Successful suppression of the early rejection of pig islets in monkeys

Primary nonfunction (PNF) is seen very frequently after xenogeneic transpla ntation 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 degreesC fur 1-2 weeks prior to transplantation. In order to investigate the rejection m echanisms in a preclinical model, we transplanted cultured porcine islets u nder the capsule of both kidneys in four cynomolgous monkeys. Islets were i solated from adult sows by means of digestion with Liberase in University o f Wisconsin solution (UWS). The digest was purified by a density gradient o f OptiPrep in UWS. Highly purified (>95%) islets were cultured 1-2 weeks in RPMI. All monkeys showed significant titers of preformed anti-pig antibodi es. The immunosuppression of the monkeys consisted of cyclophosphamide (Cy) (2 days), cyclosporin A (CsA), and prednisolone. Anticipating a fast rejec tion we carried out nephrectomies at different time points within 2 weeks a fter transplantation. Following unilateral nephrectomy, well-preserved isle ts with no signs of rejection were observed between 3 and 7 days posttransp lant. Later, between days ii and 15 posttransplant, histology in the first three animals demonstrated no islets. In the fourth monkey histology on day ii showed islets with excellent morphology and some small focal infiltrate s. The highest CsA blood levels (around 1000 ng/ml) were found in animals w ith the best graft survival. We conclude that cultured porcine islets can b e grafted without hyperacute rejection in monkeys with preformed anti-pig a ntibodies. In the presence of high levels of CsA only marginal signs of a c ellular immune response were observed 11 days after transplantation.