Repeated Vaginal SHIV Challenges in Macaques Receiving Oral or Topical Preexposure Prophylaxis Induce Virus-Specific T-Cell Responses.

Background: Preexposure prophylaxis (PrEP) for HIV prevention is a novel biomedical prevention method. We have previously modeled PrEP during rectal SHIV exposures in macaques and identified that Simian/Human Immunodeficiency Virus chimera (SHIV)-specific T-cell responses were induced in the presence of antiretroviral drugs, an observation previously termed T-cell chemo-vaccination. This report expands those initial findings by examining a larger group of macaques that were given oral or topical PrEP during repeated vaginal virus exposure.
Methods: Thirty-six female pigtail macaques received up to 20 repeat low-dose vaginal inoculations with wild-type (WT) SHIVSF162P3 (n = 24) or a clonal derivative with the tenofovir (TFV) K65R drug-resistant mutation (n = 12). PrEP consisted of oral Truvada (n = 6, WT), TFV vaginal gel (n = 6, K65R), or TFV intravaginal ring (n = 6, WT). The remaining animals were PrEP-inexperienced controls (n = 12, WT; n = 6, K65R). SHIV-specific T cells were identified and characterized using interferon γ Enzyme-Linked ImmunoSpot (ELISPOT) and multiparameter flow cytometry.
Results: Of 9 animals that were on PrEP and remained uninfected during WT SHIV vaginal challenges, 8 (88.9%) developed virus-specific T-cell responses. T cells were in CD4 and CD8 compartments, reached up to 4900 interferon γ-producing cells per million peripheral blood mononuclear cells, and primarily pol directed. In contrast, the replication-impaired K65R virus did not induce detectable T-cell responses, likely reflecting the need for adequate replication.
Conclusions: Virus-specific T-cell responses occur frequently in oral or topical PrEP-protected pigtail macaques after vaginal exposure to WT SHIV virus. The contribution of such immune responses to protection from infection during and after PrEP warrants further investigation.