Subha Karumuthil-Melethil

Intrathecal administration of AAV/GALC vectors in 10–11-day-old twitcher mice improves survival and is enhanced by bone marrow transplant

Globoid cell leukodystrophy (GLD), or Krabbe disease, is an autosomal recessive neurodegenerative disease caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). Hematopoietic stem cell transplantation (HSCT) provides modest benefit in presymptomatic patients but is well short of a cure. Gene transfer experiments using viral vectors have shown some success in extending the survival in the mouse model of GLD, twitcher mice. The present study compares three single‐stranded (ss) AAV serotypes, two natural and one engineered (with oligodendrocyte tropism), and a self‐complementary (sc) AAV vector, all packaged with a codon‐optimized murine GALC gene. The vectors were delivered via a lumbar intrathecal route for global CNS distribution on PND10–11 at a dose of 2 × 1011 vector genomes (vg) per mouse. The results showed a similar significant extension of life span of the twitcher mice for all three serotypes (AAV9, AAVrh10, and AAV‐Olig001) as well as the scAAV9 vector, compared to control cohorts. The rAAV gene transfer facilitated GALC biodistribution and detectable enzymatic activity throughout the CNS as well as in sciatic nerve and liver. When combined with BMT from syngeneic wild‐type mice, there was significant improvement in survival for ssAAV9. Histopathological analysis of brain, spinal cord, and sciatic nerve showed significant improvement in preservation of myelin, with ssAAV9 providing the greatest benefit. In summary, we demonstrate that lumbar intrathecal delivery of rAAV/mGALCopt can significantly enhance the life span of twitcher mice treated at PND10–11 and that BMT synergizes with this treatment to improve the survival further.

Construction of a hybrid β-hexosaminidase subunit capable of forming stable homodimers that hydrolyze GM2 ganglioside in vivo

Tay-Sachs or Sandhoff disease result from mutations in either the evolutionarily related HEXA or HEXB genes encoding respectively, the α- or β-subunits of β-hexosaminidase A (HexA). Of the three Hex isozymes, only HexA can interact with its cofactor, the GM2 activator protein (GM2AP), and hydrolyze GM2 ganglioside. A major impediment to establishing gene or enzyme replacement therapy based on HexA is the need to synthesize both subunits. Thus, we combined the critical features of both α- and β-subunits into a single hybrid µ-subunit that contains the α-subunit active site, the stable β-subunit interface and unique areas in each subunit needed to interact with GM2AP. To facilitate intracellular analysis and the purification of the µ-homodimer (HexM), CRISPR-based genome editing was used to disrupt the HEXA and HEXB genes in a Human Embryonic Kidney 293 cell line stably expressing the µ-subunit. In association with GM2AP, HexM was shown to hydrolyze a fluorescent GM2 ganglioside derivative both in cellulo and in vitro. Gene transfer studies in both Tay-Sachs and Sandhoff mouse models demonstrated that HexM expression reduced brain GM2 ganglioside levels.

Systemic Gene Transfer of a Hexosaminidase Variant Using an scAAV9.47 Vector Corrects GM2 Gangliosidosis in Sandhoff Mice

GM2 gangliosidosis is a group of neurodegenerative diseases caused by β-hexosaminidase A (HexA) enzyme deficiency. There is currently no cure. HexA is composed of two similar, nonidentical subunits, α and β, which must interact with the GM2 activator protein (GM2AP), a substrate-specific cofactor, to hydrolyze GM2 ganglioside. Mutations in either subunit or the activator can result in the accumulation of GM2 ganglioside within neurons throughout the central nervous system. The resulting neuronal cell death induces the primary symptoms of the disease: motor impairment, seizures, and sensory impairments. This study assesses the long-term effects of gene transfer in a Sandhoff (β-subunit knockout) mouse model. The study utilized a modified human β-hexosaminidase α-subunit (μ-subunit) that contains critical sequences from the β-subunit that enables formation of a stable homodimer (HexM) and interaction with GM2AP to hydrolyze GM2 ganglioside. We investigated a self-complementary adeno-associated viral (scAAV) vector expressing HexM, through intravenous injections of the neonatal mice. We monitored one cohort for 8 weeks and another cohort long-term for survival benefit, behavioral, biochemical, and molecular analyses. Untreated Sandhoff disease (SD) control mice reached a humane endpoint at approximately 15 weeks, whereas treated mice had a median survival age of 40 weeks, an approximate 2.5-fold survival advantage. On behavioral tests, the treated mice outperformed their knockout age-matched controls and perform similarly to the heterozygous controls. Through the enzymatic and GM2 ganglioside analyses, we observed a significant decrease in the GM2 ganglioside level, even though the enzyme levels were not significantly increased. Molecular analyses revealed a global distribution of the vector between brain and spinal cord regions. In conclusion, the neonatal delivery of a novel viral vector expressing the human HexM enzyme is effective in ameliorating the SD mouse phenotype for long-term. Our data could have implications not only for treatment of SD but also for Tay-Sachs disease (α-subunit deficiency) and similar brain disorders.

Long-Term Improvement of Neurological Signs and Metabolic Dysfunction in a Mouse Model of Krabbe’s Disease after Global Gene Therapy

We report a global adeno-associated virus (AAV)9-based gene therapy protocol to deliver therapeutic galactosylceramidase (GALC), a lysosomal enzyme that is deficient in Krabbes disease. When globally administered via intrathecal, intracranial, and intravenous injections to newborn mice affected with GALC deficiency (twitcher mice), this approach largely surpassed prior published benchmarks of survival and metabolic correction, showing long-term protection of demyelination, neuroinflammation, and motor function. Bone marrow transplantation, performed in this protocol without immunosuppressive preconditioning, added minimal benefits to the AAV9 gene therapy. Contrasting with other proposed pre-clinical therapies, these results demonstrate that achieving nearly complete correction of GALCs metabolic deficiencies across the entire nervous system via gene therapy can have a significant improvement to behavioral deficits, pathophysiological changes, and survival. These results are an important consideration for determining the safest and most effective manner for adapting gene therapy to treat this leukodystrophy in the clinic.

Immunological considerations for treating globoid cell leukodystrophy.

Globoid cell leukodystrophy (GLD, or Krabbes disease) is a severe inherited neurodegenerative disease caused by the lack of a lysosomal enzyme, GALC. The disease has been characterized in humans as well as three naturally occurring animal models, murine, canine, and nonhuman primate. Multiple treatment strategies have been explored for GLD, including enzyme replacement therapy, small‐molecule pharmacological approaches, gene therapy, and bone marrow transplant. No single therapeutic approach has proved to be entirely effective, and the reason for this is not well understood. It is unclear whether initiation of a neuroinflammatory cascade in GLD precedes demyelination, a hallmark of the disease, but it does precede overt symptoms. This Review explores what is known about the role of inflammation and the immune response in the progression of GLD as well as how various treatment strategies might interplay with innate and adaptive immune responses involved in GLD. The focus of this Review is on GLD, but these concepts may have relevance for other, related diseases.

57. Intrathecal Administration of AAV/GALC Vectors in Juvenile Twitcher Mice Improves Survival and Is Enhanced by Bone Marrow Transplant

Globoid cell Leukodystrophy (GLD) or Krabbe disease is a rapidly progressing, neurodegenerative disease caused by the deficiency of the lysosomal enzyme Galactocerebrosidase (GALC). The pathological characteristics include presence of globoid cells and decreased myelin. In its severe infantile form, the symptoms appear within the first 6 months of life and complete loss of GALC function is fatal by 2-3 years old. The murine model of infantile GLD, the twitcher mouse, has been used to evaluate potential therapeutic approaches for GLD. Hematopoietic stem cell transplantation (HSCT) provides modest benefit in presymptomatic patients and mice indicating a slowdown in the progression of the disease, but no complete cure. Neonatal gene transfer experiments using viral vectors also has shown some limited success in extending the survival of the twitcher mice. The translatability of neonatal therapy in mice to human has met with difficulties as the stage of the disease in human and mice differ due to the difference in their gestation periods. So there is a need for testing out later stage interventions for GLD treatment. In the present study, we compare multiple vector designs along with a combination treatment of AAV plus bone marrow transplant (BMT) in juvenile twitcher mice. Initially, three single stranded (ss) AAV serotypes, two natural and one engineered (with oligodendrocyte tropism), were packaged with a codon-optimized murine GALC gene driven by the beta actin promoter. The vectors were delivered via a lumbar intrathecal route for global CNS distribution on post-natal day (PND) 10-11, at a dose of 2×1011 vg per mouse. The results show a significant extension of life span of the twitcher mice for all three serotypes (AAV9, AAVrh10, and AAV-Olig001) when compared to control cohorts. The treatment produced similar survival benefit regardless of which capsid was used. The rAAV gene transfer facilitates GALC biodistribution and detectable enzymatic activity throughout the CNS as well as in sciatic nerve and liver. When combined with BMT from syngeneic wild type mice, there was significant improvement in survival and enzymatic activity over either treatment alone. Immunohistochemical analysis of the brain and spinal cord showed reduced inflammation and pathology. Additionally, we have also tested a novel self-complementary (sc) AAV vector with a minimal synthetic promoter, which would mediate a weaker overall level of GALC expression but express in more cells. Preliminary results indicate that this vector design provides a survival advantage over the ssAAV vector designs. In summary, we demonstrate that lumbar intrathecal delivery of rAAV/mGALCopt can significantly enhance the life span of twitcher mice treated at juvenile stage (PND10-11) and BMT synergizes with this treatment to further improve the survival. This effect is mediated by increased GALC activity in various parts of the nervous system as well as by the reduction in neuro-inflammation. Together, these studies detail a therapeutic approach for GLD in mice which is feasible and relevant for human translation.

363. Improvement of Sandhoff Phenotype Following Intravenous Injection of Adeno-Associated Viral Vector Expressing a Hexosaminidase Isoenzyme in Adult Sandhoff Mice: Preclinical Safety and Efficacy Study

GM2 gangliosidosis disorders stem from a Hexosaminidase A (HexA) isoenzyme deficiency. In humans, HexA is the sole enzyme able to catabolize GM2 ganglioside (GM2). The inability to effectively catabolize GM2 leads to neurodegeneration of the central nervous system. HexA is comprised of 2 subunits (α, β) and works with the GM2 activator protein (GM2AP). In the recent work by Tropak et al. (Mol Ther Met Clin Dev, in press), a hybrid subunit, named µ-subunit, was created (patent pending) by combining the stabilization and GM2AP binding sites of the β-subunit while conserving the catalytic properties of the α-subunit. The ‘µ’-subunit, coded by HEXM, can homodimerize and form a stable, functional enzyme, named HexM, which can interact with GM2AP to hydrolyse GM2. Previous work for successful correction of Sandhoff mice using AAV was only shown in neonatal mice (with immature blood-brain barrier (BBB)) and may not directly help in designing a human clinical trial. In the current study, we examined the efficacy/safety of IV injections of the scAAV9/HEXM vector at two doses in adult SD mice (with mature BBB). In addition, we also tested if an adjunct IV injection of mannitol provides any enhancement in efficacy. At 6 weeks old, the vector was injected via tail vein in cohorts of n=17 and n=15 SD mice at 2.5E+12 or 1.0E+13 vg/mouse, respectively. Another cohort of 16 mice received IV mannitol (3g/kg) prior to an IV injection of 2.5E+12 vg scAAV9/HEXM. Some mice from low dose group were euthanized at 16 weeks for direct analysis with untreated SD control mice, while the remainder were left until for terminal survival. Analysis of survival benefit, locomotor behaviour, biochemical and molecular parameters were performed. While untreated SD mice had a 16 week humane endpoint, 4 of 7 mice in higher dose group are now surviving past 56 weeks, 1 of 12 mice in the low dose cohort, and 4 of 9 mice in the mannitol cohort are surviving past 52 weeks. These increases in survival are all highly significant compared to the ~16 week humane endpoint of untreated SD mice. Behaviourally, there are no major significant differences in locomotion between the groups until after 15 weeks, when the adjunct mannitol group significantly outperforms the PBS group. Survival and behaviour monitoring, and the biochemical analyses for this study are ongoing. The preliminary results from this study show delayed onset of the SD phenotype with a single AAV9/HEXM injection and a significant benefit of a pre-injection of IV mannitol. This study is the first to show that an IV gene transfer using a scAAV/HEXM vector can provide survival and behavioural benefit in adult SD mice especially with adjunct use of mannitol. We propose that these results can advise the design of a human gene therapy trial for SD and the related Tay-Sachs disease.

551. Enhancement of Gene Therapy Treatment for Sandhoff Disease Through Complimentary Drug Therapy

GM2 gangliosidoses is a group of neurodegenerative lysosomal storage disorders caused by deficiency in the β-hexosaminidase A (HexA) enzyme. HexA is a heterodimer composed of 2 subunits; α- (encoded by the HEXA gene) and β-hexosaminidase β (Encoded by the HEXB gene). Mutations in either gene may cause inactivity of HexA leading to either Tay-Sachs disease (TSD, HEXA mutation) or Sandhoff disease (SD, HEXB mutation) respectively. TSD and SD are clinically indistinguishable phenotypes principally affecting infants and young children that are fatal before the age of 4 years; there is currently no effective available treatment. A mouse model for SD has been developed and these mice reach a humane end point at 14-17 weeks of age. Gene therapy can be an important primary therapeutic strategy, but may fall short of a complete rescue. Neuroinflammation and neurodegeneration have been identified as hallmark pathological mechanisms in GM2 gangliosidosis and can be adjunctive therapeutic targets. Neuroanti-inflammatory/neuroprotective agents like non-steroidal anti-inflammatory drugs (NSAIDs), Histone deacetylase inhibitors and pharmacological chaperones have shown ameliorating effects in SD and similar disease models when used alone. Adeno associated virus (AAV) based expression of Hexosaminidase isoenzymes has been shown to increase survival of Sandhoff mice for long term. We tested the combined role of gene therapy and neuroanti-inflammatory/neuroprotective agents in SD mice. Our methods include injecting neonatal SD mice with a relatively low dose (2×1013 vg/kg) of a novel AAV9 vector expressing Hex A using both α and β subunits. A pilot study established the survival of these mice to be approximately 24 weeks, a 55% increase in life span over vehicle-injected controls. We observed a 47% increase in Hex A activity in the midbrain of treated mice as compared to the vehicle injected controls. Cohorts received treatment with neonatal gene therapy alone or in combination with indomethacin (a NSAID), pyrimethamine (a proven pharmacological chaperone for Hex A) and ITF2357 (a histone deactylase inhibitor) to elicit their combinational therapeutic potential. Each drug is administered daily via oral gavage starting the age of 6 weeks. All treatments have been completed and mice are being monitored for survival benefit and locomotor behaviour. Further analyses of enzyme activity, GM2 ganglioside levels and copy numbers will be done. The results of this study will establish a proof-of-concept for a novel combination gene therapy approach for treatment of GM2 gangliosidoses and similar disorders.

725. Assessment of CSF Route for Gene Delivery in Sandhoff Mice Using AAV9 Expressing an Hexosaminidase Isoenzyme

GM2 gangliosidoses are a group of neurodegenerative disorders, characterized by the malfunctioning Hexosaminidase A (HexA) enzyme. HexA is formed by heterodimerization of two subunits, α and β. Hex A, in interaction with GM2 activator protein (GM2AP), is the main isoenzyme able to hydrolyze GM2 gangliosides. HexA deficiencies result in Tay-Sachs (α-subunit deficiency) or Sandhoff disease (SD, β-subunit deficiency). In the recent work by Tropak et al. (Mol Ther Methods Clin Dev, in press), a hybrid human α-subunit, named “µ” and coded by HEXM, was created (patent pending) by incorporating the dimer stabilization and GM2AP binding sites of the β-subunit while maintaining the catalytic properties of the α-subunit. The µ-subunit is able to homodimerize to form a stable and functional enzyme, named HexM, which can interact with the human GM2AP and effectively hydrolyse GM2 gangliosides. Another advantage of this subunit (~1.6 kb) is that it can be packaged in a self-complementary adeno-associated virus (scAAV/HEXM). An intravenous route of scAAV administration has been shown to be successful, but brings with it translational issues including large scale viral preparation and relatively high vector uptake by liver. We tested the cerebrospinal fluid (CSF) route, as an alternative, for delivering scAAV9/HEXM. We injected 2.5E+11 vector genomes per mouse of scAAV9/HEXM via the cisterna magna at 6 weeks of age (n=13). Our controls include treatment with scAAV9/GFP (n=3) and vehicle (n=8). One additional cohort received an IV injection of 25% mannitol (2g/kg) post-AAV9 injection (n=10). We sacrificed part of the cohorts (n=4 each group) at 16 weeks of age (humane end-point of untreated SD mice) for tissue analysis. The remainder are being monitored for long-term survival. The parameters for analyses are survival benefit, locomotor behaviour, Hexosaminidase activity, GM2 ganglioside accumulation, and vector genome biodistribution. The preliminary results from this ongoing study show a significant survival advantage to the humane endpoint in HexM treated (average 28 weeks to date) as compared to negative controls (~16 weeks). The behaviour tests showed improved locomotor activity in HexM-treated mice as compared to negative controls. Results were similar when mannitol was administered in conjunction with scAAV9/HEXM. These preliminary results indicate that the intra-CSF route of administration of AAV9/HEXM is a tractable translatable approach for SD worth further exploration. Additional studies are focused on increased dosage and methods to improve distribution.

711. Intravenous Neonatal Gene Therapy Corrects GM2 Gangliosidosis in Sandhoff Mice for Long-Term, By Using AAV Viral Vector Expressing a New Hexosaminidase Variant

GM2 gangliosidosis is a group of neurodegenerative disorders, characterized by the malfunctioning Hexosaminidase A (HexA) enzyme, for which there is no treatment. HexA is composed of two similar, but non-identical subunits, the alpha and the beta, which must interact with the GM2 activator protein, a substrate-specific cofactor, to hydrolyze GM2. Mutation in either subunit (or the activator) results in the development of GM2 gangliosidosis. In these diseases, the malfunctioning protein is unable to play its role in cleaving GM2 ganglioside, whose accumulation within the neurons of the central nervous system is ultimately toxic. The resulting neuronal death induces the primary symptoms of the disease; motor impairment, seizures, and sensory impairments. The aim of this study is to observe the long-term in vivo effects of a novel treatment in a Sandhoff (beta deficient) mouse model. The treatment utilized a new Hex isoenzyme, Hex M, which functions as a homodimer in the treatment of GM2 gangliosidosis. The HexM subunit is a variant of the human Hex alpha subunit containing critical beta-components that allow it to form stable homodimers and interact with the GM2 activator protein to reduce substrate storage. Our methods include intravenous injections of the neonatal mice with a self-complementary vector (with a synthetic promoter) expressing HexM at day 0-1. We monitored one cohort for 8 weeks and another cohort long-term (>40 weeks) for biochemical, behavioural and molecular analyses. Through the enzymatic and GM2 ganglioside lipid analyses, we see that with a slight increase in enzyme activity, there is a significant increase in the clearance of GM2 gangliosides. On behavioural tests, the treated mice outperform their knockout age matched controls. While the untreated controls die before the age of 15 weeks, treated animals have survived to more than 40 weeks and are still being monitored. The molecular analyses reveal a uniform distribution of the vector between brain and spinal cord regions. In conclusion, the neonatal delivery of our newly synthesized viral vector expressing HexM to the Sandhoff mice provided long-term correction of the disease. This study will have implications not only for treatment of Sandhoff, but also Tay-Sachs disease (alpha deficiency).