CD8A and Epstein-Barr virus infection: Although the precursor frequency of naïve T cells specific to any give epitope is low ~ 1:105 (102 cell/mouse spleen), acute infection can induce this frequency as high as107, which encompasses almost 50% of all CD8+ T cells in LCMV-infected mice, or 44% of all CD8+ cells in human PBMC after EBV infection.