Correction of the Nonlinear Dose Response Improves the Viability of Adenoviral Vectors for Gene Therapy of Fabry Disease

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Abstract
Systemic administration of recombinant adenoviral vectors for gene therapy of chronic diseases such as Fabry disease can be limited by dose-dependent toxicity. Because administration of a high dose of Ad2/CMVHI-αgal encoding human α-galactosidase A results in expression of supraphysiological levels of the enzyme, we sought to determine whether lower doses would suffice to correct the enzyme deficiency and lysosomal storage abnormality observed in Fabry mice. Reducing the dose of Ad2/CMVHI-αgal by 10-fold (from 1011 to 1010 particles/mouse) resulted in a greater than 200-fold loss in transgene expression. In Fabry mice, the reduced expression of α-galactosidase A, using the lower dose of Ad2/CMVHI-αgal, was associated with less than optimal clearance of the accumulated glycosphingolipid (GL-3) from the affected lysosomes. It was determined that this lack of linearity in dose response was not due to an inability to deliver the recombinant viral vectors to the liver but rather to sequestration, at least in part, of the viral vectors by the Kupffer cells. This lack of correlation between dose and expression levels could be obviated by supplementing the low dose of Ad2/CMVHI-αgal with an unrelated adenoviral vector or by depleting the Kupffer cells before administration of Ad2/CMVHI-αgal. Prior removal of the Kupffer cells, using clodronate liposomes, facilitated the use of a 100-fold lower dose of Ad2/CMVHI-αgal (109 particles/mouse) to effect the nearly complete clearance of GL-3 from the affected organs of Fabry mice. These results suggest that practical strategies that minimize the interaction between the recombinant adenoviral vectors and the reticuloendothelial system (RES) may improve the therapeutic window of this vector system. In this regard, we showed that pretreatment of mice with gamma globulins also resulted in significantly enhanced adenovirus-mediated transduction and expression of α-galactosidase A in the liver.