Tolerant kidney transplant patients produce B cells with regulatory properties

Abstract

Whereas a B cell-transcriptional profile has been recorded for operationally tolerant kidney graft patients, the role that B cells have in this tolerance has not been reported. In this study, we analyzed the role of B cells from operationally tolerant patients, healthy volunteers, and kidney transplant recipients with stable graft function on T cell suppression. Proliferation, apoptosis, and type I proinflammatory cytokine production by effector CD4+CD252 T cells were measured after anti-CD3/anti-CD28 stimulation with or without autologous B cells. We report that B cells inhibit CD4+CD252 effector T cell response in a dosedependent manner. This effect required B cells to interact with T-cell targets and was achieved through a granzyme B (GzmB)-dependent pathway. Tolerant recipients harbored a higher number of B cells expressing GzmB and displaying a plasma cell phenotype. Finally, GzmB+ B-cell number was dependent on IL-21 production, and B cells fromtolerant recipients but not fromother patients positively regulated both the number of IL-21+ T cells and IL-21 production, suggesting a feedback loop in tolerant recipients that increases excessive B cell activation and allows regulation to take place. These data provide insights into the characterization of B cell-mediated immunoregulation in clinical tolerance and show a potential regulatory effect of B cells on effector T cells in blood from patients with operationally tolerant kidney grafts.