HIV continues to spread globally, mainly through sexual contact. Despite advances in treatment and care, preventing transmission with vaccines or microbicides has proven difficult. A promising strategy to avoid transmission is prophylactic treatment with antiretroviral drugs before exposure to HIV. Clinical trials evaluating the efficacy of daily treatment with the reverse transcriptase inhibitors tenofovir disoproxil fumarate (TDF) or Truvada (TDF plus emtricitabine) are under way. We hypothesized that intermittent prophylactic treatment with long-acting antiviral drugs would be as effective as daily dosing in blocking the earliest stages of viral replication and preventing mucosal transmission. We tested this hypothesis by intermittently giving prophylactic Truvada to macaque monkeys and then exposing them rectally to simian-human immunodeficiency virus (SHIV) once a week for 14 weeks. A simple regimen with an oral dose of Truvada given 1, 3, or 7 days before exposure followed by a second dose 2 hours after exposure was as protective as daily drug administration, possibly because of the long intracellular persistence of the drugs. In addition, a two-dose regimen initiated 2 hours before or after virus exposure was effective, and full protection was obtained by doubling the Truvada concentration in both doses. We saw no protection if the first dose was delayed until 24 hours after exposure, underscoring the importance of blocking initial replication in the mucosa. Our results show that intermittent prophylactic treatment with an antiviral drug can be highly effective in preventing SHIV infection, with a wide window of protection. They strengthen the possibility of developing feasible, cost-effective strategies to prevent HIV transmission in humans.

A vaginal gel containing 1% tenofovir (TFV) was found to be safe and effective in reducing HIV infection in women when used pericoitally. Because of the long intracellular half-life of TFV and high drug exposure in vaginal tissues, we hypothesized that a vaginal gel containing TFV may provide long-lasting protection. Here, we performed delayed-challenge experiments and showed that vaginal 1% TFV gel protected 4/6 macaques against vaginal simian-human immunodeficiency virus (SHIV) exposures occurring 3 days after gel application, demonstrating long-lasting protection. Despite continued gel dosing postinfection, neither breakthrough infection had evidence of drug resistance by ultrasensitive testing of SHIV in plasma and vaginal lavage. Analysis of the active intracellular tenofovir diphosphate (TFV-DP) in vaginal lymphocytes collected 4 h to 3 days after gel dosing persistently showed high TFV-DP levels (median, 1,810 fmol/10 6 cells) between 4 and 24 h that exceed the 95% inhibitory concentration (IC 95 ), reflecting rapid accumulation and long persistence. In contrast to those in peripheral blood mononuclear cells (PBMCs) following oral dosing, TFV-DP levels in vaginal lymphocytes decreased approximately 7-fold by 3 days, exhibiting a much higher rate of decay. We observed a strong correlation between intracellular TFV-DP in vaginal lymphocytes, in vitro antiviral activity, and in vivo protection, suggesting that TFV-DP above the in vitro IC 95 in vaginal lymphocytes is a good predictor of high efficacy. Data from this model reveal an extended window of protection by TFV gel that supports coitus-independent use. The identification of protective TFV-DP concentrations in vaginal lymphocytes may facilitate the evaluation of improved delivery methods of topical TFV and inform clinical studies. Human immunodeficiency virus (HIV) continues to spread primarily through heterosexual routes, with women being disproportionately infected in many parts of the world (30, 35). While condoms have been shown to be one of the most reliable methods for preventing HIV transmission, such interventions are often limited by adherence and the ability of women to negotiate their use (24, 37). In the absence of an effective HIV vaccine, increasing efforts have been made toward developing vaginal gels formulated with antiretroviral (ARV) drugs, as a femalecontrolled option for women to protect themselves against HIV acquisition (10,21,33,37).Topical gels containing tenofovir (TFV), a nucleotide analogue reverse transcriptase inhibitor, have recently shown great promise against vaginal HIV transmission. Results of the CAPRISA 004 trial demonstrated for the first time that women who used a vaginal gel containing 1% TFV were 39% less likely overall to contract HIV than those who used a placebo gel (1). The trial evaluated a coitus-dependent before-and-after (BAT) modality, with one gel application administered up to 12 h before sex followed by a second gel application up to 12 h after sex. Importantly, effectiveness was found to be dependen...

Preexposure prophylaxis (PrEP) with antiretroviral drugs is a novel human immunodeficiency virus (HIV) prevention strategy. It is generally thought that high systemic and mucosal drug levels are sufficient for protection. We investigated whether GS7340, a next-generation tenofovir (TFV) prodrug that effectively delivers tenofovir diphosphate (TFV-DP) to lymphoid cells and tissues, could protect macaques against repeated weekly rectal simian-human immunodeficiency virus (SHIV) exposures. Macaques received prophylactic GS7340 treatment 3 days prior to each virus exposure. At 3 days postdosing, TFV-DP concentrations in peripheral blood mononuclear cells (PBMCs) were about 50-fold higher than those seen with TFV disoproxil fumarate (TDF), and they remained above 1,000 fmol/10 6 cells for as long as 7 days. TFV-DP accumulated in lymphoid and rectal tissues, with concentrations at 3 days exceeding 500 fmol/10 6 mononuclear cells. Despite high mucosal and systemic TFV levels, GS7340 was not protective. Since TFV-DP blocks reverse transcription by competing with the natural dATP substrate, we measured dATP contents in peripheral lymphocytes, lymphoid tissue, and rectal mononuclear cells. Compared to those in circulating lymphocytes and lymphoid tissue, rectal lymphocytes had 100-fold higher dATP concentrations and dATP/TFV-DP ratios, likely reflecting the activated status of the cells and suggesting that TFV-DP may be less active at the rectal mucosa. Our results identify dATP/TFV-DP ratios as a possible correlate of protection by TFV and suggest that natural substrate concentrations at the mucosa will likely modulate the prophylactic efficacy of nucleotide reverse transcriptase inhibitors.The human immunodeficiency virus (HIV)/AIDS pandemic remains one of our greatest public health challenges. Globally, an estimated 33.2 million people were living with HIV infection or AIDS in 2007. In that year, the annual incidence of new infections was an estimated 2.7 million, and there were an estimated 2.0 million HIV-related deaths (20). The ongoing high incidence of HIV infection and the incomplete coverage of basic HIV prevention tools underscore the need for new, highly effective biomedical HIV interventions to complement existing prevention strategies.Oral administration of antiretroviral drugs prior to and during HIV exposure (preexposure prophylaxis [PrEP]) is a novel intervention to protect high-risk HIV-1-negative people from becoming infected (3, 12, 15). Drug candidates for oral PrEP have been selected from drugs currently approved for treatment of HIV-1-infected individuals. Among the drugs available, the well-established potency and tolerability of tenofovir disoproxil fumarate (TDF), the approved oral prodrug of the nucleotide analog tenofovir (TFV), makes it an attractive candidate for PrEP. A recently concluded human trial with a daily combination of TDF and emtricitabine (FTC) (Truvada) for HIV-seronegative men or transgender women who have sex with men has shown a 44% reduction in the incidence of HIV-1, giving ...

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.

Antiretroviral-based microbicides applied topically to the vagina may play an important role in protecting women from HIV infection. Incorporation of the nucleoside reverse transcriptase inhibitor tenofovir (TFV) into intravaginal rings (IVRs) for sustained mucosal delivery may lead to increased microbicide product adherence and efficacy compared with those of conventional vaginal formulations. Formulations of a novel "pod IVR" platform spanning a range of IVR drug loadings and daily release rates of TFV were evaluated in a pig-tailed macaque model. The rings were safe and exhibited sustained release at controlled rates over 28 days. Vaginal secretion TFV levels were independent of IVR drug loading and were able to be varied over 1.5 log units by changing the ring configuration. Mean TFV levels in vaginal secretions were 72.4 ؎ 109 g ml ؊1 (slow releasing) and 1.84 ؎ 1.97 mg ml ؊1 (fast releasing). The mean TFV vaginal tissue concentration from the slow-releasing IVRs was 76.4 ؎ 54.8 g g ؊1 and remained at steady state 7 days after IVR removal, consistent with the long intracellular half-life of TFV. Intracellular tenofovir diphosphate (TFV-DP), the active moiety in defining efficacy, was measured in vaginal lymphocytes collected in the study using the fast-releasing IVR formulation. Mean intracellular TFV-DP levels of 446 ؎ 150 fmol/10 6 cells fall within a range that may be protective of simian-human immunodeficiency virus strain SF162p3 (SHIV SF162p3 ) infection in nonhuman primates. These data suggest that TFV-releasing IVRs based on the pod design have potential for the prevention of transmission of human immunodeficiency virus type 1 (HIV-1) and merit further clinical investigation.