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OBJECTIVE: Specific immune tolerance achieved by induction of lymphocyte chimerism could reduce the need for immunosuppressive therapy in pancreatic islet transplantation. The aim of the experiment was to assess the effect of pre-treatment with donor specific bone marrow on the function of allogeneic islets under the conditions of a short-term immunosuppression. METHODS: Male Lewis-Brown Norway and female Brown Norway rats were used as donors and recipients, respectively. In all recipients diabetes was induced by streptozotocin. In Group 1, 5 animals were treated only by islet transplantation. In Group 2, 7 rats underwent islet transplantation after previous 45-day therapy with tacrolimus 1 mg/kg and hydrocortisone 2 mg/kg, which was stopped 6 days after islet transplantation. Recipients in Group 3 (n = 16) were treated as Group 2 (n = 7) and, in addition, underwent transplantation of 10(8) bone marrow cells 10 days after initiation of immunosuppressive therapy. RESULTS: In Group 1, islets were rejected after a median survival time of 11 days. In Groups 2 and 3, islet function has been demonstrated for more than 70 days in all animals. CONCLUSIONS: Short-term immunosuppressive therapy prevented islet rejection for at least 70 days. Longer follow-up period is needed to show whether peripheral microchimerism induced by bone marrow transplantation will further improve islet survival in non-immunosuppressed recipients.

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Cryopreservation is the only available technique for long-term storage of pancreatic islets. The freezing/thawing protocol may cause considerable loss of viable islet tissue and impair its function in vivo. The aim of this study was to investigate glucose and insulin levels after transplantation of fresh and cryo/thawed rat islets. Rat pancreatic islets were isolated following intraductal collagenase injection and Ficoll gradient purification. After isolation, islets were cultured for 24 h and then either transplanted or frozen after stepwise addition of DMSO according to Rajotte et al. and stored in liquid nitrogen. After rapid thawing islets were stepwise transferred into RPMI medium and cultured for another 24 h. The recipients were athymic mice with streptozotocine-induced diabetes. Two hundred fresh (n=13) or cryo/thawed (n=15) islets were transplanted beneath the renal capsule. Glucose levels were measured for 14 days and blood samples for insulin determination were obtained 15 min after i.p. glucagon (10 mg/kg) administration on day 14. Glucose levels were normalized (<9 mmol/l) in all recipients within 3 days since transplantation. On day 14, mean fasting values+/-SE in fresh and cryo/thawed islet groups were 4.0+/-0.6 and 4.4+/-0.4 mmol/l, respectively (P>0.05). Fasting insulin levels were higher in the cryo/thaw than in the fresh islet group (1.67+/-0.33 vs 0.57+/-0.13 ng/ml; P<0.01). Post-glucagon levels did not differ significantly (1.45+/-0.24 vs 0.86+/-0.24 ng/ml; P=0.06). While glucagon significantly increased insulin levels (P<0.01) in the fresh islet group, no change in insulin levels was observed (P>0.05) in the cryo/thaw group. Immunohistochemical staining demonstrated fragmentation of viable islet tissue which was more apparent in the cryo/thaw group. We conclude that in a short-term study cryo/thawed rat islets produce higher insulin levels than fresh islets transplanted into nude mice. This may be due to better islet survival or loss of feed-back regulation.

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BACKGROUND: Transplantation of isolated islets of Langerhans is a perspective method of treating type 1 diabetes. The first prerequisite for its implementation is to obtain sufficient amounts of vital islets. The objective to the authors' experiments was to introduce a method of massive isolation of islets of Langerhans from dogs which would serve as a model pro obtaining islets of Langerhans from humans and would permit to use them in future in clinical practice. METHODS AND RESULTS: After excision of the dog pancreas the authors injected into the ducts a 1% collagenase solution and the tissue was deposited in a specially developed semi-automatic isolation system which consisted of a vibrating isolation chamber in which an isolation solution with controlled temperature circulated. As soon as the islets started to be released, the system was cooled and the disintegrated tissue was collected. The islets were separated from the acinar mass by centrifuging in a ficoll mass gradient. The islet function was tested by transplantation to athymic diabetic mice. A total of 15 isolations of dog islets was performed, incl. 5 which were evaluated quantitatively. In a similar way twice isolation from a human cadaverous pancreas was implemented. On average 6336 +/- 745 (+/-SD) purified dog islets were obtained. Their function was tested by normalization of the blood sugar after transplantation to diabetic mice. The authors obtained also vital highly purified human islets. CONCLUSIONS: The authors developed a method of isolation of dog and human islets of Langerhans which makes it possible to obtain sufficient amounts of vital islet tissue which could be used for transplantation. A further task will be to standardize the process and adjust it to hygienic norms essential for clinical use.

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Glucose tolerance, insulin secretion and in vitro insulin action were examined in streptozotocin-induced diabetic rats following pancreatic islet allotransplantation treated with combination of oral cyclosporine A (10 mg/kg) and hydrocortisone (1.5 mg/kg) intramuscularly. 1400 pure islets from multiple donors were implanted either into the portal vein (n = 10) or under the renal capsule (n = 11). Ten sham-operated non-diabetic animals receiving the same immunosuppressive therapy, 8 healthy animals without any treatment and 10 diabetic animals without immunosuppression following islet transplantation were used as controls. In all transplanted animals blood glucose was normalized by day 3 after transplantation with lower levels in those transplanted intraportally (p < 0.05). Non-immunosuppressed animals rejected the graft after 6.5 +/- 1.2 days after transplantation, immunosuppressed animals in both groups remained normoglycaemic till the end of the experiment on day 28. Oral glucose tolerance tests and insulin levels on days 10 and 28 improved dramatically. No differences in glucose and insulin levels between intraportal and subcapsular groups were found. Post-load glucose levels in immunosuppressed non-transplanted animals were higher on day 28 than before treatment and were also higher than in the healthy non-treated group (p < 0.05). In vitro insulin action determined by the incorporation of labelled glucose into adipose tissue was impaired only in animals in which islets were transplanted into the liver (p < 0.05 vs other groups). In conclusion, therapy with cyclosporine A and hydrocortisone prevents allogeneic islet rejection in rats during a short-term experiment. Although glucose tolerance is not completely normalized following transplantation, slight impairment is also demonstrable in healthy animals on the same drug therapy.

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