Phenotypically, three major groups have been described in humans [35], these are (i) CD28negative CD39+ CD8+ T cells which have been described in HIV infection [36], (ii) CXCR3+ CD45RA− CD62L+ CD8+ T cells (CD122+ in rodent models) that suppress IFNγ production by other T cells via IL-10 production [37] and (iii) PD-1+ CD8+ T cells that secrete IL-10 which have been described in HIV infection [38], hepatitis B (HBV) infection [39] and chronic hepatitis C (HCV) infection [40]. This evidence concerns the gene CD8A and hepatitis B virus infection.