Vascular endothelial growth factor gene delivery for revascularization in transplanted human islets

Islet transplantation is limited by islet graft failure because of poor revascularization, host immune rejection, and nonspecific inflammatory response. Human vascular endothelial growth factor (hVEGF) gene delivery is likely to promote islet revascularization and survival.

We evaluated gene expression from a bicistronic plasmid encoding hVEGF and enhanced green fluorescent protein (EGFP) (pCMS-EGFP-hVEGF). Glucose responsiveness of islets was evaluated both in vitro and in vivo, and revascularization in islet graft was evaluated by immunohistochemistry.

After transfection, hVEGF and EGFP expression levels were comparable with original monocistronic plasmids in Jurkat cells but higher and prolonged hVEGF expression in islets transfected with the bicistronic plasmid was observed, possibly as the result of differences in promoter strength and hypoxia response. The 3:1 w/w complexes showed little toxicity to islets at a dose of 5 microg DNA per 2000 islets. On glucose challenge, insulin release from transfected islets as well as secretion from islets after transplantation under the mouse kidney capsules in response to glucose stimulation, increased with time. Immunohistochemical staining of transplanted islets using mouse anti-human insulin, mouse anti-human von Willebrand factor, and rat anti-mouse CD31 antibodies suggests that islets are functional and there is new blood vessel formation.

These findings suggest that transient hVEGF gene expression by the islets may promote islet revascularization and prolong islet survival after transplantation.