PROJECT SUMMARY/ABSTRACT It is estimated that more than one million people in the United States identify as transgender. Despite recent increased visibility, transgender individuals remain marginalized and subject to health disparities, and are underrepresented in biomedical research. It is well documented that transgender persons are disproportionately affected by HIV compared to their cisgender counterparts, but the basis for this is incompletely understood. In particular, we have a very limited understanding of changes in mucosal immune defenses in the vaginal compartment in transgender men and transmasculine individuals who receive chronic testosterone therapy as part of gender affirming hormone therapy. This is relevant to understanding HIV risks as transgender men report heterosexual, non-heterosexual, and bisexual orientation, making transgender men who have sex with cisgender men a unique and understudied group. Our central hypothesis is that gender affirming hormone therapy in transgender men leads to a dysregulated innate immune microenvironment and impaired barrier function of the vaginal mucosal compartment, increasing the risk of HIV transmission during vaginal penetration. The goal of this project is to characterize the effects of cross hormone therapy on the vaginal compartment using a commercially available reconstructed vaginal tissue model that has been shown to be hormonally responsive and support infection with HIV. We propose three aims to test our hypothesis. First, we will characterize the histology of the testosterone dominant vagina in contrast to the estradiol primed vagina, looking at barrier function, mucin expression, and steady state cytokine/chemokine release. The effects of testosterone on colonization with lactobacillus will also be examined. Next, we will conduct transcriptomic studies to identify the gene expression profile of the testosterone dominant vagina to identify changes in the immunologic signaling pathways that could negatively impact host-pathogen interactions. Finally, we will examine HIV infection in the testosterone dominant vagina in comparison to the estradiol primed vagina to determine if HIV transmission is increased. At the completion of this project, we will have a broader understanding of the histologic and immunologic effects of testosterone on the vaginal compartment, identifying defensive weaknesses in the residual lower female genital tract in transgender men with an intact vagina that increase the risk of HIV transmission. We believe our data will help inform the development of strategies for individuals undergoing gender affirming hormone therapy to lessen the risk of HIV and other STI acquisition across this mucosal surface.

PROJECT NARRATIVE Transgender individuals have higher rates of HIV and other sexually transmitted infections than cisgender individuals. Transgender men or transmasculine individuals were assigned female sex at birth but identify along the masculine spectrum, and testosterone is often administered to transgender men and other transmasculine persons as part of the treatment for gender reassignment. The goal of this project is to characterize the changes that occur in the vagina as a result of testosterone exposure using a model of vaginal tissue that has been constructed from the cells found in the vagina that will allow us to mimic transmasculine physiology and determine if testosterone alters the tissue in such a way that the immune response is impaired, increasing the risk of HIV infection.