The Comparative Use of Helper-Dependent and First-Generation Adenoviruses for Rescuing Sialidase Deficiency Using In Vitro and In Vivo Model Systems

Abstract

Sialidosis is caused by the accumulation of the ganglioside GM3 and other sialoglycoproteins within the cells of the liver, kidney and brain. Currently there is no treatment for sialidosis, while other lysosomal storage disorders are being treated through enzyme replacement therapy or bone marrow transplantation. The helper-dependent, or "gutless" adenovirus system (HD) has recently been improved upon with reportedly less immunogenicity than its first-generation (FG) predecessor and lifelong transgene expression produced in its hosts. To this end, the complete mouse lysosomal sialidase gene was cloned into a HD-vector (AdmsialHD) and a FG-vector (AdmsialFG) in an attempt to rescue the sialidase deficiency and associated phenotype in B6.SM fibroblasts and in the SM/J mouse. Lysosomal sialidase levels were increased to normal levels in vitro following both AdmsialHD and AdmsialFG infections while SM/J mouse infections at doses of 5 x 10^9 particles/mouse did not yield any increase in lysosomal sialidase activity or correct the associated phenotype. Interestingly, AdmsialHD only up-regulated sialidase to high levels in sialidase-null cells whereas AdmsialFG up-regulated sialidase significantly in all cell lines tested. Together, these data suggest that the therapeutic dose for both AdmsialFG and AdmsialHD should be elevated at least 10-fold in order to achieve phenotypic rescue and that FG-vectors possess some viral property, perhaps the E4 gene products, enabling them to attain greater transgene expression relative to HD-vectors.