Successful islet transplantation has been possible in experimental animals in contrast to humans. One difference between animal models of diabetes and human islet transplantation is the presence of advanced chronic complications in humans. Even longer-term follow-up of islet transplantation in humans according to the Edmonton protocol suggests that advanced chronic complications may adversely affect allograft survival with the glucocorticoid-free immunosuppressive regimen as well. We developed a rat model of chronic complications of diabetes and compared islet allograft survival in rats with advanced chronic complications to age-matched control rats with acute onset diabetes. Islets were transplanted at either the renal supcapsular, intrahepatic, or intramuscular location. The survival of islet allografts in rats with chronic complications was decreased at all sites compared with the age-matched controls. The best survival in the rats with advanced chronic complications occurred at the renal subcapsular site. Blood sugar measurements indicated impaired glucose tolerance in most of the rats with chronic complications and surviving renal subcapsular islet allograft. Histological and gross examination of the surviving renal subcapsular islet allografts indicated disordered angiogenesis in the rats with chronic complications. Rats with successful intrahepatic islet allografts and the respective age-matched controls had comparable blood sugars. Survival of islet allografts at the intramuscular site was poor in rats with chronic complications or acute onset diabetes. We conclude that the structural or metabolic abnormalities associated with chronic poor control of diabetes impair islet allograft survival and function. This should be considered as a possible explanation for failure of islet allograft survival in human islet transplantation.
882 The CD40-CD154 pathway plays a critical role in T cell activation. Blockade of the T cell co-stimulatory molecule CD154 alone is reported to be effective in producing long-term allograft survival in non-human primates while additional treatments are required to produce the same effect in the mouse. The recent availability of anti-rat CD154 mAb [(C.D. Benjamin et al, manuscript in preparation)] has allowed for testing in the rat model for comparison. The goal of this project was to characterize the immunosuppressive effects of anti-CD154 on the rate of rejection of islet allografts in the high responder rat strain combination, DA (RT1aa) to DR-BB (RT1uu). DR-BB rats were made diabetic by an injection of streptozotocin (65 mg/kg). Reversal of diabetes was accomplished by transplanting 1200 (islet equivalency) DA islets to the renal subcapsular site. Each treatment was given IV peri-transplant (days −1, 0, +1), with weekly maintenance dosing post-transplant through week 5 and then stopped. Blood glucose levels were monitored and a return to hyperglycemia (3 consecutive days of blood glucose levels > 250 mg/dl) was an indication of rejection. All control animals promptly rejected their DA islets by day 8 post-transplant. Eight of 9 anti-CD154 treated recipients have indefinite allograft survival and currently are 95 days post-transplant. Recipients bearing long-term allografts showed a significant decrease in T cell proliferation compared to naive rats in response to donor antigen in a MLR. We conclude from these data that anti-CD154 mAb is effective as a single agent in promoting long-term islet allograft survival in the rat.
Islet transplantation for the treatment of autoimmune diabetes is more difficult because of the additional barrier presented by the autoimmunity. We tested the ability of hamster anti-rat CD154 to prevent recurrence of diabetes in renal subcapsular islet isografts in DR-BB (RT1uu) rats with established autoimmune diabetes. Experimental animals with established diabetes received intravenous injections of 15 mg/kg anti-CD154 on a specified schedule starting 2 days before renal subcapsular transplantation of an islet isograft. Control animals received either saline or hamster IgG. Plasma glucose levels >250 mg/dl over 3 days were used to indicate the recurrence of diabetes. Rats that received saline (n = 5) or control antibody (n = 3) had a recurrence of diabetes 6-11 days after transplantation. Histological examination of islet isografts from these rats showed complete destruction of the insulin-producing portion of the isograft with residual cells positive for glucagon. Recipient rats that received anti-CD154 at the 15-mg/kg dosage (n = 6) did not have a recurrence of diabetes for 308-461 days after transplantation. Islet isografts removed from the rats showed low levels of insulin immunoreactivity, high levels of insulin mRNA, and focal infiltration with lymphocytes but no evidence of islet destruction. Mean peak antibody concentration was 266 microg/ml and returned to undetectable levels by 67-88 days after transplantation. Rats that received anti-CD154 starting at 4-7 days after transplantation had a recurrence of diabetes within 11 days of the isotransplantation. Therefore, anti-CD154 as the sole immunomodulator prevented the recurrence of diabetes in islet isografts in rats with established autoimmune diabetes. This suggests that CD40/CD154 blockade is effective in preventing the insulitis or the effector phase of autoimmune diabetes.
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