From Alpha to omicron: The response of T cells.

It is critically important to understand how the adaptive immune response, elicited by vaccination or infection, recognizes SARS-CoV-2. This is especially true when considering the challenges to the immune response posed by variant evolution. Herein, we summarize our work aimed at characterizing the magnitude of the CD4 and CD8 T cell responses to SARS-CoV-2, the proteins most frequently recognized, and the associated T cell epitope repertoire. This work formed the foundation for our most recent studies aimed at understanding and predicting the ability of T cell responses induced by SARS-CoV-2 infection or vaccination to subsequently cross-recognize novel SARS-CoV-2 variants. We found that T cell responses are remarkably preserved and able to cross-recognize SARS-CoV-2 variants, from Alpha to Omicron. This is distinct from what has been observed for the SARS-CoV-2- specific antibody and B cell responses. This body of work, supported by independent studies carried out by other groups, suggests that T cells may contribute to a second line of defense against infection while also limiting viral spread and, thus, disease severity.