GRAFT PERMEABILIZATION FACILITATES GENE-THERAPY OF TRANSPLANT ARTERIOSCLEROSIS IN A RABBIT MODEL

Background-Smooth muscle cell (SMC) replication plays a central role i n the pathogenesis of transplant arteriosclerosis. One strategy to eli minate dividing cells is to express a herpesvirus thymidine kinase (tk ) gene that phosphorylates the nucleoside analogue ganciclovir into a toxic form leading to cell killing. However, medial SMCs are resistant to gene transfer unless the artery undergoes deendothelialization. We hypothesized that manipulations that increase the ''porosity'' of the artery can make SMCs prone to gene transfer without denudation. Metho ds and Results-In organ culture of rabbit aorta, longitudinal stretch and supraphysiological pressure applied for 3 hours during incubation with adenoviral vector facilitated gene transfer into medial SMCs with out denudation. Of the SMCs, 10.2 +/- 3.8% expressed a reporter gene o f human placental alkaline phosphatase (hpAP), whereas SMCs in control arteries did not express hpAP. To evaluate the feasibility of transge ne expression in arterial grafts, we performed such permeabilization-a ssisted reporter gene transfer into aortas of donor Dutch Belted rabbi ts and transplanted them into carotid arteries of recipient New Zealan d White rabbits. Unstretched transfected grafts were used as a control . SMCs expressed hpAP (7.3+/-2.4% of cells in 2 days and 4.2+/-1.9% in 2 weeks) in stretched grafts only. In the next series of experiments, we transfected stretched grafts with ADV-tk and combined transplantat ion with systemic administration of ganciclovir. Stretched ADV-hpAP gr afts were used as a control. In 2 weeks, the formation of intimal thic kening in tk-expressing grafts was significantly reduced (P<0.01) beca use of a decrease in proliferating SMCs. Conclusions-Manipulations wit hin target tissues can enhance the efficiency of gene transfer into SM Cs. Although mechanical permeabilization is clinically problematic, in principle, targeting SMC replication may provide a genetic approach t o the treatment of transplant arteriosclerosis.