Fingolimod alters intrathecal B cell maturation in multiple sclerosis patients

Abstract Background: B cells are postulated to play multiple roles in the pathogenesis of multiple sclerosis (MS) including pathogenic antibody production, antigen-presentation and pro-inflammatory cytokine secretion. Natalizumab and fingolimod are effective MS therapies that disrupt lymphocyte migration but exert differential effects on B cell maturation and trafficking. Herein, we investigated their effects on peripheral blood and cerebrospinal fluid (CSF) B cell repertoires.Methods: Paired CSF and peripheral blood (PB) lymphocytes were collected from MS patients at baseline and after 6 months of treatment with fingolimod (n = 4) or natalizumab (n = 4). B cell subsets including naïve, CD27+ memory, CD27-IgD- double-negative B cells and plasmablasts were collected by FACS and their respective heavy-chain variable region (VH) repertoires assessed by next generation deep sequencing (Illumina MiSeq).Results: Treatment with fingolimod lead to a distinct contraction of the PB B cell pool whereas natalizumab resulted in an expansion of circulating PB B cells. In contrast, CSF B cell numbers remained stable under treatment with fingolimod but decreased following natalizumab therapy. Clonal overlap between CSF and peripheral blood B cells was reduced following natalizumab treatment (-24% reduction of clonal groups) but remained stable with fingolimod therapy. Lineage analyses of CSF B cell repertoires at baseline and following therapy revealed large, clonally expanded B cell clusters in natalizumab-treated MS patients but no intrathecal clonal expansion following fingolimod therapy. Conclusions: Our findings suggest that natalizumab treatment diminishes the exchange of peripheral and intrathecal B cells but does not impact intrathecal clonal expansion. In contrast, fingolimod treatment fails to alter B cell exchange across the blood-brain-barrier but affects intrathecal clonal expansion. Sphingosine-1 phosphate receptor inhibition may impact MS disease progression by inhibiting intrathecal germinal center activity.