BackgroundDaily pre-exposure prophylaxis (PrEP) with Truvada (a combination of emtricitabine (FTC) and tenofovir (TFV) disoproxil fumarate (TDF)) is a novel HIV prevention strategy recently found to prevent HIV transmission in men who have sex with men and heterosexual couples. We previously showed that a coitally-dependent Truvada regimen protected macaques against rectal SHIV transmission. Here we examined FTC and tenofovir TFV exposure in vaginal tissues after oral dosing and assessed if peri-coital Truvada also protects macaques against vaginal SHIV infection.MethodsThe pharmacokinetic profile of emtricitabine (FTC) and tenofovir (TFV) was evaluated at first dose. FTC and TFV levels were measured in blood plasma, rectal, and vaginal secretions. Intracellular concentrations of FTC-triphosphate (FTC-TP) and TFV-diphosphate (TFV-DP) were measured in PBMCs, rectal tissues, and vaginal tissues. Efficacy of Truvada in preventing vaginal SHIV infection was assessed using a repeat-exposure vaginal SHIV transmission model consisting of weekly exposures to low doses of SHIV162p3. Six pigtail macaques with normal menstrual cycles received Truvada 24 h before and 2 h after each weekly virus exposure and six received placebo. Infection was monitored by serology and PCR amplification of SHIV RNA and DNA.ResultsAs in humans, the concentration of FTC was higher than the concentration of TFV in vaginal secretions. Also as in humans, TFV levels in vaginal secretions were lower than in rectal secretions. Intracellular TFV-DP concentrations were also lower in vaginal tissues than in rectal tissues. Despite the low vaginal TFV exposure, all six treated macaques were protected from infection after 18 exposures or 4 full menstrual cycles. In contrast, all 6 control animals were infected.ConclusionsWe modeled a peri-coital regimen with two doses of Truvada and showed that it fully protected macaques from repeated SHIV exposures. Our results open the possibility for simplified PrEP regimens to prevent vaginal HIV transmission in women.

Background Hormonal changes during menstrual cycling may affect susceptibility to HIV. Methods We determined the SHIV acquisition time point in 43 cycling pigtail macaques infected by repeated vaginal virus exposures initiated randomly in the cycle. Results SHIV infection was first detected in the follicular phase in 38 macaques (88%), and in the luteal phase in 5 macaques (12%), indicating a statistically significant timing difference. Assuming a 7-day eclipse phase, most infections occurred during or following a high-progesterone period associated with menstruation, vaginal epithelium thinning and suppressed mucosal immunity. Conclusions This raises questions whether other high progesterone conditions (pregnancy, hormonal contraception) similarly affect HIV risk.

Daily preexposure prophylaxis (PrEP) with Truvada is a proven HIV prevention strategy; however, its effectiveness is limited by low adherence. Antiretroviral drug formulations that require infrequent dosing may increase adherence and thus PrEP effectiveness. We investigated whether monthly injections of a long-acting formulation of the HIV integrase inhibitor GSK1265744 (GSK744 LA) prevented simian/human immunodeficiency virus (SHIV) infection by vaginal challenge in macaques. Female pigtail macaques (n = 12) were exposed to intravaginal inoculations of SHIV twice a week for up to 11 weeks. Half of the animals received a GSK744 LA injection every 4 weeks, and half received placebo. GSK744 LA, at plasma concentrations achievable with quarterly injections in humans, protected all six macaques from infection. Placebo controls were all infected after a median of 4 (range, 2 to 20) vaginal challenges with SHIV. Efficacy was related to high and sustained vaginal and plasma drug concentrations that remained above the protein-adjusted 90% inhibitory concentration during the dosing cycles. These data support advancement of GSK744 LA as a potential PrEP candidate for women.

Previous biochemical studies have demonstrated that synergy between non-nucleoside reverse transcriptase (RT) inhibitors (NNRTI) and nucleoside RT inhibitors (NRTIs) is due to inhibition by the NNRTI of the rate at which HIV-1 RT facilitates ATPmediated excision of NRTIs from chain-terminated template/ primers (T/P). However, these studies did not take into account the possible effects of NNRTI on the ribonuclease H (RNase H) activity of RT, despite recent evidence that suggests an important role for this activity in the NRTI excision phenotype. Accordingly, in this study, we compared the ability of efavirenz to inhibit the incorporation and excision of zidovudine (AZT) by HIV-1 RT using DNA/DNA and RNA/DNA T/Ps that were identical in sequence. Whereas IC 50 values for the inhibition of AZT-triphosphate incorporation by efavirenz were essentially similar for both DNA/DNA and RNA/DNA T/P, a 19-fold difference in IC 50 was observed between the AZT-monophosphate excision reactions, the RNA/DNA T/P substrate being significantly more sensitive to inhibition. Analysis of the RNase H cleavage events generated during ATP-mediated excision reactions demonstrated that efavirenz dramatically increased the rate of appearance of a secondary cleavage product that decreased the T/P duplex length to only 10 nucleotides. Studies designed to delineate the relationship between T/P duplex length and efficiency of AZT excision demonstrated that RT could not efficiently unblock chain-terminated T/P if the RNA/ DNA duplex length was less than 12 nucleotides. Taken together, these results highlight an important role for RNase H activity in the NRTI excision phenotype and in the mechanism of synergy between NNRTI and NRTI.