In the “Step” study (HVTN 502) evaluating the efficacy of repeated homologous boosting with the Merck rAd5 vector expressing Gag, Pol, and Nef, it was found that induction of Gag- and Pol-specific CD8+ T cells was not sufficient to prevent HIV infection or result in lower set-point viral load levels in men who became infected despite vaccination. Here, CD8A is linked to HIV infectious disease.