Dose optimization of tacrolimus for improving survival time of PEGylated islets in a rat-to-mouse xenograft model

Abstract

Improvements in preventing pancreatic islet rejection are needed for successful treatment of type 1 diabetes. Our objective was to develop an optimized protocol combining modification of islets with polyethyleneglycol (PEG) chains and administration of tacrolimus (FK506, Prograf), an immunosuppressive drug for preventing rejection following transplantation. Freshly isolated islets were incubated with different concentrations (0.25, 1.00, 10.00, and 25.00%) of FITC-labeled mPEG-SCM (MW. 20 KDa) for various incubation times. 1% mPEG-SCM incubated with islets for 1 h is optimized surface coverage condition without cell toxicity. In addition, in order to optimize the concentration of tacrolimus (FK506, Prograf), different concentrations (0.1, 0.5 or 2.0 mg/kg) were injected into the diabetic mice following transplantation of PEGylated islets. The PEGylated islet survival time in mice injected daily with 0.1 mg/kg and 0.5 mg/kg of tacrolimus was significantly better than in the group without tacrolimus injection. The graft survival time in mice injected daily with 2.00 mg/kg of exhibited no prolonged survival time. Finally, immunohistochemical staining of left kidney containing PEGylated islets (injected with 0.1 mg/kg of tacrolimus) demonstrated strong staining for insulin, glucagon, and somatostatin but very weak CD20 staining was observed in the islet transplanted area. In conclusion, 1% mPEG-SCM incubated with islets for 1 h was the optimal condition for PEGylation without affecting the cell viability. A dose of tacrolimus between 0.1-0.5 mg/kg was highly effective for inhibiting immune cell activation. These results are promising for their application in developing a novel immunosuppressive protocol for successful pancreatic islet transplantation in the treatment of type 1 diabetes.