Preclinical Development of Intrathecal Gene Therapy for AB-Variant GM2 Gangliosidosis

Abstract

AB-Variant GM2 Gangliosidosis (ABGM2), caused by impairment of GM2 activator (GM2A) protein activity, is a rare lysosomal storage disorder that results in early death, in its human infantile form. This condition is inherited as an autosomal recessive disorder, where patients experience developmental arrest and regression of attained milestones due to widespread neurodegeneration. ABGM2 results in pathological accumulation of GM2 ganglioside (GM2), an essential lipid in the plasma membrane, which are especially enriched on neuronal surfaces. Abnormal build-up of GM2 triggers a cascade of events that result in cellular apoptosis. There is currently no effective treatment beyond palliative care and there is minimal research being conducted to find a cure for ABGM2. This thesis comprises three independent studies that attempt to address these gaps in the literature surrounding ABGM2. The first study is a dose-response study that was conducted on Gm2a-/- mice, a mouse model of ABGM2 which experiences a relatively mild manifestation of the disease. A minimally efficacious dose for Adeno-associated virus (AAV)-mediated gene therapy was identified as being 1.0x1011 vector genomes (vg) per mouse. These data provided proof-of-principal that AAV can successfully deliver a GM2A transgene to the central nervous system and biochemically correct the key pathological features of ABGM2. The second study describes the successful development and characterization of a murine model (Gm2a-/-Neu3-/-) that more closely reflects the phenotypic and biochemical severity of human juvenile ABGM2. This mouse model experiences a severely compromised lifespan and abnormal accumulation of GM2, offering a more valuable animal model for ABGM2 than Gm2a-/- mice. The final study is a preliminary study that focused on two promoters (CBh and JeT) driving expression of a wild-type or codon optimized GM2A transgene, mediated by AAV, both in vitro and in vivo (Gm2a-/-Neu3-/- mice). The JeT promoter in combination with a codon optimized transgene successfully reversed GM2 accumulation associated with loss-of-function GM2A, 4 weeks post-injection. The findings in this thesis represent significant progress in ABGM2 research, offering a promising direction for future research towards a cure.