Background/Purpose:  Changes in the ratio of circulating memory, naive, and double negative CD27^–IgD^– B cell subsets are associated with a higher disease activity index in systemic lupus erythematosus (SLE) patients. Little is known about the soluble factors that may induce plasmablast differentiation from B-cell subtypes infiltrating inflamed tissue environments where they have proximity to, but often spatially separated from T-cells. We investigated the potential for SLE-associated soluble BAFF, IL-2 and IL-21 to drive plasmablast differentiation from B-cell subsets in a T-cell contact independent manner and whether CC-220, a Cullin Ring Ligase 4 Cereblon (CRL4^CRBN) E3 Ubiquitin Ligase Modulator, has an impact on generating potential autoantibody producing cells. The objective of the study was to determine the potential of BAFF, IL-2 and IL-21 to induce plasmablast differentiation from memory, naive, and lupus-associated double negative B-cell subsets and to determine the impact of CC-220 on differentiation and proliferation within these B-cell populations.

Methods:  We investigated the effects of CC-220 on plasmablast differentiation from purified B-cell subsets in in vitro models mimicking germinal center T cell contact dependent (CD40L, IL-2, IL-21) and extra-germinal center T-cell contact independent (BAFF, IL-2, IL-21) systems. Plasmablast differentiation and antibody secretion was measured 5 days post treatment of CD27⁺ memory B-cells and CD27^– naive B-cells. Sorted B-cell subsets based on the CD27 memory and the IgD class switch markers were also tested: CD27^–IgD⁺ naïve; CD27⁺IgD^– switched memory (SMe); CD27⁺IgD⁺ non switched memory (NSM); and CD27^–IgD^– double negative (DN) B cells. Plasmablast differentiation and antibody production in the absence or presence of CC-220 were analyzed by flow cytometry and ELISA, respectively.

Results:  BAFF, IL-2, and IL-21 in combination induced proliferation and plasmablast differentiation in SMe and DN B-cells, but not NSM or naive B-cells. Induced IgG secretion by BAFF, IL-2, and IL-21 was observed only from SMe and DN B-cells. Induced IgM secretion by BAFF, IL-2, and IL-21 was observed from SMe, to a lesser degree DN, but not from NSM or naive B-cells. CD40L, IL-2, and IL-21 induced B-cell proliferation and differentiation from all four subpopulations, with SMe producing the largest amount of IgG secretion followed by DN and DP and little from naive B-cells. Similar to IgG, IgM secretion was induced most from SMe, followed by NSM and DN in the CD40L, IL-2, IL-21 system. CC-220 inhibited plasmablast differentiation and antibody production in all cases, with different efficacy depending on the B-cell subpopulations and stimuli.

Conclusion:  In the presence of IL-2 and IL-21, BAFF induced proliferative and plasmablast differentiation effects are only observed on class switched CD27⁺IgD^– memory and DN CD27^–IgD^– B-cells. This is in contrast to CD40L, IL-2, and IL-21,which drives B-cell proliferation and differentiation in all four subpopulations tested. In all conditions used to induce B-cell proliferation and plasmablast differentiation, CC-220 inhibited these processes at clinically relevant concentrations (1-10 nM).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-crl4crbn-e3-ubiquitin-ligase-modulator-cc-220-inhibits-baff-mediated-plasmablast-differentiation-and-immunoglobulin-secretion-from-class-switched-cd27igd-memory-and-lupus-associated-cd27-igd-do/