Gene therapy for the treatment of neurologic and somatic mucopolysaccharidosis type II (Hunter syndrome)

    Student thesis: Doctoral thesis

    Abstract

    Mucopolysaccharidosis type II (MPSII), or Hunter syndrome, is an X-linked recessive lysosomal storage disease (LSD) caused by the deficiency in Iduronate-2-sulfatase (IDS), an enzyme involved in the stepwise degradation of the glycosaminoglycans (GAGs) heparan sulfate (HS) and dermatan sulfate (DS). The pathological accumulation of undegraded HS and DS in the lysosomes leads to cell dysfunction, causing severe neurologic and somatic disease. The most severe and most prevalent form of Hunter syndrome is characterized by chronic and progressive neurodegeneration of the central nervous system (CNS) and multisystem dysfunction; patients usually die during the second decade of life. To date, weekly intravenous enzyme replacement therapy (ERT) constitutes the only approved therapeutic option for MPSII. However, the inability of recombinant IDS to efficiently cross the blood-brain barrier (BBB) limits the efficacy of ERT in treating neurological symptoms. The therapy has several other drawbacks. Thus, an efficient therapy for the treatment of the neurodegeneration of MPSII disease represents a highly unmet medical need. In vivo gene therapy with adeno-associated vectors offers the possibility of lifelong therapeutic benefit following a single administration.

    Therefore, the present work was focused on the development of a new gene therapy approach for MPSII based on the delivery of vectors to the cerebrospinal fluid (CSF) and aimed at counteracting simultaneously the neurological and somatic pathology characteristic of the disease. Adeno-associated virus serotype 9 (AAV9) vectors containing the murine Ids gene were administered through a minimal invasive procedure to the CSF of 2-month-old MPSII mice, which already presented established pathology. The efficacy of AAV9-Ids vectors to counteract MPSII pathology after a single intra-CSF injection was evaluated 4 and 8 months after treatment. AAV9-mediated Ids gene transfer led to a significant increase in IDS activity throughout the encephalon, which resulted in full reversion of lysosomal storage lesions. In addition, correction of lysosomal dysfunction in the CNS, normalization of brain transcriptomic signature and disappearance of neuroinflammation were achieved after gene transfer. Moreover, after AAV9-Ids delivery to the CSF, vectors also transduced the liver, providing a peripheral source of the therapeutic protein that corrected storage pathology in visceral organs of treated MPSII mice. The reversion of the pathology in non-transduced somatic organs provided evidence of cross-correction by circulating enzyme. Importantly, AAV9-Ids treatment also resulted in normalization of behavioural deficits and considerably prolonged the survival of treated MPSII mice.

    The efficacy of the intra-CSF administration of AAV9 vectors containing the human IDS coding sequence was also evaluated in MPSII mice. One and a half months after gene transfer, a significant increase in IDS activity was documented throughout the encephalon, an in the liver and serum of treated MPSII mice. Consequently, pathological GAG content was reduced, or even normalized, in the CNS and in most somatic tissues of MPSII mice that received the vectors.

    Altogether, the results obtained in the present work provide a strong proof of concept that supports the clinical translation of the intra-CSF AAV9-IDS gene therapy for the treatment of Hunter patients with cognitive impairment.
    Date of Award11 Jul 2016
    Original languageEnglish
    SupervisorMaria Fatima Bosch Tubert (Director) & Virginia Haurigot Mendoça (Director)

    Keywords

    • MPSII
    • Mucopolysacaridosis type II
    • AAV

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