Effective combination antiretroviral therapy (ART) has transformed the HIV epidemic in resource-rich countries. Latently infected cells, referred to as the HIV reservoir, are rare but persist in treated patients and represent a major barrier to virus eradication. This reservoir is comprised of residual virus in plasma and latently infected peripheral blood mononuclear cell (PBMC) subpopulations that distribute into tissue compartments. The exact relationship between blood and tissue HIV reservoirs is not currently known. Much work is being done to characterize HIV reservoirs in gut and more recently lymph node tissues, whereas less is known about reservoirs in the genital tract. An improved understanding of HIV reservoir dynamics in tissue is critical to HIV eradication and cure efforts. The goal of this proposal is to help answer a fundamental question: Do measures of HIV persistence in the female genital tract provide novel insights into testable virus eradication strategies, relative to similar analyses performed in plasma and PBMC? The female genital tract has several unique features as an HIV reservoir that warrant further detailed study. First, while the presence of ongoing virus replication in blood or gastrointestinal tissues during suppressive ART remains controversial, the evidence for virus production in the female genital tract when plasma HIV-1 RNA levels are undetectable is well documented. Second, the antiretroviral drug tissue penetration of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and some protease inhibitors (PIs) into female genital tract can be substantially reduced, relative to levels in plasma or PBMC, and may create conditions favorable for local maintenance and/or replenishment of the HIV reservoir during peripherally suppressive ART. We propose an interdisciplinary study to characterize the HIV reservoir in female genital tract, identify cellula and tissue sources of HIV persistence, investigate non-T cell reservoirs, define the impact of tissue drug levels on virus evolution, and establish the relationship between blood and female genital tract reservoirs. We hypothesize that the female genital tract HIV-1 reservoir is distinct n its decay and persistence during ART, compared to that in peripheral blood. We will investigate the contribution of antiretroviral drug tissue penetration to ongoing virus evolution and latency during suppressive ART, and explore the effects of virus reactivation strategies in tissue-derived cells. Specific aims of this proposal are: 1) Define the relationship between the peripheral blood and female genital tract HIV-1 reservoirs using two groups of women: treatment- naive participants initiating antiretroviral therapy and virologically suppressed subjects on stable ART, 2) Investigate female genital tract HIV-1 evolution during suppressive ART and correlate with tissue drug concentrations, and 3) Determine the sensitivity of female genital tract tissue reservoirs to virus re-activation strategies.