Factors associated with HIV susceptibility in the female genital tract

Abstract

The majority of new HIV infections in women are transmitted through vaginal intercourse where the female genital tract (FGT) functions as the portal of viral entry. The aim of this thesis was to characterize mucosal factors within the FGT to better understand potential molecular mechanisms associated with altered HIV-susceptibility.

The vaginal microbiome and the menstrual cycle are associated with altered HIV-susceptibility, but their collective impact on the cervicovaginal milieu remains largely unknown. In Paper 1, we studied healthy, Swedish women and observed the largest changes of the genital proteome during the estradiol-dominated ovulatory phase. This phase was characterized by a decrease in neutrophil-associated proteins and pathways and an increase in epithelial barrier-promoting proteins, as compared to the progesterone-dominated luteal phase. Menstrual cycle-related changes in epithelial barrier proteins were enhanced in women with a non-Lactobacillus dominated vaginal microbiome. This study showed that female sex hormones modulated genital inflammation and epithelial barrier function and that these changes were further impacted by the vaginal microbiome.

Semen can induce an inflammatory response in the FGT, but its role in HIVtransmission is largely unknown and limited due to a lack of adequate experimental models. In Paper 2, we used a genital tissue explant model to show that seminal plasma induced genital inflammation and increased HIV-infectivity, highlighting the importance of including seminal plasma as a factor in HIV-transmission studies. The genital tissue explant model used in this study could also be suitable for studying HIV-transmission and evaluation of microbicides.

Studies in female sex workers (FSWs) at high risk of HIV-infection reveal alterations in the genital mucosal milieu. In Paper 3, we used a high-throughput bead-based affinity set-up to evaluate protein expression in genital secretions of another cohort at risk of HIV-infection, namely Kenyan HIV-seronegative women living in HIV-serodiscordant relationships. As compared to HIV-seronegative women in HIV-seroconcordant relationships, we found alterations in genital proteins involved in inflammation and epithelial barrier remodeling pathways. Such phenotype was observed despite low levels of clinical inflammation and high levels of safe sex practices in this cohort. These results suggest that women in HIV-serodiscordant relationships have a unique cervicovaginal environment, and that this may be associated with an altered susceptibility to HIV infection. However further studies would be required to fully elucidate the relationship between the observed phenotype and HIV infection risk.

Observational and experimental studies indicate that use of the injectable progestin-based contraceptive depot medroxyprogesterone acetate (DMPA) is associated with increased risk of HIV. In Paper 4, we revealed a transcriptional profile consistent with impaired epithelial integrity and increased immune activation in ectocervical tissues from Kenyan FSWs using DMPA. In situ-based imaging analysis revealed a thinner superficial epithelial layer and an altered distribution of potential HIV-target cells. Collectively, these results suggest that DMPA may weaken the epithelial barrier and contribute to increased HIV-susceptibility.

In summary, female sex hormones, living in a HIV-serodiscordant relationship and seminal factors induce changes in the FGT that may alter HIVsusceptibility. Endogenous and exogenous progesterone/progestins reduce epithelial barrier integrity and induce cervicovaginal inflammation. The knowledge gained from these studies can help guide the development of safe contraceptive methods. The aforementioned factors must be taken into consideration when designing and interpreting results from clinical studies in the HIV-prevention field, and can also help guide the development of prophylactic compounds aimed at reducing HIV-transmission.