Adeno-Associated Virus Gene Therapy in a Sheep Model of Tay–Sachs Disease

Abstract

Tay-Sachs disease (TSD) is a fatal neurodegenerative disorder caused by a deficiency of the enzyme hexosaminidase A (HexA). TSD also occurs in sheep, the only experimental model of TSD that has clinical signs of disease. The natural history of sheep TSD was characterized using serial neurological evaluations, 7 Tesla magnetic resonance imaging, echocardiograms, electrodiagnostics, and cerebrospinal fluid biomarkers. Intracranial gene therapy was also tested using AAVrh8 monocistronic vectors encoding the α-subunit of Hex (TSD α) or a mixture of two vectors encoding both the α and β subunits separately (TSD α + β) injected at high (1.3 × 10 vector genomes) or low (4.2 × 10 vector genomes) dose. Delay of symptom onset and/or reduction of acquired symptoms were noted in all adeno-associated virus-treated sheep. Postmortem evaluation showed superior HexA and vector genome distribution in the brain of TSD α + β sheep compared to TSD α sheep, but spinal cord distribution was low in all groups. Isozyme analysis showed superior HexA formation after treatment with both vectors (TSD α + β), and ganglioside clearance was most widespread in the TSD α + β high-dose sheep. Microglial activation and proliferation in TSD sheep-most prominent in the cerebrum-were attenuated after gene therapy. This report demonstrates therapeutic efficacy for TSD in the sheep brain, which is on the same order of magnitude as a child's brain.

Tay-Sachs disease

“…(21) In the post-mortem assesment, a superior HexA genome distribution and the TSD α + β vector were observed in the brain of the treated sheep compared to a sheep with TSD α, but the distribution in the spinal cord was low in all groups. (21) The analysis of isoenzymes showed a greater formation of HexA after treatment with both vectors (TSD α+β); in TSD α+β sheep that were treated with high doses, the clearance of gangliosides was more widespread. (21) After gene therapy, proliferation and microglial activation in TSD sheep increased, proving the therapeutic efficacy in the brain of the sheep, which is on the same magnitude as a child's brain.…”

“…(21) Intracranial gene therapy is tested using monoconstronic AAV/rh8 vectors, which encode the α subunit of Hex (TSD α) or a mixture of the vectors encoding the α and β subunits separately (TSD α + β) injected at a high dose (1.3x1013 vector genomes) or a low dose (4.2x1012 vector genomes). (21) In all the sheep that were treated with associated adenoviruses, there was a delay in the onset of the symptoms or a reduction of the existing ones. (21) In the post-mortem assesment, a superior HexA genome distribution and the TSD α + β vector were observed in the brain of the treated sheep compared to a sheep with TSD α, but the distribution in the spinal cord was low in all groups.…”

“…(21) In all the sheep that were treated with associated adenoviruses, there was a delay in the onset of the symptoms or a reduction of the existing ones. (21) In the post-mortem assesment, a superior HexA genome distribution and the TSD α + β vector were observed in the brain of the treated sheep compared to a sheep with TSD α, but the distribution in the spinal cord was low in all groups. (21) The analysis of isoenzymes showed a greater formation of HexA after treatment with both vectors (TSD α+β); in TSD α+β sheep that were treated with high doses, the clearance of gangliosides was more widespread.…”

“…(21) After gene therapy, proliferation and microglial activation in TSD sheep increased, proving the therapeutic efficacy in the brain of the sheep, which is on the same magnitude as a child's brain. (21) A murine model for TSD showed several of the neuropathological characteristics of the disease, mainly the accumulation of GM2 gangliosides. (2) However, it did not present its clinical signs because of the presence of a lysosomal sialidase able to hydrolyze GM2 in GA2, which is its asialo neutro derivative that interacts with HexB to degrade until it reaches glucosylceramide.…”

Improvement of motor and behavioral activity in Sandhoff mice transplanted with human CD34+ cells transduced with a HexA/HexB expressing lentiviral vector

“…These include enzyme replacement therapy, allogeneic hematopoietic stem cells (HSCs) and blood transplants, adeno-associated virus delivery of HexA and HexB, substrate reduction therapy, gene editing using a CRISPR system and chaperone therapy. [7][8][9][10][11][12][13][14][15][16][17][18][19] Enzyme replacement therapy is a straight-forward approach of injecting the wild-type (WT) HexA and/or HexB protein product, however, it does not readily enter the central nervous system (CNS). [7][8][9] Allogeneic HSC and blood transplants have been utilized to systemically deliver HexA and HexB to patients through the blood system from donors who are unaffected by TSD or SD.…”