Background: Human immunodeficiency virus type 1 (HIV-1)-specific cellular immunity contributes to the control of HIV-1 replication. HIV-1-infected volunteers who were receiving antiretroviral therapy were given a replication-defective adenovirus type 5 HIV-1 gag vaccine in a randomized, blinded therapeutic vaccination study.
Methods: HIV-1-infected vaccine or placebo recipients underwent analytical treatment interruption (ATI) for 16 weeks. The log(10) HIV-1 RNA load at the ATI set point and the time-averaged area under the curve served as co-primary end points. Immune responses were measured by intracellular cytokine staining and carboxyfluorescein succinimidyl ester dye dilution.
Results: Vaccine benefit trends were seen for both primary end points, but they did not reach a prespecified significance level of P < or = 25. The estimated shifts in the time-averaged area under the curve and the ATI set point were 0.24 (P=.04, unadjusted) and 0.26 (P=.07, unadjusted) log(10) copies lower, respectively, in the vaccine arm than in the placebo arm. HIV-1 gag-specific CD4(+) cells producing interferon-gamma were an immunologic correlate of viral control.
Conclusion: The vaccine was generally safe and well tolerated. Despite a trend favoring viral suppression among vaccine recipients, differences in HIV-1 RNA levels did not meet the prespecified level of significance. Induction of HIV-1 gag-specific CD4 cells correlated with control of viral replication in vivo. Future immunogenicity studies should require a substantially higher immunogenicity threshold before an ATI is contemplated.