Baculovirus-mediated vascular endothelial growth factor-DΔNΔC gene transfer induces angiogenesis in rabbit skeletal muscle

Background: Occluded arteries and ischemic tissues cannot always be treated by angioplasty, stenting or by-pass-surgery. Under such circumstances, viral gene therapy may be useful in inducing increased blood supply to ischemic area. There is evidence of improved blood flow in ischemic skeletal muscle and myocardium in both animal and human studies using adenoviral vascular endothelial growth factor (VEGF) gene therapy. However, the expression is transient and repeated gene transfers with the same vector are inefficient due to immune responses. Methods: Different baculoviral vectors pseudotyped with or without vesicular stomatitis virus glycoprotein (VSV-G) and/or carrying woodchuck hepatitis virus post-transcriptional regulatory element (Wpre) were tested both in vitro and in vivo. VEGF-D^ΔNΔC was used as therapeutic transgene and lacZ as a control. In vivo efficacy was evaluated as capillary enlargement and transgene expression in New Zealand White (NZW) rabbit skeletal muscle. Results: A statistically significant capillary enlargement was detected 6days after gene transfer in transduced areas compared to the control gene transfers with baculovirus and adenovirus encoding β-galactosidase (lacZ). Substantially improved gene transfer efficiency was achieved with a modified baculovirus pseudotyped with VSV-G and carrying Wpre. Dose escalation experiments revealed that either too large volume or too many virus particles caused inflammation and necrosis in the target tissue, whereas 10⁹ plaque forming units injected in multiple aliquots resulted in transgene expression with only mild immune reactions. Conclusions: We show the first evidence of biologically significant baculoviral gene transfer in skeletal muscle of NZW rabbits using VEGF-D^ΔNΔC as a therapeutic transgene.