Background/Purpose: B cells contribute to the development and progression of autoimmune diseases through multiple mechanisms. Consequently, modulating B cell activation, B cell effector function, and plasmablast development holds great therapeutic potential. CD22 (Siglec-2) is an inhibitory receptor selectively expressed on B cells and has been shown to inhibit BCR downstream signaling. Here we tether CD22 to the B cell receptor (BCR) with a CD22 x CD79b bispecific Ab (bsAb) to potently inhibit B cell activation, proliferation, cytokine production, Ig production, and plasmablast accumulation.

Methods: Binding of the bsAb to different B cells was analyzed by flow cytometry using directly conjugated-bsAb. Potential for in vitro antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) was assessed in PBMC cultures in the presence of fresh serum. Impact on BCR downstream signaling upon IgM cross-linking was determined by phospho-flow of p-Syk and p-PLCg in purified B cells. PBMC and B cells were used to assess inhibitory capacity of the bsAb on B cell activation, proliferation, and cytokine production upon IgM cross-linking. PBMC from 15 RA patients and 17 matched healthy donors (HD) were used to verify inhibitory potential in rheumatologic disease.

For in vivo pharmacology studies, CD34+ reconstituted NSG mice were dosed as indicated, and serum IgM, frequency and composition of B cells and plasmablasts (spleen, blood), and splenic B cells functionality upon IgM cross-linking were assessed at indicated time points.

Results: Our CD22xCD79b bsAb showed strong, selective binding to all CD22 expressing B cell subsets without in vitro depletion. The bsAb potently inhibited the phosphorylation of BCR downstream signaling molecules Syk and PLCg upon IgM cross-linking, which correlated with significant reductions in B cell proliferation and cytokine production. Moreover, our bsAb potently inhibited the activation of B cells in PBMC from both HD and RA patients (CD69, CD83, CD86).

In vivo treatment of CD34+NSG mice with the bsAb showed a potent, dose-dependent reduction in serum IgM levels, concomitant with profound reductions of plasmablasts in the blood and spleen. In addition, splenic B cells from treated animals showed a significant dose-dependent reduction in their capacity to produce proinflammatory cytokines upon IgM cross-linking in vitro (IL-6, IL-8, CCL3, CCL4, CCL22).

Conclusion: Together this data shows that our CD22xCD79b bsAb is a potent inhibitor of B cell activation in vitro and in vivo, making it a promising approach for the treatment of autoimmune diseases with a pathogenic B cell component.

This work was supported by Janssen R&D, LLC

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cd22-x-cd79b-bispecific-ab-potently-inhibits-b-cell-activation-and-plasmablast-accumulation/