A COVID-19 peptide vaccine for the induction of SARS-CoV-2 T cell immunity.

T cell immunity is central for the control of viral infections. CoVac-1 is a peptide-based vaccine candidate, composed of SARS-CoV-2 T cell epitopes derived from various viral proteins1,2, combined with the Toll-like receptor 1/2 agonist XS15 emulsified in Montanide ISA51 VG, aiming to induce profound SARS-CoV-2 T cell immunity to combat COVID-19. We conducted a phase I open-label trial, recruiting 36 participants aged 18 to 80 years, who received one single subcutaneous CoVac-1 vaccination. The primary endpoint was safety analysed until day 56. Immunogenicity in terms of CoVac-1-induced T-cell response was analysed as main secondary endpoint until day 28 and in the follow-up until month 3. No serious adverse events and no grade 4 adverse events were observed. Expected local granuloma formation was observed in all study subjects, while systemic reactogenicity was absent or mild. SARS-CoV-2-specific T cell responses targeting multiple vaccine peptides were induced in all study participants, mediated by multifunctional T-helper 1 CD4+ and CD8+ T cells. CoVac-1-induced interferon-γ T cell responses persisted in the follow-up analyses and surpassed those detected after SARS-CoV-2 infection as well as after vaccination with approved vaccines. Furthermore, vaccine-induced T- cell responses were unaffected by current SARS-CoV-2 variants of concern (VOC). Together, CoVac-1 showed a favourable safety profile and induced broad, potent and VOC-independent T- cell responses, supporting the presently ongoing evaluation in a phase II trial for patients with B cell/antibody deficiency.