Distinct Requirements for CD4 T Cell Help for Immune Responses Induced by mRNA and Adenovirus-Vector SARS-CoV-2 Vaccines.

CD4 T cells have been established as central orchestrators of cellular and humoral immune responses to infection or vaccination. However, the need for CD4 T cell help to generate primary CD8 T cell responses is variable depending on the infectious agent or vaccine and yet consistently required for the recall of CD8 T cell memory responses or antibody responses. Given the deployment of new vaccine platforms such as nucleoside-modified mRNA vaccines, we sought to elucidate the requirement for CD4 T cell help in the induction of cellular and antibody responses to mRNA and adenovirus (Ad)-vectored vaccines against SARS-CoV-2.