Pancreatic islet transplantation. Induction of graft acceptance by ultraviolet irradiation of donor tissue.

The effect of ultraviolet (UV) irradiation on the immunogenicity of rat pancreatic islets was examined in allograft and xenograft models. Direct UV irradiation (900 J/m2) of Lewis islets, isolated and hand-picked, does not alter pancreatic islet endocrine function in isograft experiments and results in indefinite islet allograft survival in streptozocin diabetic ACI rats without chronic immunosuppression. Direct UV irradiation, at an appropriate dose, also leads to indefinite islet xenograft survival of Lewis islets in B10-BR diabetic mice and prolonged survival of rat islets in Balb/C mice. When direct UV irradiation of islet allografts did not result in indefinite islet allograft prolongation [Wistar/Furth (W/F) to diabetic Lewis], the addition of brief peritransplant immunosuppression with cyclosporine (days 0, +1, and +2) resulted in permanent acceptance of islet allografts, a result not achieved by cyclosporine alone. The effectiveness of UV irradiation in abrogating islet allograft rejection in several experimental models is supported by in vitro studies showing that UV irradiation of stimulator cells, peripheral blood lymphocytes, splenocytes, and isolated rat dendritic cells abolishes any significant stimulation by such cells of totally histoincompatible thoracic duct responder lymphocytes. In vitro nonreactivity of mixed lymphocyte culture (MLC) with UV-irradiated stimulator cells and in vivo permanent allograft acceptance are reversed by the addition of a small number of untreated donor-type dendritic cells to either the MLC or the recipient bearing the permanent graft. The authors suggest that the primary effect of UV irradiation on immune alteration of islet allografts and xenografts is due to induction of a major metabolic change in the dendritic cells in the graft. This then leads to defective antigen presentation and results in either permanent or prolonged allograft and xenograft acceptance, depending on the degree of MLC stimulation between the islet donor and the diabetic recipient.