Topically delivered tenofovir (TFV) from intravaginal rings, tablets, or gels is being evaluated for HIV prevention. We previously demonstrated that TFV delivered vaginally by gel protected macaques from vaginal infection with SHIV. Here we investigated efficacy of the TFV gel against vaginal transmission of a TFV-resistant SHIV containing the K65R mutation (SHIV162P3K65R) and its relationship to drug levels in vaginal tissues. SHIV162P3K65R shows approximately a 5-fold reduction in susceptibility to TFV compared to wild-type SHIV. Efficacy was evaluated in pig-tailed macaques exposed vaginally twice-weekly (up to 10 weeks) to SHIV162P3K65R 30 min after receiving placebo (n = 6) or 1% TFV (n = 6) gel. Four of the six controls were infected after a median of 5 exposures. In contrast, five of six macaques that received TFV gel remained uninfected after 20 vaginal SHIV162P3K65R exposures, resulting in an estimated efficacy of 75%. The mean intracellular TFV-diphosphate (TFV-DP) concentrations in vaginal lymphocytes 4 h after a single gel dose were found to be high (1,631 fmol/106 cells, range 492–3,847) and within the in vitro IC75 range (1,206 fmol/106 cells) for SHIV162P3K65R. Both the modest resistance conferred by K65R and the high TFV-DP exposure in vaginal lymphocytes, likely explain the observed protection. The findings in this model do not predict complete loss of protection by topical TFV against vaginal exposure to HIV-1K65R viruses and provide a tissue drug target for high efficacy. These data will facilitate the development of TFV delivery platforms that have high activity on both wild-type and TFV-resistant viruses.

Receptive anal intercourse (RAI) contributes significantly to HIV acquisition underscoring the need to develop HIV prevention options for populations engaging in RAI practices. We explored the feasibility of formulating rectal suppositories with potent antiviral drugs for on-demand use. A fixed-dose combination of tenofovir (TFV) and elvitegravir (EVG) (40 mg each) was co-formulated in six different suppository bases (three fat- and three water-soluble). Fat-soluble witepsol H15 and water-soluble polyethylene glycol (PEG) based suppositories demonstrated favorable in vitro release and were advanced to assess in vivo pharmacokinetics following rectal administration in macaques. In vivo drug release profiles were similar for both suppository bases. Median concentrations of TFV and EVG detected in rectal fluids at 2 h were 1- and 2-logs higher than the in vitro IC50, respectively; TFV-diphosphate levels in rectal tissues met or exceeded those associated with high efficacy against rectal simian HIV (SHIV) exposure in macaques. Leveraging on these findings, a PEG-based suppository with a lower dose combination of tenofovir alafenamide (TAF) and EVG (8 mg each) was developed and found to achieve similar rectal drug exposures in macaques. This study establishes the utility of rectal suppositories as a promising on-demand strategy for HIV PrEP and supports their clinical development.

Background: Islatravir (ISL) is a first-in-class nucleoside reverse transcriptase translocation inhibitor with high potency and long half-life in peripheral blood mononuclear cells (PBMCs). However, treatment and prevention of HIV with oral ISL in humans has been associated with decreases in total lymphocytes, CD4 T-cells, and B-cells in a dose-dependent manner. We investigated in macaques the effects of oral ISL on lymphocytes, monocytes, granulocytes, and gene expression in PBMCs. Methods: Female pig-tailed macaques (n = 5) received an HIV pre-exposure prophylaxis dose of oral ISL adjusted allometrically once a week for 12 weeks. Complete blood counts and B- and T-cells were monitored prior to, during, and after ISL treatment, and changes in counts were evaluated by using a repeated measures model. Changes in gene expression were investigated in PBMCs during treatment and following treatment discontinuation. Results: ISL treatment was associated with declines in lymphocytes (11.9%, p = 0.0015) and monocytes (22.4%, p = 0.0003), but not granulocytes (0.3%, p = 0.9781). Total lymphocytes and monocytes returned to pre-treatment levels 6 weeks after treatment cessation (p = 0.8244 and p = 0.4620, respectively). Lymphocyte subpopulation analyses showed a significant decline in CD8 (−18.4%, p = 0.0364) and CD20 (−35.3%; p = 0.0002) cells but not CD4 cells (−7.4%; p = 0.3470). Gene set enrichment analysis showed negative enrichment (p_adj < 0.05) of gene pathways associated with immune regulation, cell proliferation, and inflammation. Conclusions: ISL treatment resulted in significant reductions in lymphocytes reproducing clinical toxicity. This effect was reversed after treatment cessation as observed in humans. Our results highlight the value of the macaque model to study immune alterations at the preclinical stage.