Abstract Type 1 diabetes mellitus (T1DM) is caused by the autoimmune destruction of the insulin-producing β cells of the pancreas. Insulin gene therapy is a promising strategy capable of overcoming the limitations of current treatments, but to become a viable option, it must provide long-term, glucose-responsive control of insulin production. We have previously achieved glucose-responsivity by incorporating glucose-inducible response elements (GIREs) upstream of a liver-specific insulin expression cassette (3xGIRE.ALB.Ins1-2xfur). In this study, 3xGIRE.ALB.Ins1-2xfur was delivered into streptozotocin-induced diabetic rats using lentivirus, resulting in remission of diabetic hyperglycemia for at least 482 days while restoring rate of weight gain in a dose-dependent fashion. Insulin immunostaining showed abundant insulin production in the liver, and qPCR showed 13-20 lentiviral integrations per cell in the liver of rats treated with high dose lentivirus. Negligible integration was found in the pancreas, kidney, spleen and muscle of LV-treated rats, confirming liver specificity. In vitro, LV.3xGIRE.ALB.Ins1-2xfur produced a 4.5-fold increase in insulin production in high glucose conditions, and in vivo, a 1.7-fold increase in insulin levels was found during an intraperitoneal glucose tolerance test. Unfortunately, limitations in large-scale lentivirus production and use of a tissue-specific promoter prevented treatment of more than one rat per batch of lentivirus. Thus, two of the LV-treated diabetic rats were undertreated, while another two rats were over treated, becoming hypoglycemic in the fed state. Nonetheless, we have established the framework for a long-term, glucose-responsive treatment for T1DM from which further improvements can be made.
Keywords: gene therapy; insulin; type 1 diabetes mellitus; lentivirus; transdifferentiation; long-term glucose control