CD8A and influenza: A prospective cohort study conducted during the H1N1 pandemic of 2009 showed that individuals who developed less severe illness harbored higher frequencies of pre-existing T cells with specificity for conserved CD8 epitopes.8 In human challenge studies, on the other hand, pre-existing CD4+, but not CD8+ T cells responding to influenza internal proteins were associated with lower virus shedding and less severe illness.9