Brief Report: Genital Microbiome, Inflammation, and Tenofovir Levels in Transgender Men and Cisgender Women Taking Oral PrEP.

Background: Little is known about the efficacy of preexposure prophylaxis (PrEP) or what biologic factors may influence HIV transmission in transgender men (TGM). In this study, we sought to explore the effect of testosterone on the vaginal microbiome, cervicovaginal fluid (CVF) tenofovir concentrations, and levels of CVF inflammatory markers in TGM on PrEP.

Methods: Cervicovaginal fluid was collected from 13 TGM (7 using testosterone) and 32 cisgender women (CGW) on PrEP. The vaginal microbiome, CVF tenofovir concentrations, and CVF inflammatory markers were determined and compared.

Results: The proportion of CVF Lactobacillus was significantly higher in CGW than in TGM (78% vs 24%, P < 0.001). Among TGM, the proportion of CVF Lactobacillus was lower, though not statistically significant, in those taking testosterone than in those not taking testosterone (14% vs 35%, P-value = 0.3). Interestingly, mean CVF tenofovir concentrations were the lowest in TGM on testosterone at 884 ng/mL compared with 3150 ng/mL in TGM not on testosterone and 1932 ng/mL in CGW; however, this difference was not statistically significant. There was no statistically significant difference in any of the genital inflammatory markers between groups and no correlation between inflammation and tenofovir levels.

Conclusions: Our findings suggest a potential correlation between testosterone use, Lactobacillus dominance, and lower TFV concentrations in CVF, which may have implications on HIV acquisition from vaginal sex in TGMT. Future studies with larger sample sizes are needed to further investigate these relationships.