Adenoviral-mediated gene transfer of a constitutively active form of the retinoblastoma gene product attenuates neointimal thickening in experimentalvein grafts

Purpose: Inappropriate or excessive vascular smooth muscle cell proliferati on leads to the development of occlusive lesions in up to 50% of vein graft s. The purpose of this study was to test the hypothesis that induced overex pression of a cytostatic nonphosphorylatable form of the retinoblastoma pro tein (Delta Rb) would attenuate neointimal thickening in experimental vein grafts. Methods: A replication-deficient adenovirus vector that encoded a nonphosph orylatable, constitutively active form of Delta Rb was constructed (Ad Delt a Rb) and contained an NH2-terminal epitope tag from the influenza hemagglu tinin molecule (KB). Forty-eight male New Zealand white rabbits underwent s urgical exposure of the external jugular vein for transfection with either 3 x 10(10) plaque-forming units/mL Ad Delta Rb (n = 16), 3 x 10(10) plaque- forming units/mL; control adenovirus (AdBglII, n = 15), or vehicle (n = 17) for 10 minutes at 120 mm Hg. After vector exposure, the vein was excised a nd interposed end-to-end into the carotid circulation. After 5 days, 12 gra fts (four from each group) were excised and assayed for genomic Delta Rb DN A with the polymerase chain reaction or for hemagglutinin molecule expressi on and localization with immunohistochemistry. The remainder of the grafts (n = 36) were perfusion-fixed after 4 weeks, and 5 mu m sections prepared f or digital planimetric analysis. Results: Polymerase chain reaction results identified the Delta Rb gene onl y in the grafts that were transfected with Ad Delta Rb. Immunohistochemical analysis results revealed transgene expression in most of the endothelial cells and in many of the smooth muscle cells. After 4 weeks, the grafts tha t were exposed to Ad Delta Rb exhibited a 22% reduction in neointimal thick ness (vehicle, 77 +/- 7 mu m; AdBglII, 75 +/- 5 eta m; Ad Delta Rb, 60 +/- 5 mu m; P = .05), and medial thickness, luminal diameter, and other paramet ers were unchanged (medial thickness: vehicle, 72 +/- 10 mu m; AdBglII, 85 +/- 7 mu m; Ad Delta Rb, 69 +/- 9 mu m; P = NS; luminal diameter: vehicle, 4.5 +/- 0.2 mm; AdBglII, 4.4 +/- 0.2 mm; Ad Delta Rb, 4.7 +/- 0.1 mm; P = N S). Conclusion: With this delivery system, adenoviral-mediated gene transfer is highly efficient and induced overexpression of Delta Rb leads to a reducti on in vein graft neointimal thickening.