose.

Figure 3: C9G and C9I formulations were tested for EPO expression in non-human primates at a single dose and assayed for secreted hEPO in the blood six hours after IV administration. Both C9G and C9I yielded significantly higher expression levels than the positive control, B2G further confirming the superior performance of the new LUNAR formulations. Hence, this lipid screen identified three LUNAR lipids that yielded greater RNA expression in mice and two LUNAR lipids in NHPs and were rapidly cleared from the liver within 48 hours after administration. This demonstrated the ability to design and execute LUNAR formulations using our advanced generation lipids with many-fold higher protein expression and ready biodegradability.

Lung Targeting

Aerosol capabilities have been developed for the CF program using our proprietary lipid nanoparticle delivery platform, LUNAR. Characterization and optimization of the aerosolized LUNAR formulations in targeting airway epithelium have been achieved in rodent (mice, rat) and nonrodent models (ferret, NHP) as depicted in the image using a reporter mRNA encapsulated in LUNAR. We expect that the validation attained for the inhaled LUNAR platform in the CF program will serve as a translatable approach to support other respiratory approaches where targeting airway epithelium is needed.

LUNAR delivery to airway epithelium demonstrated in vivo across species (rodents, ferrets, NHPs).

LUNAR Safety and Tolerability (i.v. administration)

As part of the screening method for our proprietary lipids, we conduct an initial lipid tolerability screen in Balb/C and C57Bl/6 mice strains to ascertain the initial maximum tolerated dose in rodent species(s). LUNAR formulations encapsulating hEPO mRNA with different ATX lipids are intravenously administered to these mouse strains at three and five mg/kg doses and monitored for clinical signs. Blood was drawn at six and 48 hours after LUNAR administration and assayed for both liver functions and cytokine elevations. Liver function changes are determined by measuring for any increase in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes in the blood. A significant increase in these enzymes (i.e., above five times the normal range) indicates a negative effect on liver function. The results show that many of the LUNAR formulations that were tested are tolerable up to three mg/kg in both strains of mice for LUNAR formulations containing DSPC. Moreover, there is an even greater improvement in tolerability of up to five mg/kg when the helper lipid is PCA57. Thus, with these innovations we believe that we have substantially improved both the potency and tolerability of our LUNAR platform.

Our Proprietary mRNA and Protein Design Technology

The mRNA programs in our pipeline benefit from our in-house expertise in protein and mRNA design, which helps us address many of the known challenges that face the viability of mRNA therapeutics today. We have identified several design elements of mRNA compounds that provide improved translation (the process of making protein based on the instructions/codes in the mRNA) of our mRNA therapeutics, including untranslated regions derived from species that have not previously been combined with human mRNA sequences. This platform technology is applicable to many different human mRNA sequences that we are currently investigating in our discovery efforts. We are able to engineer human protein sequences to increase the half-life of the proteins produced by our mRNA therapies and can more efficiently direct specific types of proteins to certain cellular structures of interest. These innovations are broadly applicable to several programs that are part of our mRNA discovery efforts.

In addition to these platform technologies, we have developed a proprietary tool to aid our team in the efficient design and development of new mRNA drug candidates. Our mRNA Design Suite is a cloud-based software suite with a collection of proprietary bioinformatic algorithms aimed at achieving highly improved potency of a drug substance through optimization of mRNA sequences. The algorithms were developed in house through the integration of experimentally validated optimization processes. Through multi-layered in silico quality control pipelines, mRNA Design Suite promptly generates high-quality and error-free sequences accompanied by various statistics. Additionally, mRNA Design Suite seamlessly interacts with our plasmid/mRNA production database to accelerate the process from mRNA design to gene synthesis, cloning, and mRNA production.

Our STARR mRNA Technology

Our distinct and proprietary self-amplifying mRNA (sa-mRNA) platform technology (STARR) incorporates proprietary design algorithms that optimize sa-mRNA to enhance expression of the applicable antigen while minimizing structures that could inhibit expression. The replicase, an RNA-dependent RNA polymerase, is encoded upstream of the antigen of interest and functions to increase the duration of antigen/transgene expression compared to conventional mRNA (Figure 6). When combined with LUNAR delivery, STARR has demonstrated reduced dose requirements and more durable, superior immune responses compared with conventional mRNA vaccines in preclinical studies and clinical trials.

Figure 6: The luciferase expression from an optimized sa-mRNA, STARR Technology (Green), a non-optimized sa-mRNA (Blue) and the conventional RNA (Purple). The STARR Technology was shown to yield at least a 30-fold greater expression level than conventional RNA. The STARR Technology also demonstrated a longer duration of expression compared to the conventional RNA and also the non-optimized self-amplifying RNA.

Our Proprietary Manufacturing Technology

We continue to innovate and improve our capabilities to manufacture nucleic acid medicines with high standards of quality, efficiency, and in compliance with Good Manufacturing Practices and its analogous regulations outside the U.S. Our technologies work to improve every aspect of the drug product manufacturing process from design to filling and packaging. Nucleic acid manufacturing relies on the confluence of complex technologies in the chemical and biological sciences that require extreme precision in their execution. Consequently, the nucleic acid medicines industry has faced many challenges across all steps of the manufacturing process, most notably the ability to scale processes to produce batches of adequate size while continuing to meet product specifications. Notable capabilities include:

In our efforts to improve these and other capabilities, we use qualified scale down models to optimize operating conditions for each manufacturing step for both drug substance and drug product. Optimized conditions identified by these small-scale models are applied to the cGMP manufacturing processes. This manufacturing development process is also utilized for evaluating potential additives that improve drug substance and drug product quality and efficacy, improve manufacturing efficiency and reduce manufacturing costs. Some of the major accomplishments that have been achieved using this manufacturing development process are increased drug

substance yield, reduction in drug substance impurities, increased manufacturing efficiency, and extended refrigerated and ambient temperature shelf life.

Discovery Programs

The versatile nature of our platform technologies may allow for a broad spectrum of nucleic acid medicines. We have conducted, and will continue to conduct, efforts to explore potential new drugs through our discovery and enabling technologies programs, though we are prioritizing our later stage programs.

Discovery Programs – HPV

Arcturus is advancing the development of a post-exposure HPV therapeutic vaccine candidate. Although prophylactic HPV vaccinations have substantially lowered the incidence of cervical cancer in developed countries, cervical cancer is still the fourth leading cause of cancer in women globally with the vast majority (approximately 90%) of cases in countries that have not yet widely adopted prophylactic HPV vaccinations and other cervical cancer prevention strategies, including screening and treatment. Cervical cancer typically develops years after initial HPV exposure due to a failure to clear the virus and the integration of viral oncogenes. A therapeutic vaccine which induces T-cell responses targeting the integrated HPV genes in precancerous cells could help prevent precancer and cancer in those already exposed to HPV. The Gates Foundation awarded Arcturus a grant of $3.9 million in November 2024 to support the development of such a therapeutic HPV vaccine through the clinical candidate nomination stage.

Enabling Technologies

Enabling Technologies – Cancer vaccines

Our LUNAR Cancer vaccine discovery efforts are aimed at developing an immunotherapy against a tumor via activated T-cells. We contemplate that the vaccine would encode an antigen(s) that would be specifically presented by (or associated with) a tumor, such that the vaccination would elicit T cell responses that recognize and attack the tumor. We have applied our learnings from our more-advanced LUNAR-COVID-19 vaccine program to establish both STARR (self-amplifying) and conventional mRNA platforms for immuno-oncology therapy.

In a preclinical study, our proof of concept (POC) vaccine encoding AH1 antigen of gp70 protein which is highly expressed on the surface of mouse colorectal carcinoma cell line CT26 has demonstrated clear effectiveness in a syngeneic mouse model of a colorectal CT26 cell line. With intramuscular administration of the STARR vaccine (two doses of 10 ug), treated with a checkpoint inhibitor (CPI), anti-PD1/PDL1 antibody, led to a substantial reduction of tumor growth in comparison to the CPI treatment by itself (Panel A). Moreover, the same level of efficacy was achieved with a single administration of a 0.2 ug dose of the STARR vaccine.

With various LUNAR formulations, conventional mRNA vaccine expressing the AH1 antigen also demonstrated a robust T cell response (Panel B) and reduction of tumor growth with anti-PD1/PDL1 treatment in the syngeneic mouse model. We believe that these POC results from the two platforms might lead to applicability to various types of cancer with flexibility in dosing regimens.

Our efforts to date have focused on the selection of neoantigens, and other common tumor-specific antigens encoded in the cancer vaccines. Common tumor antigens can be shared among patients, and therefore target broader patient populations, whereas a neoantigen vaccine would be a personalized vaccine specific for an individual patient. Additional advancements of the LUNAR Cancer Vaccine program include the improvement of antigen cassette designs, STARR RNA elements, and immune modulator molecules, all of which can significantly enhance T cell responses.

Figure 7: Antitumor activity and T cell response by Arcturus cancer vaccines. A. STARR vaccine expressing a tumor antigen led to a significant reduction of the tumor growth rate of a colorectal cancer cell line, CT26. B. T cell responses elicited by conventional mRNA cancer vaccine by various LUNAR formulations.

Along with these platform improvements, we sought to understand how T cell responses induced by conventional mRNA, which have shown great promise in recent personalized cancer vaccine trials, differ from T cell responses induced by our STARR platform, especially after multiple vaccinations. We compared T cell responses in mice vaccinated with either sa-mRNA (STARR) encoding 13 epitopes known to generate responses in C57BL/6 mice to those in mice vaccinated with a conventional (N1-psuedouridine modified) mRNA encoding those same epitopes. All vaccines were formulated with our LUNAR lipids. Each mouse received a series of five vaccinations with an interval of two weeks between vaccinations (Figure 8A). We found that even after five vaccinations, mice vaccinated with sa-mRNA showed more than twice the CD8+ T cell response compared to mice vaccinated with conventional mRNA vaccine (Figure 8B).

Because sa-mRNA technology allows for extended duration of antigen expression, the possibility of T cell exhaustion after multiple vaccinations was a concern. We assessed the levels of CD8+ T cells expression PD-1 or Lag-3, well characterized exhaustion markers, and found significantly lower levels of exhaustion markers in mice vaccinated with sa-mRNA compared to conventional mRNA (Figure 8C). We hypothesize that the additional innate immune stimulation from the replicase intermediates may be responsible for the reduction in exhaustion makers. CD8+ memory subsets were also analyzed. While we expected to see increases in CD8+ T cell memory subsets overall, we observed that we saw an increase in the important T cell effector (Tem) subsets at the expense of T central memory (Tcm) in sa-mRNA vaccinated mice after 5 vaccinations (Figure 8D). The generation of Tem cells is an important prognostic indicator of vaccine efficacy in cancer vaccination. Lastly, we wanted to verify that T cells induced by multiple vaccinations with sa-mRNA were functional, so we assessed the levels of granzyme B, an important cytotoxic effector molecule, in CD8 T cells before and after stimulation. Prior to stimulation sa-mRNA vaccinated mice had significantly higher granzyme B compared to conventional mRNA vaccinated mice. After peptide stimulation, T cells from sa-mRNA vaccinated mice showed increased degranulation (as indicated by levels of CD107a, a degranulation marker) compared to T cells from conventional mRNA vaccinated mice (Figure 8E). Altogether, our data indicate that our STARR platform not only delivers a higher magnitude of epitope-specific responses compared to conventional mRNA, but that the T cell response induced by the STARR platform is better suited for clinical efficacy even after multiple vaccinations by inducing highly functional and cytotoxic T cells with the relevant memory markers (Tem).

Figure 8: CD8 T cell responses after multiple vaccinations with sa-mRNA (STARR) vaccines and conventional mRNA vaccines formulated with LUNAR lipids. (A) Design of sa-mRNA vaccine encoding 13 H-2b restricted T cell epitopes (top). The conventional mRNA vaccine used the same epitope cassette. C57Bl/6 mice were vaccinated 5 times (two-week interval between vaccinations) and spleens were collected two weeks after the last vaccination (bottom). (B) Epitope specific responses to encoded epitopes were higher in sa-mRNA vaccinated mice compared to conventional mRNA vaccinated mice after 5 vaccinations. (C) The T cell exhaustion markers PD-1 and Lag-3 were assessed and lower levels of PD-1 and PD-1/Lag3 were observed on CD8+ T cells from sa-mRNA vaccinated mice. (D) Naïve (CD62L+CD44-), T central memory (Tcm; CD62L+CD44+), and T effector memory (Tem; CD62L-CD44+) were assessed in all mouse groups. sa-mRNA vaccinated mice showed the highest levels of Tem cells, an important prognostic indicator of vaccine efficacy. (E) CD8+ T cells were also assessed for granzyme B levels and surface levels of the degranulation marker, CD107A, before (top) and after (bottom) simulation with the encoded peptides. Prior to stimulation, sa-mRNA vaccinated mice had the highest levels of granzyme B. When stimulated, these cells lost granzyme B expression through degranulation, as indicated by the higher levels of CD107a, indicating functional degranulation of cytotoxic mediators was higher in sa-mRNA vaccinated mice compared to conventional mRNA vaccinated mice.

Enabling Technologies – Immuno-oncology

Cell-based therapies for hematologic malignancies using chimeric antigen receptor (CAR) T cells have made significant advances in the past decade. The success of CAR-T cells in immuno-oncology has led to a growing number of therapies utilizing other immune cell types engineered to express a variety of immunomodulatory molecules. Yet, despite their promise, extensive challenges still exist with this therapeutic approach. Some of the issues include toxicity, potential for insertional mutagenesis of the CAR construct, T cell malignancies, and an ex vivo manufacturing process that is complex, time consuming and costly. We believe that our LUNAR-I/O approach has the potential to ameliorate some of these issues. For example:

Our efforts to date have focused on targeting T lymphocytes in vivo with either CAR-mRNA or CAR-STARR (self-amplifying RNA) constructs in combination with other immunostimulatory molecules.

Supply and Manufacturing

Our supply and manufacturing strategies are focused on supporting the following:

We have built a global manufacturing footprint with our partners, including Aldevron, Catalent, Recipharm, Polymun and ARCALIS. With such collaborations, we have established an Integrated Global Supply Chain Network with our primary and secondary sourcing contract development & manufacturing organizations (CDMOs) based in the United States, EU and Asia for producing critical raw materials, drug substance, and packaged finished product.

We have manufactured and supplied gram quantities of drug substance, and have scaled-up and validated our finished drug products (COVID Vaccine) through our CDMOs for clinical studies, and commercial readiness. We continue to dedicate, resources to advance our sophisticated manufacturing know-how, including formulation of lipid nanoparticles, which improves manufacturing efficiency and capacity.

We believe we have established sufficient manufacturing capacity through our CDMOs to meet our current internal research, development, and potential commercial needs, as well as our obligations under existing agreements with our partners. Additionally, we continue to evaluate relationships with additional suppliers to increase overall capacity and diversify our supply chain.

Revenue and Collaboration Arrangements and Other Material Agreements

In addition to our internal programs, we have collaborated or partnered with other parties on discovery, development, manufacturing or other efforts based on our proprietary platform technologies. Among other collaboration arrangements,

CSL Seqirus

In November 2022, we entered into the CSL Collaboration Agreement with CSL Seqirus for the global exclusive rights to research, develop, manufacture and commercialize self-amplifying mRNA vaccines. The CSL Collaboration Agreement became effective on December 8, 2022, following clearance under the Hart-Scott-Rodino Antitrust Improvements Act.

Under the CSL Collaboration Agreement, CSL Seqirus receives global exclusive rights to our technology for vaccines against SARS-CoV-2 (COVID-19), influenza and three other infectious diseases. Specifically, the collaboration agreement grants CSL Seqirus a license to our STARR mRNA technology and LUNAR lipid-mediated delivery, as well as mRNA drug substance and drug product manufacturing expertise. CSL has also been granted global non-exclusive rights in the field of pandemic preparedness (i.e., pathogens identified as priority diseases by the WHO), with the right to convert to an exclusive license.

The CSL Collaboration Agreement sets forth how the parties will collaborate to research and develop vaccine candidates. In the COVID-19 field, we undertake activities for certain regulatory filings for our leading self-amplifying mRNA vaccine candidate in COVID-19, ARCT-154, in the United States and Europe and for research and development activities of a next-generation COVID vaccine candidate. CSL Seqirus leads and is responsible for all other research and development in COVID-19, influenza and the other fields.

We received an up-front payment of $200.0 million, with the potential to receive development milestones totaling more than $1.3 billion if all products are registered in the licensed fields. We also are entitled to potentially receive up to $3.0 billion in commercial milestones based on “net sales” of vaccines in the various fields. In addition, we are entitled to receive a 40% share of net profits from COVID-19 vaccine sales and up to low double-digit royalties of annual net sales for vaccines against influenza, pandemic preparedness and three additional infectious diseases. Entitlement to all such payments is subject to the strict conditions, requirements, royalty reduction provisions and other limitations set forth in the CSL Collaboration Agreement.

Either party may terminate the CSL Collaboration Agreement on a field-by-field basis for material breach by the other party, following notice and opportunity to cure. CSL Seqirus may also terminate the collaboration agreement in its entirety or on a field-by-field basis for any reason or no reason whatsoever, with certain limitations. The CSL Collaboration Agreement may also be terminated by CSL Seqirus for safety reasons, clinical data nonviability, commercial nonviability and other specified reasons.

In March 2024, we entered into Amendment Number Two to the CSL Collaboration Agreement to reflect updates to the development program and other adjustments consistent with our prior disclosures regarding the Collaboration and License Agreement (“Amendment Number Two”). Amendment Number Two, among other things, adjusts (i) the development plans for certain product candidates, (ii) various development milestones related to such product candidates, (iii) provisions of the CSL Collaboration Agreement related to specific royalty payments, (iii) provisions of the CSL Collaboration Agreement related to distributors, and (iv) proprietary payment calculations related to the foregoing.

On May 30, 2025, we initiated an arbitration against CSL Seqirus before the International Chamber of Commerce, seeking payment of a milestone under the CSL Collaboration Agreement based on the European Commission’s grant of marketing authorization for a presentation of KOSTAIVE® in the European Union.

In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing declining COVID-19 disease burden and more onerous U.S. regulatory requirements.

Cystic Fibrosis Foundation Agreement

On May 16, 2017, pursuant to a Development Program Letter Agreement (as amended, the “CFF Agreement”) with the CFF, CFF agreed to award us funding for a development program to identify lead CFTR mRNA sequences and LUNAR formulations, demonstrate tolerability of LUNAR CFTR mRNA, and demonstrate translatability of aerosolized LUNAR. The award includes a grant of rights to CFF know-how to assist us to research, develop, commercialize, make or otherwise exploit a product. If the award results in a successful commercialized product, we will pay CFF (i) royalties on sales of the product up to a maximum of a single-digit multiple of the total award amount actually paid to us by CFF, and (ii) thereafter, a single-digit percentage of annual net sales. Further, in the event of a license, sale or other transfer of the product or our development program technology (including a change of control transaction), we will pay CFF a percentage of such license, sale or transfer payments actually received by us or our shareholders (subject to a royalty cap). On August 1, 2019, we entered into an amendment to the CFF Agreement. Pursuant to the amendment, (i) CFF will increase the amount it will award to advance LUNAR-CF, (ii) we will provide a certain amount of matching funds for remaining budgeted costs, and (iii) the related disbursement schedule from CFF to us was modified such that (a) a disbursement was made upon execution of the amendment, (b) an agreed upon amount will be disbursed to us within thirty days of the first day of each of January, April, July and October 2020, and (c) the last payment will be disbursed upon us invoicing CFF to meet good manufacturing practices and submitting an IND application. In January 2022, the parties signed an additional amendment for CFF to fund the development of a CF ferret model for application in the development of ARCT-032, our LUNAR-CF candidate.

On September 25, 2023, we entered into an additional amendment (the “Fourth Amendment”) to the CFF Agreement, pursuant to which we and CFF agreed to: (a) increase the Amount of Award (as defined in the CFF Agreement and applicable amendment) from CFF to advance LUNAR-CF by up to $9 million (for a total to date of

up to approximately $25 million), and required Arcturus to provide $15 million in matching funds for remaining budgeted costs; (b) modify the existing rates and caps on royalties due to CFF under the CFF Agreement, including the addition of an option for Arcturus to reduce the royalty rate through a one-time payment; (c) modify the calculation of payments from Arcturus to CFF in the event of certain dispositions or licensing of cystic fibrosis or other pulmonary assets or of a change of control of Arcturus; and (d) make corresponding changes to exhibits, definitions and other provisions of the CFF Agreement.

BARDA

In August 2022, we entered into a cost reimbursement contract with the Biomedical Advanced Research and Development Authority (“BARDA”) of the U.S. Department of Health and Human Services to support the development of a low-dose pandemic influenza candidate based on our proprietary self-amplifying messenger RNA-based vaccine platform.

The contract is to support our non-clinical and pre-clinical development, early-stage clinical development through Phase 1, and associated drug product manufacturing, regulatory and quality-assurance activities over a period of three years. The contract provides for reimbursement by BARDA of Arcturus’ permitted costs incorporated into the contract, up to $63.2 million. The contract does not include the purchase of any pandemic influenza vaccine that eventually may be developed. The contract is terminable by BARDA at any time under specified circumstances, including for convenience.

This contract is part of BARDA’s ongoing efforts to bolster pandemic preparedness and response capabilities by investing in innovative medical counter-measures that can help prevent the medical consequences that result from outbreaks caused by pandemic influenza and emerging infectious diseases. In December 2024, we initiated a Phase 1 clinical trial for our H5N1 pandemic flu candidate that is supported by funding from BARDA.

ARCALIS Joint Venture

In April 2021, Arcturus and Axcelead, Inc., a company existing under the laws of Japan (“Axcelead”), formed a joint venture entity, named ARCALIS, Inc. (“ARCALIS”), which operates as a corporation under the laws of Japan. Axcelead is an integrated drug discovery solutions provider to the pharmaceutical industry in Japan, having succeeded to a portion of the drug discovery research department of Takeda Pharmaceutical Company Limited in 2017. The goal of ARCALIS is to be a contract development and manufacturing organization focused on mRNA manufacturing that would provide manufacturing services to us and also to third parties.

ARCALIS has constructed facilities for the manufacture of mRNA drug substance and mRNA-LNP liquid and lyophilized drug product financed largely by grants from the Japanese government.

In January 2025, Meiji Seika Pharma, along with ARCALIS, received Ministry of Health, Labour and Welfare (MHLW) approval for adding commercial manufacturing sites in Japan for KOSTAIVE. Domestically produced products with active pharmaceutical ingredients manufactured at ARCALIS’s Minami-soma facilities, and formulated at Meiji Seika Pharmatech, have been shipped for commercial use in Japan for the 2024-25 and 2025-26 seasons.

Legacy Arrangements

During our formative period, we entered into various collaboration, development and license agreements with larger parties in our industry, providing for the designation of targets for collaborative development using our platform technologies. Although, as we have previously reported, parties to these agreements, including Ultragenyx, continue to have exclusive rights to certain of these targets, other than as reported above, there has been no significant development activities under the programs.

Intellectual Property

Our business success depends in part on our ability to obtain and maintain intellectual property protection for our proprietary technologies, inventions and know-how, and on our ability to operate without infringing on the proprietary rights of others. We strive to protect our intellectual property through a combination of patents, trademarks, trade secrets, licensing agreements, invention assignment agreements and confidentiality agreements with employees, advisors, consultants and contractors.

We rely on continuing technological innovation to strengthen our proprietary position in the field of nucleic acid medicines. Therefore, we plan to continue to file patent applications in jurisdictions around the world as we

discover and develop novel nucleic acid technology platforms and novel nucleic acid therapeutic candidates. We cannot guarantee that future applications will be issued.

Our Patent Portfolio

As of January 31, 2026, we own over 500 patents and pending patent applications. The claims of these patents and pending applications include compositions of matter, methods of use, manufacturing processes and drug product formulations. These claims cover the use of our core platform technologies including the use of LUNAR® and lipid components to deliver nucleic acids, specific nucleic acid modalities for treating disease, as well as our proprietary technology regarding the design, manufacture, and purification of nucleic acids for use in therapy. Claims also cover the composition of matter, formulation, and use of our therapeutic candidates to prevent and/or treat target diseases including OTC deficiency, CF, COVID-19 and Influenza. If issued, our patents are expected to expire between 2028 and 2046, without taking into account any possible patent term extensions.

Our patent portfolio is built upon a strategy of robust protection for our LUNAR and STARR® platforms as described below:

Patent Terms

The term of individual patents depends on the countries in which they are obtained. The patent term is 20 years from the earliest effective date of filing a non-provisional patent application in most of the countries in which we file.

Under the Drug Price Competition and Patent Term Restoration Act (also known as the Hatch-Waxman Act), U.S. patent holders can apply for a patent term extension to compensate for the patent term lost during the FDA regulatory review process. Patent extension is only available for patents covering FDA-approved drugs. The extension can be up to five years beyond the original expiration date of the patent and cannot extend a patent term for longer than 14 years from the date of product approval. Only one patent extension is granted per approved drug. Similar provisions may be available in foreign jurisdictions, including Europe. We intend to apply for patent term extensions where possible.

Trade Secrets

We have developed valuable trade secrets to protect our product candidates and proprietary processes, including trade secrets related to the design and optimization of nucleic acids, the design and optimization of lipid compositions for delivery of nucleic acids, manufacturing and formulation processes, and analytical techniques.

Certain Risks to Intellectual Property

Our commercial success also depends in part on our non-infringement of the patents or proprietary rights of third parties. For a more comprehensive discussion of the risks related to our intellectual property, please see Item 1A “Risk Factors” – “Risks Related to Our Intellectual Property.”

The laws of some foreign countries do not protect intellectual property rights to the same extent as the laws of the United States. Many companies have encountered significant problems in protecting and defending intellectual property rights in certain foreign jurisdictions.

Our success depends in part on our ability to:

We seek to protect our proprietary technology and processes, in part, by confidentiality and invention assignment agreements with our employees, consultants, scientific advisors and other contractors. These agreements may be breached, and we may not have adequate remedies for any breach. In addition, our trade secrets may otherwise become known or be independently discovered by competitors. To the extent that our employees, consultants, scientific advisors or other contractors use intellectual property owned by others in their work for us, disputes may arise as to the rights in related or resulting know-how and inventions.

Product Approval and Government Regulation

Government authorities in the United States, at the federal, state and local level, and other countries extensively regulate, among other things, the research, development, testing, manufacture, quality control, approval, labeling, packaging, storage, record-keeping, promotion, advertising, distribution, post-approval monitoring and reporting, marketing and export and import of products such as those we are developing. Any product candidate that we develop must be authorized or approved by the FDA before it may be legally marketed in the United States and by the appropriate foreign regulatory agency before it may be legally marketed in foreign countries.

U.S. Drug Development Process

In the United States, the development, manufacturing, and marketing of human drugs and vaccines are subject to extensive regulation. The FDA regulates drugs under the Federal Food, Drug and Cosmetic Act (“FDCA”) and implementing regulations, and biological products, including vaccines, under provisions of the FDCA and the Public Health Service Act (“PHSA”). Drugs and vaccines are also subject to other federal, state and local statutes and regulations. The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local and foreign statutes and regulations require the expenditure of substantial time and financial resources. The process required by the FDA before a drug or biological product may be marketed in the United States generally involves the following:

The lengthy process of seeking required approvals and the continuing need for compliance with applicable statutes and regulations require the expenditure of substantial resources and approvals are inherently uncertain.

Before testing any compounds with potential therapeutic value in humans, the drug candidate enters the preclinical study stage. Preclinical tests, also referred to as nonclinical studies, include discovery and target identification, in vitro testing to assess biological activity, mechanism of action, and potential toxicity, as well as animal studies to assess the potential safety, pharmacokinetics, and pharmacological activity of the drug candidate.

Clinical trials involve the administration of the drug candidate to healthy volunteers or patients under the supervision of qualified investigators, generally physicians not employed by or under the trial sponsor’s direct control. Clinical trials are conducted under protocols detailing, among other things, the objectives of the clinical trial, dosing procedures, subject selection and exclusion criteria, and the parameters to be used to monitor subject safety.

Human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

Post-approval clinical trials, sometimes referred to as Phase 4 clinical trials, may be conducted after initial marketing approval. These clinical trials are used to gain additional experience from the treatment of patients in the intended therapeutic indication.

U.S. review and approval processes

The results of product development, nonclinical studies and clinical trials, along with descriptions of the manufacturing process, analytical tests conducted on the chemistry of the drug, proposed labeling and other relevant information are submitted to the FDA as part of an NDA or BLA requesting approval to market the product. The submission of an NDA or BLA is subject to the payment of substantial user fees; a waiver of such fees may be obtained under certain limited circumstances.

If a product receives regulatory approval, the approval may be significantly limited to specific diseases and dosages or the indications for use may otherwise be limited, which could restrict the commercial value of the product. Further, the FDA may require that certain contraindications, warnings or precautions be included in the product labeling. In addition, the FDA may require post marketing clinical trials, sometimes referred to as Phase 4 clinical trials, which are designed to further assess a product’s safety and effectiveness and may require testing and surveillance programs to monitor the safety of approved products that have been commercialized.

Post-approval requirements

Approved products remain subject to ongoing FDA regulation, including requirements relating to manufacturing, labeling, promotion, adverse event reporting and periodic inspections. Failure to comply with applicable requirements may result in enforcement actions, including warning letters, fines, product recalls, suspension or withdrawal of approval, or other penalties.

Regulation in Europe and Other Regions

In addition to U.S. requirements, we must obtain regulatory approvals in foreign jurisdictions prior to conducting clinical trials or marketing products outside the United States. Regulatory requirements vary by country

but generally involve processes comparable to those of the FDA, including review of clinical data, manufacturing information and product labeling.

Competition

Our Business in General

The RNA pipeline across the biopharma industry is expansive, with mostly early-stage assets. Published market reports indicate that there are 1,000+ RNA assets in development with approximately 90% in pre-clinical and Phase 1 studies RNA assets in development are across a broad therapeutic range making for a diffused therapeutic focus across the field.

Competition is intensifying in this space as both biotech and larger pharma companies invest more in RNA technology and RNA pipelines mature in three key areas: RNA platform development (targeted on build of RNA platform components and delivery), platform discovery (unlocking broader therapeutic applicability) and in technology-aided platform accelerators (accelerate RNA design, development, and production - to further leverage advantage of RNA versus traditional technologies). Pharmaceutical and biotechnology companies are heavily pursuing opportunities to build foundational platforms and to expand and accelerate RNA applications. As a result, we face competition at the technology platform and therapeutic indication levels from both large and small biopharmaceutical companies, academic institutions, governmental agencies and public and private research institutions.

Many of our competitors, including those with strategic partners, have significantly greater financial resources and expertise in research and development, manufacturing, preclinical testing, conducting clinical trials, obtaining regulatory approvals and marketing approved products than we do. These competitors also compete with us in recruiting and retaining qualified scientific and management personnel and establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies complementary to, or necessary for, our programs. Mergers and acquisitions, recently and into the future, may result in resource concentration among a potentially consolidated number of competitors.

Our success will be based in part upon our ability to identify, develop and manage a portfolio of product candidates that are safer and more effective than competing products in the treatment of our targeted patients. The commercial opportunity could be reduced or eliminated if competitors develop and commercialize products that are safer, more effective, are more convenient or are less expensive than any products we may develop in our respective areas. Our collaboration with CSL Seqirus may allow us to compete commercially on the world stage within the COVID and influenza markets.

We are aware of several other companies that are working to develop nucleic acid medicines, including gene therapy, gene editing, mRNA (including sa-mRNA), siRNA, and antisense therapeutics. Many of these companies, such as Genevant Sciences and Acuitas Therapeutics, are also developing nucleic acid delivery platforms which compete with LUNAR technology.

Below we have included what we believe to be the competitive landscape for certain of the medicines that we currently have in development.

Lung Franchise ARCT-032 (LUNAR-CF)

The lead candidate of our lung franchise is ARCT-032, an mRNA therapeutic candidate for cystic fibrosis based on our proprietary drug substance mRNA technology platform and our LUNAR lipid nanoparticle delivery platform has advanced into Phase 2 clinical development.

We are aware of product candidates of the following companies that we consider as competitors or future competitors to ARCT-032: Moderna/Vertex, Recode Therapeutics, Eloxx Pharmaceuticals, 4DMT, Spirovant, SalioGen, Splisense, Krystal Biotech, Sionna and Enterprise Therapeutics.

Liver Franchise ARCT-810 (LUNAR-OTC)

Our liver franchise has advanced into mid-stage clinical development with ARCT-810 in Phase 2 clinical development. Potential competitors include, but are not limited to, Ultragenyx and iECURE which are advancing a gene therapy program for OTC in clinical development. Additional companies working on therapies targeting people with OTC deficiency include, Bloomsbury Genetic Therapies and Moderna, which has a therapeutic candidate in pre-clinical development.

LUNAR-COVID-19 Vaccine (KOSTAIVE®)

Our vaccine franchise is based on our self-amplifying STARR technology platform and our lipid nanoparticle delivery platform called LUNAR. This franchise has advanced into the market with the approval of KOSTAIVE® in Japan and geographic expansion is underway to other markets through our collaboration with CSL Seqirus. We consider the following companies with approved or late-stage clinical development vaccines as some of our competitors or future competitors to our partnered COVID-19 vaccine franchise: Pfizer/BioNTech, Moderna, and Sanofi/Novavax. Dozens of other companies are continuing to develop COVID-19 vaccines. However, the majority of these companies use conventional mRNA (not self-amplifying) and protein-based vaccine technology as the basis for their COVID-19 vaccines.

LUNAR-FLU Vaccine

We have partnered our influenza vaccine franchise with CSL Seqirus. We consider the following companies as some of the competitors or future competitors to our partnered LUNAR-Flu vaccine franchise: Pfizer, Moderna, Novavax, and Sanofi. The flu industry is evaluating a shift to utilizing mRNA-based platforms in addition to other non-egg based technologies and traditional (egg-based) technologies.

Multiple Areas

Of the competitors noted above, the following compete with us across multiple areas of our portfolio and/or aspects of our platform technologies:

Human Capital

As of December 31, 2025, we had approximately 111 employees, of which 106 were full-time and 5 were part-time. Additionally, we are supported by contractors and scientific consultants in most areas of the business. None of our employees are represented by a labor union or covered by a collective bargaining agreement. We consider relations with our employees to be good. Our ability to advance our research, development, manufacturing and commercialization activities depends largely on our ability to attract, retain and develop qualified personnel. We compete for talent in specialized and competitive markets and support our employees through professional

development and training programs, and generally offer our employees competitive compensation and benefits, including base salary, annual incentive bonuses, equity-based compensation, healthcare and insurance benefits, retirement savings plans and generous paid time off and holidays.

Senior Leadership

On December 11, 2025, we and Andy Sassine, our former Chief Financial Officer and former member of the Board of Directors, mutually agreed to end his employment relationship in an amicable manner effective December 31, 2025. On December 12, 2025, Joe Roberts, our Controller, was appointed interim principal financial officer and interim principal accounting officer. We have initiated a comprehensive search for a new Chief Financial Officer.

Available Information

The Company was founded in 2013 as Arcturus Therapeutics, Inc., and we have maintained our principal executive offices in San Diego, California since that time. In November 2017, Alcobra Ltd., an Israeli limited company, merged with our company, changed its name to Arcturus Therapeutics Ltd. (“Arcturus Israel”), and commenced trading on Nasdaq under the symbol “ARCT.” On June 17, 2019, we redomiciled to the United States (the “Redomiciliation”) and changed our name to Arcturus Therapeutics Holdings Inc.

Our Internet address is www.arcturusrx.com. Our Annual Reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and proxy statements, and all amendments thereto, are available free of charge on our Internet website. These reports are posted on our website as soon as reasonably practicable after they are electronically filed with the SEC. The public may read and copy any materials that we file with the SEC electronically through the SEC website (www.sec.gov). The information contained on the SEC’s website is not incorporated by reference into this Annual Report on Form 10-K and should not be considered to be part thereof.

Item 1A. Risk Factors

In conducting our business, we face many risks that may interfere with our business objectives. Some of these risks could materially and adversely affect our business, financial condition and results of operations. In particular, we are subject to various risks resulting from inherent unknowns and uncertainties in the drug development and commercialization process, as well as changing economic, political, industry, regulatory, business and financial conditions. The risks and uncertainties described below are not the only ones we face.

You should carefully consider the following factors and other information in this Annual Report before you decide to invest in our common stock. If any of the negative events referred to below occur, our business, financial condition and results of operations could suffer. In any such case, the trading price of our common stock could decline, and you may lose all or part of your investment.

Risk Factor Summary

The following is a summary of certain important factors that may make an investment in our company speculative or risky. You should carefully consider the fuller risk factor disclosure set forth in this Annual Report, in addition to the other information herein, including the section of this report titled “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our financial statements and related notes.

RISKS RELATED TO OUR FINANCIAL CONDITION AND NEED FOR ADDITIONAL CAPITAL

We have a limited operating history, have incurred significant losses since our inception (with the exception of fiscal year 2022) and anticipate that we will continue to incur significant losses for the foreseeable future.

We are a global messenger RNA medicines company with a limited operating history. Since inception, our operations have been primarily limited to acquiring and licensing intellectual property rights, developing our product platform, undertaking research, partnering assets and running clinical product development programs. We only have one product that, through our partners CSL Seqirus and Meiji, is being commercialized, and it is currently only commercialized in Japan. Consequently, any predictions about our future success or viability, or any evaluation of our business and prospects, is difficult and may not be accurate. In 2025 we recognized a significant portion of our revenue from non-recurring milestone payments and license revenue under our collaboration agreement with CSL Seqirus. We may not receive any future milestone payments from CSL Seqirus. We have not recognized any revenue from product sales since our inception.

As of December 31, 2025, we had an accumulated deficit of $514.6 million.

We have devoted most of our financial resources to research and development, including our preclinical and clinical development activities. To date, we have funded our operations primarily through upfront payments, research funding and milestone payments from strategic alliances and collaborations, and through the sale of equity and convertible securities. We expect to continue to incur substantial and increased expenses, losses and negative cash flows as we expand our development activities and advance our programs. If our product candidates are not successfully developed or commercialized, including because of a lack of capital, or if we do not generate enough revenue following marketing approval, we will not achieve profitability and our business may fail. Even if we or our strategic alliance partners successfully obtain regulatory approval to market a product candidate, our revenues will also depend upon the size of any markets in which our product candidates have received market approval and our ability to achieve sufficient market acceptance and adequate market share for our products.

We expect to continue to incur significant expenses and increasing operating losses for the foreseeable future. The net losses we incur may fluctuate significantly from quarter to quarter. We anticipate that our expenses will increase substantially if and as we:

We have not generated any revenue from product sales, have generated only limited collaboration and grant revenue since inception, and may never be profitable in the long term.

Our ability to generate revenue and achieve profitability depends on our ability, alone or with strategic alliance partners, to successfully complete the development of, obtain the necessary regulatory approvals for and commercialize our product candidates. Our ability to generate revenues from product sales depends heavily on our success in:

Because of the numerous risks and uncertainties associated with pharmaceutical product development, we are unable to predict reliably the timing or amount of increased expenses and when we will be able to achieve and maintain profitability, if ever. In addition, our expenses could increase beyond expectations if we are required by the FDA, or other foreign regulatory agencies to perform studies and trials in addition to those that we currently anticipate.

Even if our internal product candidates are approved for commercial sale, or KOSTAIVE continues to achieve approvals in more countries, we anticipate incurring significant costs associated with commercializing any approved product. Even if we generate revenues from the sale of any approved products, we may not become profitable and may need to obtain additional funding to continue operations.

We expect that we will need to raise additional capital in the future, which may not be available on acceptable terms, or at all.

Developing pharmaceutical products, including conducting studies and clinical trials, is extremely expensive. We expect our research and development expenses to substantially increase in connection with our ongoing activities, particularly as we advance our product candidates towards and through clinical trials. We expect that we

will need to raise additional capital to support our operations and such funding may not be available to us on acceptable terms, or at all. As of December 31, 2025, we had unrestricted cash and cash equivalents of $230.9 million, which we expect should be sufficient to fund currently planned operations for the near future, at least the next 12 months. But if our plans change or we face unexpected circumstances, our capital resources may be depleted more rapidly than we currently anticipate. For example, our clinical trials may encounter technical, regulatory or other difficulties. Any of these events would increase our development costs more than we expect. In order to support our long-term plans, we will need to raise additional capital or otherwise obtain funding through additional strategic alliances if we choose to initiate preclinical or clinical trials for product candidates that are not currently subject to a collaboration. In any event, we will require additional capital to obtain regulatory approval for, and to commercialize, future product candidates. Even if the results of clinical studies of our product candidates are positive, the stock market might not react favorably, which would weaken our ability to raise additional capital.

A portion of our current cash balance is expected to be utilized during fiscal year 2026 to fund (i) advances to our LUNAR-CF program in clinical trials, (ii) the continued Phase 2 trial of ARCT-810, our LUNAR-OTC candidate, (iii) expenses incurred prior to customer payments under the CSL Collaboration Agreement and BARDA agreement and (iv) continued exploratory activities related to our platform and other general administrative activities.

Any additional fundraising efforts may divert our management from our day-to-day activities, which may delay and hinder our ability to develop and commercialize future product candidates. We may be unable to raise sufficient amounts of additional capital when needed and on acceptable terms, which could require us to:

We are dependent upon relationships with our collaboration partners, and the failure of these relationships could negatively affect our business and results of operations.

We are subject to a number of risks associated with our dependence on our relationships with our collaboration partners, including:

Due to these factors and other possible disagreements with our collaboration partners, we may be delayed or prevented from further developing, manufacturing or commercializing our drug products or our product candidates or we may become involved in litigation or arbitration, which would be time consuming and expensive.

If any collaboration partner were to terminate our collaborative relationship unilaterally, we would need to undertake development, commercialization or distribution or sale activities for our drug products and product candidates solely at our own expense, and/or seek one or more other partners for some or all of these activities worldwide. If we pursued these activities on our own, it would significantly increase our capital and infrastructure requirements, might limit the indications we are able to pursue for our drug products and our product candidates, and could prevent us from effectively developing and commercializing our drug products and our product candidates. If we sought to find one or more other pharmaceutical company partners for some or all of these activities, we may not be successful in such efforts, or they may result in collaborations that have us expending greater funds and efforts than our relationships with our current collaboration partners.

Our ability to use our net operating loss carryforwards and certain other tax attributes may be limited.

Under the Tax Cuts and Jobs Act, as modified by the Coronavirus Aid, Relief, and Economic Security Act, or CARES Act, U.S. federal net operating losses (“NOLs”) incurred in 2018 and in future years may be carried forward indefinitely, but the deductibility of such federal NOLs is limited. To the extent that we continue to generate taxable losses for United States federal income tax purposes, unused NOLs will carry forward to offset future taxable income (subject to any applicable limitations), if any. Under Sections 382 and 383 of the Internal Revenue Code, as amended, if a corporation undergoes an “ownership change,” generally defined as a greater than 50% change (by value) in its equity ownership over a three-year period, the corporation’s ability to use its pre-change NOLs and other pre-change tax attributes (such as research tax credits) to offset its post-change income may be significantly limited. We believe we may have triggered an “ownership change” limitation; however, we have not completed a study in accordance with Sections 382 and 383 of the Code to determine whether this ownership change has occurred or what the possible effects of an ownership change would be on our ability to use NOLs. We may also experience ownership changes in the future as a result of subsequent shifts in our share ownership. As a result, if we earn net taxable income, our ability to use our pre-change NOL carryforwards to offset U.S. federal or state taxable income may be subject to limitations, which could potentially result in increased future tax liability to us. Similar provisions of U.S. state tax law may also apply to limit our use of accumulated state tax attributes, including our state NOLs. In addition, at the state level, there may be periods during which the use of NOLs is suspended or otherwise limited, which could accelerate or permanently increase state taxes owed. As a result, even if we attain profitability, we may be unable to use a material portion of our NOLs and other tax attributes, which could negatively impact our future cash flows.

RISKS RELATED TO THE DEVELOPMENT AND COMMERCIALIZATION OF PRODUCT CANDIDATES

We are highly dependent upon our relationship with CSL Seqirus to further research, manufacture and commercialize self-amplifying mRNA vaccines against COVID-19, influenza and three other infectious diseases; CSL Seqirus has announced a significant write-down of the licensed collaboration programs.

In November 2022, we entered into the CSL Collaboration Agreement with CSL Seqirus, for the research, manufacture and global commercialization of self-amplifying mRNA vaccines against COVID-19, influenza and three other infectious diseases. If such relationship is unsuccessful, if CSL Seqirus terminates its collaboration agreement with us, or if we determine it is in our best interests to terminate the agreement, it could negatively impact our ability to generate net product revenue. Failure by CSL Seqirus to perform its duties under its collaboration agreement with us may negatively affect us. In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing decline in the COVID-19 market and more onerous U.S. regulatory requirements. Such action and CSL’s statements indicate that CSL Seqirus no longer believes that the collaboration assets will generate sufficiently probable, risk-adjusted economic benefits. The development of the licensed assets and even commercialization activity may be significantly impacted. If CSL Seqirus ceases, suspends or materially reduces development and commercialization activities of our technology under the CSL Collaboration, our business and prospects could be materially and adversely affected. Any disagreement with CSL Seqirus regarding the satisfaction of milestones, or of CSL Seqirus’ obligations toward development or commercialization of the licensed programs, could result in a dispute that could result in termination of a program, and possibly costly litigation or arbitration which may divert management attention and resources.

A potential separation of CSL Seqirus could disrupt our collaboration and materially harm our business.

Reports that CSL Limited intends to separate or spin off its vaccine business, including its subsidiary CSL Seqirus, could disrupt or adversely affect our collaboration with CSL Seqirus and materially harm our business. We cannot predict the timing, terms, structure, or ultimate consummation of any potential separation, and even the announcement or pendency of such a transaction may create uncertainty and execution risk that could adversely affect CSL Seqirus’s performance under our agreements and, as a result, our programs, timelines and costs. For example, a separation could lead to shifting strategic priorities, changes in management focus, or reduced access to corporate resources, capital, manufacturing networks or commercial infrastructure previously available to CSL Seqirus as part of the CSL group. In addition, any stand‑alone entity may have a different risk profile, capital structure, credit quality, or appetite for development and commercial investment, which could impair its ability or willingness to satisfy funding, diligence, supply, or commercialization obligations or to continue programs that were prioritized prior to the separation.

KOSTAIVE might not have a profitable commercial market.

If the prevalence of COVID-19 and public concern about the virus continues to decline, the potential market opportunity will shrink for KOSTAIVE under our collaboration with CSL Seqirus. Further, as additional COVID-19 vaccines are approved and production of existing COVID-19 vaccines improves, there may be downward pressure on prices. Therefore, even if we and CSL Seqirus can get through the extremely costly, long and risky process of developing and obtaining regulatory approval to market a vaccine globally, it may not be commercially successful. This failure could be due to reduced demand for COVID-19 vaccines, increased regulatory hurdles, lower prices, distribution problems, competitors’ products or many other reasons. Our manufacturing process for KOSTAIVE includes a step for lyophilization to enhance the stability of the vaccine product. The additional step of lyophilization adds time and costs to the overall production output, which could adversely impact the production volumes and profitability of our COVID-19 vaccines if approval to market a vaccine is achieved. Any changes to our manufacturing processes or our product format could take a long time, be expensive and be unsuccessful. It is also still unclear if the vaccines will enable adequate long-term protection, as (i) many vaccinated individuals have become ill due to “breakthrough infections” and have transmitted the virus to many others, (ii) there are millions of individuals who refuse to be vaccinated or who cannot be vaccinated due to pre-existing conditions, (iii) it is unclear how long the vaccine protection will last, and (iv) genetic mutations or variants of the virus already have had, and are expected to continue to have, an adverse impact on the efficacy of available vaccines. If we cannot, with and through our partner, develop and commercialize a vaccine that adequately addresses some of these shortcomings of vaccines currently on the market, we cannot expect to have commercial success.

KOSTAIVE only has marketing approval in Japan and Europe and may never achieve marketing approval in any other countries.

Although we have marketing approval for KOSTAIVE in Japan and Europe, we do not have approval for KOSTAIVE in any other countries and may never achieve marketing approval in any other countries. Our continued development efforts for KOSTAIVE, and the ongoing efforts to retain approval of updated versions, is dependent on the efforts of our partner, CSL Seqirus. KOSTAIVE could face increased research and development costs, including

for clinical trials, non-clinical studies and CMC, when updating COVID-19 vaccines containing new variants of concern based on WHO and FDA recommendations. If key regulatory authorities, such as the FDA, determine that our data is inadequate or unacceptable, or make the path to regulatory approval more difficult, we may not be able to achieve regulatory approval and any additional study may prove too costly for us to conduct without a strategic partner. The U.S. is the largest market for vaccines, and if we do not receive approvals to market KOSTAIVE in the U.S., the overall commercial market for KOSTAIVE could be substantially lower than the overall market of our competitors.

Even with the commercialization of KOSTAIVE in Japan, there might not be meaningful sales in Japan. Despite the approval of KOSTAIVE in Europe, KOSTAIVE has not, and might never, achieve commercialization in Europe.

We are relying on our partner, CSL Seqirus, and CSL Seqirus’ partner, Meiji Seika Pharma (Meiji), to conduct further development and commercialization of KOSTAIVE in Japan. Even if KOSTAIVE continues to be commercialized in Japan, there might not be meaningful sales, due to competition, pricing, product profile, vaccine uptake by the public or other factors. To date, demand for KOSTAIVE in Japan has been weak, and future sales may decrease and our partners may decide to cease commercialization. Although KOSTAIVE has received approval in Europe, KOSTAIVE has not, and might never, achieve commercialization in Europe, due to a numbers of factors, such as the competitiveness of different product presentations and formats and the wide market penetration of existing COVID-19 vaccine makers.

There is significant competition in the COVID-19 vaccine market, some competitors’ vaccines are already widely accepted in the market, and many of our competitors have substantially greater financial, scientific and other resources than we have.

Pfizer, Moderna and Novavax have received full approvals or emergency use authorization from the FDA and many other health regulatory authorities throughout the world, and other biopharmaceutical companies have received approvals or authorizations from many health regulatory authorities other than the FDA, for their COVID-19 vaccines and have already commercialized them on a large scale and have vaccinated billions of people around the world.

Even with the partnering of our COVID-19 program and initial commercialization in Japan, we are already at a significant competitive disadvantage to those companies with vaccines on the market, as well as many other competitors pursuing vaccine candidates. Many other competitors have significantly greater product candidate development, manufacturing and marketing resources than we do. Larger pharmaceutical and biotechnology companies have extensive experience in clinical testing and obtaining regulatory approval for their products, and may have the resources to heavily invest to accelerate discovery and development of their vaccine candidates. Our business could be further materially and adversely affected by our competitors’ commercialization of their vaccines before our vaccine candidate is approved in various countries. If the COVID-19 vaccines of our competitors are shown to be safer, more effective against multiple variants, have fewer or less severe side effects, have broader market acceptance, are more convenient or are less expensive than any vaccine candidate than KOSTAIVE, then KOSTAIVE may not achieve any commercial success even where approved. Furthermore, if any competitors are successful in producing a more efficacious vaccine or other treatment for COVID-19, or if any competitors are able to manufacture and distribute any such vaccines or treatments with greater efficiency, there may be a diversion of potential governmental and other funding away from us and toward such other parties.

We face significant competition from other biotechnology and pharmaceutical companies and our operating results will suffer if we fail to compete effectively.

The biotechnology and pharmaceutical industries are intensely competitive. We have competitors both in the United States and internationally, including major multinational pharmaceutical companies, biotechnology companies and universities and other research institutions. Many of our competitors have substantially greater financial, technical and other resources, such as larger research and development staff and experienced marketing, regulatory and manufacturing organizations. Additional mergers and acquisitions in the biotechnology and pharmaceutical industries may result in even more resources being concentrated in our competitors. Competition may increase further as a result of advances in the commercial applicability of technologies and greater availability of capital for investment in these industries. Our competitors may succeed in developing, acquiring or licensing on an exclusive basis, drug products that are more effective, safer or less costly than any product candidate that we may develop. Our existing competitors and new market entrants may respond more quickly to or integrate new or

emerging technologies such as artificial intelligence and machine learning, undertake more extensive marketing campaigns, have greater access to clinical information to support ongoing product position in the market, have greater financial, marketing and other resources or be more successful in attracting potential customers, employees and strategic partners. There can be no assurance that any products now in development, or that we may seek to develop in the future, will achieve technological feasibility, obtain regulatory approval or gain market acceptance. If we are unable to develop and launch new products, our ability to maintain or expand our market position in the markets in which we participate may be negatively impacted. Our competitors may achieve patent protection, regulatory approval, or product commercialization that would limit our ability to compete with them. These and other competitive pressures could have a material adverse effect on our business.

If we are unable to generate successful results from preclinical and clinical studies of our product candidates, or experience significant delays in doing so, our business may be materially harmed.

Other than the approval of KOSTAIVE in Japan and Europe, we have no products approved for commercial marketing and all of our product candidates are in preclinical or clinical development. Before obtaining regulatory approval for the commercial distribution of our product candidates, we or an existing or future collaborator must conduct extensive preclinical studies and clinical trials to demonstrate the safety and efficacy of our product candidates.

The success of our product candidates will depend on several factors, including the following:

If we do not achieve one or more of these factors in a timely manner or at all, we could experience significant delays or an inability to successfully complete the development or commercialization of our product candidates, which would materially harm our business.

Our platform focuses on nucleic acid technology, and mRNA drug products in particular, which are relatively new and any adverse results from nucleic acid or mRNA technologies in the industry could significantly impact our ability to develop and commercialize marketable products.

We have concentrated our therapeutic product research and development efforts on nucleic acid technology, and mRNA in particular, and our future success depends on the successful development and acceptance of this technology for drug products. The development and commercialization of drug products based on nucleic acid technologies, including mRNA, are relatively new. The scientific evidence to support the feasibility of developing product candidates based on these discoveries is both preliminary and limited. If nucleic acid or mRNA approaches to drug products encounter setbacks based on the safety, efficacy, distribution, costs or other factors, it will significantly hurt our prospects and the value of our common stock.

Our focus on nucleic acid technology for developing drugs as opposed to more proven technologies for drug development increases the risks associated with our business. If we are not successful in developing any product candidates using nucleic acid technology, we may be required to change the scope and direction of our product development activities. In that case, we may not be able to identify and successfully implement an alternative product development strategy.

Changes to our drug product presentation could significantly impact our timeline to commercialize our products.

Each of our products, including KOSTAIVE, has a certain drug product presentation. We evaluate and implement the product presentation attributes based on our considerations of regulatory and commercial potential, along with scientific feasibility. There can be no assurance that the product presentation or characteristics of any of

our products will be sufficient to achieve regulatory approval or commercialization per planned timelines. For example, the stability of our products and the vial presentations could impact the commercial attractiveness of a product, and different markets may favor different characteristics. Any changes to drug product formats will likely add additional cost and may delay approvals.

We may not be successful in our efforts to identify or discover potential product candidates.

The success of our business depends primarily upon our ability to identify, develop and commercialize messenger RNA medicines. Our research programs may initially show promise in identifying potential product candidates, yet fail to yield product candidates for clinical development for a number of reasons, including:

If any of these events occur, we may be forced to abandon our development efforts for a program or programs, which would have a material adverse effect on our business and could potentially cause us to cease operations. Research programs to identify new product candidates require substantial technical, financial and human resources. We may focus our efforts and resources on potential programs or product candidates that ultimately prove to be unsuccessful.

If clinical trials of our product candidates fail to demonstrate safety and efficacy to the satisfaction of regulatory authorities or do not otherwise produce positive results, we may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of our product candidates.

Before obtaining marketing approval from regulatory authorities for the sale of product candidates, we or our strategic alliance partners must conduct extensive clinical trials to demonstrate the safety and efficacy of the product candidates in humans. Clinical trials are expensive, difficult to design and implement, can take many years to complete and are uncertain as to the outcome. A failure of one or more clinical trials can occur at any stage of testing. The outcome of preclinical studies and early clinical trials may not be predictive of the success of later clinical trials, and interim results of a clinical trial do not necessarily predict final results. Moreover, preclinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that have believed their product candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failed to obtain marketing approval for their products. Furthermore, even if prior animal studies have demonstrated the potential safety and efficacy of our product candidates, there can be no guarantee that such results will be reproducible in preclinical studies and clinical trials involving human subjects.

Events which may result in a delay or unsuccessful completion of clinical development include:

If we or our strategic alliance partners are required to conduct additional clinical trials or other testing of any product candidates beyond those that are currently contemplated, are unable to successfully complete clinical trials of any such product candidates or other testing, or if the results of these trials or tests are not positive, are only modestly positive or if there are safety concerns, we or our strategic alliance partners may:

Our product development costs will also increase if we experience delays in testing or marketing approvals. We face risks that clinical trials may not begin as planned, may need to be restructured or may not be completed on schedule, or at all. Significant clinical trial delays also could shorten any periods during which we may have the exclusive right to commercialize our product candidates or could allow our competitors to bring products to market before we do, which would impair our ability to successfully commercialize our product candidates. Any inability to timely and successfully complete preclinical and clinical development, whether independently or with our strategic alliance partners, could result in additional costs to us or impair our ability to generate revenues from product sales, regulatory and commercialization milestones and royalties.

We may find it difficult to identify and enroll patients in our clinical studies, and the limited number of patients who have the diseases for which certain of our product candidates are being studied could delay or prevent clinical studies of certain of our product candidates.

Identifying and qualifying patients to participate in clinical studies of our product candidates is critical to our success. The timing of our clinical studies depends in part on the speed at which we can recruit patients to participate in testing our product candidates, and we may experience delays in our clinical studies if we encounter difficulties in enrollment.

In addition, certain conditions for which we plan to evaluate our current product candidates are rare genetic diseases, and have limited patient pools from which to draw for clinical studies. For example, we estimate that approximately 8,000 patients in the developed world suffer from late-onset OTC deficiency, for which LUNAR-OTC is being studied. In addition to the rarity of these diseases, the eligibility criteria of our clinical studies will further limit the pool of available study participants as we will require patients to have specific characteristics that we can measure or to assure their disease is either severe enough or not too advanced to include them in a study. The process of finding and diagnosing patients may prove costly, especially since the rare diseases we are studying are commonly underdiagnosed. We also may not be able to identify, recruit, and enroll a sufficient number of appropriate patients to complete our clinical studies because of demographic criteria for prospective patients, the

perceived risks and benefits of the product candidate under study, the proximity and availability of clinical study sites for prospective patients, and the patient referral practices of physicians. The availability and efficacy of competing therapies and clinical studies can also adversely impact enrollment.

If we are unable to promptly enroll an adequate number of patients in our studies for the foregoing or other reasons, the timeline for conducting studies and obtaining regulatory approval of potential products will be delayed, the commercial prospects of our product candidates will be harmed, and our ability to generate product revenue from any of these product candidates could be delayed or prevented. Furthermore, many of the factors that cause, or lead to, a delay in the commencement or completion of clinical studies may also ultimately lead to the denial of regulatory approval of our product candidates. Delays in achieving approval to conduct and in completing our clinical studies will increase our costs, slow down our product candidate development and approval process, and jeopardize our ability to commence product sales and generate revenue. Any of these occurrences may harm our business, financial condition, and prospects significantly.

If any of our product candidates cause undesirable side effects or have other properties impacting safety, approvals to proceed with further clinical trials may be denied or delayed and regulatory approval could be prevented, delayed or limited.

Undesirable side effects caused by our product candidates could cause us or regulatory authorities to interrupt, delay or halt clinical trials, or to deny or delay approvals to proceed with further clinical trials, and could result in a more restrictive label or the delay or denial of regulatory approval by the FDA or other regulatory authorities. It is likely that there will be side effects associated with use of our product candidates. If results of our trials reveal a high and unacceptable severity and prevalence of side effects, our trials could be suspended or terminated and the FDA or comparable foreign regulatory authorities could order us to cease further development of, or deny approval of, our product candidates for any or all targeted indications. Such side effects could also affect patient recruitment, the ability of enrolled patients to complete the trial or result in potential product liability claims. Any of these occurrences may materially and adversely affect our reputation and financial condition.

Further, clinical trials by their nature test product candidates in only samples of the potential patient populations. With a limited number of patients and limited duration of exposure in such trials, rare and severe side effects of our product candidates may not be uncovered until a significantly larger number of patients are exposed to the product candidate.

If any of our product candidates receives marketing approval, and causes serious, unexpected, or undesired side effects, a number of potentially significant negative consequences could result after we begin commercialization, including:

Any of these events could prevent us or our partners from achieving or maintaining market acceptance of the affected product and could substantially increase the costs of commercializing our future products and impair our ability to generate revenues from the commercialization of these products either by us or by our strategic alliance partners.

Even if we complete the necessary preclinical studies and clinical trials, we are required to obtain regulatory approval to commercialize a product candidate and we cannot, therefore, predict the timing of any revenue from a future product.

The extent and timing of any product revenue is highly unpredictable because regulatory authorities may not complete their review processes in a timely manner, or we may not be able to obtain regulatory approval for many reasons including:

Additional delays may result if an FDA advisory committee recommends restrictions on approval or recommends non-approval. In addition, we or our strategic alliance partners may experience delays or rejections based upon additional government regulation from future legislation or administrative action, or changes in regulatory agency policy during the period of product development, clinical trials and the review process.

Our rare disease candidates, even if approved, might not have a profitable commercial market.

Rare diseases, by definition, have a relatively small population of patients, thereby limiting the potential market size and increasing pressure on the pricing of drug products in order to have a profitable market opportunity. Further, our rare disease therapeutic candidates require dosing of drug substance in far greater quantities than in our vaccine candidates, which significantly increases the costs of manufacture. Such factors, along with political and societal pressure to minimize pricing, could impact the ability of our products to have sustainable and profitable commercial markets. Therefore, even if we can get through the extremely costly, long and risky process of developing and obtaining regulatory approval to market a drug candidate, it may not be commercially successful.

Current regulatory authorities in the United States may change or institute policies that increase challenges for clinical development, regulatory approval and commercialization of our vaccine and other programs

Leadership and policy priorities at the HHS and the FDA have changed and may continue to evolve, which could result in modifications to regulatory requirements, approval standards or development pathways applicable to vaccines and therapeutic products. Although certain regulatory initiatives may be intended to streamline development, recent FDA guidance has adversely affected the timing and expected costs of our programs. On September 5, 2025, the week prior to our planned submission of a Biologics License Application for KOSTAIVE, the FDA requested that we delay our submission and in October 2025 informed us that, although the FDA had previously agreed that our proposed data package could support a single-dose indication, upon further consideration it found that additional data from a clinical endpoint efficacy will be needed based on a revised COVID-19 vaccine regulatory framework. In addition, changes in governmental policies, funding priorities, or staffing levels, including reductions in force or work stoppages affecting federal agencies, could delay regulatory review processes or

otherwise negatively impact the development, approval or commercialization of our product candidates. Any such developments could materially adversely affect our business, financial condition and results of operations.

Even if we obtain regulatory approval for a product candidate, we will still face extensive regulatory requirements and our products may face future development and regulatory difficulties.

Even if we obtain regulatory approval in the United States, the FDA may still impose significant restrictions on the indicated uses or marketing of our product candidates, or impose ongoing requirements for potentially costly post-approval studies or post-market surveillance. The FDA may also require a risk evaluation and mitigation strategy as a condition of approval of our product candidates, which could include requirements for a medication guide, physician communication plans or additional elements to ensure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. Additionally, the manufacturing processes, packaging, distribution, adverse event reporting, labeling, advertising, promotion, and recordkeeping for the product will be subject to extensive and ongoing FDA regulatory requirements, in addition to other potentially applicable federal and state laws. These requirements include monitoring and reporting of adverse events and other post-marketing information and reports, registration, as well as continued compliance with current good manufacturing practice, or cGMP, regulations. The holder of an approved NDA must also submit new or supplemental applications and obtain FDA approval for certain changes to the approved product, product labeling or manufacturing process. If we or a regulatory agency discovers previously unknown problems with a product such as adverse events of unanticipated severity or frequency, or problems with the facility where the product is manufactured, a regulatory agency may impose restrictions relative to that product or the manufacturing facility, including requiring recall or withdrawal of the product from the market or suspension of manufacturing.

If we or our strategic partners fail to comply with applicable regulatory requirements following approval of any of our product candidates, a regulatory agency may:

Any government investigation of alleged violations of law could require us to expend significant time and resources in response and could generate negative publicity. The occurrence of any event or penalty described above may inhibit our ability to commercialize our future products, if approved, and generate revenues.

We may use our financial and human resources to pursue a particular research program or product candidate and fail to capitalize on programs or product candidates that may be more profitable or for which there is a greater likelihood of success.

As a result of our limited financial and human resources, we will have to make strategic decisions as to which targets and product candidates to pursue and may forego or delay pursuit of opportunities with other product candidates or for other indications that later prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through strategic alliance, licensing or other royalty arrangements in cases in which it would have been more advantageous for us to retain sole development and commercialization rights to such product candidate, or we may allocate internal resources to a product candidate in a therapeutic area in which it would have been more advantageous to enter into a partnering arrangement.

If we fail to comply with environmental, health and safety laws and regulations, we could become subject to fines or penalties or incur costs that could have a material adverse effect on the success of our business.

We are subject to numerous environmental, health and safety laws and regulations, including those governing laboratory procedures and the handling, use, storage, treatment and disposal of hazardous materials and wastes. Our

operations involve the use of hazardous and flammable materials, including chemicals and biological materials. Our operations also produce hazardous waste products. We generally contract with third parties for the disposal of these materials and wastes. We cannot eliminate the risk of contamination or injury from these materials. In the event of contamination or injury resulting from our use of hazardous materials, we could be held liable for any resulting damages, and any liability could exceed applicable insurance coverage we may have as well as our financial resources. We also could incur significant costs associated with civil or criminal fines and penalties.

Although we maintain workers’ compensation insurance to cover us for costs and expenses we may incur due to injuries to our employees resulting from the use of hazardous materials or other work-related injuries, this insurance may not provide adequate coverage against potential liabilities. In addition, we may incur substantial costs in order to comply with current or future environmental, health and safety laws and regulations. These current or future laws and regulations may impair our research, development or production efforts. Failure to comply with these laws and regulations also may result in substantial fines, penalties or other sanctions.

Manufacturing issues may arise that could increase product and regulatory approval costs or delay or hinder commercialization.

As we scale-up manufacturing of product candidates and conduct required stability testing, product, packaging, equipment and process-related issues may require refinement or resolution in order to proceed with any clinical trials and obtain regulatory approval for commercial marketing. We may identify significant impurities, which could result in increased scrutiny by the regulatory agencies, delays in clinical programs and regulatory approval, increases in our operating expenses, or failure to obtain or maintain approval for product candidates or any approved products. The robustness of our manufacturing supply chain to support commercial distribution has not been meaningfully tested. Furthermore, we are required by our contract manufacturers to make financial commitments in advance of the receipt of clinical data or feedback from regulatory authorities, which could result in significant financial obligations.

The commercial success of our product candidates will depend in part upon the acceptance of our product candidates by the medical community, including physicians, patients and healthcare payors.

The degree of market acceptance of any product candidates will depend on a number of factors, including:

Unless other formulations are developed in the future, we expect our compounds to be formulated in an injectable or inhalable form. Injectable medications may be disfavored by patients or their physicians in the event drugs which are easy to administer, such as oral medications, are available. If any of our products is approved, but does not achieve an adequate level of acceptance by physicians, patients and healthcare payors, we may not generate sufficient revenues from such product and we may not become or remain profitable. Such increased competition

may decrease any future potential revenue for future product candidates due to increasing pressure for lower pricing and higher discounts in the commercialization of our product.

If we are unable to establish cost-effective sales and marketing capabilities or enter into agreements with third parties to market and sell our product candidates, we may be unable to generate any revenues from product sales.

In order to market any products that may be approved, we must build our sales, marketing, managerial and other non-technical capabilities or make arrangements with outside parties to perform these services. With respect to certain of our current programs as well as future programs, we may rely completely on a strategic alliance partner for sales and marketing. In addition, we intend to enter into strategic alliances with other parties to commercialize other product candidates, if approved, including in markets outside of the United States or for other large markets that are beyond our resources. Although we might establish a sales organization if we are able to obtain approval to market any product candidates for niche markets in the United States, we will also consider the option to enter into strategic alliances for future product candidates in the United States if commercialization requirements exceed our available resources. This will reduce the potential profit generated from the sales of these products.

Our current and any future strategic alliance partners may not dedicate sufficient resources to the commercialization of our product candidates, if approved, or may otherwise fail in their commercialization due to factors beyond our control. If we are unable to establish effective alliances to enable the sale of our product candidates, if approved, to healthcare professionals and in geographical regions, including the United States, that will not be covered by our own marketing and sales force, or if our potential future strategic alliance partners do not successfully commercialize the product candidates that may be approved, our ability to generate revenues from product sales will be adversely affected.

If we are unable to establish adequate sales, marketing and distribution capabilities, whether independently or with third parties, we may not be able to generate sufficient product revenue and may not become profitable. We will be competing with many companies that currently have extensive and well-funded marketing and sales operations. Without an internal team or the support of a third party to perform marketing and sales functions, we may be unable to compete successfully against these more established companies.

KOSTAIVE has received marketing approval in Japan and Europe, and might in the future receive approvals in other countries outside of the United States. A variety of risks associated with international operations could materially adversely affect our business.

KOSTAIVE has received marketing approval in Japan and Europe and may expand into other countries outside of the United States for such product and for future potential products. As a result, we are and expect that we will be subject to additional risks related to entering into international business relationships, including:

Tariffs could adversely affect our business and financial results.

We purchase components of our product candidates, including raw materials, from U.S. domestic sources, as well as various global sources including but not limited to those located in the People’s Republic of China (“PRC”), Japan, Austria, Germany, and the United Kingdom. The current U.S. presidential administration has proposed the implementation of a number of tariffs, including tariffs on products and materials from PRC, which could increase our production costs. If tariffs make purchases of materials from certain jurisdictions untenable, we may also need to obtain materials from other sources, when possible, which could also increase our costs and delay our planned clinical trials and manufacture of our products and product candidates. Any of these factors may adversely affect our financial condition or results of operations.

If coverage and adequate reimbursement is not available for any of our future products, it would be difficult for us to sell that product profitably.

Market acceptance and sales of any product candidates that we develop will depend on coverage and reimbursement policies and may be affected by future healthcare reform measures. Government authorities and third-party payors, such as private health insurers, government payors and health maintenance organizations, decide which drugs they will pay for and establish reimbursement levels. We cannot be sure that coverage and adequate reimbursement will be available for any future product candidates. In the United States, the Centers for Medicare & Medicaid Services (“CMS”), an agency within the U.S. Department of Health and Human Services, decides whether and to what extent a new drug will be covered and reimbursed under Medicare. Private payors tend to follow the coverage reimbursement policies established by CMS to a substantial degree. It is difficult to predict what CMS will decide with respect to reimbursement for novel product candidates. Inadequate reimbursement amounts could substantially reduce the demand for, or the price of, our future products. Further, one payor’s determination to provide coverage for a product does not assure that other payors will also provide coverage for the product. If reimbursement is not available, or is available only at limited levels, we may not be able to successfully commercialize product candidates that we develop and that may be approved. Thus, even if we succeed in bringing a product to market, it may not be considered medically necessary or cost-effective, and the amount reimbursed for any products may be insufficient to allow us to sell our products on a competitive basis.

RISKS RELATED TO OUR RELIANCE ON OUTSIDE PARTIES

If our strategic alliances are unsuccessful or are terminated, we may be unable to commercialize certain product candidates and generate revenues.

We depend on alliance partners for financial and scientific resources for the clinical development, manufacture and commercialization of certain of our product candidates. Under these alliances we are likely to have limited influence and control over their approaches to development and commercialization. If strategic alliance partners do not perform in the manner that we expect or fail to fulfill their responsibilities in a timely manner, or at all, the clinical development, regulatory approval and commercialization efforts related to product candidates we have licensed to such strategic alliance partners could be delayed or terminated. These alliances will likely provide us with limited control over the course of development of a product candidate, especially once a candidate has reached the stage of clinical development. Our ability to ultimately recognize revenue from our strategic relationships will depend upon the ability and willingness of our alliance partners to successfully meet their respective responsibilities under our agreements with them.

Our ability to recognize revenues from strategic alliances may be impaired by several factors, including:

If any of our alliance partners do not elect to pursue the development and commercialization of our development candidates or if they terminate the strategic alliance, then, depending on the event:

Any of these events would have a material adverse effect on our results of operations and financial condition.

A potential separation of CSL Seqirus could disrupt our collaboration and materially harm our business.

Reports that CSL Limited intends to separate or spin off its vaccine business, including its subsidiary CSL Seqirus, could disrupt or adversely affect our collaboration and materially harm our business. We are party to a strategic collaboration with CSL Seqirus for the development and commercialization of mRNA vaccines for COVID-19, influenza and certain other infectious diseases. We cannot predict the timing, terms, structure, or ultimate consummation of any potential separation, and even the announcement or pendency of such a transaction may create uncertainty and execution risk that could adversely affect CSL Seqirus’s performance under our agreements and, as a result, our programs, timelines and costs. For example, a separation could lead to shifting strategic priorities, changes in management focus, or reduced access to corporate resources, capital, manufacturing networks or commercial infrastructure previously available to CSL Seqirus as part of the CSL group. In addition, any stand‑alone entity may have a different risk profile, capital structure, credit quality, or appetite for development and commercial investment, which could impair its ability or willingness to satisfy funding, diligence, supply, or commercialization obligations or to continue programs that were prioritized prior to the separation.

If the outside contractors we rely on to conduct some aspects of our compound formulation, research and studies do not perform satisfactorily and meet deadlines, development of our product candidates could be delayed or precluded.

We do not independently conduct all aspects of our drug discovery activities, compound formulation research or preclinical and clinical studies of product candidates. We currently rely and expect to continue to rely on outside

contractors to conduct some aspects of our preclinical and clinical studies and formulation development, but we remain responsible for ensuring that each of our IND-enabling studies and clinical trials are conducted in accordance with the study plan and protocols for the trial.

If these outside parties terminate their engagements with us or do not successfully carry out their contractual duties, meet expected deadlines or conduct our studies in accordance with regulatory requirements or our stated study plans and protocols, we will not be able to complete, or may be delayed in completing, the necessary preclinical studies to enable us or our strategic alliance partners to select viable product candidates for IND submissions and will not be able to, or may be delayed in our efforts to, successfully develop and commercialize such product candidates.

If the contract manufacturers we rely on to produce the supply of our preclinical and clinical product candidates, including materials for the manufacture of our product candidates do not timely deliver adequate quantities of quality materials, development and commercialization of our product candidates would be hindered.

We rely on outside contractors to produce the supply of our preclinical and clinical product candidates, and we intend to rely on outside contractors to produce future clinical supplies of product candidates and commercial supplies of any approved product candidates. Reliance on outside suppliers and manufacturers entails risks, some of which we would not be subject to if we manufactured the product candidates ourselves, including:

Any of these events could lead to clinical study delays or failure to obtain regulatory approval, or impact our ability to successfully commercialize future products, if approved. Some of these events could be the basis for detrimental FDA action, including injunction, product recall or seizure, or total or partial suspension of production.

Any disruption in the supply chain of raw materials for, or in the manufacturing capacity and timing for the manufacture of drug substance or drug product for, our product candidates may cause a delay in developing and commercializing these product candidates and limit the revenues that we could generate.

We have established manufacturing relationships with a limited number of suppliers to supply raw materials used to create our product candidates and with a limited number of contract manufacturers to manufacture drug substance and drug product. The availability of continued supply and manufacturing capacity from our current vendors, and the availability of additional suppliers and manufacturers, is limited. We have and may continue to experience some supplier shortages and delivery delays. If our vendors fail to supply materials or to manufacture

substances or products in the required quantities on a timely basis and at commercially reasonable prices, and we are unable to secure one or more replacement vendors in a timely manner at a substantially equivalent cost, our clinical trials may be delayed, and our commercialization prospects could be materially diminished.

Prior to marketing approval for any of our product candidates, a manufacturer and its processes are required to be qualified by the FDA. If supply from the approved manufacturer is interrupted, there could be a significant disruption in our sales of any product. An alternative vendor would need to be qualified through an NDA supplement which could result in further delay. The FDA or other regulatory agencies outside of the United States may also require additional studies if a new supplier is relied upon for commercial production. Switching vendors may involve substantial costs and is likely to result in a delay in our desired clinical and commercial timelines.

In addition, if our alliance partners elect to control manufacturing for certain programs, we may lose control over the manufacturing activities for the product candidate, which would reduce our level of manufacturing process development and would make the success of such programs dependent on our partners’ ability to manufacture timely and properly.

If the contract research organizations and clinical trial sites we rely on to conduct, supervise and monitor our clinical trials perform in an unsatisfactory manner, it may harm our business.

We and our strategic alliance partners rely on CROs and clinical trial sites to ensure the proper and timely conduct of our clinical trials. We and our strategic alliance partners have limited control or influence over their actual performance, but remain responsible for ensuring that clinical trials are conducted in accordance with the applicable protocol, legal, regulatory and scientific standards.

If we or our CROs fail to comply with applicable good clinical practices, the clinical data generated in our clinical trials may be deemed unreliable and the FDA or applicable non-U.S. regulatory agency may require us to perform additional clinical trials before approving any marketing applications. In addition, our future clinical trials will require a sufficiently large number of test subjects to adequately evaluate the safety and effectiveness of a potential drug product. Accordingly, if our CROs fail to comply with these regulations or fail to recruit a sufficient number of patients, we may be required to repeat such clinical trials, which would delay the regulatory approval process and increase our costs.

Our CROs are not our employees, and we are not able to control whether or not they devote sufficient time and resources to our clinical and nonclinical programs. These CROs may also have relationships with other commercial entities, including our competitors, for whom they may also be conducting clinical trials or other drug development activities, which could possibly harm our competitive position. If our future CROs do not successfully carry out their contractual duties or obligations, fail to meet expected deadlines, or if the quality or accuracy of the clinical data they obtain is compromised due to the failure to adhere to our clinical protocols or regulatory requirements, or for any other reasons, our clinical trials may be extended, delayed or terminated, and we may not be able to obtain regulatory approval for, or successfully commercialize our product candidates. As a result, the commercial prospects for such products and any product candidates that we develop would be harmed, our costs could increase, and our ability to generate revenues could be delayed.

We rely on other outside parties to store and distribute drug products for clinical trials. Any performance failure or delays by our distributors could delay clinical development, marketing approval or commercialization of our product candidates, resulting in additional losses and depriving us of potential product revenue.

RISKS RELATED TO OUR INTELLECTUAL PROPERTY

If we are unable to obtain or protect intellectual property rights related to our products and product candidates, we may not be able to compete effectively in our markets.

Our success depends in part on our ability to obtain and maintain patents and other forms of intellectual property rights, including in-licenses of intellectual property rights of others, for our product candidates, methods used to develop and manufacture our product candidates and methods for treating patients using our product candidates, as well as our ability to preserve our trade secrets, to prevent third parties from infringing upon our proprietary rights and to operate without infringing upon the proprietary rights of others. The strength of patents in the biotechnology and pharmaceutical field involves complex legal and scientific questions and can be highly uncertain. The patent applications that we own or in-license may fail to result in patents with claims that cover our products or methods in the United States or in other countries.

Our patents could be prevented from issuing or be invalidated after issuance for many reasons, including:

If the patent applications we hold or have in-licensed with respect to our programs or product candidates fail to issue or are invalidated or if their breadth or strength of protection is threatened, it could dissuade companies from collaborating with us to develop product candidates, and threaten our ability to commercialize, future products.

If we do not prevail in any challenge to our intellectual property rights, we could be required to cease using the related technology or to license rights to it from the prevailing party. Our business could be harmed if the prevailing party does not offer us a license at all, or on commercially reasonable terms. Our defense of a patent or patent application in such a proceeding may not be successful and, even if successful, may result in substantial costs and distract our management and other employees. Even if our patents are issued and are not challenged or invalidated, our patents and patent applications may not adequately protect our intellectual property or products, or prevent others from designing around our claims. In addition, patents have a limited lifespan. In the United States, the natural expiration of a patent is generally 20 years after it is filed. Various extensions may be available; however, the life of a patent, and the protection it affords is limited. Once the patent life has expired for a product, we may be open to competition from generic medications. Further, if we encounter delays in regulatory approvals, the period during which we could market a product candidate under patent protection could be reduced.

In addition to the protection afforded by patents, we rely on trade secret protection and confidentiality agreements to protect certain proprietary know-how, including processes for which patents are difficult to enforce, elements of our drug discovery and development processes and elements of our proprietary manufacturing processes. Although each of our employees agrees to assign their inventions to us through an employee inventions agreement, and all of our employees, consultants, advisors and any third parties who have access to our proprietary know-how, information or technology are required to enter into confidentiality agreements, such agreements may not be effective in preventing our trade secrets and other confidential proprietary information from being disclosed or accessed by competitors. In addition, competitors and others may independently discover our trade secrets and proprietary information or independently develop substantially equivalent information and techniques, and regulatory agencies may require additional disclosures of proprietary know-how.

Further, the laws of some foreign countries do not protect proprietary rights to the same extent or in the same manner as the laws of the United States. As a result, we may encounter significant problems in protecting and defending our intellectual property both in the United States and abroad. If we are unable to prevent material disclosure of the non-patented intellectual property related to our technologies to third parties, and there is no guarantee that we will have any such enforceable trade secret protection, we may not be able to establish or maintain a competitive advantage in our market, which could materially adversely affect our business.

Claims that we infringe the intellectual property rights of others, especially in the crowded and competitive field of mRNA and delivery technology patents, may prevent or delay our development and commercialization efforts.

As the biotechnology and pharmaceutical industries expand and more patents are issued and as our activities expand and mature, the risk increases that our product candidates and activities may be subject to claims of infringement of the patent rights of others. This risk is significantly heightened because of the many patents and other intellectual property rights related to messenger RNA and its delivery.

Prior to and since the outbreak of the COVID-19 pandemic, many companies have devoted substantial effort to developing vaccines and therapeutics that use mRNA technology and have developed their own intellectual property rights, applied for patents, and licensed rights to patents held by other companies or research institutions. Some of these patents may have broad claims that cover our current or expected activities.

We are aware of patent challenging and enforcement activities in connection with technologies used in mRNA-based COVID-19 vaccines. The outcomes of such activities and the advancement of our programs could give rise to third party claims of infringement against us and our partners.

Parties making claims against us may obtain injunctive or other equitable relief, which could effectively block our and our partners’ ability to further develop and commercialize products based on our platform. Defense of these claims, regardless of their merit, would involve substantial litigation expense and would be a substantial diversion of

employee and financial resources from our business. In the event of a successful claim of infringement against us, we may have to pay substantial damages, including treble damages and attorneys’ fees for willful infringement, pay significant royalties, or try to redesign our infringing products, which may be impossible or require substantial time and monetary expenditure, further delaying and commercialization and substantially reducing potential market revenue. In order to continue development, manufacture or sale of a product, we may need to obtain a license from the owner of intellectual property, which may not be available on commercially reasonable terms or at all.

If we fail to obtain licenses to necessary intellectual property or do not comply with our obligations in license agreements, we could lose important rights.

We may need to obtain licenses from owners of intellectual property to advance our research or allow commercialization of our product candidates, and we have done so from time to time. If we fail to obtain any of these licenses at a reasonable cost and on reasonable terms, we would be unable to further develop and commercialize one or more of our product candidates, which could harm our business significantly.

We may be involved in lawsuits to protect or enforce our patents or the patents of our licensees, which could be expensive, time consuming and unsuccessful.

Competitors may infringe our patents or the patents of our licensees. To counter infringement or unauthorized use, we may be required to file infringement claims, which can be expensive and time-consuming. In addition, in an infringement proceeding, a court may decide that a patent of ours or of our licensees is not valid or is unenforceable, or may refuse to stop the other party from using the technology at issue on the grounds that our patents do not cover the technology in question. An adverse result in any litigation or defense proceedings could put one or more of our patents at risk of being invalidated or interpreted narrowly and could put our patent applications at risk of not issuing.

Our defense in a lawsuit may fail and, even if successful, may result in substantial costs and distract our management and other employees. We may not be able to prevent, alone or with our licensees, misappropriation of our intellectual property rights, particularly in countries where the laws may not protect those rights as fully as in the United States.

Furthermore, because of the substantial amount of discovery required in connection with intellectual property litigation, there is a risk that some of our confidential information could be compromised by disclosure during the course of litigation. There could also be public announcements of the results of hearings, motions or other interim proceedings or developments. If securities analysts or investors perceive these results to be negative, it could have a material adverse effect on the price of our common stock.

We have filed a lawsuit alleging trade secret misappropriation and breach of contract, and any unfavorable outcome or related proceedings could materially and adversely affect our business, financial condition, results of operations, and reputation.

On September 23, 2025, we filed a lawsuit in the United States District Court for the Southern District of California against AbbVie Inc., Capstan Therapeutics, Inc., and other defendants asserting claims for trade secret misappropriation and breach of contract. The defendants filed a motion to discuss the complaint in December 2025, and we filed an opposition to that motion in January 2026. The Court has not set a case schedule. Litigation is inherently uncertain, time-consuming, and costly. We may not prevail on our claims, and the defendants may assert counterclaims against us, including challenges to our intellectual property or allegations of our own misconduct, any of which could result in adverse rulings, monetary judgments, fee or cost awards, or other relief that may be material. Even if we are successful in whole or in part, the litigation could result in substantial expense, divert management’s attention and operational resources, disrupt relationships with partners, collaborators, or customers, and require the disclosure of sensitive information in discovery that could diminish the value of our trade secrets or other confidential information. The court could deny our requested relief, limit the scope of our asserted rights, or otherwise issue rulings that adversely affect our ability to protect, use, or commercialize our intellectual property and technology. In addition, associated proceedings, including motions practice, discovery disputes, and potential appeals, could be protracted and unpredictable, particularly given that the court has not yet established a case schedule. Any of these outcomes could negatively impact our competitive position, delay or impede our research, development, manufacturing, or commercialization activities, and result in increased legal and compliance costs. As a result, this litigation and any related proceedings could materially and adversely affect our business, financial condition, cash flows, and results of operations.

If we are subject to claims that our employees, consultants or independent contractors have wrongfully used or disclosed confidential information of third parties, we could incur substantial expenses.

We employ individuals who were previously employed at other biotechnology or pharmaceutical companies. We may be subject to claims that we or our employees, consultants or independent contractors have inadvertently or otherwise used or disclosed confidential information of our employees’ former employers or other third parties. We may also be subject to claims that former employers or other parties have an ownership interest in our patents. Litigation may be necessary to defend against these claims. We may not be successful in defending these claims, and if we are successful, litigation could result in substantial cost and be a distraction to our management and other employees.

Certain of our patents are, and our future owned and in-licensed patents may be, discovered through government funded programs and thus may subject to federal regulations such as “march-in” rights, certain reporting requirements and a preference for U.S.-based companies, and the exercise of such “march-in” rights by the U.S. government could harm our business, financial conditions, results of operations and prospects.

Certain of our patents have been, and our future owned and in-licensed patents may be, discovered through government funded programs. As a result, the U.S. government may have certain rights to intellectual property embodied in our current or future products pursuant to the Bayh-Dole Act of 1980 (the “Bayh-Dole Act”), and implementing regulations, which are amended from time to time. On December 7, 2023, the Biden administration announced an initiative to control the price of prescription drugs through the use of march-in rights under the Bayh-Dole Act. These U.S. government rights in certain inventions developed under a government-funded program include a non-exclusive, non-transferable, irrevocable worldwide license to use inventions for any governmental purpose. In addition, the U.S. government has the right to require us or our licensors to grant exclusive, partially exclusive, or non-exclusive licenses to any of these inventions to a third party if it determines that: (i) adequate steps have not been taken to commercialize the invention; (ii) government action is necessary to meet public health or safety needs; or (iii) government action is necessary to meet requirements for public use under federal regulations, which are also referred to as “march-in rights.” The U.S. government also has the right to take title to these inventions if we, or the applicable licensor, fail to disclose the invention to the government and fail to file an application to register the intellectual property within specified time limits. If the U.S. government decides to exercise these rights, it is not required to engage us as its contractor in connection with doing so. To the extent any of our current or future intellectual property is generated through the use of U.S. government funding, the provisions of the Bayh-Dole Act may similarly apply. Any exercise by the government of any of the foregoing rights could harm our business, financial condition, results of operations and prospects.

RISKS RELATED TO OUR BUSINESS OPERATIONS AND INDUSTRY

We may need to expand our organization and may experience difficulties in managing this growth, which could disrupt our operations.

As of December 31, 2025, we had approximately 111 employees. In the future we may expand our employee base to increase our managerial, scientific, operational, commercial, financial and other resources and we may hire more consultants and contractors. Future growth would impose significant additional responsibilities on our management, including the need to identify, recruit, maintain, motivate and integrate additional employees, consultants and contractors. Also, our management may need to divert a disproportionate amount of its attention away from our day-to-day activities and devote a substantial amount of time to managing these growth activities. We may not be able to effectively manage the expansion of our operations, which may result in weaknesses in our infrastructure or give rise to operational mistakes, loss of business opportunities, loss of employees or reduced productivity among remaining employees. Our expected growth could require significant capital expenditures and may divert financial resources from other projects, such as the development of additional product candidates. Moreover, if our management is unable to effectively manage our growth, our expenses may increase more than expected, our ability to generate and/or grow revenues could be reduced, and we may not be able to implement our business strategy. Our future financial performance and our ability to commercialize product candidates and compete effectively will depend, in part, on our ability to effectively manage any future growth.

If we cannot continue to attract, retain and motivate key executives and qualified scientists and other personnel, we will not be able to effectively operate our business.

We are highly dependent on principal members of our executive team, and any reduction or loss of their services may adversely impact the achievement of our objectives. While we have entered into employment

agreements with each of our executive officers, any of them could leave our employment at any time, as all of our employees are “at will” employees. Recruiting and retaining other qualified employees for our business, including scientific and technical personnel, will also be critical to our success. We have in the past experienced a high number of resignations, which could recur. Competition for skilled personnel is intense and the turnover rate can be high, as we have recently seen. We may not be able to attract and retain personnel on acceptable terms given the competition among numerous pharmaceutical companies for individuals with similar skill sets. In addition, failure to succeed in preclinical studies and clinical trials may make it more challenging to recruit and retain qualified personnel. The inability to recruit any executive or key employee or the loss of the services of any executive or key employee might impede the progress of our research, development and commercialization objectives.

Our employees may engage in misconduct or other improper activities, including noncompliance with regulatory standards and requirements and insider trading.

We are exposed to the risk of employee fraud or other misconduct. Employee misconduct could have significant negative impacts on our business. Misconduct by employees could include intentional or nonintentional failures to comply with the regulations of the FDA and other regulators, to provide accurate information to the FDA and other regulators, to comply with healthcare fraud and abuse laws and regulations in the United States and abroad, to report financial information or data accurately or to disclose unauthorized activities to us. In particular, sales, marketing and business arrangements in the healthcare industry are subject to extensive laws and regulations intended to prevent fraud, misconduct, kickbacks, self-dealing and other abusive practices.

Employee misconduct could also involve the improper use of information obtained in the course of clinical trials, which could result in regulatory sanctions and cause serious harm to our reputation. Although we have adopted a code of conduct and procedures, we may not always be effective in identifying and deterring employee misconduct, controlling unknown or unmanaged risks or losses, or in protecting us from governmental investigations or other actions or lawsuits stemming from a failure to comply with these laws or regulations.

If we do not fully comply with applicable healthcare fraud and abuse laws, false claims laws and health information privacy and security laws, we could face criminal sanctions, civil penalties, contractual damages, reputational harm and diminished profits and future earnings.

If we obtain FDA approval for any of our product candidates and begin commercializing those products in the United States, our operations may be directly, or indirectly through our customers, further subject to various federal and state fraud and abuse laws, including, without limitation, the federal Anti-Kickback Statute and the federal False Claims Act (the “FCA”). These laws may impact, among other things, our proposed sales, marketing and education programs. In addition, we may be subject to patient privacy regulation by the federal government and by the U.S. states and foreign jurisdictions in which we conduct our business. The healthcare laws and regulations that may affect our ability to operate include:

In addition, the EU has established its own data security and privacy legal framework, including but not limited to Directive 95/46/EC (the “Data Protection Directive”). The European General Data Protection Regulation (“GDPR”) took effect on May 25, 2018, which contains new provisions specifically directed at the processing of health information, higher sanctions and extra-territoriality measures intended to bring non-EU companies under the regulation. We anticipate that over time we may expand our business operations to include additional operations in the EU, including potentially conducting preclinical and clinical trials. With such expansion, we would be subject to

increased governmental regulation in the EU countries in which we might operate, including regulation due to the GDPR.

If our operations are found to be in violation of any of the laws described above or any other governmental regulations or laws that apply to us, we may be subject to substantial penalties, including, without limitation, civil, criminal and administrative penalties, damages, fines, possible exclusion from Medicare, Medicaid and other government healthcare programs, additional reporting requirements and/or oversight, particularly if we become subject to a corporate integrity agreement or similar agreement to resolve allegations of non-compliance, disgorgement, imprisonment, contractual damages, reputational harm, diminished profits and future earnings, and curtailment or restructuring of our operations, any of which could adversely affect our ability to operate our business and our results of operations.

Recent and future healthcare legislation may further impact our business operations.

The United States and some foreign jurisdictions are considering or have enacted a number of legislative and regulatory proposals to change the healthcare system in ways that could affect our ability to sell our products profitably. Among policymakers and payors in the United States and elsewhere, there is significant interest in promoting changes in healthcare systems with the stated goals of containing healthcare costs, improving quality or expanding access. In the United States, the pharmaceutical industry has been a particular focus of these efforts and has been significantly affected by major legislative initiatives. For example, in March 2010, the ACA was enacted, which made a number of substantial changes in the way healthcare is financed by both governmental and private insurers. The ACA included a number of provisions that may reduce the profitability of drug products, including revising the rebate methodology for covered outpatient drugs under the Medicaid Drug Rebate Program, extending Medicaid rebates to individuals enrolled in Medicaid managed care plans, and requiring drug manufacturers to pay an annual fee based on their market share of prior year total sales of branded programs to certain federal health care programs.

We face potential product liability, and, if successful claims are brought against us, we may incur substantial liability and costs.

The use of our product candidates in clinical trials and the sale of any products for which we obtain marketing approval exposes us to the risk of product liability claims. Product liability claims might be brought against us by consumers, healthcare providers, pharmaceutical companies or others selling or otherwise coming into contact with our product candidates or products. For example, unanticipated adverse effects could result from the use of our future products or product candidates which may result in a potential product liability claim. If we cannot successfully defend against product liability claims, we could incur substantial liability and costs. In addition, regardless of merit or eventual outcome, product liability claims may result in:

We have a limited amount of product liability insurance relating to the use of our therapeutics in clinical trials. However, such insurance coverage may not be sufficient to reimburse us for any expenses or losses we may suffer. Moreover, insurance coverage is becoming increasingly expensive and in the future we may not be able to obtain or maintain insurance coverage at a reasonable cost or in sufficient amounts to protect us against losses due to liability. If and when we obtain marketing approval for product candidates, we intend to expand our insurance coverage to include the sale of commercial products; however, we may be unable to obtain product liability insurance on commercially reasonable terms or in adequate amounts. On occasion, large judgments have been awarded in class action lawsuits based on drugs that had unanticipated adverse effects. A successful product liability claim or series of claims brought against us could cause our share price to decline and, if judgments exceed our insurance coverage, could adversely affect our results of operations and business.

Cyber security risks and the failure to maintain the confidentiality, integrity, and availability of our computer hardware, software, and Internet applications and related tools and functions could result in damage to our reputation and/or subject us to costs, fines or lawsuits.

Our business requires manipulating, analyzing and storing large amounts of data. In addition, we rely on a global enterprise software system to operate and manage our business. We also maintain personally identifiable information about our employees and participants in our clinical trials. Our business therefore depends on the continuous, effective, reliable, and secure operation of our computer hardware, software, networks, Internet servers, and related infrastructure. To the extent that our hardware or software malfunctions or access to our data by internal research personnel is interrupted, our business could suffer. The integrity and protection of our employee and company data is critical to our business and our employees and participants in our clinical trials have a high expectation that we will adequately protect their personal information. The regulatory environment governing information, security and privacy laws is increasingly demanding and continues to evolve. Maintaining compliance with applicable security and privacy regulations may increase our operating costs. Although our computer and communications hardware is protected through physical and software safeguards, it is still vulnerable to fire, storm, flood, power loss, earthquakes, telecommunications failures, physical or software break-ins, software viruses, and similar events. These events could lead to the unauthorized access, disclosure and use of non-public information. The techniques used by cyber criminals are sophisticated, change frequently, may originate from less regulated and more remote areas of the world, may not be recognized until launched and can originate from a wide variety of sources, including insider threats and outside groups such as external service providers, organized crime affiliates, terrorist organizations or hostile foreign governments or agencies, or generated using artificial intelligence. As a result, we may not be able to address these techniques proactively or implement adequate preventative measures. If our computer systems are compromised, we could be subject to fines, damages, litigation and enforcement actions, and we could lose trade secrets, the occurrence of which could harm our business. In addition, any sustained disruption in internet access provided by other companies could harm our business.

Our use of artificial intelligence technologies may expose us to operational, cybersecurity, legal and reputational risks.

We permit the use of certain artificial intelligence (“AI”) tools, including large language models and AI agents hosted in data centers located in the United States. We have adopted certain enterprise AI platforms, which our employees may access following internal review and approval processes. We also utilize data exfiltration detection technologies designed to monitor AI usage and alert our security team to potential unauthorized or unsanctioned use. AI systems may generate inaccurate, incomplete or misleading outputs, which could result in operational errors, flawed decision-making or the dissemination of incorrect information. In addition, employees may inadvertently input confidential, proprietary or sensitive information into AI tools, which could result in unauthorized disclosure, cybersecurity incidents, regulatory scrutiny, litigation or reputational harm. Our reliance on third-party AI providers also subjects us to risks relating to service disruptions, security vulnerabilities, or changes in provider policies or pricing. The legal and regulatory framework governing AI is rapidly evolving, and new laws or regulations could restrict our use of AI technologies or increase compliance costs. If we fail to effectively manage risks associated with AI use, our business, financial condition and results of operations could be adversely affected.

Business interruptions could delay us in the process of developing our future products.

Our headquarters is located in San Diego, California. We are vulnerable to natural disasters such as earthquakes, mudslides, floods and wildfires, as well as other events that could disrupt our operations. We do not carry insurance for earthquakes or other natural disasters, and we may not carry sufficient business interruption insurance to compensate us for losses that may occur. Any losses or damages we incur could have a material adverse effect on our business operations.

U.S. Government agencies have special contracting authority that gives them the ability to terminate and/or modify their contracts with us.

On August 31, 2022, we entered into a cost reimbursement contract with BARDA to support the development of a low-dose pandemic influenza candidate based on our proprietary self-amplifying messenger RNA-based vaccine platform.

The contract with BARDA, as with most U.S. Government contracts, is subject to audit, and contains termination provisions allowing the government to terminate all or part of the contract at its sole discretion, which will subject us to additional risks. These risks include the ability of the U.S. Government unilaterally to:

Termination-for-convenience provisions generally enable us to recover only our costs incurred or committed, settlement expenses, and profit on the work completed prior to termination. A contractor’s rights under a termination for convenience are limited to an adjustment of profit and, with the contracting officer’s concurrence, a reduction in the estimated cost. Under the general termination for convenience procedures, a partial termination is treated as a full termination when (i) the terminated portion is clearly severable from the balance of the contract or (ii) when contract performance is virtually complete or performance of the continued portion of the contract is only on subsidiary items or is otherwise not substantial. Termination-for-default provisions do not permit these recoveries and could make us liable for excess costs incurred by the U.S. Government in procuring undelivered items from another source.

In addition, the new 2025 U.S. presidential administration has implemented or threatened reductions in force and work stoppages across several U.S. federal agencies. Any such reductions or stoppages at BARDA or other federal agencies could negatively impact our contractual relationships with these entities, which could negatively impact our business and results of operations.

Our business is subject to audit by the U.S. Government, and a negative audit could adversely affect our business.

Several U.S. Government agencies, such as the Defense Contract Audit Agency (the “DCAA”), routinely audit and investigate government contractors. These agencies review, among other things, a contractor’s performance under its contracts, incurred costs, cost structure and compliance with applicable laws, regulations and standards.

The DCAA also reviews the adequacy of, and a contractor’s compliance with, its internal control systems and policies, including the contractor’s purchasing, property, estimating, compensation and management information systems. Any costs found to be improperly allocated to a specific contract will not be reimbursed, while such costs already reimbursed must be refunded. If an audit uncovers improper or illegal activities, we may be subject to civil and criminal penalties and administrative sanctions, including:

In addition, we could suffer serious reputational harm if allegations of impropriety were made against us.

A prolonged U.S. federal government shutdown could materially and adversely affect our business, operations, and legal proceedings.

On October 1, 2025, the federal government of the United States began a shutdown at 12:01 a.m. EDT as a result of congressional failure to pass appropriations legislation for the 2026 fiscal year, which began that day, and lasted for 43 days. Subsequent partial federal government shutdowns occurred in January and February of 2026. A continued and prolonged shutdown could materially and adversely affect our business, operations, financial condition, and legal matters. A federal government shutdown may result in the furlough of federal employees, reduced availability of government services, and suspension or delay of activities by key agencies that regulate, fund, or interact with our business, including the SEC, the FDA, the HHS, and the U.S. Patent and Trademark Office. During such periods, review and approval of our filings, applications, and submissions could be delayed, and we may be unable to access or rely upon certain government data or systems. In addition, the Administrative Office of the U.S. Courts and federal judiciary operations rely on appropriated funds and fee-based reserves that may be exhausted in the event of an extended shutdown. If federal court funding lapses or is limited to “essential” functions only, civil litigation, bankruptcy proceedings, and regulatory enforcement actions involving us or our affiliates could be postponed or suspended. Any such delay could impede our ability to resolve disputes, enforce contractual rights, or obtain timely judicial relief, which may have a material adverse effect on our financial position or prospects. Such conditions could negatively impact our access to financing, timing of capital-raising transactions, and the liquidity or trading volume of our securities. Accordingly, the current federal government shutdown, or uncertainty regarding the continuity of government operations could have a material adverse effect on our business, results of operations, and stock price.

RISKS RELATED TO OUR COMMON STOCK

We do not intend to pay dividends on our common stock so any returns to investors will be limited to the value of our shares.

We have never declared or paid any cash dividends on our common stock. We currently anticipate that we will retain future earnings for the development, operation and expansion of our business and do not anticipate declaring or paying any cash dividends for the foreseeable future.

The market price of our common stock has been, and is expected to continue to be, highly volatile and investors may not be able to resell shares at or above the price at which they purchased the shares.

The trading price of our common stock has been and is likely to continue to be volatile. For example, during the year ended December 31, 2025, our Common Stock closed at a high price of $23.16 on October 21, 2025 and closed at a low price of $5.90 on November 20, 2025. Our share price could be subject to wide fluctuations in response to a variety of factors, including but not limited to the following factors:

In addition, companies trading in the stock market in general, and Nasdaq in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of these companies, particularly companies in our industry. Broad market and industry factors may negatively affect the market price of our common stock, regardless of our actual operating performance.

The requirements of being a publicly traded company may strain our resources and divert management’s attention.

As a publicly traded company, we have incurred, and will continue to incur, significant legal, accounting and other expenses that we did not incur as a private company. In addition, the Sarbanes-Oxley Act of 2002 (the

"Sarbanes-Oxley Act"), as well as rules subsequently implemented by the SEC and Nasdaq have imposed various requirements on public companies. In July 2010, the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) was enacted. There are significant corporate governance and executive compensation related provisions in the Dodd-Frank Act that require the SEC to adopt additional rules and regulations in these areas such as “say on pay” and proxy access. Shareholder activism, the current political environment and the current high level of government intervention and regulatory reform may lead to substantial new regulations and disclosure obligations, which may lead to additional compliance costs and impact the manner in which we operate our business in ways we cannot currently anticipate. Our management and other personnel will need to devote a substantial amount of time to these compliance initiatives. Moreover, these rules and regulations will increase our legal and financial compliance costs and will make some activities more time-consuming and costly. For example, we expect these rules and regulations to make it more difficult and more expensive for us to obtain director and officer liability insurance and we may be required to incur substantial costs to maintain our current levels of such coverage.

Failure to comply with these requirements could subject us to enforcement actions by the SEC, divert management’s attention, damage our reputation, and adversely affect our business, results of operations, or financial condition. In particular, if our independent registered public accounting firm is not able to render the required unqualified attestation, it could result in a loss of investor confidence in the accuracy, reliability, and completeness of our financial reports.

If we are subject to securities class action litigation, we would incur substantial costs and diversion of management’s attention.

We may be at risk of securities class action litigation. This risk is especially relevant for us due to our dependence on positive clinical trial outcomes and regulatory approvals of each of our product candidates. In the past, medicines, biotechnology and pharmaceutical companies have experienced significant stock price volatility, particularly when associated with binary events such as clinical trials results and product approvals. If we face such litigation, it could result in substantial costs, divert management’s attention and resources, and have a very material adverse effect on our business, operating results and prospects.

Sales of a substantial number of shares of our common stock in the public market by our existing shareholders could cause our share price to fall.

If our existing shareholders sell, or indicate an intention to sell, substantial amounts of our common stock in the public market, the trading price of our common stock could decline significantly. As of December 31, 2025, 2,048,139 shares of our common stock may be sold pursuant to Rule 144 under the Securities Act of 1933, as amended (the “Securities Act”). Those shareholders are eligible to sell those shares in the public market without restriction, except for shareholders who are deemed our “affiliates” under Rule 144 under the Securities Act. In addition, common stock that is either subject to outstanding options or reserved for future issuance under our employee benefit plans, may become eligible for sale in the public market to the extent permitted by vesting schedules and Rule 144 under the Securities Act. If common stock is sold, or if it is perceived that it will be sold, in the public market, that could cause the trading price to decline.

Future sales and issuances of our common stock or rights to purchase common stock, including pursuant to our equity incentive plans, could result in additional dilution of the percentage ownership of our shareholders and could cause our share price to fall.

We expect that significant additional capital will be needed in the future to continue our planned operations. To the extent we raise additional capital by issuing equity securities (including but not limited to securities issued in connection with the Sales Agreement, as defined below), our shareholders may experience substantial dilution.

Pursuant to our 2019 Omnibus Equity Incentive Plan, as amended, our management is authorized to grant options and other equity-based awards to our employees, directors and consultants. We may issue and sell additional shares of common stock, convertible securities or other equity securities in one or more capital-raising or other transactions at prices and in a manner we determine from time to time, any of which may result in material dilution to investors and/or our existing shareholders. New investors could also be issued securities with rights superior to those of our existing shareholders.

On December 23, 2022, we entered into a Controlled Equity Offering℠ Sales Agreement (as amended, the “Sales Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) and Wells Fargo Securities, LLC (“Wells Fargo”), relating to shares of our common stock. On August 7, 2023, we entered into Amendment No. 1 to the Sales

Agreement with Cantor, Wells Fargo and William Blair & Company (“William Blair”). In accordance with the terms of the Sales Agreement, we may offer and sell shares of our common stock having an aggregate offering price of up to $200,000,000 from time to time through Cantor, Wells Fargo, or William Blair, each acting as our sales agent. As of the date hereof, we have sold an aggregate of 1,179,201 shares of our common stock under the Sales Agreement for aggregate gross proceeds of approximately $12 million, leaving an aggregate of approximately $188 million of shares of our common stock remaining for future sale under the Sales Agreement.

We may be unable to comply with the applicable continued listing requirements of Nasdaq.

Our common stock is currently listed on Nasdaq. In order to maintain this listing, we must satisfy minimum financial and other continued listing requirements and standards, including a minimum closing bid price requirement for our common stock of $1.00 per share. There can be no assurance that we will be able to comply with the applicable listing standards. For example, if we were to fail to meet the minimum bid price requirement for 30 consecutive business days, we could become subject to delisting. Although Nasdaq may provide us with a compliance period in which to regain compliance with the minimum bid price requirement, we may not be able to regain compliance within the period provided by Nasdaq. In order to regain compliance with such requirement, the closing bid price of our common stock would need to meet or exceed $1.00 per share for at least 10 consecutive business days during the compliance period. If we were not able to regain compliance within the allotted compliance period for this requirement or any other applicable listing standard, including any extensions that may be granted by Nasdaq, our common stock would be subject to delisting. In the event that our common stock is delisted from Nasdaq, liquidity will be reduced, and the trading price of our common stock can be expected to decline immediately. If our common stock is not eligible for quotation or listing on another market or exchange, trading of our common stock could be conducted only in the over-the-counter market or on an electronic bulletin board established for unlisted securities such as the Pink Sheets or the OTC Bulletin Board. In such event, it could become more difficult to dispose of, or obtain accurate price quotations for our common stock and there would likely also be a reduction in our coverage by securities analysts and the news media, which could cause the price of our common stock to decline further.

Item 1B. Unresolved Staff Comments

None.

Item 2. Properties

We have two properties located in San Diego, California. Our principal place of business is located at 10285 Science Center Drive, San Diego, California. The property consists of approximately 43,234 square feet and is leased through September 2032.

Our other property is located at 10628 Science Center Drive, Suite 250, San Diego, California and consists of approximately 24,700 square feet of office space and laboratory space, which was vacated in December 2025 and is leased through March 2027.

We believe that our property is suitable for the conduct of our business.

Item 3. Legal Proceedings

From time to time, we may be involved in various legal proceedings and subject to claims that arise in the ordinary course of business, and the results of litigation and claims are inherently unpredictable and uncertain. Other than as set forth below, we are not currently a party to any material legal proceedings.

On September 23, 2025, we filed a lawsuit against AbbVie Inc., Capstan Therapeutics, Inc. and other defendants in the United States District Court for the Southern District of California, asserting claims for trade secret misappropriation and breach of contract. The defendants filed a motion to discuss the complaint in December 2025, and we filed an opposition to that motion in January 2026. The Court has not set a case schedule.

On May 30, 2025, we initiated an arbitration against CSL Seqirus before the International Chamber of Commerce, seeking payment of a milestone under the CSL Collaboration Agreement based on the European Commission’s grant of marketing authorization for a presentation of KOSTAIVE® in the European Union. On July 25, 2025, CSL Seqirus submitted an Answer in the arbitration contending that it does not have a current obligation to pay the milestone. The arbitration is ongoing with a hearing scheduled to occur in the third quarter of 2026.

Item 4. Mine Safety Disclosures

Not applicable.

PART II

Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

Market for our Common Stock

Our common stock is listed on the Nasdaq under the symbol “ARCT”.

Holders of Common Stock

As of February 27, 2026, there were eight registered holders of record of our common stock. Because many of our outstanding shares are held in accounts with brokers and other institutions, the number of beneficial owners is significantly greater than the number of record holders. This number of holders of record also does not include stockholders whose shares may be held in trust by other entities.

Dividends

We have never declared or paid any cash dividends on our common stock. We currently intend to retain all available funds and any future earnings to support our operations and finance the growth and development of our business. Any future determination related to our dividend policy will be made at the discretion of the Board and will depend upon, among other factors, our results of operations, financial condition, capital requirements, contractual restrictions, business prospects and other factors the Board may deem relevant.

Stock Performance Graph

The following graph compares the Company’s cumulative stockholder return since December 31, 2020 with the Nasdaq Composite Index, and the Nasdaq Biotechnology Index. The graph is based on the assumption that $100 had been invested in Company common stock.

Securities Authorized for Issuance under Equity Compensation Plans

Information about our equity compensation plans is incorporated herein by reference to Item 12 of Part III of this Annual Report.

Recent Sales of Unregistered Securities

None.

Purchases of Equity Securities by the Issuer and Affiliated Purchasers

None.

Item 6. Reserved

Not applicable.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

You should read the following discussion and analysis together with the consolidated financial statements and related notes included elsewhere herein.

This report includes forward-looking statements which, although based on assumptions that we consider reasonable, are subject to risks and uncertainties which could cause actual events or conditions to differ materially from those currently anticipated and expressed or implied by such forward-looking statements.

Discussions of 2023 items and year-to-year comparisons between 2024 and 2023 that are not included in this Form 10-K can be found within Management’s Discussion and Analysis of Financial Condition and Results of Operations in our Annual Report on Form 10-K for the year ended December 31, 2024.

Overview

We are a messenger RNA medicines company focused on the development of liver and respiratory rare disease therapeutics. We have ongoing Phase 2 clinical studies for our RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF).

We developed the world’s first approved self-amplifying messenger RNA (sa-mRNA) vaccine, KOSTAIVE® (“KOSTAIVE”), which we have partnered with Seqirus, Inc. (“CSL Seqirus”), a part of CSL Limited. KOSTAIVE has achieved approval in Japan, the European Union and the United Kingdom as a vaccine against COVID-19, and sales of KOSTAIVE began in Japan in October 2024.

We have several key platform technologies that we leverage to develop and advance a pipeline of mRNA-based therapeutics for rare genetic disorders with significant unmet medical needs and vaccines for infectious diseases. Current mRNA medicines have two critical components: the messenger RNA (“mRNA”) constructs and the lipid nanoparticles (“LNP”) which help deliver the mRNA to disease-relevant target tissues. We have extensive expertise in the design and optimization of mRNA constructs, including with respect to a type of mRNA technology known as self-amplifying mRNA (sa-mRNA). Our proprietary self-amplifying mRNA technology platform, or STARR® (“STARR”), has been demonstrated to induce a robust, longer-lasting and broader humoral immune response at lower dose levels than conventional mRNA-based vaccines. Our proprietary LNP delivery system, LUNAR® (“LUNAR”), is intended to address the major hurdle in RNA drug development, namely the effective and safe delivery of RNA to disease-relevant target tissues. LUNAR may enable multiple nucleic acid medicines. We also have significant expertise and valuable know-how in the development and scalability of complex and robust manufacturing processes required to deliver the next generation of nucleic acid medicines.

Our internal pipeline includes RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF), both rare diseases. In our vaccine program, we have partnered with CSL Seqirus, one of the world’s leading influenza vaccine providers, on the development and commercialization of mRNA vaccines for COVID-19, influenza and three other infectious diseases. In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing declining COVID-19 disease burden and more onerous U.S. regulatory requirements.

In our CF program, we enrolled and completed dosing in the three initially planned cohorts of our Phase 2 multiple ascending dose study of ARCT-032, confirming the safety and tolerability of ARCT-032 dosed daily for four weeks. This study was initiated in December 2024 and was designed to identify a safe and effective dose regimen in those with Class I (null) CFTR mutations and people with CF who do not benefit from CFTR modulators. In the study, six CF adults with Class I CFTR mutations inhaled 10 mg doses of ARCT-032 daily over 28 days. Interim results released in October 2025 demonstrated that the treatment was generally safe and well tolerated. Treatment-related adverse events (AEs) that were identified in the single-dose Phase 1 study were also observed in some participants for the first few doses but ceased with continued dosing. Bronchospasm has not been reported in this study thus far, neither with nor without albuterol pretreatment. One serious adverse event (SAE) occurred in a participant after the end of the dosing period. The safety review committee found no convincing evidence that the SAE is related to ARCT-032 and approved the study to proceed. We intend to initiate a 12-week safety and preliminary efficacy study in up to 20 CF participants in the first half of 2026, after the third cohort completes treatment. ARCT-032 has received Orphan Drug Designation by the U.S. Food and Drug Administration (the “FDA”) and Orphan Medicinal Product Designation by the European Medicines Agency (the “EMA”) for the treatment of CF, and Rare Pediatric Disease Designation from the FDA.

KOSTAIVE is the brand name approved in Japan and Europe for ARCT-154, which is the version of the sa-mRNA COVID vaccine encoding the ancestral strain of SARS-CoV-2, and also for updated variant-specific versions of this vaccine. We may use KOSTAIVE or the specific internally generated name, such as ARCT-154, ARCT-2301 and ARCT-2303, to identify a version of the vaccine.

In our OTC program, we have continued to conduct a Phase 2 double-blind multiple-dose study of ARCT-810. Five patients with OTC deficiency have now completed dosing, and a sixth patient has initiated dosing. A type C meeting with the FDA to discuss our plans for a proposed future pediatric study under the RDEP (Rare Disease Evidence Principles) is scheduled for the first half of 2026. ARCT-810 has received Orphan Drug Designation from the FDA and Orphan Medicinal Product Designation from the EMA for treatment of OTC deficiency, as well as Fast Track Designation and Rare Pediatric Disease Designation from the FDA.

Commercial sales of KOSTAIVE began in October 2024 in Japan by Meiji Seika Pharma, Ltd. (“Meiji”), CSL Seqirus’ exclusive partner in Japan, marking the first commercial sales of an Arcturus-developed product. In September 2025, Meiji launched a new presentation of KOSTAIVE in Japan. The product is a 2-dose vial lyophilized presentation incorporating the updated XEC variant strain. Approval for offshore manufacturing of the 2-dose vial lyophilized presentation was granted by Japan in August 2025, followed by approval for onshore manufacturing in January 2026. KOSTAIVE was approved by the European Commission (EC) in February 2025 and by the United Kingdom in January 2026, providing further validation of our platform by additional significant regulatory authorities.

In December 2024, we initiated dosing of an sa-mRNA vaccine candidate against pandemic avian influenza (bird flu) in a Phase 1 trial funded by the Biomedical Advanced Research and Development Authority (“BARDA”). The study results were received in the second half of 2025, indicating a favorable tolerability and safety profile and the ability to induce a robust and durable humoral immune response in young and older adults.

We also improved our platform technologies and advanced our early-stage research activities and manufacturing process development and operations. We conducted exploratory platform development activities, including the evaluation of genome editing, and new targeting approaches, where our LUNAR and STARR platforms could be useful for identification and development of additional products for our portfolio.

Our activities since inception have consisted principally of performing research and development activities, clinical research activities, general and administrative activities and raising capital to fund those efforts. Our activities are subject to significant risks and uncertainties, including failing to secure additional funding before we achieve sustainable revenues and profit from operations. As of December 31, 2025, we had an accumulated deficit of $514.6 million.

Liquidity and Capital Resources

From the Company’s inception through the year ended December 31, 2025, the Company has funded its operations principally with the proceeds from revenues earned through collaboration agreements and government contracts, the sale of capital stock and long-term debt. During fiscal year 2025, we received milestone payments totaling $39.1 million from CSL Seqirus. At December 31, 2025, the Company’s balance of cash and cash equivalents, including restricted cash, was $232.8 million.

CSL Seqirus, Inc. Collaboration and License Agreement

In November 2022, we entered into the CSL Collaboration Agreement with CSL Seqirus for the global exclusive rights to research, develop, manufacture and commercialize self-amplifying mRNA vaccines. The CSL Collaboration Agreement became effective on December 8, 2022, following clearance under the Hart-Scott-Rodino Antitrust Improvements Act.

Under the CSL Collaboration Agreement, CSL Seqirus receives global exclusive rights to our technology for vaccines against SARS-CoV-2 (COVID-19), influenza and three other infectious diseases. Specifically, the collaboration agreement grants CSL Seqirus a license to our STARR mRNA technology and LUNAR lipid-mediated delivery, as well as mRNA drug substance and drug product manufacturing expertise. CSL has also been granted global non-exclusive rights in the field of pandemic preparedness (i.e., pathogens identified as priority diseases by the WHO), with the right to convert to an exclusive license.

The CSL Collaboration Agreement sets forth how the parties will collaborate to research and develop vaccine candidates. In the COVID-19 field, we undertake activities for certain regulatory filings for our leading

self-amplifying mRNA vaccine candidate in COVID-19, ARCT-154, in the United States and Europe and for research and development activities of a next-generation COVID vaccine candidate. CSL Seqirus leads and is responsible for all other research and development in COVID-19, influenza and the other fields.

We received an up-front payment of $200.0 million, with the potential to receive development milestones totaling more than $1.3 billion if all products are registered in the licensed fields. We also are entitled to potentially receive up to $3.0 billion in commercial milestones based on “net sales” of vaccines in the various fields. In addition, we are entitled to receive a 40% share of net profits from COVID-19 vaccine sales and up to low double-digit royalties of annual net sales for vaccines against influenza, pandemic preparedness and three additional infectious diseases. Entitlement to all such payments is subject to the strict conditions, requirements, royalty reduction provisions and other limitations set forth in the CSL Collaboration Agreement.

Either party may terminate the CSL Collaboration Agreement on a field-by-field basis for material breach by the other party, following notice and opportunity to cure. CSL Seqirus may also terminate the collaboration agreement in its entirety or on a field-by-field basis for any reason or no reason whatsoever, with certain limitations. The CSL Collaboration Agreement may also be terminated by CSL Seqirus for safety reasons, clinical data nonviability, commercial nonviability and other specified reasons.

In March 2024, we entered into Amendment Number Two to the CSL Collaboration Agreement to reflect updates to the development program and other adjustments consistent with our prior disclosures regarding the Collaboration and License Agreement (“Amendment Number Two”). Amendment Number Two, among other things, adjusts (i) the development plans for certain product candidates, (ii) various development milestones related to such product candidates, (iii) provisions of the CSL Collaboration Agreement related to specific royalty payments, (iii) provisions of the CSL Collaboration Agreement related to distributors, and (iv) proprietary payment calculations related to the foregoing.

On May 30, 2025, we initiated an arbitration against CSL Seqirus before the International Chamber of Commerce, seeking payment of a milestone under the CSL Collaboration Agreement based on the European Commission’s grant of marketing authorization for a presentation of KOSTAIVE®in the European Union.

In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing declining COVID-19 disease burden and more onerous U.S. regulatory requirements.

Wells Fargo Credit Agreement

On April 21, 2023, the Company’s wholly-owned subsidiary, Arcturus Therapeutics, Inc. entered into a credit agreement with Wells Fargo Bank, National Association (“Wells Fargo”) whereby Wells Fargo agreed to make a $50.0 million revolving credit line available to the Company (as amended, the “Wells Fargo Loan”) with each Wells Fargo Loan evidenced by a revolving line of credit note (each, a “Note”). On June 26, 2024, the parties entered into Amendment No. 1 to the Wells Fargo Loan, whereby the term was extended by one year to April 2026.

Borrowings under the agreement bore interest at a rate of 1.00% above either the Daily Simple SOFR or Term SOFR (as such terms are defined in the Wells Fargo Loan), with “SOFR” being the rate per annum equal to the secured overnight financing rate as administered by the Federal Reserve Bank of New York. If an Event of Default (as defined in the credit agreement) had occurred, then all Wells Fargo Loans would bear interest at a rate equal to 2.00% above the interest rate applicable immediately prior to the occurrence of the Event of Default.

The original term of the agreement was two years, with an option for one-year renewals subject to Wells Fargo approval and the Company furnishing to Wells Fargo a non-refundable commitment fee equal to 0.25% of the Wells Fargo Loan amount for each such renewal. There was no penalty for terminating the agreement and no penalty for terminating the facility prior to the maturity date of the Wells Fargo Loan. As collateral, the Company had agreed to pledge $55.0 million in cash to be held at the Company’s securities accounts with Wells Fargo Securities, LLC, an affiliate of Wells Fargo, pursuant to a security agreement.

In December 2025, the Company terminated the credit agreement and related security agreement, and the $55.0 million of cash previously pledged as collateral was released and is no longer classified as restricted cash.

Grant from the Biomedical Advanced Research and Development Authority

On August 31, 2022, we entered into a cost reimbursement contract (the “BARDA Contract”) with the Biomedical Advanced Research and Development Authority (“BARDA”), a division of the Office of the Assistant Secretary for Preparedness and Response (“ASPR”) within the U.S. Department of Health and Human Services (“HHS”) to support the development of a low-dose pandemic influenza candidate based on our proprietary self-amplifying messenger RNA-based vaccine platform. The BARDA Contract is to support our non-clinical and pre-clinical development, early-stage clinical development through Phase 1, and associated drug product manufacturing, regulatory and quality-assurance activities over a period of three years. It provides for reimbursement by BARDA of our permitted costs up to $63.2 million. As of December 31, 2025, the remaining available funding net of revenue earned was $26.7 million.

General Financial Resources

A portion of our current cash balance is expected to be utilized during fiscal year 2026 to fund (i) advances to our LUNAR-CF program in clinical trials, (ii) the continued Phase 2 trial of ARCT-810, our LUNAR-OTC candidate, (iii) expenses incurred prior to customer payments under the CSL Collaboration Agreement and BARDA agreement and (iv) continued exploratory activities related to our platform and other general administrative activities.

Our future capital requirements are difficult to forecast and will depend on many factors that are out of our control. If we are unable to maintain sufficient financial resources, our business, financial condition and results of operations will be materially and adversely affected. There can be no assurance that we will be able to obtain additional needed financing on acceptable terms or at all. Additionally, equity or debt financings may have a dilutive effect on the holdings of our existing shareholders.

We expect to continue to incur additional losses in the long term, and we will need to raise additional debt or equity financing or enter into additional partnerships to fund development. Our ability to transition to profitability is dependent on regulatory approvals and subsequent sales of KOSTAIVE, and identifying and developing other successful mRNA drug and vaccine candidates. If we are not able to achieve planned milestones or incur costs in excess of our forecasts, we will need to reduce discretionary spending, discontinue the development of some or all of our programs, which will delay part of our development programs, all of which will have a material adverse effect on our ability to achieve our intended business objectives.

Funding Requirements

We anticipate that we will continue to generate losses for the foreseeable future, and we expect the losses to increase as we continue the development of, and seek regulatory approvals for, our product candidates, and begin commercialization of our products. As a result, we will require additional capital to fund our operations in order to support our long-term plans. We believe that our current cash position will be sufficient to meet our anticipated cash requirements through at least the next twelve months, assuming, among other things, no significant unforeseen expenses and continued funding from partners at anticipated levels. We intend to seek additional capital through equity and/or debt financings, collaborative or other funding arrangements with partners or through other sources of financing when and as needed. Should we seek additional financing from outside sources, we may not be able to raise such financing on terms acceptable to us or at all. If we are unable to raise additional capital when required or on acceptable terms, we may be required to scale back or discontinue the advancement of product candidates, reduce headcount, liquidate our assets, file for bankruptcy, reorganize, merge with another entity, or cease operations.

Our future funding requirements are difficult to forecast and will depend on many factors, including but not limited to the following:

The following table shows a summary of our cash flows for the years ended December 31, 2025 and 2024:

Operating Activities

Net cash used in operating activities was $74.3 million for the year ended December 31, 2025, compared to $59.7 million for the year ended December 31, 2024. The $14.5 million increase was primarily due to a $29.7 million increase in accounts receivable and a $21.2 million decrease in accrued liabilities, reflecting the timing of billings, collections, and payments, as well as a $12.6 million decrease in share-based compensation due to reduced headcount and a lower stock price. These changes were partially offset by a $31.3 million smaller decrease in deferred revenue compared to the prior year, a $15.2 million reduction in net loss, a $7.5 million increase in cash provided by prepaid expenses and other assets, and the net impact of other working capital and non-cash items, which together reduced the overall increase in cash used in operating activities.

Investing Activities

Net cash used in investing activities of $0.2 million in 2025 and $0.6 million in 2024 reflected the acquisition of property and equipment.

Financing Activities

Net cash provided by financing activities was $13.4 million for the year ended December 31, 2025, compared to $5.4 million in 2024. The primary driver of the increase was an $11.7 million increase in proceeds from the issuance of common stock under our Sales Agreement for at‑the‑market equity offerings, partially offset by a $3.6 million decrease in proceeds from the exercise of stock options.

Results of Operations

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with the consolidated financial statements included in this Annual Report. Our historical results of operations and the year-to-year comparisons of our results of operations that follow are not necessarily indicative of future results.

Revenues

We enter into arrangements with pharmaceutical and biotechnology partners and government agencies that may contain upfront payments, license fees for research and development arrangements, research and development funding, milestone payments, option exercise and exclusivity fees and royalties on future sales. The following table summarizes our total revenues for the periods indicated:

Revenue decreased by $70.3 million during the year ended December 31, 2025 as compared to the year ended December 31, 2024. The decrease during 2025 primarily relates to a $72.2 million decrease in revenue related to the CSL collaboration agreement, primarily due to a $33.1 million decrease in milestone achievements during 2025 as compared to 2024, and a $15.8 million decrease in revenue related to CSL commercial supply agreements, along with decreased revenue recognition from amortization during 2025 as a result of reduced development activities. The decrease was partially offset by an increase in grant revenue of $0.9 million related to the reimbursable research and development expenses for the agreements with BARDA and the Gates Foundation.

Operating Expenses

Our operating expenses consist of research and development and general and administrative expenses.

The following table presents our total research and development expenses by category:

Research and Development Expenses, net

Our research and development expenses consist primarily of external manufacturing costs, in-vivo research studies and clinical trials performed by contract research organizations, clinical and regulatory consultants, personnel related expenses, facility related expenses and laboratory supplies related to conducting research and development activities.

Research and development expenses were $112.2 million for the year ended December 31, 2025, compared with $195.2 million for the year ended December 31, 2024. The decrease was primarily driven by lower manufacturing and clinical costs related to the LUNAR‑COVID program, reflecting the program’s transition from a development program to the commercial phase. Additional decreases were attributable to lower manufacturing costs for the LUNAR‑CF and LUNAR‑FLU programs, as well as lower clinical costs associated with the LUNAR‑OTC

program. These reductions were partially offset by higher clinical costs for Phase 2 of the LUNAR‑CF program. Payroll and benefits expenses also decreased, primarily due to lower stock‑based compensation expense and a reduction in headcount.

Early-stage programs represent programs that are in the pre-clinical or Phase 1 clinical stage and may be partnered or unpartnered, and primarily includes the LUNAR-FLU program which is partnered with CSL Seqirus. Discovery technologies represent our efforts to expand our product pipeline and are primarily related to pre-partnered studies and new capabilities assessment. A few of our programs are part of our collaborative relationships. The related expenses may be partially offset with funds that have been reimbursed or awarded to the Company and consist of external manufacturing costs, lab supplies, equipment, and consulting and professional fees. Expenses for both early-stage programs and discovery technologies are expected to decrease as we shift our focus to later-stage programs.

Payroll and benefits primarily consists of employee salaries and benefits, share-based compensation and consultant costs. We expect that payroll and benefits costs will not increase over the next twelve months

Facilities and equipment expenses include rent, common area maintenance (“CAM”) costs, depreciation, shipping costs and various other costs related to the operation of our two office and laboratory locations. These costs increased primarily due to a lease‑related impairment recognized in the fourth quarter after the Company vacated an office location with no further operational use.

General and Administrative Expenses

General and administrative expenses consist primarily of salaries and related benefits for our executive, administrative and accounting functions and professional service fees for legal and accounting services as well as other general and administrative expenses.

General and administrative expenses were $46.1 million and $52.8 million for the years ended December 31, 2025 and 2024, respectively. The decrease was primarily due to reduced share-based compensation expense as well as reduced payroll and benefits associated with reductions in headcount.

Finance income (expense), net

Interest income is generated on cash and cash equivalents. The decrease in interest income from 2024 to 2025 was the result of lower interest rates during the year ended 2025 and a decrease in cash and cash equivalents.

Critical Accounting Policies and Estimates

Our significant accounting policies are summarized in “Note 2 Summary of Significant Accounting Policies,” included in our consolidated financial statements included elsewhere in this annual report on Form 10-K.

The preparation of our consolidated financial statements in conformity with “GAAP” requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, assumptions related to revenue recognition, accrual of research and development expenses, determination of incremental borrowing rates, and the valuations of stock options. We based our estimates on historical experience, known trends and other market-specific or other relevant factors that we believe to be reasonable under the circumstances. On an ongoing basis, management evaluates these estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Revenue Recognition

We recognize revenue when control of the products and services is transferred to our customers in an amount that reflects the consideration we expect to receive from our customers in exchange for those products and services. This process involves identifying the contract with a customer, determining the performance obligations in the contract, determining the contract price, allocating the contract price to the distinct performance obligations in the contract, and recognizing revenue when the performance obligations have been satisfied.

Our collaboration agreements typically contain promised goods and services, including technology licenses or options to obtain technology licenses, research and development and regulatory services. Upon entering into a collaboration agreement, we are required to make the following judgments:

Identifying the performance obligations and measuring progress

Our assessment of what constitutes a separate performance obligation requires us to apply judgment. Specifically, we are required to identify which goods and services we are required to provide under the contract are distinct, if any. For performance obligations that are satisfied over time, we typically use the percentage-of-completion method which requires us to estimate the total forecasted costs required to complete the performance obligation. Adjustments to these estimates could materially impact the timing and amount of recognized revenue. If actual costs exceed initial estimates, revenue recognized to date may need to be adjusted downward, negatively impacting current period results. Conversely, favorable cost variances could accelerate revenue recognition.

Determining the transaction price, including any variable consideration

To determine the transaction price, we review the amount of consideration we are eligible to earn under the agreement. We apply a constraint to any payments we may receive in the future to avoid significant reversals since the payments are typically not probable because they are contingent upon certain future events.

We are required to reassess the total transaction price at each reporting period to determine if we should include additional payments that have become probable in the transaction price.

Allocating the transaction price to each of our performance obligations

When we allocate the transaction price to more than one performance obligation, we make estimates of the relative stand-alone selling price of each performance obligation because we do not typically sell our goods or services on a stand-alone basis. The estimate of the relative stand-alone selling price requires us in some cases to make significant judgments. In cases where we deliver a license at the start of an agreement, we use valuation methodologies, such as costs to recreate plus margin, to value the license. Additionally, when we estimate the selling price for research and development and regulatory services, we make estimates, including: the number of internal hours we will spend on the services, the cost of work we and third parties will perform and the cost of clinical trial material we will use.

The revenue we recognize each period is comprised of several types of revenue, including license fees, amortization from upfront payments, milestone payments, research and development and other services. Each of these types of revenue require us to make various judgments and estimates.

Amortization from Upfront Payments

For certain agreements, we recognize revenue from the amortization of upfront payments as we perform research and development, technology transfer and consulting services. We use an input method to estimate the amount of revenue to recognize each period. This method requires us to make estimates of the total costs we expect to incur in order to complete our promised research and development services or the total length of time it will take us to complete our promised research and development services. If we change our estimates, we may have to adjust our revenue.

Milestone Payments

When recognizing revenue related to milestone payments, we typically judge and estimate whether the milestone payment is probable (discussed in detail above under “Determining the transaction price, including any variable consideration”).

License Fees

In some cases, we deliver a license upon execution of an agreement. If we determine that our partner has full use of the license and we do not have any additional material performance obligations related to the license after delivery, then we consider the license to be a separate performance obligation. We generally recognize as license revenue the total amount of the transaction price we determine to be allocated to the performance obligation based upon the relative stand-alone selling price of a license when we deliver the license to our partner. We discuss the estimates we make related to the relative stand-alone selling price of a license in detail above under “Allocating the transaction price to our performance obligations.”

Research and Development Expenses, Including Clinical Trial Accruals/Expenses

Research and development costs consist of salaries and benefits, including share-based compensation, laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on our behalf, such as clinical research organizations, or CROs, and contract manufacturing organizations, or CMOs. Research and development costs are expensed as incurred.

Clinical trial expenses are a significant component of research and development expenses, and we outsource a significant portion of these clinical trial activities to third parties. Third-party clinical trial expenses include investigator fees, site and patient costs, CRO costs, and costs for central laboratory testing and data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through costs. These inputs are required to be estimated due to a lag in receiving the actual clinical information from third parties. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the balance sheets as prepaid assets or accrued expenses. These third-party agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future research and development activities are recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. When evaluating the adequacy of the accrued expenses, we analyze progress of the studies, including the phase or completion of events, invoices received and contracted costs. We make estimates of our accrued balances as of each balance sheet date based on facts and circumstances known to our internal personnel at that time. We periodically confirm the accuracy of our estimates with the service providers and make adjustments if necessary. Judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made. Our historical clinical trial accrual estimates have not been materially different from our actual costs.

Leases

We cannot readily determine the interest rate implicit in the lease, therefore, we use our incremental borrowing rate to measure lease liabilities. The incremental borrowing rate is the rate of interest that we would have to pay to borrow over a similar term, and with a similar security, the funds necessary to obtain an asset of a similar value to the right-of-use, or ROU, asset in a similar economic environment. The incremental borrowing rate therefore reflects what we ‘would have to pay’, which requires estimation when no observable rates are available or when they need to be adjusted to reflect the terms and conditions of the lease. We estimate the incremental borrowing rate using observable inputs (such as market interest rates) when available and are required to make certain entity and asset-specific estimates. The incremental borrowing rate used in the calculation of the present

value of lease payments in calculating lease liabilities and the corresponding ROU requires the use of significant judgment by management.

Share-Based Compensation

We recognize compensation expense related to stock options granted to employees and nonemployees based on the estimated grant date fair value and recognize forfeitures as they occur. We estimate the grant date fair value, and the resulting share-based compensation expense, using the Black-Scholes option-pricing model for service-based and performance-based awards. The grant date fair value of the share-based awards is recognized on a straight-line basis over the requisite service period, which is typically the vesting period of the respective awards. The Black-Scholes option-pricing model requires the use of highly subjective assumptions to determine the fair value of share-based awards. Such assumptions involve inherent uncertainties and the application of significant judgment. As a result, if factors or expected outcomes change and we use significantly different assumptions or estimates, our share-based compensation could be materially different.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

Our primary exposure to market risk is interest income and expense sensitivity, which is affected by changes in the general level of United States interest rates. Due to the nature of our investments, we believe that we are not subject to any material market risk exposure. We do not hold a material balance in foreign currencies or engage in derivative financial instruments that could materially impact our financial position.

Item 8. Financial Statements and Supplementary Data

The consolidated financial statements and related financial statement schedules required to be filed are listed in the Index to Consolidated Financial Statements and are incorporated herein and in Item 15 of Part IV of this Annual Report on Form 10-K.

Item 9. Changes in and Disagreements with Accountants on Accounting and Financial Disclosure

None.

Item 9A. Controls and Procedures

Evaluation of Disclosure Controls and Procedures

Our disclosure controls and procedures (as defined in Rules 13a-15(e) or 15d-15(e)) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”) are designed to ensure that information required to be disclosed in the reports that we file or submit under the Exchange Act is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms and to ensure that information required to be disclosed is accumulated and communicated to management, including our principal executive and financial officers, to allow timely decisions regarding disclosure. Our Chief Executive Officer and Principal Financial Officer, with assistance from other members of management, have reviewed the effectiveness of our disclosure controls and procedures, and, based on their evaluation, have concluded that the disclosure controls and procedures were effective as of December 31, 2025.

Management’s Report on Internal Control Over Financial Reporting

Our management is responsible for establishing and maintaining an adequate system of internal control over financial reporting and for the assessment of the effectiveness of internal control over financial reporting as defined in Rule 13a-15(f) under the Exchange Act. Our internal control over financial reporting is designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with “U.S. GAAP” and includes those policies and procedures that: (1) pertain to the maintenance of records that accurately and fairly reflect our transactions and the dispositions of our assets; (2) provide reasonable assurance that our transactions are recorded as necessary to permit preparation of financial statements in accordance with “GAAP” and that our receipts and expenditures are being made only in accordance with appropriate authorizations; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of our assets that could have a material effect on our financial statements.

Management assessed our internal control over financial reporting as of December 31, 2025 based on the criteria established in Internal Control-Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission. Management's assessment included evaluation of such elements as the

design and operating effectiveness of key financial reporting controls, process documentation, accounting policies, and our overall control environment. This assessment is supported by testing and monitoring performed both by our Internal Audit function and our Finance function.

Based on our assessment, management concluded that our internal control over financial reporting was effective as of December 31, 2025.

Management reviewed the results of its assessment with our Audit Committee. The effectiveness of our internal control over financial reporting as of December 31, 2025 has been audited by Deloitte & Touche LLP, an independent registered public accounting firm, and their opinion is stated in their report, which is included in Part II, Item 8 of the Annual Report on Form 10-K.

Remediation of Previously Reported Material Weakness

As previously reported in Part II, Item 9A. “Controls and Procedures” of our Annual Reports on Form 10-K for the fiscal year ended December 31, 2024, we identified a material weakness related to information technology general controls (“ITGCs”) that support the financial reporting process. Specifically, the remediated material weakness related to ineffective controls over (i) user access to ensure appropriate segregation of duties and adequate restriction of user and privileged access to financial applications, programs and data, to the appropriate personnel; (ii) program change management for financial applications to ensure that information technology (“IT”) program and data changes affecting financial IT applications and underlying accounting records are identified, tested, authorized and implemented appropriately; and (iii) IT operations controls to ensure that critical interface jobs are monitored.

We have completed execution of our remediation plan for this material weakness and, as of December 31, 2025, successfully remediated this material weakness by implementing the following measures:

Changes in Internal Control over Financing Reporting

Other than the remediation efforts completed and described above, there were no changes in our internal control over financial reporting during the fiscal quarter ended December 31, 2025 that materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.
 

Inherent Limitations on Effectiveness of Disclosure Controls and Procedures, and Internal Controls Over Financial Reporting

Our management, including our principal executive officer and principal financial officer, does not expect that our disclosure controls and procedures or our internal control over financial reporting will prevent all errors and all fraud. A control system, no matter how well designed and operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Further, the design of a control system must reflect the fact that there are resource constraints, and the benefits of controls must be considered relative to their costs.

Because of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, have been detected. These inherent limitations include the realities that judgments in decision-making can be faulty, and that breakdowns can occur because of a simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons, by collusion of two or more people or by management override of the controls. The design of any system of controls is also based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions; over time, controls may become inadequate because of changes in conditions, or the degree of compliance with policies or procedures may deteriorate. Due to inherent limitations in a cost-effective control system, misstatements due to error or fraud may occur and not be detected.

Report of Independent Registered Public Accounting Firm

To the Stockholders and the Board of Directors of Arcturus Therapeutics Holdings Inc.

Opinion on Internal Control Over Financial Reporting

We have audited the internal control over financial reporting of Arcturus Therapeutics Holdings, Inc. and subsidiaries (the “Company”) as of December 31, 2025, based on criteria established in Internal Control — Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission (COSO). In our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control — Integrated Framework (2013) issued by COSO.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the consolidated financial statements as of and for the year ended December 31, 2025, of the Company and our report dated March 3, 2026, expressed an unqualified opinion on those financial statements.

Basis for Opinion

The Company’s management is responsible for maintaining effective internal control over financial reporting and for its assessment of the effectiveness of internal control over financial reporting, included in the accompanying Management's Report on Internal Control over Financial Reporting. Our responsibility is to express an opinion on the Company’s internal control over financial reporting based on our audit. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether effective internal control over financial reporting was maintained in all material respects. Our audit included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, testing and evaluating the design and operating effectiveness of internal control based on the assessed risk, and performing such other procedures as we considered necessary in the circumstances. We believe that our audit provides a reasonable basis for our opinion.

Definition and Limitations of Internal Control Over Financial Reporting

A company’s internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company’s internal control over financial reporting includes those policies and procedures that (1) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use, or disposition of the company’s assets that could have a material effect on the financial statements.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become

inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

/s/ Deloitte & Touche LLP

San Diego, California

March 3, 2026

Item 9B. Other Information

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

Not Applicable.

PART III

Item 10. Directors, Executive Officers and Corporate Governance

Information required by this item will be contained in our Definitive Proxy Statement for our 2026 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A with the Securities and Exchange Commission within 120 days of December 31, 2025. Such information is incorporated herein by reference.

Item 11. Executive Compensation

Information required by this item will be contained in our Definitive Proxy Statement for our 2026 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A with the Securities and Exchange Commission within 120 days of December 31, 2025. Such information is incorporated herein by reference.

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters

Information required by this item will be contained in our Definitive Proxy Statement for our 2026 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A with the Securities and Exchange Commission within 120 days of December 31, 2025. Such information is incorporated herein by reference.

Item 13. Certain Relationships and Related Transactions, and Director Independence

Information required by this item will be contained in our Definitive Proxy Statement for our 2026 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A with the Securities and Exchange Commission within 120 days of December 31, 2025. Such information is incorporated herein by reference.

Item 14. Principal Accounting Fees and Services

Information required by this item will be contained in our Definitive Proxy Statement for our 2026 Annual Meeting of Stockholders, to be filed pursuant to Regulation 14A with the Securities and Exchange Commission within 120 days of December 31, 2025. Such information is incorporated herein by reference.

PART IV

Item 15. Exhibits, Financial Statement Schedules

(a)

(1) The information required by this item is included in Item 8 of Part II of this Annual Report.;

(2) Financial statement schedules not listed above have been omitted because information required to be set forth therein is not applicable, not required, or the information required by such schedules is shown in the consolidated financial statements or the notes thereto.

(3) See the exhibit index preceding the signature pages to this Annual Report, which is incorporated by reference herein.

(b) See the exhibit index preceding the signature pages to this Annual Report, which is incorporated by reference herein.

(c) Not applicable.

Item 16. Form 10-K Summary

None.

Exhibit Index