Abstract
We report the restoration of euglycaemia in chemically induced diabetic C57BL/6 mice and spontaneously diabetic Non Obese Diabetic (NOD) mice by intravenous systemic administration of a single-stranded adeno-associated virus (ssAAV2/8) codon optimised (co) vector encoding furin cleavable human proinsulin under a liver-specific promoter. There were no immunological barriers to efficacy of insulin gene therapy in chemically induced C57BL/6 mice, which enjoyed long-lasting correction of hyperglycaemia after therapy, up to 250 days. Euglycaemia was also restored in spontaneously diabetic NOD mice, although these mice required a 7–10-fold higher dose of vector to achieve similar efficacy as the C57BL/6 mice and the immunodeficient NODscid mice. We detected CD8+ T cell reactivity to insulin and mild inflammatory infiltration in the livers of gene therapy recipient NOD mice, neither of which were observed in the treated C57BL/6 mice. Efficacy of the gene therapy in NOD mice was partially improved by targeting the immune system with anti-CD4 antibody treatment, while transfer of NOD mouse AAV2/8-reactive serum to recipients prevented successful restoration of euglycaemia in AAV2/8-HLP-hINSco-treated NODscid mice. Our data indicate that both immune cells and antibodies form a barrier to successful restoration of euglycaemia in autoimmune diabetic recipient mice with insulin gene therapy, but that this barrier can be overcome by increasing the dose of vector and by suppressing immune responses.
Highlights
The beta cells of the pancreas produce insulin, which in turn induces upregulation of the glucose transporter GLUT4 in many cell types, allowing efficient glucose uptake
When the beta cells are destroyed or incapacitated, as happens in type 1 diabetes, insulin is no longer produced in sufficient amounts and the tissues are unable to metabolise glucose despite it being abundant in the circulation
Male C57BL/6 mice were injected with streptozotocin to destroy the beta cells, and female Non Obese Diabetic (NOD) mice were monitored for diabetes and selected for treatment once consecutive tests proved them to be irreversibly diabetic
Summary
The beta cells of the pancreas produce insulin, which in turn induces upregulation of the glucose transporter GLUT4 in many cell types, allowing efficient glucose uptake. When the beta cells are destroyed or incapacitated, as happens in type 1 diabetes, insulin is no longer produced in sufficient amounts and the tissues are unable to metabolise glucose despite it being abundant in the circulation. This disease was deadly until the 1920s when the insulin protein was identified [1], and administration of exogenous insulin has remained the available therapy for the disease since this discovery. We have demonstrated that the vector used for haemophilia therapy can be successfully modified to express insulin, and can restore euglycaemia in immunocompromised chemically induced
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