Mucopolysaccharidosis Type VII Evaluation of Bone Marrow Transplantation and Non-Autologous Somatic Cell Gene Therapy

Abstract

Deficiency in β-glucuronidase activity (EC 3.2.1.31) leads to the lysosomal storage disease mucopolysaccharidosis type VII not only in humans but also in a recently discovered murine mutant, the gus^mps/gus^mps mouse. Clinical and pathologic abnormalities common to the human and mouse phenotypes include shortened life span, dwarfism, dysmorphic facial features, skeletal deformities, corneal clouding, mental retardation and abnormal lysosomal storage material in the brain and peripheral organs. In the first part of this thesis, neonatal gus^mps/gus^mps mice and their normal littermates were transplanted with syngeneic normal bone marrow. Neurological function was then evaluated with two behavioral tests: the grooming test, a developmentally regulated and genetically based activity, and the Morris water maze test, which assessed spatial learning abilities. The results of these tests indicated that the behavioral deficits in the mutant mice were not restored to normal. Treated normal mice also showed significant functional deterioration, indicating the detrimental consequence of this therapy in the neonatal period. The second part of this thesis focused on a novel approach to somatic gene therapy using microcapsules. A non-autologous fibroblast cell line engineered to secrete high levels of β-glucuronidase was enclosed in perm-selective and immuno- protective microcapsules and implanted into the peritoneal cavity of gus^mps/gus^mps mice. During the 4 weeks of therapy, the biochemical and histological abnormalities of the mutant mice had significantly improved. β-Glucuronidase activity was restored to >50% of normal in the plasma and 11.3%-65.8% in the kidney, liver and spleen. No significant activity was found in the brain. As well, the secondary elevations of other lysosomal enzymes such as β-hexosaminidase and α-galactosidase had decreased in the kidney, liver, and spleen. Urinary glycosaminoglycan content had decreased in the treated mutants indicating that the β-glucuronidase was exerting a therapeutic effect. However, after three and a half weeks of therapy, the treated mutants became severely ill and developed haemorrhagic ascites. Since normal mice treated with similar microcapsules showed no adverse effects, we hypothesized that an immune response had been generated against the foreign protein (β-glucuronidase) by the mutants, leading to the high morbidity. Thus in spite of the biochemical and histological correction observed after bone marrow transplantation and somatic cell gene therapy, the long term efficacy of these treatments needs to be further evaluated.