High Doses of a Helper-Dependent Adenoviral Vector Yield Supraphysiological Levels of <i>α</i> ₁ -Antitrypsin with Negligible Toxicity

Abstract

Optimal gene therapy for many disorders will require efficient transfer to cells in vivo, high-level and long-term expression, and tissue-specific regulation, all in the absence of significant toxicity or inflammatory responses. While recombinant adenoviral vectors are efficient for gene transfer to hepatocytes, their usefulness is limited by short duration of expression related, at least in part, to immune responses to viral proteins and by a low capacity for foreign DNA. A number of systems have been developed for producing adenoviral vectors devoid of all viral coding sequences. Using AdSTK109, a vector lacking all viral coding sequences and carrying the complete human α1-antitrypsin (hAAT) genomic DNA locus, we have demonstrated sustained expression for longer than 10 months in mice. Utilizing high doses of this vector for hepatic gene transfer in mice, we find that supraphysiological levels of hAAT can be achieved without hepatotoxicity. Limited data are available to assess the efficacy and toxicity of helper-dependent adenoviral vectors with all viral coding sequences deleted. Using intravenous administration of high doses of a helper-dependent vector expressing hAAT in mice, we found long-term and high-level expression with minimal hepatic toxicity. The data suggest that helper-dependent vectors have substantially less acute and chronic, nonimmune-related toxicity likely related to the elimination of leaky viral gene expression. It may be possible to administer higher doses of helper-dependent adenoviral vectors with less toxicity compared with earlier generations of vectors.