Effect of the Diabetic State on Islet Engraftment and Function in a Large Animal Model of Islet-Kidney Transplantation.

In islet transplantation, in addition to immunologic and ischemic factors, the diabetic/hyperglycemic state of the recipient has been proposed, although not yet validated, as a possible cause of islet toxicity, contributing to islet loss during the engraftment period. Using a miniature swine model of islet transplantation, we have now assessed the effect of a persistent state of hyperglycemia on islet engraftment and subsequent function. An islet-kidney (IK) model previously described by our laboratory was utilized. Three experimental donor animals underwent total pancreatectomy and autologous islet transplantation underneath the renal capsule to prepare an IK at a load of ≤1,000 islet equivalents (IE)/kg donor weight, leading to a chronic diabetic state during the engraftment period (fasting blood glucose >250 mg/dL). Three control donor animals underwent partial pancreatectomy (sufficient to maintain normoglycemia during islet engraftment period) and IK preparation. As in vivo functional readout for islet engraftment, the IKs were transplanted across an immunologic minor or class I mismatch barrier into diabetic, nephrectomized recipients at an islet load of ∼4,500 IE/kg recipient weight. A 12-d course of cyclosporine was administered for tolerance induction. All experimental donors became diabetic and showed signs of end organ injury, while control donors maintained normoglycemia. All recipients of IK from both experimental and control donors achieved glycemic control over long-term follow-up, with reversal of diabetic nephropathy and with similar glucose tolerance tests. In this preclinical, large animal model, neither islet engraftment nor subsequent long-term islet function after transplantation appear to be affected by the diabetic state.

Assessing the effect of immunosuppression on engraftment of pancreatic islets.

BACKGROUND: In addition to ischemia and immunologic factors, immunosuppressive drugs have been suggested as a possible contributing factor to the loss of functional islets after allogeneic islet cell transplantation. Using our previously described islet-kidney (IK) transplantation model in miniature swine, we studied whether an islet-toxic triple-drug immunosuppressive regimen (cyclosporine+azathioprine+prednisone) affects the islet engraftment process and thus long-term islet function. METHODS: Donor animals underwent partial pancreatectomy, autologous islet preparation, and injection of these islets under the autologous kidney capsule to prepare an IK. Experimental animals received daily triple-drug immunosuppression during the islet engraftment period. Control animals did not receive any immunosuppression during this period. Four to 8 weeks later, these engrafted IK were transplanted across a minor histocompatibility mismatched barrier into pancreatectomized, nephrectomized recipient animals at an islet dose of approximately 4500 islet equivalents/kg recipient weight. Cyclosporine was administered for 12 days to the recipients to induce tolerance of the IK grafts and the animals were followed long-term. RESULTS: Diabetes was corrected by IK transplantation in all pancreatectomized recipients on both the control arm (n=3) and the experimental arm (n=4) of the study and all animals showed normal glucose regulation over the follow-up period. Intravenous glucose tolerance tests performed at 1, 2, and 3 or more months after IK transplantation showed essentially equivalent glycemic control in both control and experimental animals. CONCLUSION: In this preclinical in vivo large animal model of islet transplantation, the effect of triple-drug immunosuppression on islet function does not negatively affect islet engraftment as assessed by the long-term function of engrafted islets.