An Observational Study of the Impact of Systemic B-cell Depletion on Cervicovaginal Mucosal Environment

Importance Emerging data show that B-cell depleting chemotherapies, which are increasingly used to treat autoimmune disorders and multiple sclerosis, can be associated with mucosal side effects such as inflammatory vaginitis. Objective Evaluate the impact of rituximab treatment on vaginal mucosal immune markers, endocervical immune cell populations and vaginal microbiome. Design Cross-sectional observational study conducted between 2022 – 2024. Setting Academic medical center, Boston Massachusetts. Participants We enrolled women aged >18 years who were either 1) receiving rituximab for autoimmune renal disease or were 2) healthy controls Exposure Treatment with rituximab, an anti CD20 monoclonal antibody. Main outcome and measure We compared endocervical immune cell populations, vaginal fluid immune markers, vaginal fluid immunoglobulins and vaginal microbiome composition between individuals being treated with rituximab and healthy controls. Results We enrolled 26 women treated with rituximab for autoimmune renal disease and 26 healthy controls. Median circulating and endocervical B-cell and plasma cell proportions were significantly lower in treated participants compared to controls. Median vaginal fluid IgA concentrations were significantly lower in participants treated with rituximab, while ILE, IgM, IgG1, IgG2, IgG3 and IgG4 were not different between groups. Total T cell frequencies were similar between groups, but the proportion of activated T cells (CD4+CD38+HLADR+) was significantly lower in people treated with rituximab. Concentrations of IL10, IL13, IL17, IL21, IL23, IL4, ITAC and TNFa were elevated in vaginal fluid from the rituximab group, while IL-8 was lower. A CST-IV-C, low- Lactobacillus pattern of vaginal microbiota was more common in the rituximab group. Conclusions and Relevance Systemic B-cell depletion is associated with reduced vaginal fluid IgA, a more diverse microbiome composition, and increases in many vaginal fluid immune markers compared to healthy controls. The reduction in vaginal fluid IgA may provide opportunities for vaginal bacteria to induce inflammation. Key points Question How does circulating B-cell depletion impact the vaginal microenvironment? Findings In this cross-sectional study of 52 women, B cell and plasma cell proportions were significantly lower in both blood and vaginal mucosa among rituximab-treated participants compared to healthy controls. Vaginal IgA concentrations, but not other immunoglobulins, were significantly lower in rituximab treated participants. In treated participants, vaginal cytokine concentrations were elevated, and microbiome composition shifted toward non– Lactobacillus -dominant communities. In six people with inflammatory vaginitis, both circulating and endocervical B cells were lowest in people with the most severe symptoms. Meaning Systemic B cell depletion is associated with alterations in vaginal mucosal immune markers and microbiome composition which increase local inflammation.