Efficient and selective adenovirus-mediated gene transfer into vascular neointima

Background. Previous attempts to target arterial smooth muscle cells (SMCs) for gene delivery using liposomal or retroviral methods were limited by low transfection efficiency. We therefore evaluated the efficiency of adenovirus-mediated gene delivery in cultured vascular SMCs and in an in vivo model of balloon injury-induced SMC cell proliferation. Methods and Results. We used a recombinant adenovirus, Ad.RSVβgal, which contained the β-galactosidase (β-gal) histochemical marker gene. For in vitro studies, rat aortic SMCs were incubated in media containing Ad.RSVβgal for 5 to 120 minutes. The proportion of SMCs expressing the β-gal gene product increased from 25% (5-minute exposure) to 80% (120-minute exposure). For in vivo studies, uninjured and injured rat carotid segments were incubated with 0.5 to 1.0×10⁹ pfu Ad.RSVβgal for 45 minutes. Uninjured arteries showed adenovirus-mediated gene transfer limited to the endothelium. Injured arteries were exposed to adenovirus 0, 3, 7, or 12 days after injury. In these segments, β-gal expression was minimal with infection at 0 or 3 days after injury but marked when infection was delayed until 7 or 12 days after injury. Neointimal cells constituted the dominant target of adenovirus gene transfer, with efficiency of gene transfer ranging from 10% to >75%. Medial SMCs, whether covered or uncovered by neointimal cells, were minimally infected. Infection with a control adenovirus vector showed no β-gal staining. Conclusions. Recombinant adenovirus selectively targets neointimal cells with high-efficiency gene transfer. This suggests that adenovirus vectors should be useful in targeting cells for the delivery of genes whose products may be relevant to the treatment of restenosis.