868. Enhancement of Gene Therapy Approaches for the Correction of Farber Disease

Abstract

Glycogen Storage Disease type II (GSD-II) results in the accumulation of glycogen within the lysosomes of primarily the cardiac and skeletal muscles. Functional inhibitions similar to those of muscular dystrophies are common in GSD-II patients. However the most detrimental form of GSD-II affects infants, who are completely lacking muscle expression of the glycogen reducing enzyme, acid-a-glucosidase (human GAA). Most affected infants die within the first year of life due to cardio-respiratory failure, while juvenile and adult forms will more likely progress to skeletal muscle inadequacy. Recent enzyme replacement therapy (ERT) with hGAA has prolonged the life span of affected infants, but long term care and large-scale production of the enzyme remain realistic caveats of ERT. Developments within our laboratory show the promise of adenovirus mediated gene transfer of the hGAA gene into liver tissues, and its ability for profuse and long-term expression of hGAA protein. Various improvements of the adenovirus including the removal of viral genes necessary for replication have yielded high potency and minimal immune responses when injected into GAA knockout (KO) murine models. Based upon these previous studies, we hypothesized that advanced generation, fully deleted adenovirus based vectors would have an even more decreased propensity to generate antivirus and/or transgene immune responses. We have therefore constructed a fully deleted adenovirus capable of expressing high levels of the hGAA gene, facilitated via use of a liver specific enhancer, promoter and other gene expression elements. Intravenous delivery of this vector into GAA knockout mice has produced long term hGAA protein secretion from the liver, (currently up to 56 days post injection). Longer term studies are currently in progress. Interestingly, at lower vector doses, antibody titers to hGAA are detectable as measured by ELISA, but at much higher vector doses anti-hGAA antibody no longer becomes detectable. This seeming paradox may be due to the fact that the large amounts of hGAA being secreted into the plasma from the liver of animals injected with higher doses of the vector, “sequesters” the low amounts of anti-hGAA antibody being produced within the same animals. We are currently investigating whether the low anti-hGAA antibody titers are correlated to specific properties of the fully deleted adenovirus vector system per se, and/or the various constituents utilized to induce hGAA expression from the vector. Furthermore, we will assess how the efficacy of the fully deleted Ad vectors might be impacted upon by the diminished immune responses afforded by their use. In summary, this unique gene transfer system may be a viable method for gene therapy of GSD-II, and perhaps may lead to an alternative or adjunctive therapy relative to current, ERT based strategies to treat GSD-II.