ULTRAVIOLET-LIGHT IRRADIATION REDUCES HUMAN ISLET IMMUNOGENICITY WITHOUT ALTERING ISLET FUNCTION

Allograft rejection is the major cause for failure in clinical islet transplantation for diabetic patients. A reduction of donor islet immunogenicity is potentially a useful approach for altering recipient's immune responses. Studies in animal models have shown the immunomodulatory properties of ultraviolet (UV)-B light that are beneficial for allograft survival. However, there is a narrow window between the doses required for immunomodulation and those toxic to beta-cells. In addition, this window Varies between one species to another. Our study was designed to determine, in vitro, the UV-B dose for human islets that effectively reduces immunogenicity and maintains islet viability and normal function. Islets were isolated from donor pancreas by collagenase digestion and density gradient centrifugation on Euro-Ficoll. Static incubation and perifusion tests were used to measure glucose-sti mulated insulin release. Viability was also assessed by histology and function of UV-irradiated islets transplanted under the renal capsule of athymic mice. The immunogenicity of UV-treated islets was determined in vitro with mixed islet lymphocyte culture using healthy human peripheral blood lymphocytes as responders. At a dose of 300 J/m(2). both functional assays detected no impairment of insulin release. At 500 J/m(2), a slight decrease of stimulated insulin release was observed only in the perifusion system. At the levels of 600 and 900 J/m(2), a clear alteration was observed in both basal and stimulated insulin release. Islets irradiated at 300 J/m(2) and transplanted into athymic mice stained strongly for insulin and responded to high glucose challenge in in vivo perfusion performed at two weeks. The immunogenicity of UV-irradiated islets was significantly decreased by 43 - 81% at 300 J/m(2) and 51 - 70% at 500 J/m(2). This effect was still present when tested as late as 9 days after irradiation, but only if islets were irradiated immediately after isolation. We conclude that UV-B irradiation at a dose of 300 J/m(2) can effectively reduce immunogenicity of human islets without adverse effects on beta-cell survival and function. This low dose UV-B irradiation may be a realistic treatment of human islets prior to transplantation.