Date of Award
10-24-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Mucopolysaccharidosis type I (MPS I) is a pediatric lysosomal storage disorder caused by biallelic pathogenic variants in the α-L-iduronidase (IDUA) gene that lead to the loss of a functional form of IDUA enzyme. Loss of this necessary enzyme leads to pathogenic accumulation of glycosaminoglycans (GAG) in lysosomes, leading to cellular distention and dysfunction. IDUA is necessary in every cell of the body and, as a result, a loss of function leads to clinical manifestations of the disease such as developmental delay, cardiac dysfunction, bone disease (dysostosis multiplex), upper respiratory complications, and premature death. A range of severity occurs, with Hurler syndrome identified as the most severe form and typically associated with complete loss of function of IDUA. The least severe form is classified as Scheie syndrome, and Hurler-Scheie represents an intermediate category. The scientific advances that have been made in the treatment of MPS I will be discussed in Chapter One of this dissertation. There are currently two clinically available treatments for MPS I: hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT). HSCT has strict criteria for eligibility and is only used for Hurler syndrome patients who are less than three years old at the time of treatment. ERT, however, can be used for MPS I at any age. While these treatments have been lifesaving and increase lifespan for patients who receive them, they are non-curative as evidenced by continued disease in the cardiovascular, skeletal, and central nervous systems. As a result, modifications to available treatments and development of new treatments for greater efficacy in MPS I is necessary ERT consists of recombinant human IDUA administered via intravenous (IV)ƒintra infusion. The effectiveness of treatment depends on the property of cross-correction, in which mannose-6-phosphate receptors on the lysosomal surface mediate intracellular uptake and trafficking of exogenously administered IDUA to the endosomal-lysosomal system. This treatment must be readministered weekly for life, and some manifestations of MPS I are not corrected with this treatment as mentioned above. Additional treatments used in conjunction with ERT are being studied to ameliorate the portions of MPS I that are not effectively treated by ERT alone including the cardiovascular system. Due to the involvement of the renin angiotensin system in MPS I related cardiac disease, an angiotensin II receptor blockade (losartan) is a candidate for additional or synergistic benefits when treated alongside ERT. Due to this, we explored the use of both treatment methods in the murine model of MPS I and evaluated inflammation through serum cytokine levels. The results of this study are outline in Chapter Two of this dissertation. While the angiotensin II receptor blockade alone lowered MPS I related inflammation, we observed increased cytokine levels in mice treated with ERT alone and hypothesized these may be a result of anti-drug antibodies (ADA) as both ERT treated groups developed anti-IDUA antibodies. To better understand the role of ADAs in enzyme replacement therapy for MPS I, a study was designed to test how these antibodies may be affecting the distribution of ERT. Outcomes of treatment using immune compromised MPS I animals given ERT alone or a combination of ERT with anti-IDUA antibodies to imitate an anti-drug antibody reaction is outlined in Chapter Three. Biochemical results from several tissue types displayed altered distribution of ERT corresponding with presence of anti-IDUA antibodies. Potentially more poignantly, a difference in skeletal structure was observed in animals treated with and without anti-IDUA antibodies. The skeletal disease in MPS I is another aspect that is not corrected with ERT and is associated with some of the most debilitating characteristics of MPS I for patients. ERT has not previously been shown to affect dysostosis multiplex, however, in the study outlined in Chapter Three, we observed that MPS I mice treated with ERT and no antibodies had a cortical bone structure similar to carrier animals who show no disease effects. Additionally, the ERT alone treated animals had significantly different cortical structure from control knockout mice and mice treated with ERT and antibodies. This result alters the current understanding of the role of ADAs in MPS I and can inform future treatment. Finally, while ERT is effective to treat MPS I, it is non-curative and requires regular re-administration. To this end, alternative therapies for MPS I have been highly sought after and one such approach is gene therapy. While several vector systems have been explored in the pursuit of a gene therapy treatment for mucopolysaccharidoses type I (MPS I), adenoviral (Ad) vectors have been highly understudied. Ad vectors are non-integrating, have a large packaging capacity, and can be targeted to specific cell types using fiber and hexon modifications. In Chapter Four, a novel gene therapy approach is presented utilizing a modified Ad expressing IDUA to target endothelial cells in vivo, potentially circumventing hepatotoxicity by de-targeting the liver. To accomplish this targeting, we have modified an Ad vector to include a myeloid binding peptide (MBP) on the Ad fiber which has been shown to increase viral pulmonary endothelial cell transduction. Using validated viral vectors, we conducted in vivo studies in adult and newborn mice testing two Ad vectors, one including the MBP modification and the other not, administered through IV injections. Our results indicates that the cell targeting of the vector functions properly and enables further development of gene therapy for MPS I.
Language
English (en)
Chair and Committee
Patricia Dickson
Committee Members
David Curiel; Jonathan Cooper; Mark Sands; Xiaoxia Cui
Recommended Citation
Hurt, Sarah, "Treatment Modifications and Development for Mucopolysaccharidosis Type I" (2024). Arts & Sciences Electronic Theses and Dissertations. 3275.
https://openscholarship.wustl.edu/art_sci_etds/3275