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Item 1. Business

2025-03-06 compared with 2024-03-14 · 548 added, 654 removed, 1107 unchanged (52% of the section changed)

We are a global messenger RNA medicines company focused on the development of infectious disease vaccines and therapeutics for liver and respiratory rare diseases.

In addition to our messenger RNA (“mRNA”) platform, our proprietary lipid nanoparticle (“LNP”) delivery system, LUNAR ® , may enable multiple nucleic acid medicines.

Our proprietary self-amplifying mRNA technology (Self-Transcribing and Replicating RNA, or STARR ® , technology) may provide longer-lasting RNA and sustained protein expression at lower dose levels as compared to conventional mRNA.

We are leveraging our proprietary LUNAR platform and our nucleic acid technologies to develop and advance a pipeline of mRNA-based vaccines and therapeutics for infectious diseases and rare genetic disorders with significant unmet medical needs.

We continue to expand this platform by adding new innovative delivery solutions that allow us to expand our efforts.

Our proprietary LUNAR technology is intended to address the major hurdles in RNA drug development, namely the effective and safe delivery of RNA therapeutics to disease-relevant target tissues.

We believe the versatility of our platform to target multiple tissues, its compatibility with various nucleic acid therapeutics, and our expertise in developing scalable manufacturing processes can allow us to deliver on the next generation of nucleic acid medicines.

In June 2020, we initiated our first clinical study, a Phase 1 study for our mRNA-based therapeutic candidate for ornithine transcarbamylase (“OTC”) deficiency.

We launched our COVID-19 vaccine program in March 2020, and in November 2023, our self-amplifying mRNA vaccine against COVID-19, ARCT-154, received marketing approval in Japan.

In November 2022, we entered into a Collaboration and License Agreement (the “CSL Collaboration Agreement”) with Seqirus, Inc.

(“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 three other respiratory infectious diseases and global non-exclusive rights to pandemic pathogens.

The CSL Collaboration Agreement became effective on December 8, 2022.

The collaboration (“CSL Collaboration”) combines CSL Seqirus’ established global vaccine commercial and manufacturing infrastructure with Arcturus’ manufacturing expertise and innovative STARR self-amplifying mRNA and LUNAR delivery platform technologies.

Our vaccines franchise, led by a self-amplifying mRNA-based COVID-19 program under license to CSL Seqirus, made significant strides in 2023, highlighted by the marketing authorization approval in Japan of ARCT-154.

The approval is the world’s first for a self-amplifying RNA (sa-mRNA) COVID-19 Vaccine.

In August 2023, we successfully completed the 12-month safety follow-up of the pivotal Phase 1/2/3 study in Vietnam of ARCT-154 that completed dosing in April 2022 of over 19,000 participants.

In February 2023, Meiji Seika Pharma Co., Ltd.

(“Meiji”), a Japanese leader in the area of infectious diseases, completed dosing of a Phase 3 clinical trial of ARCT-154 in Japan to evaluate the safety and immunogenicity of a booster dose of ARCT-154, and to assess the non-inferiority of ARCT-154 to a licensed mRNA vaccine, administered as a booster.

Meiji conducted the study under its exclusive partnership with CSL Seqirus for the distribution of ARCT-154 in Japan.

The study enrolled 828 adult participants, with half in the ARCT-154 group and half in a comparator group (Comirnaty®, Pfizer-BioNTech).

The results of this study demonstrated that a booster dose of ARCT-154 elicited a numerically higher immune response (meeting the non-inferiority criteria) against the original Wuhan-Hu-1 virus strain and a superior immune response against Omicron BA.4/5 subvariant of SARS-CoV-2 virus compared to a booster dose of the conventional mRNA vaccine Comirnaty®.

These Phase 3 study results were used to support the approval of ARCT-154 in Japan for primary immunization and as a booster dose.

Within the framework of the CSL Collaboration, we continue the development of the COVID-19 vaccine to establish a differentiated platform and address routine recommendations for periodic vaccine composition updates in a timely manner.

In 2023, we, along with our partner CSL Seqirus, developed a bivalent version of the self-amplifying mRNA vaccine (Bivalent ARCT-2301), including the Wuhan-Hu1 strain and Omicron BA.4/5 subvariant.

The clinical study with this vaccine candidate was initiated in September 2023 in Japan.

The immunogenicity and safety of Bivalent ARCT-2301 are being compared with those of the bivalent composition of the licensed conventional mRNA COVID-19 vaccine.

The LUNAR-FLU program, also under the CSL Collaboration, has made significant progress as well.

In 2023, we generated a comprehensive non-clinical data package to support a Phase 1 clinical trial with a novel seasonal influenza mRNA vaccine candidate and received all necessary approvals to initiate the Phase 1 study in Australia.

We initiated dosing in this study in January 2024 with the intention of assessing the dose response of the investigational vaccine and comparing the safety and immunogenicity with the licensed standard of care.

Overall, 132 healthy individuals (84 young adults and 48 older adults) are planned to be recruited in this Phase 1 clinical study.

In August 2023, we entered into an amendment to the CSL Collaboration Agreement, pursuant to which CSL Seqirus made a $17.5 million milestone payment related to a development milestone for the LUNAR-FLU program.

We continue to advance our rare disease pipeline and collaborations.

In our ornithine transcarbamylase (OTC) deficiency program, the Phase 1b single ascending dose study conducted in the United States of ARCT-810 (LUNAR-OTC) in adults with OTC deficiency completed enrollment and dosing of all four cohorts (N=16 subjects).

The trial assessed safety, tolerability and pharmacokinetics of a single dose of ARCT-810, as well as various exploratory biomarkers of drug activity.

The final database lock occurred in December 2023.

A Phase 2 multiple-dose study of ARCT-810 in OTC-deficient adolescents and adults initiated dosing in December 2022 and plans to enroll approximately 24 participants in two dose cohorts.

The study is being conducted in the UK and several countries in the European Union.

ARCT-810 received Orphan Drug Designation from the FDA and the European Medicines Agency (the “EMA”) for treatment of OTC deficiency.

ARCT-810 was also granted Fast Track Designation in May 2023 and Rare Pediatric Disease Designation in June 2023.

Our mRNA therapeutic candidate for cystic fibrosis, ARCT-032 (LUNAR-CF), successfully achieved the recruitment target and administration in a First-in-Human study in New Zealand, a Phase 1 single ascending dosing study with 32 healthy participants (eight subjects in each of four dose cohorts).

In August 2023 we received regulatory approval for a protocol amendment to transition to a Phase 1b clinical study of ARCT-032 in up to eight adults with CF, with each participant receiving two administrations of ARCT-032.

Dosing began in patients with CF in November 2023 and enrollment is ongoing.

The FDA granted Rare Pediatric Disease Designation for ARCT-032 in October 2023.

ARCT-032 was granted Orphan Drug Designation by the FDA in November 2023 and Orphan Medicinal Product Designation by the EMA in February 2024.

We also continued to improve our platform technologies and to advance our early-stage research activities and manufacturing process development and operations.

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.

Also, with our sourcing partners, we manufactured cGMP batches (current good manufacturing practices) yielding significant quantities of clinical trial materials for global studies of our candidates, including ARCT-810 (LUNAR-OTC), ARCT-032, (LUNAR-CF), ARCT-154 (LUNAR-COV19) and ARCT-2301 (Bivalent LUNAR-COV19).

We are a messenger RNA medicines company focused on the development of infectious disease vaccines and opportunities within liver and respiratory rare diseases.

We developed the world’s first approved self-amplifying messenger RNA (sa-mRNA) vaccine, KOSTAIVE ® (“KOSTAIVE”).

KOSTAIVE achieved approval in Japan in 2023 as a vaccine against COVID-19.

Sales of KOSTAIVE began in Japan in October 2024, marking our transition to a commercial stage company.

We have several key platform technologies that we leverage to develop and advance a pipeline of mRNA-based vaccines and therapeutics for infectious diseases and for rare genetic disorders with significant unmet medical needs.

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 believe we are among the world leaders in both areas.

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 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 therapeutics to disease-relevant target tissues.

LUNAR may enable multiple nucleic acid medicines.

The approval of KOSTAIVE in Japan was a significant milestone which validates our LUNAR and STARR platforms, as well as sa-mRNA more generally as a meaningful modality.

Finally, we 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 Seqirus, Inc.

(“CSL Seqirus”), a part of CSL Limited and one of the world’s leading influenza vaccine providers, on the development and commercialization of mRNA vaccines for COVID-19, influenza and certain other infectious diseases.

We made significant progress in 2024.

Commercial sales of KOSTAIVE began in October 2024 in Japan by Meiji Seika Pharma (“Meiji”), CSL Seqirus’ exclusive partner in Japan, marking the first commercial sales of an Arcturus-developed product.

In February 2025, we received approval of KOSTAIVE from the European Commission (EC), which provided further validation of our platform by another significant regulatory authority.

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.

We initiated dosing in a Phase 1 clinical trial of a novel seasonal influenza sa-mRNA vaccine candidate under our collaboration with CSL Seqirus in January 2024.

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”).

In our OTC program, we completed dosing of eight subjects in August 2024 in a Phase 2 double-blind multiple-dose study of ARCT-810.

In the second quarter of 2024, we expanded the Phase 2 clinical program of ARCT-810 with an open-label, multiple-dose study which initiated dosing in December 2024.

ARCT-810 has received Orphan Drug Designation from the FDA and Orphan Medicinal Product Designation from the European Medicines Agency (the “EMA”) for treatment of OTC deficiency, as well as Fast Track Designation and Rare Pediatric Disease Designation from the FDA.

In our CF program, we initiated dosing in December 2024 in a Phase 2 multiple ascending dose study of ARCT-032 designed to identify a safe and effective dose in people with Class I (null) CFTR mutations and other CF patients who do not benefit from CFTR modulators.

In July 2024, we completed dosing and follow-up visits for seven participants in a safety and tolerability Phase 1b clinical study in New Zealand of ARCT-032 in adults with CF.

ARCT-032 has received Orphan Drug Designation by the FDA and Orphan Medicinal Product Designation by the EMA for the treatment of CF, and Rare Pediatric Disease Designation from the FDA.

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 potentially be useful for identification and development of additional products for our portfolio.

Also, with our sourcing partners, we manufactured cGMP (current good manufacturing practices) batches yielding significant quantities of clinical trial materials for global studies of our candidates, and with our collaborator, CSL Seqirus, we have established commercial production processes for the COVID-19 vaccine program.

Nucleic Acid Medicines and an Introduction to Arcturus’ Platform Technologies

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The general objectives of these therapies include:

• to introduce a gene product (e.g., mRNA, CRISPR, gene therapy) that encodes for a functional protein to replace an absent or defective protein;

• to restore a functional protein by correcting its encoding mRNA sequence;

• to reduce the amount of a target protein in a patient by binding to and destroying the associated target mRNA (antisense and small interfering RNA (“siRNA”));

• to introduce proteins from viruses or malfunctioning proteins obtained from certain cancers to train the immune system to recognize these proteins and clear these viruses or cancer cells (nucleic acid vaccines).

• to introduce a gene product (e.g., mRNA or DNA) that encodes for a functional protein to replace an absent or defective protein;

• to restore a functional protein by genomic DNA editing of the corresponding gene resulting in the correction of the mRNA sequence;

• to reduce the amount of a target protein in a patient by binding to and destroying the associated target mRNA (antisense DNA or small interfering RNA (“siRNA”));

• to express proteins from viruses or unique proteins only found in cancer and not in non-cancerous cells resulting in the induction of protective immunity against specific viral pathogens or immune mediated elimination of cancer cells.

Brief Introduction to our LUNAR and STARR Technology Platforms

A key challenge for nucleic acid medicines is the safe and effective delivery of the nucleic acid molecule.

We have developed a novel lipid-mediated delivery system called LUNAR.

LUNAR is a multi-component drug delivery system that incorporates a mixture of novel biodegradable lipids.

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 acids 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, certain hormones, and most of the cell membrane that is not made up of protein.

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 lipids, termed ATX, with over 250 to date.

We continue to expand our library of proprietary synthetic lipids, termed ATX, with 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.

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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 may trigger rapid and prolonged antigen expression within host cells affording individuals protective immunity against infectious pathogens.

We have clinically shown that the combination of LUNAR and STARR technology can result in lower dose requirements with superior immune response and sustained protein expression compared to non-self-amplifying RNA-based vaccines, which may enable production of greater volumes of vaccine doses more quickly.

Development Programs

Our Internal Programs Pipeline

Vaccines in Development

Self-amplifying RNA-based prophylactic vaccines developed with STARR trigger rapid and prolonged antigen expression within host cells which may provide protective immunity against infectious pathogens.

We have clinically shown that the combination of LUNAR and STARR technology can result in lower dose requirements with superior immune response and sustained protein expression compared to conventional RNA-based vaccines, which may enable production of greater volumes of vaccine doses more quickly.

(i) Commercialized in Japan

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.

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In 2020, we initiated the development of our first self-amplifying mRNA vaccine candidate to protect against COVID-19.

In December 2022 we entered into the CSL Collaboration Agreement, which 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 a Phase 3 clinical study in Japan that completed dosing in February 2023, ARCT-154, administered as a booster dose, achieved a numerically higher immune response (meeting the non-inferiority criteria) against the original Wuhan-Hu-1 virus strain, and a superior immune response against Omicron BA.4/5 subvariant of SARS-CoV-2 virus compared to a booster dose of the conventional mRNA vaccine Comirnaty®.

In November 2023, ARCT-154 was approved for primary immunization and as a booster dose in Japan.

This approval marks the world’s first approval for a self-amplifying RNA (sa-mRNA) COVID-19 Vaccine.

In collaboration with CSL, and CSL's partner Meiji, we continue to generate clinical data to support using the self-amplifying vaccine platform for seasonal updates of the COVID-19 vaccine.

Our influenza vaccine franchise continued to expand, with the initiation of the Phase 1 clinical trial in January 2024 for the seasonal influenza candidate vaccine under our collaboration with CSL and our continued efforts under our pandemic influenza vaccine program with BARDA.

Development Program

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 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.

In November 2023, ARCT-154 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 initiated in January 2024 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.

KOSTAIVE ® and COVID-19 Vaccine Program

Coronaviruses are a family of viruses that can lead to respiratory illness.

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Throughout the pandemic, there have been surges of infections as protective health measures have waxed and waned.

Uncontrolled viral spread has led to approximately half a billion cases worldwide and the selection of viral variants that are more contagious, pathogenic, or both.

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.

Despite the expeditious Emergency Use Authorization (“EUA”) and rollout of vaccines in many countries, vaccine efficacy rates vary widely to currently circulating variants.

The current recommendations include seasonal vaccination of risk populations against COVID-19, using vaccine compositions, including the new emergent SARS-CoV-2 variants.

As the world pivots from a pandemic to an endemic response to SARS-CoV-2 infections, primary and booster 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.

As such, through the CSL collaboration, we are developing the next generation of mRNA vaccines, which have demonstrated encouraging immunogenicity data, including neutralizing antibody responses against various variants of concern, including Omicron, boosting pre-existing immunity to SARS-CoV-2.

Our initial COVID-19 vaccine candidate, ARCT-021, developed in conjunction with Duke-NUS Medical School, is based on our STARR (self-amplifying mRNA) technology platform and demonstrated antibody and cell-mediated immunogenicity and an excellent safety profile through Phase 2 clinical trials.

This vaccine was designed to promote immune responses to the spike protein of the SARS-CoV-2 virus, the critical part of the virus that allows infection to occur.

Our next-generation COVID-19 vaccine candidate, ARCT-154, is also based on our STARR (self-amplifying mRNA) technology platform and our LUNAR platform.

Additional changes were implemented for new generation vaccine candidates to further improve the immunogenicity and tolerability profile and increase vaccine efficacy.

These changes include codon optimization for replicon and spike protein, additional mutations for stabilization of spike protein in pre-fusion confirmation, and changes in the manufacturing process to improve the impurity profile and reduce the amount of double-stranded RNA.

Marketing Authorization Approval of ARCT-154 in Japan

In November 2023, ARCT-154 received marketing authorization approval from the Japanese Ministry of Health, Labour and Welfare for use as a primary immunization and booster in Japan.

The approval was based on positive clinical data from several ARCT-154 studies, including the pivotal 19,000 subject efficacy, safety and immunogenicity study performed in Vietnam as well as the pivotal Phase 3 booster study in Japan.

Marketing Authorization Application for ARCT-154 in Europe

CSL Seqirus and Arcturus submitted a European Medicines Agency (EMA) marketing authorization application for ARCT-154 for active immunization to prevent COVID-19 caused by SARS-CoV-2 in individuals 18 years of age and older.

The application was accepted by EMA for review and the review procedure started on August 17, 2023.

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 promote immune responses to the spike protein of the SARS-CoV-2 virus, the critical part of the virus that allows infection to occur.

KOSTAIVE is the brand name approved in Japan and Europe for ARCT-154, which is the version of the sa-mRNA COVID-19 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 the vaccine.

The approval 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, all as further described below, are significant milestones in the advancement of our vaccines franchise.

The recent approval of KOSTAIVE (ARCT-154 version) by the EMA in January 2025 provides further validation of our platform by another significant regulatory authority, in addition to expanding the potential commercialization of KOSTAIVE.

During 2024, several important publications were released relating to our studies, which are summarized below.

• In May 2024, Nature Communications published results from the 19,000 subject study performed in Vietnam, with results demonstrating that two 5µg doses of ARCT-154 were well-tolerated, immunogenic and provided significant protection against multiple strains of COVID-19.

This publication relates to the study described below – “ Pivotal Phase 1/2/3 Study in Vietnam” .

• In November 2024, npj Vaccines, a Nature Portfolio journal, published the results of Phase 3c of the pivotal Phase 1/2/3 study in Vietnam, demonstrating higher immune response and protective efficacy of ARCT-154 compared to an approved adenovirus-vector COVID-19 vaccine (DOI:

10.1038/s41541-024-01017-5).

• In October 2024, Lancet Infectious Diseases published the follow-up article ‘12-month persistence of immune responses to self-amplifying mRNA COVID-19 vaccines:

ARCT-154 versus BNT162b2 vaccine’ (https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(24)00615-7/fulltext), which confirmed a better neutralizing immune response against a panel of SARS-CoV-2 strains in pre-immunized Japanese adults boosted with ARCT-154 compared with the conventional mRNA vaccine, BNT162b2, which persisted up to 12 months post-vaccination, including in those age 50 years and older.

This publication relates to the study described below – “ Phase 3 Study of Bivalent Version of KOSTAIVE (COVID-19 Vaccine) Candidate in Japan ”.

Approval of KOSTAIVE in Japan

KOSTAIVE (ARCT-154 version) received marketing authorization approval in November 2023 from the Japanese Ministry of Health, Labour and Welfare for use as a primary immunization and booster in Japan for adults 18 years and older.

The approval was based on positive clinical data from several ARCT-154 studies, including a 19,000-participant efficacy, safety and immunogenicity study performed in Vietnam, as well as a Phase 3 booster study in Japan.

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.

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, and clinical evidence supporting the safety and immunogenicity of KOSTAIVE (bivalent, BA.4/5 and ancestral strain).

In January 2025, CSL Seqirus’ partner Meiji announced that it 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.

Clinical Studies of KOSTAIVE (COVID-19 vaccine)

In connection with the development of KOSTAIVE, we have conducted or are conducting the studies described below.

Pivotal Phase 1/2/3 Study in Vietnam

During 2021, we entered into a collaboration with Vinbiocare Biotechnology Joint Stock Company (“Vinbiocare”), a member company of the Vingroup Joint Stock Company (Vingroup) group of companies.

As part of a collaboration with Vinbiocare, ARCT-154, our investigational next-generation, self-amplifying mRNA-based vaccine for COVID-19, was advanced into a Phase 1/2/3 study in Vietnam, funded and sponsored by Vinbiocare (the “Vinbiocare Study”).

The trial is randomized, observer-blinded, placebo, and active-controlled and is intended to assess the safety, immunogenicity, and efficacy of ARCT-154.

As part of a collaboration with Vinbiocare, ARCT-154, our next-generation, self-amplifying mRNA-based vaccine for COVID-19, was advanced into a Phase 1/2/3 study in Vietnam, funded and sponsored by Vinbiocare (the “Vinbiocare Study”).

The trial was randomized, observer-blinded, placebo and active-controlled, and intended to assess the safety, immunogenicity, and efficacy of ARCT-154.

The Phase 3 arm of the Phase 1/2/3 study was initiated in September 2021.

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The Phase 3b placebo-controlled efficacy portion of the study enrolled over 16,000 participants.

In February 2022, Vinbiocare provided safety and immunogenicity data from the placebo-controlled Phase 1/2/3a portions of the study with approximately 1,000 participants.

In April 2022, Vinbiocare shared results from the vaccine safety and efficacy analysis of Phase 3b participants.

The primary efficacy endpoint in the placebo-controlled Phase 3b portion of the study was met.

Analysis of the data demonstrated that two 5-mcg doses of ARCT-154 administered 28 days apart resulted in vaccine efficacy of 56.6% (95% CI;

48.7% - 63.3%) for protection against COVID-19 overall and 93.3% (95% CI;

80.5% - 98.9%) against severe COVID-19.

Nine COVID-19-related deaths were reported in the placebo group and one in the ARCT-154 vaccinated group.

The single death in the ARCT-154 vaccination arm occurred in an older age group participant who was also at increased risk of severe COVID-19.

During the window when COVID-19 cases in the study were routinely collected, the prevalent SARS-CoV-2 strain associated with COVID-19 infections in Vietnam was Delta.

In the Phase 3b study population comprising 8,059 ARCT-154 recipients and 8,041 placebo recipients, and although local solicited AEs were reported more frequently by ARCT-154 recipients than placebo recipients (52.3% versus 15.3%) after Dose 1 or 2, the majority of solicited local AEs were mild or moderate in intensity.

Solicited local AEs of severe intensity were infrequent in ARCT-154 recipients (0.6%) and mainly consisted of injection site pain and tenderness.

Also, systemic solicited AEs were reported by ARCT-154 recipients more frequently than the placebo recipients (60.5% versus 40.8%), and most solicited systemic AEs were mild or moderate in intensity.

Solicited systemic AEs of severe intensity were reported by 2.7% of ARCT-154 recipients.

No Grade 4 solicited AE was reported in the study.

Local and systemic AEs were less frequent after the second dose than after the first dose of ARCT-154 and generally resolved within three days.

In the entire Phase 3b population and throughout the study, SAEs considered related to the study vaccine were infrequent and reported by 10 ARCT-154 recipients and five placebo recipients from Day 1 to Day 92, and 1 ARCT-154 recipient who had formerly received two placebo doses, from Day 92 to the end of the study.

The administration of the third dose (early booster dose) of the ARCT-154 vaccine approximately two months after the primary vaccination series was not associated with any safety concerns.

No clinically meaningful differences in the safety profile were observed when comparing different subgroups in terms of age/risk groups, sex, or site/region.

No signs of disease enhancement (VAERD) were observed during the study period, judging by the reduction in the severity of the COVID-19 cases observed after one or two doses of the ARCT-154 vaccine.

No case of myocarditis or pericarditis was reported.

Two doses of ARCT-154 were immunogenic in the adult study population without previous exposure to SARS-CoV-2 infection in terms of the induction of neutralizing and IgG-binding antibodies specific to the ancestral strain of SARS-CoV-2.

Moreover, two doses of ARCT-154 induced cross-neutralization responses to Alpha, Beta, Gamma, and Delta/B.1.617.2 variants of concern when measured by the ACE2 surrogate virus neutralization assay.

ACE2 surrogate neutralization panel, showing geometric mean concentrations of neutralizing antibody responses (with 95% confidence intervals) obtained for participants across a range of SARS-CoV-2 variants.

Data from participants with verified COVID-19 were left out of the analysis.

The administration of the third dose of ARCT-154 (early booster after 2-dose primary series) was associated with a further increase in immune responses to the ancestral SARS-CoV-2 strain and Delta and Omicron BA.1 variants of concern.

In August 2023, we submitted the primary manuscript with efficacy, immunogenicity and safety results of the pivotal Phase 1/2/3 clinical study of ARCT-154 in Vietnam.

The preprint of this article is available on https://doi.org/10.21203/rs.3.rs-3329097/v1.

The peer review of the manuscript is ongoing by Nature Communications.

Pivotal Phase 3 Non-Inferiority Study of ARCT-154 in Japan

Meiji is sponsoring a randomized, multicenter, Phase 3, observer-blind, active-controlled comparative study to evaluate the safety and immunogenicity of a booster dose of ARCT-154 and to evaluate the non-inferiority of ARCT-154 over COMIRNATY (Monovalent, Original strain).

The study targeted a total of 780 adult participants, with half in the ARCT-154 group and half in a comparator group, and completed enrollment with 828 participants in February 2023.

Subjects were eligible if they had received three doses of approved mRNA COVID-19 vaccines with the last dose as COMIRNATY at least three months prior to screening.

The immunogenicity of ARCT-154 was non-inferior to COMIRNATY against the SARS-CoV-2 (Wuhan strain), thus meeting the primary objective of the study.

Furthermore, the immunogenicity of ARCT-154 was superior to COMIRNATY against SARS-CoV-2 (Omicron BA.4/5 strain).

(A) Geometric mean titers (GMT) of surrogate neutralizing antibodies at Days 1 (baseline) and 29, and geometric mean-fold rises (GMFR) in titers from Day 1 to Day 29;

B) GMT Ratio;

C) seroresponse rates (SRR) at Day 29;

D) SRR Difference - Study ARCT-154-J01.

GMT – Geometric Mean Titer;

SRR – seroresponse rate.

All values are from the Per Protocol Subset 1 (PPS-1) and are shown with 95% confidence intervals in parentheses.

Solid circles (●) represent the Wuhan variant, and open circles (○) represent the Omicron BA.4/5 variant.

Vertical dashed lines represent the threshold for achieving the non-inferiority comparison of ARCT-154 to Comirnaty.

In addition, the immunogenicity results of ARCT-154 compared to COMIRNATY were not affected by age, sex, time since the last vaccination, antibody titer against SARS-CoV-2 (Wuhan and Omicron BA.4/5 strains) before administration of the study vaccine, and brands of the vaccines administered in the past.

Six months after vaccination, GMTs and SRRs of neutralizing antibodies against SARS-CoV-2 (Wuhan and Omicron BA.4/5 strains) remained higher in ARCT-154 recipients than in COMIRNATY recipients.

Geometric mean titers (with 95% CI bars) of surrogate neutralizing antibodies against the SARS-CoV-2 Wuhan-Hu-1 (panel A) and Omicron BA.4/5 (panel B) strains up to six months after vaccination with one booster dose of either ARCT-154 or BNT162b2.

Geometric mean titer ratios (95% CI) for ARCT-154/ BNT162b2 are shown for Days 29, 91 and 181, and geometric mean-fold rises over baseline (GMFR) with 95% CI are shown for each group at Days 29, 91 and 181.

No safety concerns were raised from the study.

No deaths or ARCT-154-related SAEs were reported.

The proportions of subjects with the solicited local AEs of injection-site swelling, induration, and erythema were lower after administration of ARCT-154 than after administration of COMIRNATY, and the proportion of subjects with solicited systemic AEs was similar in both study arms.

The proportion of subjects with Grade 3 or higher solicited AEs was low in both study arms.

Rates of solicited local reactions and systemic adverse events in the two study groups with severity.

In summary, the pivotal Phase 3 Non-Inferiority Study of ARCT-154 in Japan met all primary and secondary immunogenicity endpoints, including a secondary pre-defined superiority assessment over Comirnaty (Omicron BA.4/5 strain).

The study 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 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 were used as a basis for vaccine licensure in Japan and the European Union.

In August 2023, we submitted the primary manuscript with efficacy, immunogenicity and safety results of the pivotal Phase 1/2/3 clinical study of ARCT-154 in Vietnam ( https://www.nature.com/articles/s41467-024-47905-1 ).

Later, we published the results of Phase 3c part of the study, comparing the immunogenicity and efficacy of ARCT-154 and licensed adenoviral vector vaccine ChAdOx-1S, demonstrating higher immunogenicity and relative vaccine efficacy (19.8% (95% CI:

4.0–33.0)) of ARCT-154 compared to ChAdOx-1S ( https://pmc.ncbi.nlm.nih.gov/articles/PMC11585660/ ).

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

Meiji sponsored a randomized, multicenter, Phase 3, observer-blind, active-controlled comparative study to evaluate the safety and immunogenicity of a booster dose of ARCT-154 and to evaluate the non-inferiority of ARCT-154 over COMIRNATY® (Monovalent, Original strain).

The study completed enrollment in February 2023 with 828 participants, with half in the ARCT-154 group and half in a comparator group.

The study met all primary and secondary immunogenicity endpoints, including a secondary pre-defined superiority assessment over COMIRNATY (Omicron BA.4/5 strain).

Overall, the safety and immunogenicity results of the study support the favorable benefit/risk profile of the ARCT-154 vaccine when administered as a booster dose in adult individuals who previously received other mRNA COVID-19 vaccines.

On July 13, 2023, an article reporting the study results titled “Booster dose of self-amplifying SARS-CoV-2 RNA vaccine vs.

mRNA vaccine:

a Phase 3 comparison of ARCT-154 with Comirnaty” was posted on medRxiv.org at https://www.medrxiv.org/content/10.1101/2023.07.13.23292597v1.

In December 2023, Lancet Infectious Diseases published results of the study showing that a booster dose of ARCT-154, a novel, self-amplifying messenger RNA (sa-mRNA) vaccine, elicited a numerically higher immune

response (meeting the non-inferiority criteria) against the original Wuhan-Hu-1 virus strain, and a superior immune response against Omicron BA.4/5 subvariant of SARS-CoV-2 virus compared to a booster dose of the conventional mRNA vaccine Comirnaty®.

ARCT-154 results were achieved with one-sixth the dose of Comirnaty® (5 μg vs 30 μg).

In January 2024, Arcturus and Meiji submitted the article ‘Persistence of immune responses of a self-amplifying RNA COVID-19 vaccine (ARCT-154) versus BNT162b2’ to Lancet Infectious Disease, with a 6-month follow-up results from this study.

These additional data demonstrate the extended persistence of neutralizing antibodies after ARCT-154 compared with conventional mRNA vaccine in the clinical setting, indicating longer-lasting immunity and implying a longer duration of protection by ARCT-154 (Figure above).

The manuscript was published on February 1, 2024 (https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(24)00060-4/fulltext).

Phase 1/2 Study in United States, Singapore, and South Africa

In January 2022, we announced immunogenicity data for participants of a Phase 1/2 study being conducted in the United States and Singapore.

Results from the arms where participants were dosed with five mcg of ARCT-154 as a booster after at least five months of being vaccinated with two doses of Comirnaty (Pfizer-BioNTech) showed encouraging increases in levels of neutralizing antibody activity against D614G and several variants of concern (VoCs) and variants of interest (VoIs).

On August 7, 2023, we announced that Phase 1/2 clinical trial data demonstrated one-year durability of immune response following ARCT-154 booster vaccine administration as measured using validated microneutralization (MNT) assays.

The geometric mean fold rise (GMFR) in neutralizing antibodies remained greater than 10-fold above baseline for one year across a panel of SARS-CoV-2 variants, including ancestral strain with the D614G mutation, Beta (B.1.351), Delta (B.1.617.2), and Omicron (BA.1, BA.2 and BA.4/5), for participants receiving ARCT-154 booster.

The results of this study were presented as a poster at the 9th Influenza Conference of the European Scientific Working Group on Influenza (ESWI) in Valencia, Spain.

Geometric mean fold rise (GMFR) of neutralizing antibodies against SARS-CoV-2 variants (versus pre-booster levels) after ARCT-154 booster vaccination measured by validated pseudovirus microneutralization assays (N=12).

Error bars represent the 95% CI.

Participants who received any COVID-19 vaccines or had laboratory-confirmed SARS-CoV-2 infection during the follow-up period were excluded from immunogenicity analysis at sampling times after the event.

Phase 3 Study of Bivalent Version of COVID-19 Vaccine Candidate in Japan

On September 29, 2023, Meiji initiated an additional Phase 3 clinical study with a bivalent version of our COVID-19 vaccine candidate (ancestral strain, ARCT-154 and Omicron BA.4/5) to further support immunogenicity and safety data for our self-amplifying mRNA platform, which may facilitate the timely release of future seasonal

updates of our COVID-19 vaccine against evolving variants of concern.

The study will compare the investigational vaccine, ARCT-2301 and COMIRNATY (ancestral strain and BA.4/5), to evaluate safety and immunogenicity between observer-blind groups.

Preliminary results of his study are expected by the end of Q1 2024.

The results of this study of the bivalent version of our COVID-19 vaccine candidate are not required for approval of ARCT-154 in Japan but will facilitate the timely release of future seasonal updates of the COVID-19 vaccine without the need for additional clinical data.

Geometric mean titers (GMT) of surrogate neutralizing antibodies at Days 1 (baseline) and 29, and geometric mean-fold rises (GMFR) in titers from Day 1 to Day 29;

B) GMT Ratio;

C) seroresponse rates (SRR) at Day 29;

D) SRR Difference – Study ARCT-2301-J01.

GMT – Geometric Mean Titer;

SRR – seroresponse rate.

All values are from the Per Protocol Subset 1 (PPS-1) and are shown with 95% confidence intervals in parentheses.

Solid circles (●) represent the Wuhan variant, open circles (○) represent the Omicron BA.4/5 variant, and open squares ( ☐ ) represent the Omicron XBB.1.5 variant.

Vertical lines represent the threshold for achieving the non-inferiority and superiority comparisons of ARCT-154 to Comirnaty .

Bivalent ARCT-2301, when administered intramuscularly as a booster dose in subjects who had received three to five doses of authorized mRNA COVID-19 vaccines at least three months before the recruitment, demonstrated immunological superiority over the comparator vaccine (Comirnaty® bivalent:

Wuhan strain/Omicron strain BA.4/5), as measured by GMT ratios and seroresponse rates differences for both vaccine strains (prototype Wuhan strain and Omicron BA.4/65 variant).

In addition, ARCT-2301 induced a higher immune response against the epidemiologically dominant Omicron XBB.1.5 variant.

COVID-19 Vaccine Platform Stability Data

Current data regarding the product format, stability and cold chain characteristics of our lyophilized self-amplifying mRNA COVID-19 vaccine compares favorably to existing smaller non-self-amplifying COVID-19 vaccine stability requirements.

The lyophilized powder of ARCT-154 demonstrated room temperature stability for four days (25°C;

60% RH), refrigerator stability for five months (2-8°C), and long-term stability for 24 months (-25°C to -15°C).

The vaccine stability data are supportive for shipping at 2-8°C.

Notably, the vaccine remains stable in the event of temperature cycling.

Development Program

LUNAR-qsFLU (Quadrivalent Seasonal Influenza)

In October 2024, Lancet Infectious Diseases published the follow-up article ‘12-month persistence of immune responses to self-amplifying mRNA COVID-19 vaccines:

ARCT-154 versus BNT162b2 vaccine’, which confirmed a better neutralizing immune response against a panel of SARS-CoV-2 strains in pre-immunized Japanese adults boosted with ARCT-154 compared with the conventional mRNA vaccine, BNT162b2, which persisted up to 12 months post-vaccination, including in those age 50 years and older.

Phase 3 Study of Bivalent Version of KOSTAIVE (COVID-19 Vaccine) Candidate in Japan

In September 2023, Meiji initiated a Phase 3 clinical study with ARCT-2301, a bivalent version of KOSTAIVE (ancestral strain and Omicron BA.4/5) to further support immunogenicity and safety data for our self-amplifying mRNA platform, which may facilitate the timely release of future seasonal updates of our COVID-19 vaccine against evolving variants of concern.

The study enrolled 930 healthy adults and individuals with comorbidities, who previously received three to five doses of mRNA COVID-19 vaccines, including the last booster at least three months prior to recruitment, and compared the investigational vaccine (ARCT-2301) and COMIRNATY (ancestral strain and BA.4/5) to evaluate safety and immunogenicity between observer-blind groups.

The bivalent vaccine met the primary study endpoint (non-inferiority).

Both the geometric mean titer (GMT) ratio and seroresponse rate (SRR) difference of neutralizing antibodies against SARS-CoV-2 (Omicron BA.4/5 and Wuhan strains) met pre-specified non-inferiority and superiority criteria versus COMIRNATY.

There were no causally-associated severe or serious adverse events with ARCT-2301.

As with the monovalent vaccine, the bivalent sa-mRNA formulation demonstrated superior immunogenicity over the conventional bivalent mRNA vaccine COMIRNATY, a higher immune response persisting up to six months after a booster dose, and improved breadth, supporting the robustness of the sa-mRNA vaccine platform for future vaccine strain updates.

The study results were presented at OPTIONS XII for the Control of Influenza conference in Brisbane, Australia, in September 2024.

Phase 3 Co-administration Study of KOSTAIVE (Monovalent XBB1.5) and Seasonal Influenza Vaccines

In March 2024, Arcturus and CSL Seqirus initiated a Phase 3 pivotal study with the ARCT-2303 candidate vaccine containing the XBB1.5 Omicron variant.

The study aimed to generate additional immunogenicity and safety data in multiple ethnicities to support regulatory filings in the U.S.

and globally.

In addition, the study assessed the co-administration of the ARCT-2303 vaccine with the age-appropriate seasonal influenza vaccines.

Overall, 1,499 adults, including older adults, were recruited in the study in Australia, Costa Rica, Honduras and the Philippines.

The study results showed that all four primary study objectives and key secondary study objectives were met.

ARCT-2303 demonstrated a superior immune response compared to ARCT-154 as measured by neutralizing antibodies against Omicron XBB.1.5 in terms of GMT ratio and SRR difference.

Co-administration of ARCT-2303 and quadrivalent influenza vaccine (QIV;

Flucelvax, CSL) in adults 18-64 years old showed a noninferior immune response compared to standalone QIV.

Co-administration of ARCT-2303 and QIV also showed a noninferior immune response compared to standalone ARCT-2303.

Co-administration of ARCT-2303 and adjuvanted QIV (Fluad, CSL) in adults 65 years of age and above showed similar results for co-administered and separately administered groups.

The safety and reactogenicity of co-administered vaccines were comparable with 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.

In conjunction with our collaborator, CSL Seqirus, we are working to optimize KOSTAIVE’s formulation to better meet the needs of healthcare professionals and their patients.

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.

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Food and Drug Administration (“FDA”)) then make the final decision of which strains should be covered by vaccines licensed in their country.

Our LUNAR-qsFLU (qs;

quadrivalent seasonal) program, now exclusively licensed to 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.

Our LUNAR-FLU (seasonal) program, now exclusively licensed to 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.

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In addition, we do not expect mRNA vaccines to face the challenge from mutations common to egg-grown vaccines.

Increasing evidence supports that immunity against neuraminidase (NA), the second most abundant influenza surface protein, along with hemagglutinin (HA) specific immunity protects against influenza disease (Krammer et al, mBIO, 2018).

While most currently licensed vaccines contain some neuraminidase, the amount is not standardized, and currently licensed vaccines do not induce robust anti-neuraminidase immune responses.

LUNAR-qsFLU, targets both the HA and NA, and may have a protective benefit over current vaccines during seasons even when vaccine strains are not well matched to circulating strains (Sandbulte et al, PNAS, 2011).

LUNAR-qsFLU has been designed to take advantage of our expertise in both LUNAR lipid delivery systems and our STARR self-amplifying mRNA technology.

This platform has 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 aspiration of creating a highly effective influenza vaccine for use in general and high-risk populations.

Working with CSL Seqirus, we have generated a comprehensive non-clinical data package to support the initiation of the Phase 1 clinical trial with a novel influenza mRNA vaccine candidate.

LUNAR-FLU has been designed to take advantage of our expertise in both LUNAR lipid delivery systems and our STARR self-amplifying mRNA technology.

This platform has 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.

Working with CSL Seqirus, we generated a comprehensive non-clinical data package to support the initiation of the Phase 1 clinical trial with a novel influenza sa-mRNA vaccine candidate.

A Phase 1 dose-finding safety and immunogenicity study was initiated in January 2024 in Australia and is ongoing.

In non-clinical studies, the immunogenicity of ARCT-2138 was compared with those of three licensed influenza vaccines in naïve mice.

Naïve BALB/c mice were vaccinated once with 2 µg of ARCT-2138 or one-fifth of the human dose for comparator vaccines.

All vaccines contained antigens from the FDA recommended strains for the 2022/2023 influenza season for cell or egg-based vaccines.

Smaller doses than the full adult dose of the comparator vaccines was given due to limitation in the injection volume in the hind legs of mice (50µl per leg, total 100µl).

ARCT-2138 was dosed at 2 µg which is a five times lower dose than was tested in humans (10 µg) based on clinical dose escalation studies performed with ARCT-021.

The most significant differences in HAI titers were observed between ARCT-2138 and cell-based and recombinant influenza vaccines.

While a significant increase in HAI titers was observed for H1N1 and B Victoria antigens at day 56 for ARCT-2138 compared to the adjuvanted influenza vaccine, no difference was observed between these vaccine groups for H3N2 antigen, and the immune response for B Yamagata antigen was lower after ARCT-2138.

Neurominidase antibody responses were assessed at days 42 and 70.

As with HAI titers, ARCT-2138 elicited significant higher antibody titers for all four vaccine strains and at all time points analyzed when compared

to titers from mice immunized with cell-based and recombinant influenza vaccines.

ARCT-2138 neuraminidase antibody response were slightly, but significantly, higher for all vaccine strains except B Yamagata compared to mice immunized with adjuvanted influenza vaccines.

Altogether, the animal study data indicates that ARCT-2138 elicited higher antibody titers in mice than licensed cell-based and recombinant influenza vaccines and moderately higher titers for most antigens compared to an adjuvanted influenza vaccine.

HAI and NI Titers after Vaccination with ARCT-2138 and Licensed Comparator Vaccines.

Naïve BALB/c mice were vaccinated once with ARCT-2138 (2 µg) or once with one of three licensed vaccines (1/5 human dose) and assessed for HAI and NI titers for each of the antigens from the FDA recommended strains for the 2022/2023 Northern Hemisphere influenza season.

Antigens used to determine inhibition titers were from cell-based vaccine strains only.

ARCT-2138 showed similar or superior responses to (A) all four HAs and (B) all four NAs present in the licensed comparator.

Geometric mean with geometric SD shown.

Significance determined by 2-way ANOVA multiple comparisons test comparing ARCT-2138 to licensed vaccines at each time point (****=p<0.0001;

no asterisks=not significant).

Development Program

LUNAR-pandFLU (Influenza)

Our LUNAR-pandFLU program continues to progress under the award from the Biomedical Advanced Research and Development Authority (“BARDA”) that we obtained in 2022.

The program includes all non-clinical, manufacturing, and regulatory support to advance a vaccine to protect against disease caused by H5N1 highly-pathogenic avian influenza.

Non-clinical safety and pharmacology studies are ongoing, and a pre-IND meeting was granted.

Enrollment for a Phase 1 clinical trial designed to evaluate the safety and immunogenicity of ARCT-2304 (LUNAR-pandFLU candidate vaccine) is expected to begin before the end of 2024.

Pandemic Avian Influenza Program (H5N1 Influenza)

Our LUNAR-H5N1 program, which is part of the CSL Collaboration Agreement, 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.

The Phase 1 study of ARCT-2304, a self-amplifying mRNA (sa-mRNA) vaccine candidate, also known as LUNAR-H5N1, initiated dosing in December 2024.

The randomized placebo-controlled Phase 1 trial (NCT06602531) is being conducted at multiple sites in the U.S.

and designed to enroll approximately 200 healthy adults (120 participants 18-59 years old;

80 participants 60-80 years old).

The primary objective of this initial clinical trial is to evaluate safety and immune responses of three different dose levels and two different vaccination schedules of ARCT-2304 vaccine.

Immune responses are measured by hemagglutination inhibition (HAI), virus microneutralization (MN) and neuraminidase enzyme-linked lectin assays (ELLA).

The clinical study is fully funded by Biomedical Advanced Research and Development Authority (BARDA).

For a more comprehensive discussion of the funding award, please see Item 1 “Business” – “Revenue and Collaboration Arrangements and Other Material Agreements” – “BARDA.”

Preclinical Ferret Studies of ARCT-2304 (LUNAR-H5N1)

Several ferret challenge studies have been conducted to establish the efficacy of ARCT-2304, our clinical candidate for the LUNAR-pandFLU program.

ARCT-2304 vaccinated ferrets were challenged with the same influenza strain, H5N1 A/Indonesia/5/2005, encoded by the vaccine and protected all ferrets from lethal challenge.

Robust HAI and NI titers were observed after two doses of the vaccine and nasal titers in the days following challenge were lower than in either the unvaccinated ferrets (PBS) or ferrets vaccinated with an adjuvanted recombinant trimeric hemagglutinin (rHA).

Further, fewer signs of lung damage were observed in ARCT-2304 ferrets compared to either unvaccinated or rHA vaccinated ferrets.

In a separate experiment, ARCT-2304 vaccinated ferrets were challenged with an antigenically drifted strain from a different clade of H5N1, A/Vietnam/1203/2004.

ARCT-2304 vaccinated ferrets were compared to unvaccinated ferrets and to ferrets receiving an adjuvanted trimeric rHA vaccine encoding either the same strain as encoded by ARCT-2304 (A/Indonesia) or the challenge strain (A/Vietnam).

ARCT-2304 vaccinated ferrets were protected from death from this antigenically drifted strain.

While HAI and NI titers were lower against A/Vietnam than against A/Indonesia, ARCT-2304 vaccinated ferrets had the lowest nasal wash titers of any group and showed no signs of lung damage in contrast to unvaccinated ferrets and ferrets vaccinated with adjuvanted trimeric rHA protein.

A) Ferrets were vaccinated twice (day 0 & 28) with either ARCT-2304 (5µg) or an adjuvated (Addavax) recombinant trimeric HA protein (15µg) and challenged 3 weeks (day 49 post-vaccination) after the last vaccination with a lethal dose of the homologous H5N1 A/Indonesia/5/2005 strain.

All vaccinated ferrets survived infection while all unvaccinated (PBS) ferrets succumbed to the infection by day 7 post-infection.

ARCT-2304 ferrets had the highest HAI and NI titers among vaccinated groups both prior to and after challenge.

In addition, nasal wash titers were lowest in the ARCT-2138 vaccinated ferrets.

B) Ferrets were vaccinated twice (day 0 & 28) with either ARCT-2304 (5µg) or an adjuvated (Addavax) recombinant trimeric HA protein (15µg) encoding the same strain at ARCT-2304 (A/Indonesia) or the challenge strain (A/Vietnam) and challenged 4 weeks (day 56 post-vaccination) after the last vaccination with a lethal dose of H5N1 A/Vietnam/1203/2004 strain.

While lower HAI and NI titers were observed against the heterologous A/Vietnam strain, all vaccines elicited protection from lethal infection.

Similar to the heterologous challenge, however, the lowest nasal wash titers were observed in the ARCT-2304 vaccinated group.

Rare Disease Program

Medicines in Development

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.

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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 ammonia scavengers to try to prevent accumulation of ammonia.

Current standard of care for OTC deficiency is a low-protein diet, dietary supplements, and nitrogenscavengers to try to prevent accumulation of ammonia.

Life-threatening episodes of high ammonia levels can still occur, requiring treatment with dialysis or hemofiltration.

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We have retained worldwide development and commercialization rights to ARCT-810.

LUNAR-OTC has received orphan drug designation from the FDA and the EMA for treatment of OTC deficiency.

ARCT-810 was also successfully granted Fast Track Designation in May 2023 and Rare Pediatric Disease Designation (RPDD) in June 2023.

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.

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

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

A Phase 1b study in stable OTC-deficient adults completed dosing in the United States in August 2023.

The trial is designed to assess safety, tolerability and pharmacokinetics of a single dose of ARCT-810, as well as exploratory biomarkers of drug activity.

The Phase 1b study is a single ascending dose, placebo-controlled study that enrolled 16 adults with mild OTCD.

ARCT-810 was generally safe and well tolerated.

A Phase 2 multiple-dose study of ARCT-810 in OTC-deficient adolescents and adults initiated dosing in December 2022 and plans to enroll approximately 24 participants in two dose cohorts.

The study is being conducted in the UK and several other countries in the European Union.

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 study 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 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.

Patient follow-up is completed, and data management and analysis are ongoing.

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.

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 cystic fibrosis transmembrane conductance regulator (CFTR) gene.

ARCT-032, our lead development candidate for the treatment of cystic fibrosis, uses our LUNAR platform to deliver a codon-optimized CFTR mRNA into airway epithelial cells.

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.

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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 cystic fibrosis in the United States (and an estimated 105,000 people have been diagnosed with CF across 94 countries), and CF can affect people of every racial and ethnic group.

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), and CF can affect people of every racial and ethnic group.

Approximately 800 people are newly diagnosed with CF each year in the United States.

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We are initially focusing ARCT-032 on these groups of patients, as they currently have the highest unmet need for CF therapies.

We made significant progress on the LUNAR-CF program in 2023.

Following on our activities of 2022, which included reproducible demonstration of restoration of CFTR function in human bronchial epithelial cell cultures from CF donors and the completion of the first-in-human enabling GLP toxicology studies, in 2023 we

initiated and successfully achieved the recruitment target in a Phase 1 single ascending dose study of ARCT-032 (LUNAR-CF), our mRNA therapeutic candidate for CF, in 32 healthy participants (eight subjects in each of four dose cohorts).

In August 2023 we received regulatory approval of a protocol amendment to transition to a Phase 1b clinical study of ARCT-032 in up to eight adults with CF, with each participant receiving two administrations of ARCT-032.

We initiated Phase 1b enrollment in October 2023.

ARCT-032 was granted Orphan Drug Designation by the FDA in November 2023 and Orphan Medicinal Product Designation by the EMA in February 2024.

The FDA granted Rare Pediatric Disease Designation for ARCT-032 in October 2023.

In 2023, we initiated and 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.

A subsequent protocol amendment to transition to a safety and tolerability Phase 1b clinical study of ARCT-032 in adults with CF received regulatory approval in August 2023 and completed dosing and follow-up visits for seven CF participants in August 2024, with each CF participant having received two administrations of ARCT-032 separated by two days.

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.

Each participant in the Phase 2 CF study (NCT06747858) is expected to receive daily treatments of ARCT-032 over a period of 28 days.

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.

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Our comprehensive data set showcasing the potential for ARCT-032 as a disease-modifying treatment has been presented at the major CF conferences in North America and Europe.

For example, we recently presented data at the North American Cystic Fibrosis Conference in November 2023 that demonstrated that a single dose of ARCT-032, administered in the airways of CF ferrets by microsprayer, effectively doubled the mucociliary transport rate in vivo.

In vitro proof of concept of ARCT-032 was obtained using HBE cells cultured in an air-liquid interface system, a model system that has been shown to be highly correlated with clinical trial results with CFTR modulator drugs.

HBE cells cultured in this manner undergo extensive differentiation, resulting in an in vitro model that is representative of the in vivo airway epithelium.

The cells exhibit a pseudostratified morphology and are comprised of a heterogeneous cell population, including ionocytes, ciliated, basal, and secretory cells.

Work performed at University of Alabama at Birmingham (UAB) demonstrated that ARCT-032 (LUNAR-CFTR) treatment resulted in significantly higher chloride activity when compared to negative control (LUNAR-TdTomato).

More importantly, after treatment with ARCT-032, cultures derived from patients with CF with the F508del mutation (F508del+/+) demonstrated that the chloride current had been restored, i.e., the chloride efflux was similar to HBE cells from people without CF (WT) that were used as a positive control (figure below).

Additionally, western blot analysis of protein in the HBE cells showed higher levels of mature CFTR protein (C-band) in ARCT-032 treated cells when compared to non-CF donor control cells.

Functional Measurement of Chloride Activity and Western Blot Protein Expression Analysis in Human CF F508del+/+ Cells Transduced With ARCT-032

Isc = short-circuit current;

WT = wild type (healthy subjects).

A significant increase in chloride activity was observed in cultured cells from CF donors (F508del) treated

with LUNAR-CFTR (ARCT-032) compared to those treated with LUNAR-TdTomato (negative control).

ARCT-032 restored the levels of chloride efflux to the wild-type range observed for healthy human donors.

** p<0.001 (unpaired t-test)

Western blot demonstrates robust mature (C-band) CFTR protein expression specific to ARCT-032 treated CF cells (F508del+/+) comparable to WT cells, and not present in the LUNAR buffer or TdTomato controls.

The use of F508del HBEs allowed us to compare the activity of ARCT-032 with Vertex Pharmaceutical’s Trikafta (elexacaftor/tezacaftor/ivacaftor), a highly effective CFTR modulator combination approved for patients with F508del and other CFTR mutations.

Chloride conductance was measured in presence or absence of a chloride gradient in ALI-cultured F508 HBE cells (solid bars) or WT HBEs (textured bars) 24 hours following a single treatment with ARCT-032 (blue circles), LUNAR-TdT (red circles) or Trikafta (green circles).

The measurements were performed in three separate studies at different times.

ALI-cultured HBE cell monolayers derived from either three different CF patients carrying the F508del mutation or from an equal number of healthy donors carrying the WT CFTR.

The cells were transfected with a single, 20 µg dose of ARCT-032 or LUNAR-TdT, a formulation carrying TdTomato encoding mRNA that was used as a negative control.

When the HBE monolayer was tested for transepithelial chloride currents in presence of a chloride gradient, a single 20 µg treatment with ARCT-032 resulted in significantly increased chloride conductance compared to the LUNAR-TdT control at 24 hours post-treatment (Figure 1).

Importantly, ARCT-032-restored chloride efflux in F508del HBEs matched the chloride efflux observed in wild type HBEs from non-CF donors.

In absence of a chloride gradient, ARCT-032 driven chloride currents were lower than those with a chloride gradient but matched the activity of Trikafta tested alongside (Figure 1).

Our results from the UAB studies without chloride gradients are comparable to those previously obtained at CF Foundation Therapeutics under similar experimental conditions.

Next, ARCT-032 activity was evaluated in CF HBEs carrying the nonsense mutations (G542X/R1162X) which are associated with a severe CF phenotype due to the complete absence of CFTR expression (CFTR null).

CF patients harboring these and other nonsense mutations are not eligible to be treated with the approved CF modulators such as Trikafta and are a primary target population of patients for ARCT-032 treatment.

We demonstrated that a single 20 µg treatment with ARCT-032 resulted in a significantly higher CFTR-mediated chloride conductance compared to the LUNAR-TdT used as a negative control (Figure 2).

These observations highlight the potential applicability of ARCT-032 treatment in CF patients non-responsive to currently approved CF modulators.

Chloride conductance measured in G542X/R1162X nonsense mutation carrying HBEs or WT HBEs at 24 hours following a single treatment with ARCT-032 (blue circles) or LUNAR-TdT (red circles) or buffer (black circles).

Additional preliminary results have indicated that a single 20 µg treatment with ARCT-032 could impart substantial CFTR activity in F508del HBEs for at least three days while the activity is still detectable at five days from the treatment (Figure 3A).

This highlights the efficacy of transfection and the stability of translated CFTR protein.

Furthermore, we have demonstrated that treatment of F508 HBEs with multiple smaller doses (3 µg and 5 µg) of ARCT-032 can achieve CFTR activity comparable to a larger single dose (20 µg) (Figure 3B).

Together, these results have demonstrated the ability of ARCT-032 to generate a functional and stable CFTR protein in a dose and treatment amenable manner.

A) Time-course study in F508del HBEs carried out in presence of a chloride gradient following a single treatment with ARCT-032 indicated substantial CFTR activity for three days and detectable activity for at least five days.

B) Under no chloride gradient conditions, treatment of F508del HBEs with multiple smaller doses (3µg or 5µg) of ARCT-032 achieved CFTR function comparable to a single larger dose (20µg).

As mentioned, earlier work has shown successful transduction of airway epithelial cells with LUNAR-mRNA in multiple species of healthy animals.

We recently achieved similar success in a CF animal model.

In collaboration with the University of Iowa and supported by the Cystic Fibrosis Foundation, a double transgenic ferret model of CF was used to assess transduction of bronchial epithelial cells in diseased ferrets.

Ferrets with the G551D mutation maintained on VX-770 (ivacaftor) developed a CF phenotype including thick mucus in the lungs upon withdrawal from VX-770 treatment.

LUNAR-Cre was administered to the airways by microsprayer, and the Cre recombinase mRNA-transduced cells switched off TdTomato expression (shown in red) and expressed EGFP (cells in green).

This demonstrated the ability of LUNAR-Cre to penetrate the mucus layer and transduce the target pulmonary epithelial cells in CF-diseased ferrets.

Penetration of LUNAR-mRNA Through Mucus

Photomicrographs of the pulmonary epithelium of G551D CFTR/Rosa transgenic ferrets following microsprayer administration of LUNAR Cre.

The ferrets express TdTomato protein (red) by default;

introduction of Cre recombinase mRNA (via LUNAR-Cre) results in Cre protein expression and excision of TdTomato enabling expression of EGFP (green).

The panel on the left shows transduction with LUNAR-Cre of pulmonary epithelial cells lining the trachea, as evidenced by the conversion of TdTomato expression in red to EGFP expression in green.

The panel on the right illustrates the ability of LUNAR-Cre LNPs to penetrate the mucus (outlined by a blue box) in a smaller bronchiole and transduce the underlying epithelial cells.

The red-fluorescing cells are not transduced by LUNAR-Cre.

Sections were counterstained with DAPI (blue).

Further experiments with G551D CFTR-transgenic ferrets demonstrated in vivo proof of concept of ARCT-032 (LUNAR-CFTR) in this model system.

The G551D ferrets are initially maintained on VX-770 treatment and develop typical findings of CF lung disease upon withdrawal of the drug.

This enables the evaluation of therapeutic interventions.

Following withdrawal of VX-770, the ferrets were treated with either ARCT-032 or LUNAR-TdTomato (negative control) administered by a microsprayer.

Mucociliary clearance was assessed by PET/CT scan while maintained on VX-770, a few weeks after VX-770 withdrawal, and 24 hours following dosing.

As shown in figure below, after a single administration of ARCT-03 the mucociliary clearance in CF ferrets 2 (green line) was about twice that of the ‘VX-770 Off’ baseline (black line), and comparable to or greater than that for ‘VX-770 On’ (turquoise line).

LUNARhCFTR = ARCT-032;

LUNARdT = LUNAR-TdTomato;

MCC = mucociliary clearance;

VX-770 = ivacaftor.

x-axis represents time in minutes.

After VX-770 washout, G551D CFTR ferrets were treated as shown and PET/CT scanned.

MCC was assessed post first dose.

Discovery Program

Discovery Program – Phenylketonuria (PKU)

Phenylketonurea (PKU) is an inherited metabolic disease characterized by the buildup of the amino acid phenylalanine (Phe) in the body due to the lack or deficient activity of the enzyme responsible for its metabolism, phenylalanine hydroxylase (PAH).

In PKU patients, high levels of phenylalanine affect normal nervous system function and can lead to brain disfunction and intellectual disability.

Globally, approximately 1:10,000 newborns carry mutations in the PAH gene responsible for the PKU disease.

Dietary restriction (low protein diet) has been the main therapeutic treatment to control Phe levels and, although successful, outcomes are not always optimal, and patients often have difficulty adhering to restrictions.

There are only two approved treatments for PKU:

Palynziq®, which requires injections that may lead to an immune response against Palynziq® as it is an enzyme derived from bacteria, and the synthetic PAH co-factor, BH4, Kuvan®, which only helps a subpopulation of PKU patients.

The LUNAR PKU program attempts to address the unmet needs of PKU patients by delivering mRNA encoding the PAH protein formulated in LUNAR lipid nanoparticles to the PAH-deficient liver, restoring PAH function and reducing blood Phe to healthy levels.

In a PKU mouse model, we have shown that we can deliver a functional human PAH mRNA to the liver and reduce Phe to safe levels (Phe < 0.3 mM).

Presently, the program is aiming to increase the duration of the efficacy after a single dose treatment to reduce the frequency of dosing and improve the effectiveness of the therapy.

Proof of concept studies in PKU mice show that engineering of PAH mRNA and protein lead to a significant increase in the duration of the efficacy, longer than six (6) days, as compared to the original, first-generation PAH mRNA (~24-48 hours).

Additional in vivo efficacy and tolerability studies are underway to finalize a candidate drug product composed of the optimized PAH mRNA and LUNAR formulations.

LUNAR PAH mRNA reduces phenylalanine plasma levels in a PKU mouse model after a single dose.

Discovery Programs – Vaccine Programs (Lyme Disease and Gonorrhea)

Based on the clinical and regulatory validation of LUNAR and STARR technologies provided by the approval of ARCT-154, our next-generation vaccine for COVID-19, we have initiated new vaccine discovery programs for Lyme disease and gonorrhea.

The new discovery programs rely on the evidence of superior immunogenicity, durability, and breadth of immune response compared to conventional mRNA vaccines, as observed in the COVID-19 program.

Lyme disease is a bacterial infection and is the most common vector-borne disease in the United States.

Infection can spread to joints, the heart and the nervous system.

Gonorrhea is a sexually transmitted disease (STD) that can infect the mucous membranes of the reproductive tract.

It is the second most commonly reported bacterial sexually transmitted infection in the United States.

We selected these diseases based on high unmet medical needs, good understanding of the path forward in vaccine target selection, and demonstration of proof of concept, as well as platform advantages that may be translated in a favorable vaccine product.

Enabling Technologies

Enabling Technologies – LUNAR-Genome Editing

Genome editing therapies are based on the ability to modify a specific DNA sequence in the human genome.

All genome editing molecular tools can be programmed to target a DNA sequence of interest.

Although the diversity of programmable gene editing tools is increasing, all of them are based on a DNA binding component (either a protein or, as in the case of CRISPR-clustered regularly interspaced short palindromic repeats, an RNA sequence) plus a DNA modifier component (a protein that can either make double strand breaks on the DNA (nuclease), single strand breaks (nickase), or make chemical modification in the DNA (base editors)).

One of the main roadblocks to applying genome editing as a therapy to treat human disease is the delivery of the genome editing tool components into the cells, either ex-vivo or in vivo, applying them directly into the human body and targeting the right organ.

The LUNAR-Genome editing program aims to leverage the ability of our LUNAR-mRNA technology to deliver any type of genome editing tools into target cells.

Some of the genome editing tools are based on protein components working in pairs (TALEN-Transcriptional Activator-Like Effector Nuclease, ZFN-Zinc Finger Nuclease) or as a single protein (meganuclease), while other tools could have a combination of RNA and protein component (CRISPR).

We have delivered mRNAs coding for TALEN proteins encapsulated in our LUNAR formulations acting on different targets, and also CRISPR Cas9 mRNA to edit the targeted DNA sequence.

To test the efficacy of the different genome editing strategies as a proof of concept, we utilized target genes that encode proteins that are well known, that are involved in diseases and can be detected in the plasma, which facilitated the readout of the experiments.

For evaluation of the LUNAR TALEN mRNA strategy, we designed TALEN pairs targeting either the mouse Pcsk9 gene or the human LPA gene which are involved in lipid metabolism and are associated with cardiovascular disease.

The Pcsk9 gene is expressed only in the liver, and the PCSK9 protein is secreted into the blood circulation.

PCSK9 binds and downregulates the low-density lipoprotein (LDL) receptors (LDLR) present in the hepatocytes cell membrane, therefore reduction of PCSK9 protein levels increases LDLR (defined below) levels and its availability to take and reduce LDL-Cholesterol from the blood (Figure below.

A single intravenous dose of LUNAR-TALEN PCSK9 mRNA encapsulated LUNAR LNPs into wildtype mice led to insertions and deletions in the PCSK9 genomic DNA sequence which resulted in the inactivation of the PCSK9 gene and, consequently, a reduction of PCSK9 protein levels in the mouse plasma of the treated mice (Figure below.

Bottom Left).

Examination of the targeted PCSK9 DNA sequence extracted from different organs did not show any DNA modifications except for the liver, which is explained by the liver specificity of this LUNAR formulation (Figure below.

Bottom Right).

PCSK9 involvement in LDL-Cholesterol metabolism.

PCSK inhibits LDL-Receptor activity and increases LDL-Cholesterol in circulation.

Elimination of PCSK9 protein after editing the Pcsk9 target gene Bottom Left:

LUNAR-PCSK9 TALEN mRNA dosing of mice at time Day 0 reduces levels of PCSK9 in circulation.

Bottom Right:

Genome editing evaluation by sequencing shows INDEL (insertion/deletions) only in DNA extracted from the liver but not from other tissues .

Lipoprotein(a), Lp(a), is a causal risk factor for cardiovascular disease.

Numerous epidemiological studies have shown an association between higher circulating Lp(a) concentrations and an increased risk of atherosclerotic and aortic calcification cardiovascular disease.

Lipid-lowering drugs do not effectively reduce Lp(a) levels that are mainly regulated by the genomic structure of the apo(a) gene named LPA .

LPA is expressed only in the liver and natural homozygous loss of this gene in humans has not been associated with adverse phenotypes, which makes LPA a candidate for genome editing therapies.

We designed and tested our LUNAR-TALEN-LPA technology in primary human hepatocytes and in a transgenic mouse model containing the human LPA gene.

Like the PCSK9 model, either one or two intravenous doses of LUNAR-TALEN-LPA mRNA encapsulated LUNAR LNPs led to a significant reduction of Lp(a) levels in serum that correlated with the reduction of LPA mRNA expression and the presence of gene editing in the LPA target sequence.

LUNAR-TALEN-LPA mRNA reduces human Lp(a) plasma levels and hepatic mRNA levels in a human Lp(a) transgenic mouse model after either one or two doses.

Enabling Technologies - CRISPR/Cas9

Our efforts in CRISPR/Cas9 genome engineering are focused on generating proof-of-concept for our platform technology.

To test the ability to deliver CRISPR/Cas9 complexes to the liver, we used a single guide RNA known to target the mouse TTR gene and an mRNA encoding the Cas9 nuclease, both encapsulated in a proprietary LUNAR LNP ( LUNAR-Cas9-TTR ).

The transthyretin (TTR) protein is expressed only in the liver and is secreted into the blood.

In humans, mutations in the TTR gene can cause transthyretin amyloidosis (ATTR), which is a progressive and fatal disorder resulting from the deposition of insoluble amyloid fibrils in different tissues of the body, predominantly the nervous system and the heart, resulting in organ failure.

Reduction of TTR production by CRISPR/Cas9-mediated gene editing has been shown to halt disease progression (Fig.

LUNAR-Cas9-TTR formulations were injected intravenously into wild-type mice.

After a single dose, there was a significant reduction in the amount of TTR protein detected in the mouse serum at the doses tested (Fig.2, Bottom left).

This reduction of TTR protein correlated with the deletions detected in the targeted TTR genomic DNA extracted from the liver of the LUNAR-Cas9-TTR treated mice (Fig.2, Bottom right).

Further, when our constructs were compared to a competitor’s results, using a similar Cas9 mRNA and TTR -targeting sgRNA, a significantly greater amount of gene editing was observed using the Arcturus mRNA and lipid nanoparticles.

Demonstration of efficacy of the LUNAR mRNA platform with different genome editing technologies and targets will enable future discovery efforts toward the identification of new potential therapies.

TTR protein containing mutations aggregates and deposits forming amyloid fibers in different organs causing cardiomyopathies or neuropathies.

TTR levels in the serum were reduced in mice treated with LUNAR-Cas9-TTR.

Quantitation of genome editing by DNA sequencing analysis showed a significant amount of INDELs (insertion/deletions) in the livers of mice treated with LUNAR-Cas9-TTR.

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 hints for the possible applicability to various types of cancer with flexibility in dosing regimens.

Our current effort focuses 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.

Antitumor activity and T cell response by Arcturus cancer vaccines.

STARR vaccine expressing a tumor antigen led to a significant reduction of the tumor growth rate of a colorectal cancer cell line, CT26.

T responses elicited by conventional mRNA cancer vaccine by various LUNAR formulations.

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.

RNA-driven CAR expression in lymphocytes or immune cell types would be transient and therefore expected to have a lower side effect profile;

There is no integration into the germline DNA allowing for co-delivery of multiple therapeutic molecules without the risk of insertional mutagenesis;

Generation of CAR-expressing cells by a process that is quicker and cheaper, particularly when targeting specific immune cell subtypes in vivo.

The goal of the LUNAR-I/O program is to leverage the inherent advantages of both RNA and LUNAR technology to maximize clinical effectiveness of CAR-expressing cells.

To this end, initial experiments have demonstrated that our proprietary LUNAR lipid nanoparticles can transfect > 90% of both primary human CD8+ and CD4+ T lymphocytes in vitro.

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

Platform Technology Overview

For example, we presented data at the North American Cystic Fibrosis Conference in November 2023 that demonstrated that a single dose of ARCT-032, administered in the airways of CF ferrets by microsprayer, effectively doubled the mucociliary transport rate in vivo.

Platform Technologies and R&D Programs

We have four key proprietary platform technologies:

• lipid-mediated delivery (LUNAR ® )

• mRNA and protein design

• self-amplifying mRNA (STARR ® )

• manufacturing and formulation for mRNA medicines

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.

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We strive to use these proprietary innovations to benefit each mRNA medicine in our pipeline.

We continue to invest in our LUNAR lipid-mediated delivery of mRNA (encoding CRISPR-Cas9, TALEN, zinc finger proteins, and meganucleases), siRNA, DNA, microRNA, and antisense oligonucleotide technology platforms to improve their efficacy and safety profile, further expanding their applications.

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 systemically administered mRNA therapeutics.

As such, we consider ourselves a leader in the research and development of mRNA therapeutics for multiple indications.

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 formulations are a multi-component, lipid-mediated drug delivery system that utilizes our proprietary lipids, called ATX lipids.

LUNAR is a multi-component, lipid-mediated drug delivery system that utilizes our proprietary lipids, called ATX lipids.

Each of our ATX lipids contain an ionizable head group and a biodegradable lipid backbone.

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

• Design and incorporate novel ATX lipids and formulations to enrich our library of proprietary ATX lipids for target cell/tissue specificity, improved tolerability and translatability to larger species;

• Develop and improvise manufacturing processes for LUNAR formulations to ensure RNA encapsulation across compositions and scales;

• Design, manufacture and incorporate novel ATX lipids into formulations to enrich our library of proprietary ATX lipids for target cell/tissue specificity, improved tolerability and translatability to larger species;

• Develop, optimize and innovate manufacturing processes for LUNAR formulations to ensure RNA encapsulation across compositions and scales;

• Develop stabilization strategies (e.g.

lyophilized presentation) for LUNAR formulations to mitigate frozen storage;

• Continually assess and improvise LUNAR screening funnel to enable rigorous selection of ATX lipids for various programs.

lyophilized presentation) for LUNAR formulations to mitigate the need for frozen storage and to extend shelf-life;

• Continually optimize and innovate LUNAR screening paradigm to enable rigorous selection of ATX lipids for various therapeutic programs and routes of administration.

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

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ATX lipids are rationally designed to fit their respective 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 and LUNAR composition for the particular nucleic acid therapeutic candidate, the desired route of administration, and target cell type.

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.

New ATX lipids are chemically synthesized and used to package both siRNAs for inhibiting target protein expression and mRNAs expressing a secreted protein.

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.

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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.

In the top two figures, mice were injected intravenously with 4 different LUNAR lipid formulations containing mRNA expressing human erythropoietin (EPO).

The LUNAR lipids that were screened were LUNAR96, LUNAR97, LUNAR98 and LUNAR2 at 0.1 mg/kg 0.3 mg/kg RNA doses.

LUNAR lipid 2 formulation is a positive control to which expression from the other formulations is compared.

Expression of Human EPO in Mice 6 hours After IV Administration (Figure 2)

Mouse Liver Clearance of LUNAR Lipids 48 hours After IV Administration (Figure 3)

Expression of Human EPO in Non-Human Primates 6 Hours After IV Administration (Figure 4)

mice were injected intravenously with 4 different LUNAR lipid formulations containing mRNA expressing human erythropoietin (EPO).

The LUNAR lipids that were screened were C9G, C9H, C9I and B2G at 0.1 mg/kg and 0.3 mg/kg RNA doses.

LUNAR 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 EPO, a secreted protein.

The figure below the mouse human EPO expression figure shows the clearance of the LUNAR lipids from the liver 48 hours after administration of 0.1mg/kg and 0.3 mg/kg RNA doses.

LUNAR 96, 97 and 98 yielded much higher expression levels of EPO than LUNAR 2, the positive control for both doses tested.

The mouse liver clearance figure shows that the residual amount of LUNAR96 and LUNAR98 were below the limit of detection and the residual amount of LUNAR97 was at least 10-fold less than the remaining amount of LUNAR2 at the 0.1 mg/kg RNA dose and at least two-fold less than the residual amount of LUNAR2 at the higher RNA dose.

LUNAR96 and LUNAR98 formulations were tested for EPO expression in non-human primates at a single dose and assayed for secreted EPO in the blood 24 hours after IV administration.

Both LUNAR96 and LUNAR98 yielded significantly higher expression levels than the positive control, LUNAR2 further confirming the superior performance of the new LUNAR formulations.

Hence, this lipid screen identified 3 LUNAR lipids that yielded greater RNA expression in mice and 2 LUNAR lipids in NHPs, and were rapidly cleared from the liver within 48 hours after administration.

shows the clearance of the LUNAR 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 EPO 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.

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 Cystic Fibrosis program using our proprietary lipid nanoparticle delivery platform, LUNAR.

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 Cystic Fibrosis program will serve as a translatable approach to support other respiratory approaches where targeting airway epithelium is needed.

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 airways epithelium demonstrated in vivo across species (rodents, ferrets, NHPs)

Liver Targeting

As proof of concept for augmenting LUNAR liver-targeting capabilities, we are developing LUNAR formulations containing a propriety hepatocyte targeting agent.

Alternate Liver Targeting

As proof of concept for augmenting LUNAR liver-targeting capabilities, we have developed data on LUNAR formulations containing a propriety hepatocyte targeting agent.

Traditional lipid nanoparticle-mediated delivery to hepatocytes occurs via uptake by the low-density lipoprotein receptor (LDLR).

We evaluated this targeting agent in an LDLR-deficient mouse model and found that only the LUNAR formulations with this targeting agent were able to deliver mRNA to the hepatocytes compared to LUNAR formulations that did not contain the targeting agent.

Based on these promising data, we are expanding these platform development efforts.

LUNAR Safety (i.v.

LUNAR’s advanced generation lipids have excellent liver targeting capabilities on their own.

But diseases mediated by LDLR deficiency such as familiar hypercholesterolemia require alternate liver targeting and LUNAR delivery approaches.

Therefore, we evaluated this targeting agent in an LDLR-deficient mouse model and found that only the LUNAR formulations with this targeting agent were able to deliver mRNA to the hepatocytes compared to LUNAR formulations that did not contain the targeting agent.

Based on this promising data, we are expanding these platform development efforts.

LUNAR Safety and Tolerability (i.v.

administration)

LUNAR-CF - ARCT-032 Nonclinical Safety Profile

Arcturus has instituted a robust ATX lipid screening paradigm to ensure that we identify formulations with suitable properties for the intended drug’s target product profile, whether is it a protein replacement therapy, a gene editing treatment, or a vaccine.

Drug product safety is a key feature in that profile.

A recent example of the outcome of these efforts is the nonclinical safety profile we obtained with ARCT-032 that has enabled the first-in-human trials.

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

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Our STARR mRNA Technology

In addition to our LUNAR lipids technology, our platform technologies include our distinct and proprietary self-amplifying RNA (saRNA) platform, termed STARR.

The STARR platform includes proprietary algorithms that inform the design and optimization of saRNA to enhance expression of the applicable antigen while minimizing structures that might inhibit expression.

The replicase, an RNA-dependent RNA polymerase, is encoded upstream of the antigen of interest and functions to amplify transcripts and increase the duration of antigen expression compared to non-self-amplifying (conventional) mRNA.

Our distinct and proprietary self-amplifying mRNA (sa-mRNA) platform (STARR) includes proprietary algorithms that inform the design and optimization of sa-mRNA to enhance expression of the applicable antigen while minimizing structures that might 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 expression compared to conventional (conventional) mRNA.

The enhanced expression leads to higher immunogenicity at lower doses than conventional mRNA vaccines in preclinical studies (Figure 6 below).

The above results show the luciferase expression from an optimized saRNA, STARR Technology (Green), a non-optimized saRNA (Blue) and the conventional RNA (Purple).

The STARR Technology yields at least a 30-fold greater expression level than conventional RNA.

The STARR Technology also produces a longer duration of expression compared to the conventional RNA and also the non-optimized self-amplifying RNA.

We believe the combination of LUNAR and STARR technology can provide lower dose requirements by generating a superior immune response and sustained protein expression as compared to non-self-amplifying RNA-based vaccines.

We believe this LUNAR/STARR technology will enable us to simplify and increase the speed of vaccine production.

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.

Vaccine candidates with STARR technology have been demonstrated to induce a longer-lasting and broader humoral immune response at lower dose levels than conventional mRNA-based vaccines.

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:

• mRNA Drug Substance Manufacturing – We have developed the ability to manufacture mRNA drug substance with high product yield and exceptional product purity.

In addition, we have developed reliable and efficient testing methodologies for characterizing mRNA drug substance.

We continue to innovate in this area to further improve the cost, yield, purity and stability of mRNA drug substance.

• Drug Product Formulation – The formulation of mRNA drug substance with our LUNAR delivery platform is essential to achieving effective in vivo delivery and translation of the mRNA.

We have developed advanced processes and know-how that enable us to manufacture lipid-encapsulated compounds at large volumes to help ensure that lipid-encapsulated compounds that meet key product specifications, including purity, particle size, concentration, stability, and percent encapsulation, in both liquid and lyophilized product formats.

The continued advancement of these capabilities is an important focus of our platform development.

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 – Vaccine Programs (Lyme Disease and Gonorrhea)

Based on the clinical and regulatory validation of LUNAR and STARR technologies provided by the approval of KOSTAIVE, a self-amplifying messenger RNA (sa-mRNA) vaccine for COVID-19, we initiated vaccine discovery programs for Lyme disease and gonorrhea.

The discovery programs rely on the evidence of superior immunogenicity, durability, and breadth of immune response compared to conventional mRNA vaccines, as observed in the COVID-19 program.

Lyme disease is a bacterial infection and is the most common vector-borne disease in the United States.

Infection can spread to joints, the heart and the nervous system.

Gonorrhea is a sexually transmitted disease (STD) that can infect the mucous membranes of the reproductive tract.

It is the second most commonly reported bacterial sexually transmitted infection in the United States.

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 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 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.

Moreover, the same level of efficacy was achieved with a single administration of a 0.2 ug dose of the STARR vaccine.

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.