Characterization of female genital tract immunological markers and molecular vaginal microbiota: relevance for risk of HIV transmission and HIV prevention

Majority of HIV transmission occurs through heterosexual intercourse. Even though the per-act probability of transmission is low, it does occur and has resulted in an epidemic that is over 30 years old and yet to be fully controlled. The HIV/AIDS epidemic has affected more women than men, especially in Sub-Saharan Africa where 60% of those living with HIV are women. Vaginal microbicides are a female-controlled HIV prevention option whose early development faced challenges that necessitated the search for safety biomarkers in clinical trials. This is the context in which this PhD project was carried out. We started out with a group of 30 healthy Caucasian women in Antwerp, Belgium and characterized cellular and soluble immunity and the vaginal microbiome in the lower female genital tract. We also conducted both a cross-sectional and longitudinal characterization of the female genital tract in 430 sexually active women from Sub-Saharan Africa (Kenya, Rwanda and South Africa).

Briefly, we demonstrated a wide range in concentrations of selected soluble immune mediators in cervicovaginal lavages. We also described a number of physiological and behavioural factors that were associated with differences in concentrations of these immune mediators in the lower female genital tract. A sub-cohort of 40 bacterial vaginosis (BV)-free women followed longitudinally displayed relative stability of individual vaginal microbiota species – these were either consistently present or absent. As generally expected, bacteria that are generally linked with good vaginal health, L. crispatus and L. vaginalis, were associated with lower levels of pro-inflammatory cytokines and higher levels of protective antimicrobial proteins. In contrast, BV-associated A. vaginae, G. vaginalis and P. bivia were associated with increased pro-inflammatory cytokines. Vaginal dysbiosis (specifically BV) was characterized by a clear pro-inflammatory signature and reduced levels of IP-10, SLPI and total protein. Sexual activity and lack of a menstrual cycle due to progestin use were both found to be disruptive of the vaginal microbiota, mainly resulting in lower numbers of lactobacilli species.

Based on our findings, we propose pro-inflammatory IL-1 (α and β), IL-6, IL-8, IL-12(p70); anti-inflammatory IL-1RA; the chemokine IP-10; and the antimicrobial protein SLPI as a smaller panel of soluble biomarkers for consideration for safety measurement of candidate vaginal microbicides. Additionally, the assessment of microbicide safety should include clinical examination for visible signs of vaginal epithelia irritation and the effect of candidate microbicides on cellular markers of inflammation as well as the vaginal microbiome. To do this, there will be a need for large-scale coordination for harmonization of sample collection, processing, assays and the interpretation of results. An ideal outcome would be point-of-care tools that can be easily used in clinical setting in resource-limited settings to predict microbicide safety but more importantly, to identify women with increased susceptibility to HIV infection. These women can then be targeted with combination sexually transmitted infections (including HIV) prevention and possible multiple prevention technology interventions for better sexual and reproductive health outcomes.