Business Description

Overview We are a messenger RNA medicines company focused on the development of liver and respiratory rare disease therapeutics. We have ongoing Phase 2 clinical studies for our RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF). We developed the world’s first approved self-amplifying messenger RNA (sa-mRNA) vaccine, KOSTAIVE ® (“KOSTAIVE”), which we have partnered with Seqirus, Inc. (“CSL Seqirus”), a part of CSL Limited. KOSTAIVE has achieved approval in Japan, the European Union and the United Kingdom as a vaccine against COVID-19, and sales of KOSTAIVE began in Japan in October 2024. We have several key platform technologies that we leverage to develop and advance a pipeline of mRNA-based therapeutics for rare genetic disorders with significant unmet medical needs and vaccines for infectious diseases. Current mRNA medicines have two critical components: the messenger RNA (“mRNA”) constructs and the lipid nanoparticles (“LNP”) which help deliver the mRNA to disease-relevant target tissues. We have extensive expertise in the design and optimization of mRNA constructs, including with respect to a type of mRNA technology known as self-amplifying mRNA (sa-mRNA). Our proprietary self-amplifying mRNA technology platform, or STARR ® (“STARR”), has been demonstrated to induce a robust, longer-lasting and broader humoral immune response at lower dose levels than conventional mRNA-based vaccines. Our proprietary LNP delivery system, LUNAR ® (“LUNAR”), is intended to address the major hurdle in RNA drug development, namely the effective and safe delivery of RNA to disease-relevant target tissues. LUNAR may enable multiple nucleic acid medicines. We also have significant expertise and valuable know-how in the development and scalability of complex and robust manufacturing processes required to deliver the next generation of nucleic acid medicines. Our internal pipeline includes RNA therapeutic candidates to potentially treat ornithine transcarbamylase (OTC) deficiency and cystic fibrosis (CF), both rare diseases. In our vaccine program, we have partnered with CSL Seqirus, one of the world’s leading influenza vaccine providers, on the development and commercialization of mRNA vaccines for COVID-19, influenza and three other infectious diseases. In CSL Limited’s half-year results presented on February 11, 2026, CSL Limited reported an accounting write-down of approximately $430 million attributable to our collaboration agreement with CSL Seqirus, citing declining COVID-19 disease burden and more onerous U.S. regulatory requirements. In our CF program, we enrolled and completed dosing in the three initially planned cohorts of our Phase 2 multiple ascending dose study of ARCT-032, confirming the safety and tolerability of ARCT-032 dosed daily for four weeks. This study was initiated in December 2024 and was designed to identify a safe and effective dose regimen in those with Class I (null) CFTR mutations and people with CF who do not benefit from CFTR modulators. In the study, six CF adults with Class I CFTR mutations inhaled 10 mg doses of ARCT-032 daily over 28 days. Interim results released in October 2025 demonstrated that the treatment was generally safe and well tolerated. Treatment-related adverse events (AEs) that were identified in the single-dose Phase 1 study were also observed in some participants for the first few doses but ceased with continued dosing. Bronchospasm has not been reported in this study thus far, neither with nor without albuterol pretreatment. One serious adverse event (SAE) occurred in a participant after the end of the dosing period. The safety review committee found no convincing evidence that the SAE is related to ARCT-032 and approved the study to proceed. We intend to initiate a 12-week safety and preliminary efficacy study in up to 20 CF participants in the first half of 2026, after the third cohort completes treatment. ARCT-032 has received Orphan Drug Designation by the U.S. Food and Drug Administration (the “FDA”) and Orphan Medicinal Product Designation by the European Medicines Agency (the “EMA”) for the treatment of CF, and Rare Pediatric Disease Designation from the FDA. KOSTAIVE is the brand name approved in Japan and Europe for ARCT-154, which is the version of the sa-mRNA COVID vaccine encoding the ancestral strain of SARS-CoV-2, and also for updated variant-specific versions of this vaccine.…