CD8A and influenza: However, due to the fact that the average human is exposed on multiple occasions to influenza infection during their lifetime, and that our universal CD8+ T cell epitope library contains the most conserved influenza A epitopes, it is reasonable to assume that some, if not most, of the IFNγ+ CD8+ T cells, responding to such epitopes, were present before the pandemic and thus may have provided cross-protective immunity against the 2009 pandemic strain.