Porcine islet xenotransplantation is a viable strategy to treat diabetes. Its translation has been limited by the pre-clinical development of a clinically available immunosuppressive regimen. We tested two clinically relevant induction agents in a non-human primate (NHP) islet xenotransplantation model to compare depletional versus nondepletional induction immunosuppression. Neonatal porcine islets were isolated from GKO or hCD46/GKO transgenic piglets and transplanted via portal vein infusion in diabetic rhesus macaques. Induction therapy consisted of either basiliximab (n = 6) or rhesus-specific anti-thymocyte globulin (rhATG, n = 6), combined with a maintenance regimen using B7 costimulation blockade, tacrolimus with a delayed transition to sirolimus, and mycophenolate mofetil. Xenografts were monitored by blood glucose levels and porcine C-peptide measurements. Of the six receiving basiliximab induction, engraftment was achieved in 4 with median graft survival of 14 days. All six receiving rhATG induction engrafted with significantly longer xenograft survival at 40.5 days (P = 0.03). These data suggest that depletional induction provides superior xenograft survival to nondepletional induction, in the setting of a costimulation blockade-based maintenance regimen.

Background Thrombosis is a known consequence of intraportal islet transplantation, particularly for xenogeneic islets. To define the origins of thrombosis after islet xenotransplantation and relate it to early inflammation, we examined porcine islets transplanted into non‐human primates using a dual‐transplant model to directly compare islet characteristics. Methods α1,3‐Galactosyltransferase gene‐knockout (GTKO) islets with and without expression of the human complement regulatory transgene CD46 (hCD46) were studied. Biologically inert polyethylene microspheres were used to examine the generic pro‐thrombotic effects of particle embolization. Immunohistochemistry was performed 1 and 24 hours after transplantation. Results Xeno‐islet transplantation activated both extrinsic and intrinsic coagulation pathways. The intrinsic pathway was also initiated by microsphere embolization, while extrinsic pathway tissue factor (TF) and platelet aggregation were more specific to engrafted islets. hCD46 expression significantly reduced TF, platelet, fibrin, and factor XIIIa accumulation in and around islets but did not alter intrinsic factor activation. Layers of TF+ cells emerged around islets within 24 hours, particularly co‐localized with vimentin, and identified as CD3+ and CD68+ cells inflammatory cells. Conclusions These findings detail the origins of thrombosis following islet xenotransplantation, relate it to early immune activation, and suggest a role for transgenic hCD46 expression in its mitigation. Layers of TF‐positive inflammatory cells and fibroblasts around islets at 24 hours may have important roles in the progressive events of thrombosis, inflammatory cell recruitment, rejection, and the ultimate outcome of transplanted grafts. These suggest that the strategies targeting these elements could yield more progress toward successful xenogeneic islet engraftment and survival.

Kidney allotransplantation is a life-saving operation with superior mortality and economic outcomes compared with dialysis. 1,2 In the United States, approximately 70% of kidney recipients are treated with depletional induction, typically rabbit antithymocyte globulin (RATG). Multiple clinical studies have shown that RATG reliably decreases the incidence of acute rejection. [3][4][5] As such, depletional induction with RATG is increasingly considered as a therapeutic approach for novel immunosuppressive regimens in preclinical investigation. Nonhuman primates such as rhesus monkeys are commonly used preclinically to test new immunosuppressants.Rabbit antithymocyte globulin is a polyclonal antibody preparation that is developed by immunizing large numbers of rabbits with thymocytes from another species. 6 It works by a variety of mechanisms including direct depletion of lymphocytes and interference

Thymic output and homeostatic mature cell proliferation both influence T cell repopulation following depletional induction, though the relative contribution of each and their association with recipient age have not been well studied. We investigated the repopulating T cell kinetics in kidney transplant recipients who underwent alemtuzumab induction followed by belatacept/rapamycin‐based immunosuppression over 36‐month posttransplantation. We focused specifically on the correlation between repopulating T cell subsets and the age of patients. Substantial homeostatic Ki67‐expressing T cell proliferation was seen posttransplantation. A repertoire enriched for naïve T (TNaïve) cells emerged posttransplantation. Analysis by generalized estimating equation linear models revealed a strong negative linear association between reconstituting TNaïve cells and advancing age. A relationship between age and persistence of effector memory cells was shown. We assessed thymic output and found an increase in the frequency of recent thymic emigrants (RTEs, CD4+CD31+) at 12‐month posttransplantation. Patients under 30 years of age showed significantly higher levels of CD4+CD31+ cells than patients over 55 years of age pre‐ and posttransplantation. IL‐7 and autologous mature dendritic cells (mDCs) induced CD57− cell proliferation. In contrast, mDCs, but not IL‐7, induced CD57+ cell proliferation. This study establishes the relationship between age and thymic output during T cell homeostatic repopulation after alemtuzumab induction. Trial Registration: ClinicalTrials.gov ‐ NCT00565773.