In the absence of an effective vaccine, administration of antiretroviral drugs prior to human immunodeficiency virus type 1 (HIV-1) exposure (pre-exposure prophylaxis or PrEP) may be a reliable method to protect high-risk HIV-negative individuals from infection. Daily oral tenofovir and FTC (Truvada) is currently approved for use as PrEP in high-risk individuals but has had limited success in human clinical trials to date, mainly due to adherence issues. Rilpivirine (RPV) is the most recent reverse transcriptase inhibitor approved for antiretroviral therapy (ART) for HIV-1. Drug-resistant mutations detected in patients failing RPV-containing regimens conferred mainly low-level resistance to RPV and RPV is active against most mutants selected by other drugs. RPV has been formulated into injectable long-acting nanoparticles (RPV-LA) for use as long-lasting PrEP to be administered by healthcare providers. Development of resistance or transmission of RPV-resistant variants during PrEP has not been previously addressed, particularly their impact on subsequent ART. A case has recently been described of a woman who became HIV-1-infected during RPV-LA treatment and subsequently developed RPV-resistant virus in the presence of sub-therapeutic plasma RPV concentration. We propose to investigate vaginal transmission of wild-type (WT) HIV-1 and drug-resistant variants in the presence and absence of therapeutic and subtherapeutic concentrations of RPV-LA PrEP or Truvada, using a novel animal model that will also allow us to investigate the dynamics of infection and dissemination in the female genital tract in real-time. Using an innovative new reporter virus system and a well-characterized humanized mouse model, we hypothesize that a prevalent HIV-1 mutant resistant to both RPV and Truvada (E138K/M184I) will be transmitted in the absence of drug and in the presence of Truvada PrEP, but will lead to an abortive infection of local CD4+ target cells in the genital trac in the presence of therapeutic RPV-LA concentrations. However, transmission or development of drug-resistant HIV-1 will lead to faster virologic failure during subsequent ART.