Combination of Anti-BTLA Antibody (6B2) and Anti-PD-1 Antibody (PIM-2) Induced Indefinite Survival of Fully MHC-Mismatched Murine Cardiac Allograft.

Abstract

Background: Programmed death (PD)-1 and B and T lymphocyte attenuator (BTLA) had been implicated in the regulation of autoimmune and may potentially play an important role in alloimmune responses. In this study, we investigated the effect of anti-PD-1 monoclonal antibody (mAb) (PIM-2) and anti-BTLA mAb (6B2) in fully MHC-mismatched murine model of cardiac allograft transplantation. Methods: CBA mice underwent transplantation of C57BL/6 hearts and received a single dose (100μg) of 6B2 on the day of transplantation (day 0) or four doses on day 0, 3, 6 and 9. Moreover, CBA recipients were also given one dose of combination of 6B2 and PIM-2 on day 0. Adoptive transfer was performed to determine whether regulatory cells were generated. Cell-proliferation and cytokine assessments were also performed. Result: Untreated CBA mice rejected C57BL/6 allografts acutely (median survival time [MST], 7 days). When CBA recipients were given one and four doses of 6B2, the allograft survivals were significantly prolonged (MSTs, 46 and >100 days, respectively). Moreover, when CBA mice were given with combination for one dose of 6B2 and PIM-2, the allograft survival was indefinitely prolonged (MST, >100 days). Secondary CBA recipients given whole splenocytes from primary combination-treated CBA recipients with C57BL/6 cardiac allografts 30 days after grafting had prolonged C57BL/6 allograft survival (MST, >30 days). Proliferation of splenocytes and interferon-γ production were suppressed and interleukin-4 production was increased in combination-treated mice. Conclusion: Combination of anti-BTLA mAb (6B2) and anti-PD-1 mAb (PIM-2) could induce hyporesponsiveness of fully MHC-mismatched cardiac allografts and may generate regulatory cells.