The research laboratory has focused on understanding the disease process and developing treatments for MLD. Cultured fibroblast cell lines from patients with MLD and the mouse model of MLD have been extensively studied. Successes with both the cell lines and the mouse model have informed experiments designed to accumulate further preclinical safety data.
In MLD, mutations in the ARSA gene cause the loss of the activity of the enzyme arylsulfatase A (ARSA) resulting in the accumulation of a lipid, sulfatide, in the central and peripheral nervous systems. This causes a progressive neurodegeneration. The mouse model of MLD also accumulates sulfatide in the brain especially the cerebellum.
The blood brain barrier protects the brain but is a major impediment to treating MLD and other lysosomal storage diseases with a neurological component. We have developed a strategy to treat the MLD mouse using adult mice with a mature blood brain barrier. This mimics the clinical situation where almost all patients with MLD are diagnosed at an age when the blood brain barrier is formed. The therapy is to surgically access the lateral ventricle of the brain. The lateral ventricle is filled with cerebral spinal fluid (CSF) and contains the choroid plexus that produces the CSF. The measure of success for the treatment is the reduction of the concentration of
sulfatide in the cerebellar region of the brain to levels seen in wild type mice.
The treatment is gene therapy using a lentivirus – based gene therapy vector (LV-hARSA) that contains DNA that codes for a functional ARSA. Surgical delivery of LV-hARSA into the lateral ventricle of adult MLD mice results in the widespread transduction of cells within the choroid plexus and ependymal cells throughout the CNS and stable expression for months.
Ependymal cells line the CSF containing compartments in the brain. A single dose of LV-hARSA delivered into the lateral ventricle of adult MLD mice reduces cerebellar sulfatide concentrations by 18% to the same level as seen in wild type mice. More than 100 mice and rats have been treated and tolerated both the surgical procedure and LVhARSA without adverse events.
The gene therapy vector, LH-hARSA, introduces a correct ARSA gene sequence into the chromosomes of the choroid plexus and ependymal cells that are transduced. Detailed studies to identify the location of the integrated ARSA gene within those chromosomes have been completed as part of a safety assessment and demonstrated a clinically favorable integration site profile. Further safety studies have been successfully completed using both the mouse model of MLD and cultured
cells obtained from patients with MLD. These studies have not identified vector – caused toxicity.
Research is ongoing to assess the potential of cell therapy in the mouse model of MLD using mesenchymal stem cells. Mesenchymal stem cells expressing green fluorescent protein introduced with a foamy virus vector are seen to have migrated from the lateral ventricle (left) to distant areas of the mouse brain.
A pre – clinical trial application meeting with Health Canada to discuss a potential clinical trial using intra-cerebroventricular delivery has informed the direction of future research to prepare for a clinical trial application. Other ongoing research is targeted at developing strategies to impact peripheral nerve disease.
– Research Summary