CD4 and infection: This T cell response was directed mainly against the S protein, especially after viral challenge which can be explained by the higher number of CD4+ T cell epitopes and more efficient presentation of S peptides on MHCII which has been shown to directly support and correlate with cytotoxic T cell activity (43) These results indicate that PolyPEPI-SCoV-2 generates a pool of memory cells that can be quickly mobilized upon infection, leading to amelioration of disease severity.