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...