Lentiviral Gene Therapy for MLD

Metachromatic leukodystrophy (MLD) is a rare lysosomal storage disease. This disease is an inherited single gene autosomal recessive defect. MLD is caused by a mutation in the ARSA gene encoding arylsulfatase A which leads to a deficiency in sulfatide degradation, resulting in its accumulation in oligodendrocytes, Schwann cells and some neurons. A critical level of sulfatide storage can trigger demyelination, the hallmark of MLD, which results in multiple neurological symptoms. MLD has different onset ages including late infancy (1-2 years), adolescence (4 years-before sexual maturity) and adulthood (after sexual maturity). MLD patients are normally rescued by hematopoietic stem cell transplantation (HSCT) from a matched healthy donor. However, HSCT must be performed at a very early stage of the disease thus restricting its therapeutic opportunies in MLD patients. This trial aims to treat MLD using a safety and efficiency improved self-inactivating lentiviral vector carrying a functional MLD gene to correct the genetic defect by intracerebral injection to delivery the lentiviral vector carrying a normal ARSA gene to correct the pathogenic defect. The primary objectives are to evaluate the safety of the improved self-inactivating lentiviral vector TYF-ARSA, the in vivo gene transfer clinical protocol and the efficacy of degradative metabolite in patients at the time of treatment, assessment of vector integration sites, and finally the long-term correction of the related pathological symptoms.