GM1 is a genetic disorder that occurs when a person has very low amounts of a vital enzyme, β-galactosidase. The absence of this enzyme affects nerve cells (called neurons) in the brain and spinal cord, components of the central nervous system (CNS). GM1 gangliosidosis involves small compartments within cells called lysosomes. Lysosomes contain various enzymes that break down (or metabolize) larger molecules into smaller components for reuse or recycling elsewhere in the cell. This avoids the buildup of too many of these components within the cell. The absence of a lysosomal enzyme result in the buildup of excess waste in the cells of the impacted organ or system, causing a Lysosomal Storage Disease (LSD). GM1 is a fatal LSD, which causes developmental regression, mobility deterioration, seizures, visual impairment, and neurodegeneration. It currently has no cure or effective treatment.
Each LSD is rare on its own, but collectively LSDs impact a significant number of people, with about 1 in 100,000 to 1 in 200,000 infants born with GM1 gangliosidosis each year. Our project focus on developing effective treatments that are desperately needed for CNS disorders, like GM1 gangliosidosis.
Our therapeutic strategy is based on ex vivo gene therapy (GT), which works by providing a functional copy of the defective gene, in this case the gene encoding the β-galactosidase (GLB1), using a vector that allows the gene to penetrate inside the patient's cells and then express itself. Specific aims of the projects are the development of such therapeutic vector, the investigation of its therapeutic efficacy in vitro, in GM1-patient derived primary cells, and the validation of the whole gene therapy strategy in the murine model of the disease, i.e. mice affected by GM1.
After a work-intensive design and characterization step of a therapeutic vector encoding the human β-galactosidase, we tested its therapeutic potential in vitro. In GM1 patient-derived primary fibroblasts, a single vector copy resulted sufficient to restore the normal level of β-gal activity in this cell-type, and an average of 2 vector copies per cell determined a complete metabolic correction, removing GM1 ganglioside accumulations in few weeks. Preliminary data of β-gal activity in the blood of GM1 mice receiving the gene therapy, indicate a reconstitution of ~12% of the murine enzymatic activity, approximately equivalent to the human physiological level. Overall, considering the promising in vitro data produced in the cellular model of the disease, and the encouraging preliminary results in vivo, we hope and believe this study will generate a proof of concept for a future clinical development of an efficacious ex vivo GT for infantile GM1-gangliosidosis.
