Resolution of Neurotoxicity and β-Cell Toxicity in an Islet Transplant Recipient following Substitution of Tacrolimus with MMF

Calcineurin inhibitors such as tacrolimus have well-recognized efficacy in organ transplantation but side effects of nephrotoxicity, neurotoxicity, and beta-cell toxicity that can be particularly detrimental in islet transplantation. Neuro- and nephrotoxicity have been demonstrated in multiple islet transplant recipients despite the relatively low serum maintenance levels typically used (3-5 ng/ml). We describe a single patient in whom symptoms and signs of neurotoxicity necessitated substitution of tacrolimus with mycophenolate mofetil (MMF), which resulted in complete symptom resolution over the subsequent 9 months. Concomitantly noted were an almost immediate improvement in glycemic control and an improved response to stimulation testing, suggesting remission of tacrolimus-induced beta-cell toxicity and insulin resistance. At 18 months post-"switch," 30 months posttransplant, the patient remains insulin independent with good glycemic control. The goal to remove calcineurin inhibitors from regimens of islet transplantation is a worthy one.