Biodistribution, kinetics, and efficacy of highly phosphorylated and non-phosphorylated beta-glucuronidase in the murine model of mucopolysaccharidosis VII

Enzyme replacement therapy in mucopolysaccharidosis type II (Hunter syndrome): a preliminary report

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is an X-linked disease caused by a deficiency of the enzyme iduronate-2-sulphatase (IDS), which results in the lysosomal accumulation of glycosaminoglycans (GAG). This paper describes a knockout mouse model of MPS II which has been used to assess the effect of enzyme replacement therapy. Therapy with IDS results in a marked decrease in urinary GAGs, as well as reduced GAG accumulation in several tissues. These studies have been used to support the first clinical trial of recombinant IDS in patients with Hunter syndrome.

Biodistribution and efficacy of donor T lymphocytes in a murine model of lysosomal storage disease

Lymphocyte-directed gene transfer has been proposed as potential therapy to treat certain congenital immunological deficiencies as well as other genetic diseases such as lysosomal storage diseases (LSDs). To understand better the extent to which adoptively transferred peripheral T lymphocytes (PTLs) are able to ameliorate LSDs we utilized the beta-glucuronidase-deficient mouse as a model system. PTLs (1 x 10(7)) isolated from the spleen of syngeneic mice overexpressing ( approximately 8-fold) human beta-glucuronidase (GUSB) were injected intravenously into young adult beta-glucuronidase-deficient mice without myeloablative conditioning. Using biochemical and histochemical assays, we were able to track the donor lymphocytes in vivo. Donor lymphocytes were detected in relatively high numbers in liver, spleen, small intestine, mesenteric lymph node, and thymus for at least 5 months, the last time point of analysis. Although liver and spleen had the highest total GUSB activity, histopathologic analysis demonstrated minimal to no correction of lysosomal distention at all time points studied. By contrast, we have shown in earlier studies that administration of similar numbers of macrophages reduced lysosomal storage in several organs, including liver and spleen. To understand this difference in efficacy, we compared the relative level of GUSB released into the medium by nonactivated and activated PTLs as well as by macrophages. Macrophages released >50-fold excess enzyme compared to either activated or nonactivated PTLs. These data suggest that a LSD can be more effectively treated by directing a gene therapy approach to a hematopoietic lineage other than T lymphocytes.

Uptake of recombinant iduronate-2-sulfatase into neuronal and glial cells in vitro

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a congenital storage disorder resulting from mutations on the iduronate-2-sulfatase (IDS) gene. The disease shows variable clinical phenotypes from severe to mild with progressive neurological dysfunction. The therapeutic options for treatment of MPS II are limited and currently no specific therapies are available; the problem is further compounded by difficulties in delivering therapeutic agents to the central nervous system (CNS). In this work, as a potential treatment for this disease, the transfer of the recombinant IDS enzyme into brain cells has been studied in vitro. Two different approaches to obtain recombinant IDS have been utilized: production of the recombinant enzyme by a transfected human clone (Bosc 23 cells); production of the recombinant enzyme by adenoviral transduction of neuronal (SK-N-BE) or glial (C6) cells. Our data indicate that the transfected as well as the infected cells produce a large amount of the IDS enzyme, which is efficiently endocytosed into neuronal and glial cells through the mannose 6-phosphate (M6P) receptor system. Somatic gene therapy appears therefore to be suitable to correct IDS deficiency in brain cells.

Enzyme replacement and enhancement therapies: lessons from lysosomal disorders

The past decade has witnessed remarkable advances in our ability to treat inherited metabolic disorders, especially the lysosomal storage diseases, a group of more than 40 disorders, each of which is caused by the deficiency of a lysosomal enzyme or protein. During the past few years, both enzyme replacement and enhancement therapies have been developed to treat these disorders. This review discusses the successes and shortcomings of these therapeutic strategies, and the contributions that they have made to treating lysosomal storage diseases.

Evaluation of pathological manifestations of disease in mucopolysaccharidosis VII mice after neonatal hepatic gene therapy

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. Intravenous injection of a retroviral vector expressing canine GUSB into neonatal MPS VII mice resulted in transduction of 6 to 35% of hepatocytes, which secreted GUSB into blood. Serum GUSB activity was stable for 6 months at 600 (low expression) to 10,000 (high expression) U/ml, and enzyme was modified appropriately with mannose 6-phosphate. The average serum GUSB activity (3531 U/ml) is the highest long-term expression reported for MPS VII mice after gene therapy. Secreted enzyme was taken up by other tissues, as the average enzyme activity was >13% of normal in somatic organs and 2% of normal in brain. Low expression markedly reduced histopathological evidence of lysosomal storage in liver, spleen, kidney, small intestine, neurons, and glial cells. High expression appeared to be more effective than low expression at reducing lysosomal storage in aorta, heart valves, thymus, bronchial epithelium, cornea, and retinal pigmented epithelium. Future experiments will determine if greater pathological improvements will consistently be observed in retrovirus-treated MPS VII mice with higher serum GUSB activity relative to animals with lower activity and if these result in clinical benefits.

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.

Enzyme replacement therapy for the mucopolysaccharide storage disorders

The mucopolysaccharide storage disorders are a group of lysosomal storage disorders associated with deficiencies of lysosomal enzymes required for the normal sequential degradation of glycosaminoglycans, formerly known as mucopolysaccharides. The accumulation of glycosaminoglycans in a wide variety of tissues results in a complex and progressive disease leading to death in the first or second decade in most patients. Studies of enzyme replacement in animal models of mucopolysaccharide disorders have demonstrated the potential of parenterally administered enzyme to reduce glycosaminoglycan storage and microscopic pathology. Clinical studies of enzyme replacement therapy are currently underway for mucopolysaccharidosis I, mucopolysaccharidosis VI and mucopolysaccharidosis II. The complexity and heterogeneity of the mucopolysaccharide disorders provide significant challenges for clinical study design and evaluation. Innovative clinical development strategies may be needed to lower the development cost and time for complex rare disease therapies to assure that such patients receive therapies they deserve.