Gritstone bio, Inc. announced the presentation of results from three ongoing Phase 1 studies evaluating its self-amplifying mRNA (samRNA) vaccine candidates against COVID-19 (part of the company?s CORAL program) at IDWeek 2023, occurring October 11-15, 2023, in Boston, MA. Gritstone will present further follow up data from the CORAL-CEPI and CORAL-BOOST studies (most recent prior presentation in April 2023, press release). Representatives from the Infectious Diseases Clinical Research Consortium (IDCRC), a clinical trials network established by the National Institute of Allergy and Infectious Disease (NIAID), will present the first results from the CORAL-NIH study, a Phase 1 study conducted by IDCRC and supported by NIAID).

Results across these studies generally reaffirm and extend previous CORAL findings that Gritstone?s next-generation samRNA-based approach, which incorporates both Spike and other viral targets (?Spike plus?), can induce potent and durable immune responses with potential to drive broad and long-lasting clinical protection. Key Highlights from IDWeek Poster Presentations: CORAL-CEPI and CORAL-BOOST presentations (presented by Gritstone) CORAL-CEPI Presentation (Abstract 1538194, Poster Presentation): Durable Immune Response Induced by Self-amplifying mRNA (samRNA) SARS-CoV-2 Vaccine Candidates in Vaccine-naïve HIV Negative and People Living with HIV (PLWH) Populations Date/Time: Saturday, Oct 14, 2023, 12:15 - 1:30 PM Poster #: 2372 Presenter: Atul Nagare, MD and Location: BCEC Poster Hall. CORAL-CEPI (NCT05435027) is a Phase 1 study evaluating samRNA-based COVID-19 vaccine candidates containing Spike plus other viral targets in HIV negative (virus-naïve and convalescent) and people living with HIV (PLWH) populations in South Africa (N = 342).

Results presented from Group A, B and C (n = 242) demonstrated: All doses (3ug, 10ug, and 30ug) were well tolerated in both HIV-negative participants and PLWH irrespective of SARS-CoV-2 serostatus at baseline. High IgG and neutralizing antibody responses were induced and sustained for at least 12 months. Spike and non-Spike T cell responses were increased and/or maintained in the majority of individuals across all dose levels.

T cell data from PLWH are still being evaluated. CORAL-BOOST Presentation (Abstract 1530224, Poster Presentation): Durable Immune Response Induced by a Self-amplifying mRNA (samRNA) SARS-CoV-2 Vaccine Candidate in Adults Previously Vaccinated with mRNA or Adenovirus Primary Series Date/Time: Saturday, Oct 14, 2023, 12:15 - 1:30 PM Poster #: 2346 Presenter: Meghan G. Hart Location: BCEC Poster Hall CORAL-BOOST (NCT05148962) is a Phase 1 study evaluating a samRNA-based COVID-19 vaccine candidate containing spike plus other viral targets in older adults =60 years of age (N = 40). Results presented from cohorts 1 - 4 (n = 37) demonstrated: Vaccine candidate was well tolerated as a booster regardless of primary vaccination series (samRNA administration post-Vaxzevria or samRNA administration post-mRNA).

Robust, durable binding and high neutralizing antibodies were induced and sustained for up to at least 12 months against SpikeD614G and variants of concern. Broad T cell responses induced against Spike and non-Spike T cell epitopes included in the vaccine. Use of T cell receptor sequencing assays to assess T cell response breadth.

CORAL-NIH presentation (presented by IDCRC): CORAL-NIH Presentation (Abstract 1530224, Poster Presentation): An Interim Report of the Safety, Reactogenicity, and Immunogenicity of a Self-amplifying mRNA (samRNA) COVID-19 Vaccine GRT-R910 as a Booster in Healthy Adults Date/Time: Saturday, Oct 14, 2023, 12:15 - 1:30 PM Poster #: 2395 Presenter: Jennifer Whitaker Location: BCEC Poster Hall CORAL-NIH (NCT04776317) is a Phase 1 study of a samRNA-based vaccine candidate containing spike plus other viral targets as a booster in healthy adults in the United States and sponsored and executed by the National Institute of Allergy and Infectious Diseases (NIAID) (N = 150). Results presented from adults across all age groups and dose levels (n = 48) demonstrated: Vaccine candidate was well-tolerated with no safety signals identified. Durable boosting of humoral immune responses to Spike and variants of concern, and high neutralizing antibody responses to at least 6 months were observed for all vaccine groups.

Results are consistent across Phase 1 trials of GRT-R910 and similar vaccines (GRT-R912 and GRT-R914).