1. ¹Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
2. ²Pediatric Cardiology, Baylor College of Medicine, Houston, TX

Abstract

Helper-dependent adenoviral vectors (HDAds) hold tremendous potential for liver-directed gene therapy because they can mediate long-term transgene expression without chronic toxicity. However, due to a nonlinear dose-response, high doses are required to achieve efficient hepatic transduction resulting in dose-dependent acute toxicity. To overcome this important obstacle, we have developed a minimally invasive method to preferentially deliver low dose HDAd into the liver of 30 kg baboons to achieve efficient hepatic transduction. Briefly, a single sausage-shaped balloon occlusion catheter was percutaneously positioned in the inferior vena cava (IVC) of baboon 1 to occlude hepatic venous outflow (Fig. 1A). 1x10¹¹ vp/kg of a HDAd expressing the baboon alpha-fetoprotein (bAFP) marker was injected directly into the occluded liver via a percutaneously placed hepatic artery (HA) catheter and left to dwell within the liver for 15 min before balloon deflation. As controls, 1x10¹¹ vp/kg was administered to baboon 2 by peripheral intravenous injection and baboon 3 by HA injection without balloon occlusion. All procedures were uneventful, well tolerated, and following recovery from anesthesia, all three animals returned to their normal, active pre-injection states with no clinical manifestations of toxicity. Mild transaminitis was observed for all animals, peaking at 24 to 48 h post-vector but returning towards baseline the next day: For ALT, a 2.3, 1.1, and 1.4-fold increase over baseline were observed for baboons 1, 2 and 3, respectively. For AST, a 4.8, 1.6 and 2.8-fold increase were observed for baboons 1, 2 and 3, respectively. Importantly, serum bAFP levels increased 425-fold over baseline for baboon 1 (from 4.5 ng/ml at a baseline to 1914 ng/ml), while only a modest increase of 12-fold and 5.6-fold were observed for baboon 2 (from 9 ng/ml to 109 ng/ml) and baboon 3 (from 18 ng/ml to 103 ng/ml), respectively (Fig. 1B). To date, these bAFP levels have been sustained (at least 56 days). These results suggest that the therapeutic index of HDAd can be significantly improved by delivering the vector preferentially into the liver using a minimally invasive balloon occlusion catheter technique and may be a first step towards clinical application of HDAd for liver-directed gene therapy.