Quantification of Estradiol's Impact on Nucleotides in Cellular Populations of the Lower GI Tract

Participants will be enrolled, and sampling visits will be scheduled to correspond with their menstrual cycles. Five days prior to the first scheduled sampling visit, participants will come to the clinic to have a repeat urine pregnancy test performed to verify eligibility. After verification, participants will be given a single dose of the study medication, Truvada®. Study staff will witness the dose and assess for any adverse reactions post dose. Participants will be sent home with a supply of 4 additional doses of Truvada® for them to take at scheduled times for the next 4 days with study staff observing via video call. Study staff will assess for adverse events during each dosing call. Starting 72 hours before each sampling visit, participants will be required to switch to a low fiber diet and abstain from inserting anything rectally. Twelve hours prior to each sampling visit, participants will be required to abide by a clear liquid diet. Participants will be seen as an outpatient at the Clinical Translational Research Center (CTRC) at University of North Carolina at Chapel Hill (UNC) for these sampling visits. At these visits, participants will have blood samples drawn to measure peripheral blood mononuclear cells and serum hormone concentrations. Participants will also have rectal cells collected via cytobrush and rectal tissue collected via rectal biopsy. After all samples have been collected, participants will be evaluated for adverse events and be discharged. Within 14 days of completion of the second sampling visit, for a follow-up visit. At this visit, blood will be obtained to check safety labs.