P24.07
Background: Pre-exposure prophylaxis (PrEP) is an effective HIV prevention tool in high-risk populations, including subjects participating in vaccine trials. While the primary mode of action for the protective effect of PrEP against HIV infection is likely direct anti-viral activity, nonhuman primate studies suggest that PrEP allows for development of HIV-specific immune responses by aborting infections in HIV-exposed subjects, thus providing a source of immunologic priming.
Methods: Within a randomized, placebo-controlled trial among African heterosexual HIV serodiscordant couples in which PrEP demonstrated high efficacy for HIV prevention, we assessed whether enhanced development of HIV-specific T-cell responses was associated with PrEP use. Peripheral blood mononuclear cells from the Partners PrEP Study were used to test for HIV-specific T-cell responses in 230 HIV exposed seronegative (HESN; 79 women, 151 men), half of whom received daily emtricitabine/tenofovir PrEP and half placebo for 12 months; all HESN were randomly selected amongst those with high HIV risk based on an empiric score. HIV-specific CD4+ and CD8+ T-cell responses were detected by intracellular cytokine staining using global potential T-cell epitope 11mer peptide pools for Gag, Env, and Tat using published protocols.
Results: We detected CD4+ T-cell responses to HIV in 8.7% of HESN individuals on PrEP and 9.6% of HESN individuals on placebo (p=0.62). HIV-specific CD8+ T-cell responses were detected in 20.0% of HESN individuals on PrEP and 17.4% of HESN individuals on placebo (p=0.53). The magnitude of the CD4+ and CD8+ T-cell responses did not differ significantly between individuals receiving PrEP versus placebo.
Conclusions: In a randomized, placebo comparison, we found no evidence that PrEP usage alters either the frequency or magnitude of peripheral blood CD4 and CD8 HIV-specific responses in HESN. Therefore, it is unlikely that combining PrEP with an HIV vaccine would enhance T-cell immunity.
