Non-clinical immunogenicity, biodistribution and toxicology evaluation of a chimpanzee adenovirus-based COVID-19 vaccine in rat and rhesus macaque

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Abstract
Coronavirus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 has rapidly expanded into a serious global pandemic. Due to the high morbidity and mortality of COVID-19, there is an urgent need to develop safe and effective vaccines. AdC68-19S is an investigational chimpanzee adenovirus serotype 68 (AdC68) vector-based vaccine which encodes the full-length spike protein of SARS-CoV-2. Here, we evaluated the immunogenicity, biodistribution and safety profiles of the candidate vaccine AdC68-19S in Sprague Dawley (SD) rat and rhesus macaque under GLP conditions. To characterize the biodistribution profile of AdC68-19S, SD rats were given a single intramuscular injection of AdC68-19S 2 × 1011 VP/dose. Designated organs were collected on day 1, day 2, day 4, day 8 and day 15. Genomic DNA was extracted from all samples and was further quantified by real-time quantitative polymerase chain reaction (qPCR). To characterize the toxicology and immunogenicity profiles of AdC68-19S, the rats and rhesus macaques were injected intramuscularly with AdC68-19S up to 2 × 1011vp/dose or 4 × 1011vp/dose (2 and fourfold the proposed clinical dose of 1 × 1011vp/dose) on two or three occasions with a 14-day interval period, respectively. In addition to the conventional toxicological evaluation indexes, the antigen-specific cellular and humoral responses were evaluated. We proved that multiple intramuscular injections could elicit effective and long-lasting neutralizing antibody responses and Th1 T cell responses. AdC68-19S was mainly distributed in injection sites and no AdC68-19S related toxicological reaction was observed. In conclusion, these results have shown that AdC68-19S could induce an effective immune response with a good safety profile, and is a promising candidate vaccine against COVID-19.

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