BACKGROUND: K-cells function as targets for insulin gene therapy. In a previous study, we constructed EBV-based plasmids expressing rat preproinsulin controlled by glucose-dependent insulinotropic polypeptide promoters. In the present study, we attempted to correct hyperglycemia in vivo using genetically engineered K-cells in a mouse model of type 1 diabetes. METHODS: K-cells expressing insulin were transplanted under the kidney capsules of STZ-induced diabetic mice. The blood glucose levels and body weights of the experimental animals were measured daily. After four weeks, the mice were injected intra-peritoneally with 2 g/kg glucose following a 6 hr fast. Blood glucose levels were measured immediately following glucose injections. All animals were sacrificed at the end of the glucose tolerance study, and pancreas and graft-bearing kidney tissue samples were stained with antibodies against insulin, glucagon, and C-peptide. RESULTS: The body weights of K-cell-transplanted diabetic mice increased after transplantation, whereas those of untreated diabetic control mice continued to decline. The blood glucose levels of K-cell-transplanted diabetic mice decreased gradually during the two weeks following transplantation. After intra-peritoneal injection of glucose into K-cell-transplanted diabetic mice, blood glucose levels increased at 30 minutes, and were restored to the normal range between 60 and 90 minutes, while untreated control diabetic mice continued to experience hyperglycemia. Kidney capsules containing transplanted K-cells were removed, and sections were stained with anti-insulin antibodies. We detected insulin-positive cells in the kidney capsules of K-cell-transplanted diabetic mice, but not in untreated control mice. CONCLUSION: We detected glucose-dependent insulin secretion in genetically engineered K-cells in a mouse model of type 1 diabetes. Our results suggest that genetically modified insulin producing K-cells may act as surrogate beta-cells to effectively treat type 1 diabetes.