160. Successful Treatment of Neonatal Metachromatic Leukodystrophy Model Mice by Low Dose of Self-Complementary AAV Type9 Vector Expressing ASA

2016 
Metachromatic leukodystrophy (MLD) is a lysosomal storage disease (LSD) caused by a functional deficiency of the lysosomal enzyme arylsulfatase A (ASA) and characterized by severe neurological symptoms due to widespread and progressive demyelination in the both central and peripheral nervous systems. Enzyme replacement therapy (ERT) has been applied to treat certain types of LSDs, but correction of neurological abnormalities is usually hampered by the blood brain barrier (BBB). We have previously shown that MLD mice can be treated by intravenous (IV) injection of classical single-stranded AAV type 9 vector expressing ASA (ssAAV9/ASA) for neonate and self-complementary AAV9/ASA (scAAV9/ASA) for adult. To develop the clinical MLD gene therapy, it is important to decrease the amount of viral vectors because of safety. In this study, we evaluated the therapeutic potential of scAAV9/ ASA-mediated systemic transduction of neonatal MLD mice at 10 times lower dose (2 × 1011 v.g./body) compared to the treatable dose of the ssAAV9/ASA (2 × 1012 v.g./body). We generated both ssAAV9/ASA and scAAV9/ASA to intravenously inject then into the neonatal MLD mice (n=6-9). ELISA analysis showed that sustained high-level expression of ASA was detected in the brain and spinal cord of the scAAV9/ASA-treated mice (cerebral cortex, 2.1 times; cerebellum, 2 times; spinal cord, 5.5 times) compared to the ssAAV9/ASA for more than one year. Furthermore, in the behavior test, both scAAV9/ASA and ssAAV9/ASA-treated mice showed a significant improvement in their ability to traverse narrow balance beams, as compared to the non-treated MLD mice (latency; 7.2±0.9, 9.3±1.1 vs. 16.6±0.8 sec, P<0.05: slips; 3.4±0.8, 3.6±0.6 vs. 7.3±1.8 times, P<0.05). These data clearly demonstrate that MLD model mice can be treated by systemic neonatal transduction with low dose of scAAV9/ASA. Therefore, neonatal gene therapy would be an important option for parents faced with the prenatal diagnosis of a genetically affected child. Since ten times lower dose of scAAV9/ASA is enough to treat the neonatal MLD mice compared to ssAAV9/ASA, transduction strategy to use scAAV9/ASA should be safe and more practical for the clinical MLD gene therapy.
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