Comprehensive analysis of B cell repopulation in ocrelizumab-treated patients with multiple sclerosis by mass cytometry and proteomics.

Ocrelizumab, an anti-CD20 antibody, depletes CD20(+) B cells, which subsequently repopulate over months. Little is known about changes in other immune cell populations and molecular markers associated with B cell repopulation. Here, we performed a comprehensive characterization of immune cells from ocrelizumab-treated patients with multiple sclerosis (MS) using mass cytometry. About 50% of patients showed naive B cell repopulation after 6 months mainly with a transitional phenotype, whereas CD27(+) memory B cells only rarely repopulated. This repopulation was associated with a reduction of memory T cells and activated myeloid cells, as well as reduced expression of activation/migration markers in both cell types. A plasma proteomics analysis identified proteins including TNFRSF13C, associated with B cell depletion and repopulation. Plasma levels of neurofilament light-chain protein declined after ocrelizumab treatment was not linked with B cell repopulation. These findings identify potential soluble markers for monitoring of ocrelizumab treatment in MS.