Effect of transplantation site and culture pretreatment on islet xenograft survival (rat to mouse) in experimental diabetes without immunosuppression of the host.

Recently, we reported on indefinite islet graft survival in allotransplantation (rat to rat). This was achievable without the use of any immunosuppression by performing transplantation of culture-pretreated (22 degrees C) islets of Langerhans under the renal capsule (r.c.) of chemically induced diabetic recipients. The aim of this study was to test this successful islet modulation technique in a xenogeneic animal model. Six groups of chemically induced diabetic, inbred, C57BL/6J mice received by transplantation either into the liver via the portal vein (i.po.) or under the renal capsule (r.c.) 300-350 either freshly or culture-pretreated (37 degrees C and 22 degrees C) Lewis rat islets without any immunosuppressive therapy. Histology was performed after rejection or post-transplant normoglycaemia (> 120 days) for evaluation of the graft. Transplantation of freshly isolated islets resulted in 75% graft rejection 17 days after transplantation. Using culture pretreatment at 37 degrees C, we noted 75% graft rejection 31 days after transplantation. In contrast, culture pretreatment at 22 degrees C resulted in a marked prolongation of xenograft survival, 75% graft rejection occurring 58 days after transplantation, and in two cases there was indefinite graft survival (> 120 days). Statistical analysis showed a significant prolongation of xenograft survival after culture pretreatment, with the most beneficial effect appearing after low-temperature culture at 22 degrees C (P < 0.05). Interestingly, xenograft survival was markedly prolonged only using the r.c. approach. Statistical comparison revealed a highly significant prolongation using the r.c. as transplantation site compared with i.po. (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)