Graft Protective and Intercellular Immunomodulatory Effects by Adoptive Transfer of an Agonistic Anti-BTLA mAb (3C10) Induced CD4+CD25+ Regulatory T Cells in Murine Cardiac Allograft Transplant Model

Background We demonstrated that an agonistic anti-B and T lymphocyte attenuator antibody (3C10) prolonged cardiac survival by inducing regulatory T cells (Treg). However, the mechanisms of immune tolerance in the recipients remained unclear. In this study, we investigated the graft-protective and intercellular immunomodulatory effects of adoptive transfer (AT) of 3C10-induced Tregs in a murine cardiac allograft transplant model. Methods Thirty days after transplantation of a C57BL/6 heart into the primary 3C10-treated CBA recipients, splenic CD4+CD25+ cells from these recipients (3C10/AT group) or naïve CBA mice (no-treatment group) were adoptively transferred into secondary CBA recipients with a C57BL/6 heart. To confirm the requirement for 3C10-induced Tregs, we administered an anti-interleukin-2 receptor alpha antibody (PC-61) to secondary CBA recipients. Additionally, histologic and fluorescent staining, cell proliferation analysis, flow cytometry, and donor-specific antibody (DSA) measurements were performed. Results 3C10/AT-treated CBA recipients resulted in significantly prolonged allograft survival (median survival time [MST], >50 days). Allografts displayed prolonged function with preservation of vessel structure by maintaining high numbers of splenic CD4+CD25+Foxp3+ Treg and intramyocardial CD4+Foxp3+ cells. DSA levels were suppressed in 3C10/AT-treated CBA recipients. Moreover, PC-61 administration resulted in a shorter MSTs of cardiac allograft survivals, a detrimental increase in DSA production, and enhanced expression of programmed cell death (PD)-1. Conclusion AT of 3C10-induced Tregs may be a promising graft-protective strategy to prolong allograft survival and suppress DSA production, driven by the promotion of splenic and graft-infiltrating Tregs and collaboration with PD-1+ T cells and Treg.