247. Gene Therapy with a Retroviral Vector Expressing Canine β-Glucuronidase to Juvenile (7 Week Old ) Dogs Improves the Biochemical Manifestations of MPS VII

Abstract

Top of pageAbstract Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease due to deficiency of |[beta]|-glucuronidase (GUSB). Manifestations include bone and joint disease, heart disease, and neurological dysfunction. The MPS VII dog has a missense mutation in GUSB (R166H) that results in clinical manifestations that resemble those in humans. We have previously demonstrated that neonatal gene therapy with 3|[times]|109 TU/kg of a retroviral vector (RV) expressing canine GUSB from the human |[alpha]|1-antitrypsin promoter (hAAT-cGUSB-WPRE) resulted in transduction of hepatocytes and 195+/-36 U/ml of GUSB in serum. This resulted in a marked improvement in cardiac, bone and joint, and other manifestations. However, most patients with MPS VII are not identified at birth, and it will be necessary to determine the effect of transfer into older animals. Seven week-old MPS VII dogs were injected IV with 1|[times]|1010 transducing units (TU)/kg of hAAT-cGUSB-WPRE. Some received a cumulative dose of hepatocyte growth factor (HGF) over 24 hours of 2.5 mg/kg, then were injected with RV at 24, 48, 72, and 96 hours after the first dose of HGF (HGF/RV). Others received RV once a day for 4 days without preceding HGF (RV alone). Dogs that received HGF/RV or RV alone at 7 weeks had transduced hepatocytes and achieved stable expression of GUSB in serum at 185+/-54 U/ml or 51+/-5 U/ml for up to 1 year, respectively, although differences were not statistically significant. The serum GUSB achieved per TU/kg given was 28% and 8%, respectively, of that achieved after neonatal gene transfer, which likely reflects lower levels of hepatocyte replication in juveniles. Some animals were sacrificed at 6 months after gene transfer, and organs analyzed for biochemical correction of disease. The results in both juvenile transfer groups were similar and were pooled for statistical analyses. MPS VII results in elevation of the secondary lysosomal enzyme |[beta]|-hexosaminodase (|[beta]|-hex) and glycosaminoglycan (GAG) levels, and normalization of these occurs with successful therapies. In liver, spleen, jejunum, and lung, GUSB activity was 1% to 15% of normal levels and there was a marked reduction in |[beta]|-hex and GAG levels. In thymus, pancreas, kidney, and muscle, GUSB activity was 0.25% to 1% of normal and there was a marked or partial reduction in |[beta]|-hex and GAG levels. However, brain GUSB activity was only 0.2% of normal and there was little reduction in |[beta]|-hex (GAG was not evaluable as untreated MPS VII dogs do not have elevated brain GAG levels). Despite these biochemical improvements, the mobility of the dogs was only slightly improved and all were unable to walk by 12 months or earlier. We conclude that gene therapy into juvenile dogs results in expression similar to that observed after neonatal gene transfer, and marked biochemical improvements in somatic organs. This is the first demonstration of using juvenile gene therapy to improve disease in a large animal model for LSD. However, there was little biochemical improvement in brain, and the bone disease remained severe.