PROJECT SUMMARY The physiologic intersections of HIV, antiretroviral therapy (ART) and feminizing hormonal therapy (FHT) are critical but incompletely understood elements of optimizing care for transgender women (TW). Worldwide, HIV prevalence rates among TW have reached epidemic levels. HIV infection is characterized by persistent inflammation and immune activation that contributes to multiple metabolic disturbances. ART also contributes to these disturbances, and FHT modulates inflammatory, metabolic, and coagulation pathways and causes gain of fat and loss of lean mass. However, the degree to which these perturbations translate into altered cardiometabolic disease risk is not well understood, particularly in the setting of concomitant HIV infection. The Féminas study enrolled 220 adult TW in Lima, Peru for extensive sociodemographic and biologic characterization and access to standardized FHT and ART for HIV treatment or HIV pre-exposure prophylaxis (PrEP), depending upon HIV serostatus. Serum and plasma samples were collected pre- and post-FHT and PrEP or ART (hereafter referred to jointly as ART). Using data and stored samples from Féminas participants and complementary in vitro experiments, we aim to determine how the intersections of HIV infection, ART and FHT affect inflammatory pathways and cardiometabolic risk in TW. Specifically, we aim: 1) To determine the individual and combined in vivo effects of HIV, ART and FHT on circulating metabolic, inflammatory and coagulation biomarkers in Féminas participants; and 2) To determine the individual and combined in vitro effects of HIV, ART and FHT on immune and cellular function. We hypothesize that HIV+ TW will have greater perturbations in biomarker profiles than HIV- TW pre-FHT and/or pre-ART, that FHT and ART will induce overlapping but unique changes in inflammatory and metabolic profiles that are greater than the changes seen in HIV- TW initiating FHT alone, and that changes in biomarker profiles will be associated with available estimates of clinical disease. We also hypothesize that the concentrations of estrogen provided as FHT in Féminas (approximately 120 pg/mL estradiol and 600 pg/mL estrone) will lead to significant changes in cellular activation, immuno-metabolic cytokine profiles, and estrogen and androgen receptor expression that differ by HIV and ART status. This pilot project will elucidate mechanisms of cardiometabolic disease risk and immuno- metabolic perturbations in TW on FHT, including whether inflammatory and metabolic changes induced by FHT ART are antagonistic, additive or synergistic. These data are extremely novel, have not previously been documented in the setting of HIV and modern FHT, and aim to inform care and improve quality of life for TW.