Gene Therapy for Mucopolysaccharidosis Type II
2022-12
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Gene Therapy for Mucopolysaccharidosis Type II
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2022-12
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Abstract
Mucopolysaccharidosis type II (Hunter syndrome, MPS II) is an inherited X- linked recessive disease caused by deficiency of iduronate-2-sulfatase (IDS). IDS hydrolyzes the C2 sulfate ester bond of terminal -L-iduronic acid residues on the glycosaminoglycans (GAGs) heparan sulfate and dermatan sulfate. Insufficient IDS results in the accumulation of these GAGs within lysosomes and leads to progressive and multisystemic disease. Disease manifestations include, but are not limited to, cardiopulmonary dysfunction, arthropathy, dysostosis multiplex, and for the neuronopathic form neurological impairment and death by early adolescence. Currently, the only approved treatment for MPS II is enzyme replacement therapy (ERT, Elaprase®); allogeneic hematopoietic stem cell transplantation (HSCT) is conducted on a trial basis. ERT is expensive, time consuming, and administered IDS enzyme does not readily cross the blood brain barrier, leaving the neurological manifestations of MPS II unaddressed. Thus, there is a great need to develop new and better therapies for MPS II that can address these limitations.Ex vivo lentiviral vector (LVV) based gene therapy is a promising approach to treat MPS II. Chapter II evaluates the efficacy of this strategy by the transplantation of hematopoietic stem and progenitor cells (HSPCs) transduced with a (LVV) carrying a codon optimized human IDS cDNA regulated by a strong, constitutively active MNDU3 promoter into MPS II mice. Treated mice exhibited supraphysiologic levels of IDS enzyme activity in plasma, peripheral blood mononuclear cells (PBMCs), and in peripheral tissues. Additionally, urine GAG excretion, GAG content in peripheral tissues,
and zygomatic arch diameter were normalized. Importantly, IDS levels in the brains of
MNDU3-IDS engrafted animals were restored to 10-20% that of wild-type mice, which was sufficient to normalize brain GAG storage and prevent the emergence of neurocognitive deficits. Thus, these results demonstrate the potential effectiveness of ex vivo LVV transduced HSPCs as a source of bioavailable IDS for patients with MPS II.
In vivo gene therapy with an adeno-associated virus (AAV) vector is another approach for the treatment of MPS II. Clinical testing of cerebrospinal fluid (CSF)- directed administration of AAV9.CB7.hIDS (RGX-121) is currently underway to treat the neurological manifestations of MPSII. However, it is unknown if IT administration of RGX-121 will also improve systemic manifestations of MPS II or whether supplemental systemic administration will be required. Additionally, a potential minimum effective dose required to alleviate disease manifestations has so far been undetermined. Chapter III compares the delivery of RGX-121 by two routes of administration (ROA), intrathecal (IT) and intravenous (IV), at a range of doses. Doses of 1x107gc and 1x108gc were ineffective. A dose of 1x109gc by either ROA resulted in plasma IDS activity at or above wild type levels but was insufficient to achieve wild type levels of IDS or GAGs in most tissues, including the brain. However, doses of 1x1010gc and 1x1011gc by either ROA resulted in supraphysiological plasma IDS activity, and at or above wild type IDS levels and commensurate GAG reduction in nearly all tissues. Notably, these same doses by either ROA showed normalization of zygomatic arch diameter compared to untreated controls, thereby demonstrating that peripheral manifestations are corrected by both IV and IT ROAs. Administration of 1x1011gc IT resulted in the highest quantifiable levels of IDS activity and greatest reduction in GAG content in the brain, as well as the prevention of neurocognitive deficits. Thus, a 1x1010gc dose of RGX-121 by either ROA was sufficient to normalize metabolic and skeletal outcomes in MPS II mice, but neurologic benefit required IT administration of 1x1011gc, suggesting the prospect of a similar direct benefit in humans.Current MPS II gene therapy studies use IDS deficient strains, but future preclinical work with human cells require the use of an immunodeficient MPS II mouse model of the disease. Chapter IV details the generation and characterization of an NSG- MPS II mouse strain, where CRISPR/Cas9 was employed to knock out a portion of the murine IDS gene on the immunodeficient NSG background. No IDS activity was detected in the plasma, PBMCs, or tissues of these mice. GAG analysis revealed elevated levels of storage material in those same tissues and in the urine. Histopathology showed vacuolized cells in both the periphery and CNS. NSG-MPS II mice also recapitulated skeletal and neurocognitive manifestations associated with MPS II in humans. This immunodeficient model of MPS II will therefore be useful for testing potential treatments for MPS II involving xenotransplantation of human cells. Overall, the data in this work provide preclinical data supporting two different gene therapy approaches for the treatment of MPS II, as well as the development of an immunodeficient of the disease for future studies.
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University of Minnesota Ph.D. dissertation. December 2022. Major: Molecular, Cellular, Developmental Biology and Genetics. Advisor: Scott McIvor. 1 computer file (PDF); x, 193 pages.
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Smith, Miles. (2022). Gene Therapy for Mucopolysaccharidosis Type II. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/252506.
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