246. Comparison of rAAV2-Mediated Expression of Human and Murine β-Glucuronidase in Adult MPS VII Mice

Abstract

Top of pageAbstract Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease (LSD) caused by a deficiency of -glucuronidase. This enzyme deficiency results in the accumulation of glycosaminoglycans in most organs including the brain. We previously demonstrated that intrahepatic administration of a recombinant adeno-associated virus type 2 (rAAV2) vector carrying the murine -glucuronidase cDNA leads to improvement in both the peripheral and central manifestations of disease in adult MPS VII mice. The objective of this study was to compare the effects of rAAV2-mediated expression of human to murine -glucuronidase in this disease model. Methods: rAAV2 vectors carrying the murine -glucuronidase (Gusb) cDNA and human -glucuronidase (GUSB) cDNA under the transcriptional direction of the human elongation factor-1 promoter were administered to 7-week old MPS VII mice (n=3, each vector). Mice received 1.31011 DNase resistant particles by intrahepatic injection and were sacrificed 6 months post-vector administration. Tissues and sera were evaluated as indicated for vector genomes (quantitative PCR assay), -glucuronidase activity (fluorometric assay), and -galactosidase activity (fluorometric assay). Results: In the livers of the rAAV2-hGUSB (human)-injected group, the mean level of vector genomes was 2.6-fold lower than in the group receiving rAAV2-mGusb (murine) (P=0.03). There was no difference in hepatic -glucuronidase activity between the rAAV2-hGUSB-injected (11267% of normal, wild-type levels; meanS.E.M.) and rAAV2-mGusb-injected (16242%) groups. However, hepatic gene transfer was more variable in the group receiving rAAV2-hGUSB; one mouse had 4% of wild-type -glucuronidase activity and 5-fold less vector genomes than the other mice in this group. -Glucuronidase activity within the serum of individual mice in the rAAV2-hGUSB group was 0, 86, and 135% and in the rAAV2-mGusb group 8, 11, and 26% of wild-type. The -glucuronidase serum-to-liver ratio was 0.00, 0.37, and 1.31 in the rAAV2-hGUSB group and 0.08, 0.07, and 0.10 in the rAAV2-mGusb group. In the brain, vector genomes were detected at <1 copy per 1000 cell genome equivalents and -glucuronidase activity was no different from control MPS VII mice in both groups of mice. -Galactosidase levels (secondarily elevated by the storage abnormality) were reduced in the brains of the rAAV2-hGUSB (16425% of wild-type) and rAAV2-mGusb (1618% of wild type) groups as compared to control MPS VII (24836% of wild-type) mice (rAAV2-hGUSB vs. control, P<0.02; rAAV2-mGusb vs. control, P<0.01). Summary: These data demonstrate that the human and murine -glucuronidase transgenes delivered by an rAAV2 vector have different properties in MPS VII mice. In this study, the vector carrying the human transgene resulted in a lower and more variable levels of transduction than the vector carrying the murine transgene. Also, the human -glucuronidase transgene resulted in higher serum enzyme levels than those observed with the murine transgene. Despite the differences, biochemical improvement of disease within the brain was observed for both transgenes.