Xenotransplantation of adult porcine islets in diabetic mice. A study of UVB irradiation, cryopreservation and immunosuppression on graft survival time.

The major obstacle for successful xenotransplantation of islets to large animals and human diabetics is the host rejection. To address the rejection problem, we studied the efficacy of UV-B irradiation, cryopreservation and immunosuppression on the in vivo functional time and immunogenicity of adult porcine islets (PI) in outbred CD1 mice. Exposure of PI to UV-B irradiation between 300-1800J/M2 did not affect the cellular viability as assessed by fluorescein diacetate or their daily insulin secretion in vitro. Fresh PI normalized the blood glucose (BG) of diabetic CD1 mice for 3.1+/-0.6 (n = 8, mean+/-SEM) days. Islets treated with 600J/M2 UV-B irradiation or cryopreservation had similar graft functional times to fresh islets upon transplantation in diabetic CD1 mice. Immunosuppression with cyclosporin A (CsA), antilymphocyte serum (ALS) and FK506 prolonged the functional time of fresh pig islets to 7.9+/-0.9 (n = 9), 6.2+/-1.3 (n = 5) and 24.2+/-10.4 (n = 12) days, respectively. However, additional pretransplant treatment with either UV-B irradiation or cryopreservation did not further increase the functional time of pig islets in mice immunosuppressed with CsA. Furthermore, there was no apparent difference in the frequency of appearance of cytotoxic antibodies and antibody titers in the recipients of UV-B irradiated or cryopreserved pig islet compared with non-treated islets. The UV-B irradiation and cryopreservation of PI before transplantation with the present protocols did not appear to have significant effect on the islet immunogenicity when assessed by in vivo survival duration and anti-donor antibody titer production.