We aimed to define phenotypic and functional profiles of circulating B cells during early reconstitution following anti-CD20 antibody initiation.

Anti-CD20 therapy which depletes the majority of circulating B cells and a small subset of T cells is highly efficacious in limiting new disease activity in multiple sclerosis (MS). Untreated MS patients exhibit an abnormal balance between pro-inflammatory and regulatory cytokine-producing B cells, however relatively little is known about the profiles of B cell subpopulations that would reconstitute early after treatment.

Peripheral blood mononuclear cells (PBMC) were serially isolated and cryopreserved using strict standard operating procedures at baseline, at 3-4 months and at 6-7 months, after initial anti-CD20 (ocrelizumab) infusion in 7 previously treatment-naive MS patients. Functional immune phenotyping was subsequently performed in batch using multi-parametric flow cytometry panels developed and validated for use with cryopreserved PBMC.  

B cells were largely but not completely depleted 3 months after treatment initiation. Specifically, plasmablasts and CD11c⁺ B cells (implicated as pro-inflammatory in other systemic autoimmune diseases), were less efficiently depleted.  By 6 month following initial treatment, B cells were partially repopulated, though to differing extents across individuals. In general, CD10⁺ transitional B cells (implicated as anti-inflammatory), as well as a subset of memory B cells, were preferentially repopulated. These repopulating B cells exhibited decreased levels of surface activation markers, and increased levels of proliferation markers and surface regulatory markers. The ratios of IL-6/IL-10-producing B cells were significantly diminished at early repletion compared to the treatment-naïve baseline.

Our data first unexpectedly demonstrate diminished susceptibility of the CD11c⁺ B cell subset to ocrelizumab. B cell reconstitution early after B cell exhibits a degree of heterogeneity across MS patients, however in general the pro-inflammatory/anti-inflammatory imbalance of B cells seen in untreated patients appears improved even after an initial cycle of ocrelizumab.