Adventitial delivery minimizes the proinflammatory effects of adenoviral vectors

Purpose: Adenovirus-mediated arterial gene transfer is a promising tool in the study of vascular biology and the development of vascular gene therapy. However, intraluminal delivery of adenoviral vectors causes vascular infla mmation and neointimal formation. Whether these complications could be avoi ded and gene transfer efficiency maintained by means of delivering adenovir al vectors via the adventitia was studied. Methods: Replication-defective adenoviral vectors encoding a beta-galactosi dase (beta-gal) gene (AdRSVnLacZ) or without a recombinant gene (AdNull) we re infused into the lumen or the adventitia of rabbit carotid arteries. Two days after infusion of either AdRSVnLacZ (n = 8 adventitial, n = 8 luminal ) or AdNull (n = 4 luminal), recombinant gene expression was quantitated by histochemistry (performed on tissue sections) and with a beta-gal activity assay (performed on vessel extracts). Inflammation caused by adenovirus in fusion was assessed 14 days after infusion of either AdNull (n = 6) or vehi cle (n = 6) into the carotid adventitia. Inflammation was assessed by means of examination of histologic sections for the presence of neointimal forma tion and infiltrating T cells and for the expression of markers of vascular cell activation (ICAM-1 and VCAM-1). To measure the systemic immune respon se to adventitial infusion of adenovirus, plasma samples (n = 3) were drawn 14 days after infusion of AdNull and assayed for neutralizing antibodies. Results: Two days after luminal infusion of AdRSVnLacZ, approximately 30% o f luminal endothelial cells expressed beta-gal. Similarly, 2 days after inf usion of AdRSVnLacZ to the adventitia, approximately 30% of adventitial cel ls expressed beta-gal. beta-gal expression was present in the carotid adven titia, the internal jugular vein adventitia, and the vagus nerve perineuriu m. Elevated beta-gal activity (50- to 80-fold more than background; P < .05 ) was detected in extracts made from all AdRSVnLacZ-transduced arteries. Th e amount of recombinant protein expression per vessel did not differ signif icantly between vessels transduced via the adventitia (17.1 mU/mg total pro tein [range, 8.1 to 71.5]) and those transduced via a luminal approach (10. 0 mU/mg total protein [range, 3.9 to 42.6]). Notably, adventitial delivery of AdNull did not cause neointimal formation. In addition, vascular inflamm ation in arteries transduced via the adventitia tie, T-cell infiltrates and ICAM-1 expression) was confined to the adventitia, sparing both the intima and media. Antiadenoviral neutralizing antibodies were present in all rabb its after adventitial delivery of AdNull. Conclusion: Infusion of adenoviral vectors into the carotid artery adventit ia achieves recombinant gene expression at a level equivalent to that achie ved by means of intraluminal vector infusion. Because adventitial gene tran sfer can be performed by means of direct application during open surgical p rocedures, this technically simple procedure may be more clinically applica ble than intraluminal delivery. Moreover, despite the generation of a syste mic immune response, adventitial infusion had no detectable pathologic effe cts on the vascular intima or media. For these reasons, adventitial gene de livery may be a particularly useful experimental and clinical tool.