HIV-1 vaccine-induced immunity in the test-of-concept Step Study: a case-cohort analysis.

The article presents a case-cohort analysis which assessed the MRKAd5 HIV-1 gag/pol/nef vaccine for vaccine-induced immunity and potential contributions to infection risk. The study was performed in response to the results of the Step Study which found higher HIV-1 incidence in vaccine-treated men than in placebo-treated men with pre-existing adenovirus serotype 5 immunity. Validated interferon-γ ELISPOT and intracellular cytokine staining assays were used to characterise HIV-specific T cells to assess for immunogenicity. Flow cytometric studies were conducted to establish the effects of vaccine and pre-existing Ad5 immunity on infection risk. The MRKAd5 HIV-1 gag/pol/nef vaccine was found to be highly immunogenic for inducing HIV-specific CD8+ T cells.