Modulation of genital tract CD4+ T cell subsets by chlamydia and cervicovaginal microbiota
Seth M. Bloom1,2,3, Nondumiso N. Xulu2, Nomfuneko A. Mafunda1,2, Mara Farcasanu1,2,3, Matthew R. Hayward1,2,3, Kendall R. Jackson2, Douglas S. Kwon1,2,3*
1Massachusetts General Hospital; 2Ragon Institute of MGH, MIT and Harvard, 3Harvard Medical School
Mucosal CD4+ T cells are critical to female genital tract (FGT) health, helping control bacterial, viral, and fungal infections while serving as primary targets for HIV transmission. Immune responses to FGT infections are known to depend on T helper subsets including TH17 and regulatory (Treg) cells in mouse models, but human studies have been hampered by paucicellular samples, small cohort size, and STI co-infections. FGT TH17 cells (often experimentally defined by markers CCR6 and/or CD161) have been studied in context of inflammation and HIV, but FGT Tregs remain poorly characterized. Using flow cytometry and bacterial 16S gene sequencing, we examined CD4+ T cell subsets in cervical cytobrush samples from a cohort of 119 HIV-negative South African women (ages 18-24) and investigated whether they were influenced by STIs and FGT microbiota composition. We enriched for TH17 cells and Tregs by gating on CD161+CCR6+ and CD25+CD127Lo- cells respectively. Median cervical CD161+CCR6+ and CD25+CD127Lo- CD4+ T cell frequencies were 48.0% and 12.4% respectively. Subjects with chlamydia had higher numbers of activated CD4+ T cells and higher frequency of CD25+CD127Lo-, lower frequency of CD161+CCR6+, and lower ratio of CD161+CCR6+ / CD25+CD127Lo- CD4+ T cells (p < 0.002 for each). To assess effects of non-STI microbiota on FGT T cells, we used 16S gene sequencing to classify STI-negative women into microbial cervicotypes. We found significant cervicotype-related differences in CD25+CD127Lo- CD4+ T cell frequency and CD161+CCR6+ / CD25+CD127Lo- ratio. These were largely explained by Gardnerella vaginalis abundance, which was positively associated with CD25+CD127Lo- CD4+ T cell frequency (p = 0.0016) and negatively associated with CD161+CCR6+ / CD25+CD127Lo- ratio (p = 0.0035). No differences were seen in peripheral blood, confirming that effects were due to local, not systemic, factors. In summary, we characterized FGT CD4+ T cell subsets and showed they were modulated by both chlamydia and the non-STI microbiota. Future work will investigate the mechanistic basis for these findings and implications for adaptive immunity and HIV.