Objective: We evaluated the effect of transplanted cell type, time, and region of the heart on transgene expression to determine the potential of combined gene and cell delivery for myocardial repair.
Methods: Lewis rats underwent myocardial cryoinjury 3 weeks before transplantation with heart cells (a mixed culture of cardiomyocytes, smooth muscle cells, endothelial cells and fibroblasts, n = 13), vascular endothelial growth factor-transfected heart cells (n = 13), skeletal myoblasts (n = 13), vascular endothelial growth factor-transfected skeletal myoblasts (n = 13), or medium (control, n = 12). Vascular endothelial growth factor expression in the scar, border zone, and normal myocardium was evaluated at 3 days and at 1, 2, and 4 weeks by means of quantitative polymerase chain reaction. Transplanted cells and vascular endothelial growth factor protein were identified immunohistologically on myocardial sections.
Results: Vascular endothelial growth factor levels were very low in control scars but increased transiently after medium injection. Transplantation with heart cells and skeletal myoblasts significantly increased vascular endothelial growth factor expression in the scar and border zone. Transplantation of vascular endothelial growth factor-transfected heart cells and vascular endothelial growth factor-transfected skeletal myoblasts further augmented vascular endothelial growth factor expression, resulting in 4- to 5-fold greater expression of vascular endothelial growth factor in the scar at 1 week. Peak vascular endothelial growth factor expression was greater and earlier in vascular endothelial growth factor-transfected heart cells than in vascular endothelial growth factor-transfected skeletal myoblasts. Vascular endothelial growth factor was primarily expressed by the transplanted cells. Some of the transplanted heart cells and vascular endothelial growth factor-transfected heart cells were identified in the endothelial layer of blood vessels in the scar.
Conclusions: Transplantation of heart cells and skeletal myoblasts induces vascular endothelial growth factor expression in myocardial scars and is greatly augmented by prior transfection with a vascular endothelial growth factor transgene. Vascular endothelial growth factor expression is limited to the scar and border zone for 4 weeks. Both heart cells and skeletal myoblasts may be excellent delivery vehicles for cell-based myocardial gene therapy.