Immunomodulatory capacity of B cells make them a promising therapeutic tool for autoimmune and alloimmune response in patients. We found that transplant tolerance induced by a short course of anti-CD45RB was B cell-dependent. Subsequently, adoptive transfer of regulatory B cells from tolerant to naïve hosts transferred tolerance. Recently we have expanded naive B cells in an ex vivo culture system. In this study, we evaluated the efficacy of their phenotype, function, and mechanism to promote allograft survival.

To generate ex vivo expanded B cells, splenic B cells were isolated from B6 mice and cultured on monolayers of irradiated NIH-3T3 cells expressing the CD40 T cell ligand with supplements of anti-TIM-1, IL-4, IL-21, and BAFF for 8 days. For adoptive transfer experiments, these cultured B cells were purified by cell-sorting to avoid 3T3 cell contamination. The sorted B cells were then IV injected into diabetic B cell-deficient [mu]MT mice that received simultaneous Balb/c islets. Allograft survival was measured by blood glucose level. Ex vivo expanded B cells showed a high-level expression of TIM-1, CD9, and CD25, which are associated with regulatory B cell markers, and increased expression of CD80/CD86 activation markers. We observed that adoptive transfer of ex vivo expanded B cells promoted allograft survival compared to naïve B cells (p value=0.0155*) and half of these recipients showed indefinite graft survival. TIM1+ B cells were sorted among the expanded B cells and then transferred to diabetic [mu]MT mice. These mice also accepted allo-islet grafts well (P value=0.036*). Regulatory B cells have been demonstrated to be IL-10-dependent in other models, thus we tested if ex vivo expanded regulatory B cells are also IL-10-dependent. Transfer of ex vivo expanded IL-10-deficient B cells resulted in rapid rejection of all allograft without prolongation compared to wild-type B cells (P value=0.040*). In addition, B cells from TGF-β-/-, IL-4-/-, and OB1 (BCR transgenic mice) were unable to significantly prolong graft survival.

The ex vivo culture system quantitively expands B cells and qualitatively develops B cells into regulatory B cells. These regulatory B cells prolong allografts via an IL-10, TGF-β, IL-4-dependent pathway and suggest a diverse B cell repertoire is required. These findings may provide a novel and effective in vivo treatment for transplantation settings.

CITATION INFORMATION: Lee K., Deng K., Kojima L., Dai C., Rickert C., Yeh H., Markmann J. Ex Vivo Expanded Regulatory B Cells Promote Allograft Survival through IL-10-Dependent Pathway Am J Transplant. 2017;17 (suppl 3).

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