Correction of Both Hepatic and Brain Lysosomal Glycosaminoglycan Storage Using a Single Gene Transfer Vector in a Murine Model of Mucopolysaccharidosis VII

Abstract

Purpose: Lysosomal storage disorders (LSDs) are chracterized by cellular accumulation of glycosaminoglycans (GAGs), due to the deficiency of GAG-degrading enzymes. Mucopolysaccharidosis type VII (MPS-VII) is caused by β-glucuronidase (GUSB) deficiency, inherited as autosomal recessive trait. GAG accumulation affects the liver, spleen, cornea and bones, as well as the brain. GUSB is secreted into plasma and endocytosed by cells via the mannose-6-phosphate receptor. Thus, hepatic GUSB expression following gene therapy results in “cross-correction” of all abdominal viscera. However, brain lesions are not ameliorated, because GUSB does not cross the blood-brain barrier. Our purpose was to test if recombinant simian virus 40 (rSV40) vectors would not only transduce the abdominal viscera, but also cross the blood-brain barrier to transduce neural cells. Methods: The T-antigen gene of the SV40 genome was replaced with human GUSB encoding sequences. The recombinant viral genome was transfected into COS-7 cells for packaging the vector (SV-GUSB). Viral titer was determined by infecting primary MPS VII mouse skin fibroblasts and staining for GUSB activity. MPS-VII micewere injected with SV-GUSB (107 rfu). Serial serum GUSB levels were measured. Mice were sacrificed at intervals after the injection. GUSB expression, GUSB activity and histological clearance of GAG deposits was examined in various tissues. Results: Two weeks after SV-GUSB injection, serum GUSB activity increased from undetectable levels to 40–150% of normal. Southern blot analysis showed transduction of multiple organs (liver > spleen > kidney > lung > brain), but not spermatozoa. All abdominal viscera were repleted with GUSB in two weeks. In addition, a significant number of brain cells, including neural cells and microglia exhibited GUSB activity and clearance of the GAG deposits in two months. Molecular analysis showed integration of the transgene into the host genome along with life-long expression. Conclusions: rSV40 vectors are the first gene transfer vehicles that permit efficient correction of LSD lesions in both abdominal organs and the brain after intravenous administration. This integrating, non-immunogenic vector can be administered repeatedly and is an attractive vehicle for comprehensive gene therapy of MPS-VII.