Background/Purpose: B cells are critical players in the orchestration of properly regulated immune responses.  This is achieved through the finely regulated participation of multiple B cell populations with different antibody-dependent and independent functions, a balance that we postulate is perturbed in autoimmune diseases such as RA and may be corrected after B cell depletion therapy (BCDT).

Methods: B cells from 13 RA patients were analyzed by multi-color flow cytometry at baseline and longitudinally after BCDT. Expression of CXCR3, CD21, CD95, and anchor markers (IgD, CD19, CD27, CD38, CD24 and live/dead/T-cell exclusions) were used to subset memory B cells.  Expression of MitoTracker Green extrusion, CD10, IgM, CD23 and anchor markers were used to subset transitional B cells. RA patients met ACR criteria for classification, and activity was assessed based on DAS28. Cytokine expression in distinct purified B cell subsets or total B cells in PBMCs were examined by flow cytometry after 88 hours stimulation (CpG 2006, anti-CD40, IL2, and BAFF) and 5 hr culture with PMA and ionomycin.

Results: In RA patients both CD27+IgD- switched memory (SM) and CD27-IgD- double negative memory (DN) contained higher fractions of CD95+ and CD21- activated B cells (DN CD95+: RA 28.9+3.9 vs. HC 10.7+1.2, p<0.0001; DN CD21-: RA 41.6+7.3 vs. HC 27.3+2.7, p=0.03). After BCD (1 month) the predominant B cell populations were memory (increase in DN from baseline 6.9+4.4 vs. 1 month 47.7+29.7, p=0.007; SM baseline 14.2+9.7 vs. 1 month 36.1+25.9, p=0.05).  Notably, the residual memory B cells displayed a high fraction of CD95+ (DN 59.4+20.3, SM: 52.8+16.3) and CD21- (DN 94.6+2.9, SM: 73.1+22.2) compared to pre-depletion (CD95+: DN 28.9, p=0.03; SM: 38.7+18.0, p=0.1; CD21-: DN 41.6, p=0.0005; SM: 24.9, p=0.006;) suggesting some resistance of these activated populations to anti-CD20. Reconstitution occurred between 4 and 12 months with a variable distribution of transitional, naïve, and memory B cell subsets. At a reconstitution time-point (12 month), the fraction of activated memory remained high (CD95+ SM 91.4+4.6, p=0.001 vs. baseline; CD21- SM  70.4+12.4, p=0.009 vs. baseline), but there was a shift to a naïve/transitional dominant B cell compartment. The critical role of B cells as secretors of cytokines in a polarized fashion was highlighted by the propensity of CD27+ memory B cells to produce pro-inflammatory (TNF) over regulatory (IL10) cytokines (TNF: SM 28.2+5.4% vs. transitional 13.6+2.9, p=0.05; IL10: SM 3.5+0.7 vs. transitional 9.8+1.5, p=0.008). The effects of BCD on B cell cytokine secretion are under investigation.

Conclusion: Our results support the hypothesis that the clinical and immunological outcome of B cell depletion therapy depends on the relative balance of protective and pathogenic B cell subsets established after B cell depletion and upon B cell repopulation.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/activated-memory-b-cell-compartment-in-rheumatoid-arthritis-impact-of-b-cell-depletion-therapy/