No evidence of rebound MS disease activity with presence of CD20+ T cells at B-cell reconstitution after treatment with rituximab

In the last decade, the increased use of anti-CD20 treatment in patients with multiple sclerosis (pwMS) has been highly effective in reducing relapse rates and new inflammatory disease activity. A growing amount of evidence has implicated CD20+ T cells as the disease pathogenic cells and possible targets of anti-CD20 agents. Aim: We here aimed to characterise CD20+ T cells in pwMS who have been treated with rituximab and extended the dosing interval due to the COVID-19 pandemic and compared them to other treatments and healthy donors. Method: We characterised CD20+ T cells using flow cytometry in a cohort of pwMS with blood sampling 437±214 days after anti-CD20 treatment (Rituximab, n=47;Ocrelizumab, n=4) and compared with other disease modifying treatments (DMT, n=18) and healthy donors (HD, n=15). Results: B cells constituted 2.82±1.58 % of peripheral blood mononuclear cells from anti-CD20 treated pwMS at time of sampling. We neither found a correlation between time since last dose and levels of CD20+ T cells, nor differences in CD20+ T-cell percentages in anti-CD20 treated pwMS as compared to other DMTs and HD. In addition, independently of the treatment, approximately 40% of CD20+ T cells displayed a CD4+ phenotype enriched for memory cells. Furthermore, CD4+CD20+ T cells in rituximab-treated pwMS included 43.9±19.9 % PD1+, 15.9±10.5 % follicular helper T cells (Tfh), 4.8±4.4 % regulatory T cells (Treg) and 71.9±19.1 % memory cells. Memory CD4+CD20+ T cells were, based on chemokine receptors CXCR3 and CCR6 expression, divided into 33.9±15.5 % Th1, 13.3±7.7 % Th2, 17.5±8.2 % Th17 and 35.1±10.8 % Th1/17. Of note, rituximabtreated pwMS displayed significantly higher levels of Treg cells among CD20+ T-cell populations as compared to HD (4.8% vs 2.3%;p=0.0423). No evidence of clinical rebound disease activity was observed in the cohort despite presence of CD20+ T cells. Conclusion: Our findings suggest that CD20+ T cells at B-cell reconstitution after rituximab treatment do not induce rebound disease activity. Further studies are needed to molecularly define and contrast CD20+ T cells being present in pwMS at treatment start and after B-cell reconstitution, respectively, in order to better determine their role in the immunopathogenesis of MS.