The presence of Tat during ex vivo priming of naïve CD8+ T cells by the SSI peptide epitope, and during in vivo priming by the HIV-1 Gag protein and by infection with HSV1, favored the activation of antigen-specific CTLs (Figures 1, 2), but no effect was detected on bystander resting T cells (Figure 4). The gene discussed is TAT; the disease is infection.