Pre-existing antibodies targeting a linear epitope on SARS-CoV-2 S2 cross-reacted with commensal gut bacteria and shaped vaccine induced immunity (preprint)

ABSTRACT

The origins of pre-existing SARS-CoV-2 cross-reactive antibodies and their potential impacts on vaccine efficacy have not been fully clarified. In this study, we demonstrated that S2 was the prevailing target of the pre-existing S protein cross-reactive antibodies in both healthy human and SPF mice. A dominant antibody epitope was identified on the connector domain of S2 (1147-SFKEELDKYFKNHT-1160, P144), which could be recognized by pre-existing antibodies in both human and mouse. Through metagenomic sequencing and fecal bacteria transplant, we proved that the generation of S2 cross-reactive antibodies was associated with commensal gut bacteria. Furthermore, six P144 specific monoclonal antibodies were isolated from naïve SPF mice and proved to cross-react with commensal gut bacteria collected from both human and mouse. Mice with high levels of pre-existing S2 cross-reactive antibodies mounted higher S protein specific binding antibodies, especially against S2, after being immunized with a SARS-CoV-2 S DNA vaccine. Similarly, we found that levels of pre-existing S2 and P144 reactive antibodies correlated positively with RBD specific binding antibody titers after two doses of inactivated SARS-CoV-2 vaccination in human. Finally, we provided data demonstrating that immunization of a SARS-CoV-2 S DNA vaccine could alter the gut microbiota compositions of mice.