Therapeutic neonatal hepatic gene therapy in mucopolysaccharidosis VII dogs.

Dogs with mucopolysaccharidosis VII (MPS VII) were injected intravenously at 2-3 days of age with a retroviral vector (RV) expressing canine beta-glucuronidase (cGUSB). Five animals received RV alone, and two dogs received hepatocyte growth factor (HGF) before RV in an attempt to increase transduction efficiency. Transduced hepatocytes expanded clonally during normal liver growth and secreted enzyme with mannose 6-phosphate. Serum GUSB activity was stable for up to 14 months at normal levels for the RV-treated dogs, and for 17 months at 67-fold normal for the HGF/RV-treated dog. GUSB activity in other organs was 1.5-60% of normal at 6 months for two RV-treated dogs, which was likely because of uptake of enzyme from blood by the mannose 6-phosphate receptor. The body weights of untreated MPS VII dogs are 50% of normal at 6 months. MPS VII dogs cannot walk or stand after 6 months, and progressively develop eye and heart disease. RV- and HGF/RV-treated MPS VII dogs achieved 87% and 84% of normal body weight, respectively. Treated animals could run at all times of evaluation for 6-17 months because of improvements in bone and joint abnormalities, and had little or no corneal clouding and no mitral valve thickening. Despite higher GUSB expression, the clinical improvements in the HGF/RV-treated dog were similar to those in the RV-treated animals. This is the first successful application of gene therapy in preventing the clinical manifestations of a lysosomal storage disease in a large animal.

Transduction of hepatocytes after neonatal delivery of a Moloney murine leukemia virus based retroviral vector results in long-term expression of beta-glucuronidase in mucopolysaccharidosis VII dogs.

The use of Moloney murine leukemia virus (MLV)-based retroviral vectors (RV) can result in stable in vivo expression in the liver, but these vectors only transduce replicating hepatocytes. As newborn animals exhibit rapid growth, we evaluated the ability of MLV-based RV to transduce hepatocytes in neonatal dogs. I.v. injection of a beta-galactosidase-expressing RV at 3 days after birth resulted in transduction of 9% of hepatocytes. Prior treatment with human hepatocyte growth factor at 2.5 mg/kg did not increase transduction. Although cells from the spleen were also transduced with moderate efficiency, cells from other organs were not. Neonatal dogs with mucopolysaccharidosis VII (MPS VII) received an i.v.injection of an RV containing the canine beta-glucuronidase (cGUSB) cDNA. At several months after transduction, clusters of hepatocytes that expressed high levels of cGUSB were present in the liver, which probably derived from replication of transduced hepatocytes. At 6 months after transduction, serum GUSB levels were 73% that of homozygous normal dogs and were 34% of the peak values observed at 1 week. We conclude that neonatal delivery of an MLV-based RV results in stable transduction of hepatocytes in dogs. This approach could result in immediate correction in patients with an otherwise-lethal genetic deficiency.