Activated CD4 ⁺ CCR5 ⁺ T cells in the rectum predict increased SIV acquisition in SIVGag/Tat-vaccinated rhesus macaques

Significance A major obstacle to developing an effective T-cell–based AIDS vaccine is that the immunization may activate CD4 + T cells, possibly making them more susceptible to infection by HIV. We tested several vaccine candidates and their effects on mucosal CD4 + T cells in a simian model of HIV infection [i.e., Simian immunodeficiency virus (SIV) infection of rhesus macaques]. We find that the immunizations did not protect the animals against infection; however, a lower set-point viral load was observed in the vaccinated animals. Importantly, this study showed that the presence of higher levels of activated CD4 + T cells in mucosal tissues is associated with increased risk of breakthrough SIV infection in vaccinated animals.