In the acute phase of infection, control of HIV-1 and SIV viremia has been correlated with the appearance of virus specific CD8+ T cells [2]–[5] and depletion of CD8+ T cells during the chronic phase of SIV infection was associated with a rise in viral load, implicating the importance of CD8+ T cells in controlling SIV replication [5]. Here, CD8A is linked to infection.