SYSTEMIC DELIVERY OF THE INTERLEUKIN-1 RECEPTOR ANTAGONIST PROTEIN USING A NEW STRATEGY OF DIRECT ADENOVIRAL-MEDIATED GENE-TRANSFER TO SKELETAL-MUSCLE CAPILLARY ENDOTHELIUM IN THE ISOLATED RAT HINDLIMB

Current gene therapy strategies using adenoviral vectors to target the lung or liver have been complicated by an acute inflammatory response that can result in loss of transgene expression as well as tissue inj ury and necrosis. Skeletal muscle comprises 40% of total body weight; it possesses a high density, accessible capillary network that is resi stant to injury and thus may be a logical target for adenoviral vector s. We hypothesized that adenoviral transduction of the rat skeletal mu scle capillary bed during vascular isolation would achieve efficient g ene transfer sufficient to achieve systemic serum levels of a recombin ant protein without significant tissue injury. During vascular isolati on of the hindleg, a replication-incompetent adenovirus (Ad) encoding for either the marker gene, human placental alkaline phosphatase (hpAP ), or interleukin-1 receptor antagonist (IL-1ra) was infused and subse quently flushed from the circulation after a 30-min dwell period. Gene transfer over a 10(9)-10(12) particle/ml range to the gastrocnemius c apillary endothelium and muscle fibers was highly efficient and titer- dependent, reaching maximum transduction rates of 71 +/- 7% and 25 +/- 5%, respectively, 5 days after gene transfer (n = 3-8 rats/group, p < 0.05). hpAP transgene expression was barely detectable at 14 days. No significant tissue injury or necrosis of the skeletal muscle was obse rved at 5 and 14 days, and distant organ gene transfer was minimal or absent. Gastrocnemius muscle from rats (n = 4) given Ad-IL-1ra had 241 +/- 66 pg IL-1ra/mg protein at 5 days, while those given Ad-hpAP, neg ative control (n = 3) had 35 +/- 14 pg IL-1ra/mg protein (p < 0.05). A d-IL-1ra rats (n = 4) had serum levels of 185 +/- 20 pg/ml IL-1ra at 5 days whereas Ad-hpAP control rats (n = 5) had no IL-1ra detectable (p < 0.0001). Athymic rats given Ad-IL-1ra (n = 6) had serum levels of 4 93 +/- 62 pg/ml IL-1ra 14 days after transduction, and IL-1ra was dete cted for up to 98 days. Sera from Ad-IL-1ra athymic rats significantly inhibited IL-1 beta-induced (1 ng/ml) prostaglandin E(2) (PGE(2)) pro duction from cultured endothelial cells by 82 +/- 2% (p < 0.001). Thus , this gene transfer strategy is the first to result in substantial tr ansduction of both skeletal muscle capillary endothelium and fibers, s ufficient to achieve pharmacologic levels of IL-1ra. Although no acute tissue injury or necrosis was observed, persistence of transgene expr ession in athymic rats suggests that loss of expression in normal rats was by an immune-mediated mechanism.