Background: The inability to quantify sexual exposure to HIV limits the power of HIV prevention trials of vaccines, microbicides, and preexposure prophylaxis in women. We investigated the detection of HIV-1 and Y chromosomal (Yc) DNA in vaginal swabs from 83 participants in the HPTN 035 microbicide trial as biomarkers of HIV exposure and unprotected sexual activity.
Methods: One hundred forty-three vaginal swabs from 85 women were evaluated for the presence of Yc DNA (Quantifiler Duo DNA quantification kit; Applied Biosystems) and total HIV-1 DNA (single-copy in-house quantitative polymerase chain reaction assay). Y DNA detection was paired with self-reported behavioral data with regard to recent coitus (≤1 week before collection) and condom usage (100% vs. <100% compliance).
Results: Yc DNA was detected in 62 (43%) of 143 swabs. For the 126 visits at which both behavioral data and swabs were collected, Yc DNA was significantly more frequent in women reporting less than 100% condom usage (odds ratio, 10.69; 95% confidence interval, 2.27-50.32; P = 0.003). Notably, 27 (33%) of 83 swabs from women reporting 100% condom usage were positive for Yc DNA. HIV DNA was only detected in swabs collected postseroconversion.
Conclusions: The use of Yc DNA in HIV prevention trials could reliably identify subgroups of women who have unprotected sexual activity and could provide valuable exposure-based estimates of efficacy.