Accelerated rejection of allografts has been a clinical challenge in solid organ transplantation particularly in sensitized recipients with donor-specific antibodies (DSA) and memory cell repertoires. Although, current antirejection drugs effectively control de novo alloimmune responses however are inefficient suppressing memory cells. In this study, we evaluated the efficacy of anti-CD40L (MR1)-Ab and rapamycin (Rapa) in combination with ethylenecarbodiimide (ECDI)-fixed donor splenocytes (SP) in a mouse model of allogeneic pancreatic islet transplantation using sensitized recipients. Recipients (C57BL6/J) were sensitized using donor (BALB/c) splenocytes 8-10 weeks prior to the transplantation. Recipients received MR1 Ab on day -7, -4, 0 and +4, rapa on day -7 to +10 while ECDI-SP were infused on day -7 and +1. Pre-transplant evaluation of the serum samples confirmed sensitization. Sensitized recipients without any treatment acutely rejected the islets on day 3-4 compared to naïve mice where rejection occurred ~day20. MR1/Rapa moderately but significantly prolonged the survival of grafts up to 20-25 days. ECDI-SP alone proved ineffective in prolonging graft survival; however its combination with MR1/Rapa significantly prolonged graft survival for up to 150 days. We observed a positive correlation of prolonged graft survival with the reduction in (i) isotype-switched (IgD^–CD19⁺) B cells, (ii) memory B cells specific for BALB/c MHC-II (I-E^d), identified using tetramer-staining, and (iii) germinal center formation assessed 2 weeks post-transplantation. Similarly sensitized recipients with prolonged graft survival showed reduced IFNγ production by T cells in MLR despite the presence of memory phenotype (based on the expression of CD44 and CD62L). In contrast, the presence of pre-formed DSA did not correlate with acute graft rejection as recipients with similar DSA levels revealed different graft outcomes (significantly prolonged survival in MR1/Rapa/ECDI-SP > MR1/Rapa > untreated group). In conclusion, our data demonstrates that (i) accelerated islet rejection in sensitized recipients is primarily a cell-mediated event and (ii) combining ECDI-SP with MR1/Rapa effectively controls memory T and B cells thereby prolonging islet survival in sensitized mice.

CITATION INFORMATION: Dangi A, Kang H.-K, Zhang X, Luo X. A Combination of Anti-CD40L-Ab, Rapamycin, and Donor Apoptotic Cells Prolongs Allogeneic Pancreatic Islet Survival in Sensitized Mice by Regulating Memory Responses. Am J Transplant. 2017;17 (suppl 3).

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