Gene Transfer in Baboons Using Prosthetic Vascular Grafts Seeded with Retrovirally Transduced Smooth Muscle Cells: A Model for Local and Systemic Gene Therapy

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Abstract
Prosthetic vascular grafts containing retrovirally transduced autologous vascular smooth muscle cells were studied as a model for introduction of human genes into baboons. Retroviral vectors encoding β-galactosidase (β-Gal) (LNPoZ) or human purine nucleoside phosphorylase (LPNSN-2), a control gene, were used for ex vivo transduction of autologous baboon smooth muscle cells obtained from vein biopsies. Transduced cells were placed into a collagen solution and seeded into the interstices of polytetrafluoroethylene vascular grafts. Endothelial cells were then seeded onto the luminal surface of the grafts to reduce thrombus formation. One LNPoZ-seeded graft and one LPNSN-2-seeded control graft were implanted bilaterally into the aorto–iliac circulation of each of 4 animals. All grafts remained patent until they were removed after 3–5 weeks and examined histochemically for vector-expressing cells. All histological cross-sections from the β-Gal vector seeded grafts contained cells staining blue with the X-Gal chromogen. For the four grafts, the mean fraction of LNPoZ expressing cells was 10%, with a range of 2–20%, while no sections from the control grafts contained stainable cells. Smooth muscle cells expressing the reporter gene were localized within the graft wall but not in the newly forming intima or outer capsule of fibrous tissue. Implantation of transduced cells within this type of vascular graft may provide a useful approach for long-term local and systemic gene therapy. Prosthetic (PTFE) vascular grafts seeded with transduced autologous vascular smooth muscle cells were introduced into baboons. Cell seeding was accomplished by the intercalation of smooth muscle cells into the interstices of the PTFE graft matrix. Vascular endothelial cells were seeded onto the luminal surface of the grafts to provide an antithrombogenic surface. Grafts were implanted into the aorto-iliac circulation of 4 animals and at up to 5 weeks β-Gal-expressing cells were observed in all grafts treated with LNPoZ-transduced cells; all grafts remained patent. This strategy for the implantation of genetically modified vascular smooth muscle cells may provide a useful approach to long-term local and systemic gene therapy.