We have previously shown that by using CD39 and FoxP3 we were able to delineate two populations of antigen-specific CD4+CD25+CD134+ T cells with different origin and function, namely Tregs and Teffs (Fig 6A) and [6,9] and that CD39+ Tregs are potent suppressors of HIV-specific responses in both natural infection and vaccination [9,34]. This evidence concerns the gene CD4 and infection.