Control of IBMIR in Neonatal Porcine Islet Xenotransplantation in Baboons

Abstract

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.The instant blood-mediated inflammatory reaction (IBMIR) is a major obstacle to the engraftment of intraportal pig islet xenografts in primates. Higher expression of the galactose-a1,3-galactose (aGal) xenoantigen on neonatal islet cell clusters (NICC) than on adult pig islets may provoke a stronger reaction, but this has not been tested in the baboon model. Here, we report that WT pig NICC xenografts triggered profound IBMIR in baboons, with intravascular clotting and graft destruction occurring within hours, which was not prevented by anti-thrombin treatment. In contrast, IBMIR was minimal when recipients were immunosuppressed with a clinically relevant protocol and transplanted with NICC from aGal-deficient pigs transgenic for the human complement regulators CD55 and CD59. These genetically modified (GM) NICC were less susceptible to humoral injury in vitro than WT NICC, inducing significantly less complement activation and thrombin generation when incubated with baboon platelet-poor plasma. Recipients of GM NICC developed a variable anti-pig antibody response, and examination of the grafts 1 month after transplant revealed significant cell-mediated rejection, although scattered insulin-positive cells were still present. Our results indicate that IBMIR can be attenuated in this model, but long-term graft survival may require more effective immunosuppression or further donor genetic modification.

Current status of islet xenotransplantation

“…Indeed, when compared to wild type pig islet recipients, improved graft survival has been demonstrated using hCD46 transgenic pig islets [10] and α1,3-galactosyl transferase-gene knockout (GTKO) pig islets [11]. Others have also seen variable survival gains using multiple genetically engineered pigs in both cynomolgus monkeys [12] and baboons [13].…”

Gene Editing, Gene Therapy, and Cell Xenotransplantation: Cell Transplantation Across Species

“…hCD46 expression in porcine islets increased graft survival to more than 3 months compared to only 46 days in the case of wild-type islets transplanted to immunosuppressed macaques [34]. Transgenic neonatal porcine islets expressing CD55 and CD59 on a GGTA1-KO background were less susceptible to humoral injury in vitro and did not cause intraportal thrombosis in baboons but suffered from cell-mediated rejection [35]. The impact of tissue factor knockdown in neonatal porcine islets on IBMIR was demonstrated in vitro by treating islets with tissue factor-specific antisense RNA and exposing them to human blood.…”

“…Encapsulated islets implanted in poorly vascularized sites might escape this reaction at least in the early stages of engraftment but IBMIR causes a quick loss of up to 60% of islets implanted in the portal vein [32]. Transgenic expression of human CD46 [33•, 34], CD55, and CD59 [35] and knockdown of tissue factor gene [36] were shown to avoid this early damage to the graft by decreasing IBMIR both in vivo and in vitro. hCD46 expression in porcine islets increased graft survival to more than 3 months compared to only 46 days in the case of wild-type islets transplanted to immunosuppressed macaques [34].…”

Current Concepts of Using Pigs as a Source for Beta-Cell Replacement Therapy of Type 1 Diabetes

“…In STZ-induced diabetic rhesus monkeys with immunosuppression, GTKO was shown to be advantageous for survival and engraftment of NICCs, which express high levels of αGal [58]. In combination with transgenic expression of hCD55 and hCD59, GTKO NICCs clearly attenuated IBMIR after intraportal transplantation into nondiabetic baboons [59]. Data from an elegant "dual islet transplant model," which allows comparison of different islet preparations within the same recipient, showed that in the absence of immunosuppression, a robust inflammatory response may precede IBMIR, masking the beneficial effect of GTKO observed in previous studies [60•].…”