Atypical memory B cells contribute to heterogeneous vaccine responses in ocrelizumab-treated patients with multiple sclerosis

Background and ObjectivesPatients with multiple sclerosis (pwMS) treated with ocrelizumab (OCR), a B-cell-depleting therapy, exhibit heterogeneous humoral responses to SARS-CoV-2 mRNA vaccination. The mechanisms underlying this variability remain incompletely understood. We performed a longitudinal analysis of B-cell subset dynamics and antigen-specific T cell responses in OCR-treated pwMS and healthy controls to determine how immune cell composition, timing of OCR infusion, and lymphocyte dynamics influence humoral response outcomes. MethodsBased on post-vaccination anti-Spike IgG titers measured by multiplex bead immunoassay, pwMS were categorized as super-responders (SR), responders (R), or non-responders (NR). A 35-marker spectral flow cytometry panel was used to characterize T- and B-cell subsets longitudinally, at baseline and following stimulation with a SARS-CoV-2 peptide pool. ResultsCD4+ and CD8+ T cell populations were preserved across OCR-treated pwMS, and SARS-CoV-2-specific T cells remained detectable for more than 6 months after vaccination. In contrast, residual B-cell subset composition distinguished responders from non-responders. DN2-like B cells (CD19+CD27-IgD-T-bet+CD11c+CXCR5-) persisted despite repeated OCR infusions and were enriched in SR compared with NR. Repletion of mature naive B cells in peripheral blood correlated with time since last OCR infusion and with stronger humoral immune responses. ConclusionsB-cell subsets that resist OCR-mediated depletion may contribute to vaccine responsiveness in OCR-treated pwMS. Altered repletion kinetics of naive B cell subsets in non-responders suggest that specific B-cell populations may serve as predictive biomarkers of vaccine-induced humoral immunity, despite preserved T-cell responses.