Assessment of Recombinant Adenoviral Vectors for Hepatic Gene Therapy

Abstract

Recombinant adenoviral vectors have recently been used to transfer genes into a number of different cell types in vitro and in vivo. A recombinant adenoviral vector bearing the Escherichia coli β-galactosidase (β-gal) gene was used to quantitate the frequency of hepatocyte transduction in the mouse after direct viral infusion into the portal vein. When 10¹⁰ adenoviral particles were infused, over 95% of the hepatocytes were transduced in vivo as determined by x-gal staining. The transduction protocol is relatively safe in that there is no detectable helper virus production in transduced animals and that very few extrahepatic cells are transduced by this method. There is also no evidence of significant liver pathology unless substantially greater quantities of virus are used. However, the transduced hepatocytes do not appear to persist in vivo because the percentage of hepatocytes expressing β-gal declined over time. Four months after the procedure, 0.5–10% of the hepatocytes contain detectable β-gal activity in vivo. The change in β-gal-positive cells correlates with decreasing amounts of adenoviral DNA. Thus, current recombinant adenoviral vectors may have clinical applications in gene therapy for acute hepatic disorders. This study demonstrates that the recombinant adenovirus can be used to transfer genes into greater than 95% of mouse hepatocytes in vivo. The expression from the majority of transduced hepatocytes is slowly lost over a 3- to 4-month period. This vector system has the advantage of being a very efficient means of gene transfer into the liver; the disadvantage of the system relates to the transient nature of expression in most of the transduced hepatocytes. Further experimentation will be required to determine whether a significant number of transduced hepatocytes will remain indefintely.