Background Gonadal hormones can modify immune function, which may impact susceptibility to infectious diseases, including Human Immunodeficiency Virus (HIV). There is limited knowledge about how hormonal contraceptives (HC) influence the immune response during the course of use. The CHIME study aims to evaluate the effect of long-acting progestin-based hormonal contraceptives (depot medroxyprogesterone acetate, etonogestrel implant, and levonorgestrel intrauterine device) on immunologic changes in the female genital tract (FGT) and systemic compartment. Methods CHIME is an observational cohort study where participants attend 2 visits prior to initiating the HC method of their choice, and then attend 6 visits over 12 months with biological sampling (vaginal swabs, cervicovaginal lavage, cytobrush and blood) for immunological, bacteriological, and virological analyses at each visit. Immune profiling will be evaluated by multi-color flow cytometry to determine how different T-cell subsets, in particular the CD4 T-cell subsets, change during the course of contraceptive use and whether they have different profiles in the FGT compared to the systemic compartment. The study aims are (1) to characterize the alterations in FGT and systemic immune profiles associated with three long-acting progestin-only HC and (2) to evaluate the vaginal microenvironment, determined by 16 s rRNA sequencing, as an individual-level risk factor and moderator of genital and systemic immune profile changes following exposure to three commonly used HC. Data collection started in March 2019 and is scheduled to be completed in October 2024. Discussion The CHIME study aims to contribute to the body of research designed to evaluate the comparative impact of three long-acting progestin-only HC on innate and adaptive immune functions to understand how immunologic effects alter STI and HIV susceptibility.

Female sex hormones are known to regulate the immune functions of the female genital tract (FGT). While the majority of immune cells found in the FGT are T cells and Natural Killer cells (NK cells), very few studies have focused on NK cells in the FGT in contrast to numerous studies focusing on T-cells. Here, we characterized the distribution, phenotype and function of NK cells in FGT of HIV seronegative women using different mucosal sampling methods; cervicovaginal lavage (CVL), endocervical cytobrush (CB), and cervicovaginal biopsy and compared them to blood. We isolated cells from blood and FGT and performed multi-color flow cytometry to identify cellular phenotypes. First, we looked at the distribution of CD56brightand CD56dimpopulations of NK cells across the samples and found that CD56brightNK cells were lower in the FGT tissues compared to blood. Between the CD56brightand CD56dimpopulations, the CD56dimpopulation was significantly reduced in the follicular phase compared to the luteal phase in tissues. The NK cells within the FGT samples express higher levels of tissue resident markers CD69 and CD103. The co-expression of CD69+CD103+ markers seem to be significantly higher in follicular phase compared to luteal phase in tissues. These cells have high proliferative capacity with high levels of HLADR expression, suggesting that these cells are highly functional and activated. The gut tissue homing marker alpha4beta7 expression significantly reduced in the follicular phase, however other homing markers CCR5 and CCR7 expression were elevated in the follicular phase. Altogether, these data demonstrate that FGT is enriched with tissue resident NK cells with high activation and proliferation profile with distinct homing potential.