Pancreatic Transdifferentiation in Porcine Liver Following Lentiviral Delivery of Human Furin-Cleavable Insulin

Type I diabetes mellitus (TID) results from the autoimmune destruction of the insulin-producing pancreatic beta-cells. Gene therapy is one strategy being actively explored to cure TID by affording non beta-cells the ability to secrete insulin in response to physiologic stimuli. In previous studies, we used a novel surgical technique to express furin-cleavable human insulin (INS-FUR) in the livers of streptozotocin (STZ)-diabetic Wistar rats and nonobese diabetic (NOD) mice with the use of the HMD lentiviral vector. Normoglycemia was observed for 500 and 150 days, respectively (experimental end points). Additionally, some endocrine transdifferentiation of the liver, with storage of insulin in granules, and expression of some beta-cell transcription factors (eg, Pdx1, Neurod1, Neurog3, Nkx2-2, Pax4) and pancreatic hormones in both studies. The aim of this study was to determine if this novel approach could induce liver to pancreatic transdifferentiation to reverse diabetes in pancreatectomized Westran pigs. Nine pigs were used in the study, however only one pig maintained normal fasting blood glucose levels for the period from 10 to 44 days (experimental end point). This animal was given 2.8 x 10(9) transducing units/kg of the lentiviral vector expressing INS-FUR. A normal intravenous glucose tolerance test was achieved at 30 days. Reverse-transcription polymerase chain reaction analysis of the liver tissue revealed expression of several beta-cell transcription factors, including the key factors, Pdx-1 and Neurod1, pancreatic hormones, glucagon, and somatostatin; however, endogenous pig insulin was not expressed. Triple immunofluorescence showed extensive insulin expression, as was previously observed in our studies with rodents. Additionally, a small amount of glucagon and somatostatin protein expression was seen. Collectively, these data indicate that pancreatic transdifferentiation of the liver tissue had occurred. Our data suggest that this regimen may ultimately be used clinically to cure TID, however more work is required to replicate the successful reversal of diabetes in increased numbers of pigs.