Anti-CD20 B cell depletion is associated with elevated mucosal-originating circulating regulatory IgA B cells in multiple sclerosis

Therapy with anti-CD20 monoclonal antibodies is highly efficacious in various autoimmune diseases including multiple sclerosis (MS), a prototypic autoimmune inflammatory disease of the central nervous system (CNS). However, which B cell subsets and altered B cell-regulating factors mediate the clinical efficacy of anti-CD20 treatment is unclear. To address this gap in knowledge, we performed longitudinal high-dimensional single-cell transcriptomic and proteomic profiling of blood, cerebrospinal fluid (CSF), and intestinal samples from people with MS (pwMS), combined with immune profiling in a preclinical autoimmune encephalomyelitis model during anti-CD20 therapy. CSF analyses were performed using previously published datasets. Multisite intestinal profiling was conducted in one anti-CD20-treated patient with MS and one control participant. By applying algorithm-guided analyses of flow cytometry, single-cell transcriptomic, and immune receptor repertoire data, we found that anti-CD20 B cell depletion was associated with increased frequencies of regulatory mucosal-derived IgA-producing B cells in the periphery and CSF, together with increased B cell receptor clonal overlap between mucosal and systemic compartments, indicating enhanced trafficking of IgA B cells from gut mucosal tissues to the systemic circulation and the CNS. Moreover, we demonstrated that higher levels of B cell-activating factor and a proliferation-inducing ligand were related to favorable outcomes in pwMS during anti-CD20 treatment. Together, our findings suggest that mucosal immune regulatory mechanisms may be harnessed by anti-CD20 B cell depletion, opening previously unknown therapeutic avenues for MS.