Successful Suppression of the Early Rejection of Pig Islets in Monkeys

Abstract

Primary nonfunction (PNF) is seen very frequently after xenogeneic transplantation of islets of Langerhans. In a pig-to-rat model we recently observed that no PNF occurs when the islets are kept in culture at 37 degrees C for 1-2 weeks prior to transplantation. In order to investigate the rejection mechanisms in a preclinical model, we transplanted cultured porcine islets under the capsule of both kidneys in four cynomolgous monkeys. Islets were isolated from adult sows by means of digestion with Liberase in University of Wisconsin solution (UWS). The digest was purified by a density gradient of OptiPrep in UWS. Highly purified (>95%) islets were cultured 1-2 weeks in RPMI. All monkeys showed significant titers of preformed anti-pig antibodies. The immunosuppression of the monkeys consisted of cyclophosphamide (Cy) (2 days), cyclosporin A (CsA), and prednisolone. Anticipating a fast rejection we carried out nephrectomies at different time points within 2 weeks after transplantation. Following unilateral nephrectomy, well-preserved islets with no signs of rejection were observed between 3 and 7 days posttransplant. Later, between days 11 and 15 posttransplant, histology in the first three animals demonstrated no islets. In the fourth monkey histology on day 11 showed islets with excellent morphology and some small focal infiltrates. The highest CsA blood levels (around 1000 ng/ml) were found in animals with the best graft survival. We conclude that cultured porcine islets can be grafted without hyperacute rejection in monkeys with preformed anti-pig antibodies. In the presence of high levels of CsA only marginal signs of a cellular immune response were observed 11 days after transplantation.

Current status of xenotransplantation research and the strategies for preventing xenograft rejection

“…GCs have been used as first-line medication during the induction and maintenance phases after transplantation to prevent acute rejection. In pig-to-primate xenotransplantation, immunosuppressive GC regimens have also been used in most trials ( 142 – 144 ). In an islet xenotransplantation study, all monkeys experienced a normalization of all diabetic and glycemic parameters within four days of GCs administration, suggesting a reversal of diabetes mellitus ( 145 ).…”

“…In baboon-to-monkey liver xenotransplantation, two monkeys survived for 91 and 1076 days, respectively, with cyclosporin administered after transplantation, for example, at doses of 3 to 8 mg/kg/day ( 139 ), or 20 mg/kg intravenously two hour before transplantation followed by oral administration on next three days ( 143 ). In a cardiac xenograft transplantation, the highest cyclosporin blood levels (around 1000 ng/ml) correlated with the highest graft survival rate of the host animals ( 142 ).…”

Pancreatic islet xenotransplantation

“…There are data to suggest that islet xenograft rejection in primates is far more robust, even when the islets avoid direct contact with the circulation [40]. In cynomolgous monkeys, porcine islets survived to 53 days when transplanted under the renal capsule and rejection was suppressed with antihuman thymocyte globulin (ATG), anti‐IL‐2R mAb, cyclosporine and steroids [41, 42]. Interestingly, when islets were transplanted intraportally in the same model, none could be detected, again supporting the conclusion that non‐T‐cell mediated mechanisms are involved in their destruction.…”

Extrahepatic transplant sites for islet xenotransplantation

“…Although islet xenografts can survive for a long time in rodents, it is much more difficult to achieve this in primates, a necessary precursor to clinical trials. In this regard, initial reports demonstrated limited survival after the infusion of pig islets in non‐diabetic primates [6–8]. However, remarkable results were more recently obtained at the University of Minnesota and Emory/Edmonton in diabetic primates [9,10].…”