Chronic immune activation is a central driver of HIV-1 infection and progression to AIDS (1, 2, 4–6), and can be partially attributed to the rapid and massive depletion of gastrointestinal CCR5+CD4+ T cells following infection (57, 58), which compromises the integrity of the mucosal barrier and facilitates translocation of bacteria from the gut (1, 2, 59). This evidence concerns the gene CCR5 and AIDS.