Immunogenicity of candidate SARS-CoV-2 DNA vaccines based on the spike protein

Coronavirus disease 2019 caused by the novel human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently a major threat to public health worldwide. To deal with the needs of vaccine, we developed four DNA vaccine candidates against SARS-CoV-2, based on the full-length spike (S) or truncated S protein. Following mice vaccination, we measured T-cell response and antigen-specific neutralizing antibody (NAb) titer. All four candidates induced humoral immune responses, including elevated levels of total IgG and NAbs, and cell-mediated immune responses, including multiple cytokine expression. However, the full-length S DNA vaccine enhanced the immune responses most significantly. We then evaluated its appropriate antigen dose and vacci-nation schedule. Although all immunized groups showed higher immune response than the control group, inoculation with 50 mu g antigen led to the highest NAb titer. Immunity was significantly increased after the third inoculation. Thus, the full-length S DNA vaccine can potentially prevent SARS-CoV-2 infection.