Ex Vivo Gene Therapy Treats Bone Complications of Mucopolysaccharidosis Type II Mouse Models through Bone Remodeling Reactivation

Comparative dose effectiveness of intravenous and intrathecal AAV9.CB7.hIDS, RGX-121, in mucopolysaccharidosis type II mice

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal disease caused by iduronate-2-sulfatase (IDS) deficiency, leading to accumulation of glycosaminoglycans (GAGs) and the emergence of progressive disease. Enzyme replacement therapy is the only currently approved treatment, but it leaves neurological disease unaddressed. Cerebrospinal fluid (CSF)-directed administration of AAV9.CB7.hIDS (RGX-121) is an alternative treatment strategy, but it is unknown if this approach will affect both neurologic and systemic manifestations. We compared the effectiveness of intrathecal (i.t.) and intravenous (i.v.) routes of administration (ROAs) at a range of vector doses in a mouse model of MPS II. While lower doses were completely ineffective, a total dose of 1 × 109 gc resulted in appreciable IDS activity levels in plasma but not tissues. Total doses of 1 × 1010 and 1 × 1011 gc by either ROA resulted in supraphysiological plasma IDS activity, substantial IDS activity levels and GAG reduction in nearly all tissues, and normalized zygomatic arch diameter. In the brain, a dose of 1 × 1011 gc i.t. achieved the highest IDS activity levels and the greatest reduction in GAG content, and it prevented neurocognitive deficiency. We conclude that a dose of 1 × 1010 gc normalized metabolic and skeletal outcomes, while neurologic improvement required a dose of 1 × 1011 gc, thereby suggesting the prospect of a similar direct benefit in humans.

An empowered, clinically viable hematopoietic stem cell gene therapy for the treatment of multisystemic mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II), or Hunter syndrome, is a rare X-linked recessive lysosomal storage disorder due to a mutation in the lysosomal enzyme iduronate-2-sulfatase (IDS) gene. IDS deficiency leads to a progressive, multisystem accumulation of glycosaminoglycans (GAGs) and results in central nervous system (CNS) manifestations in the severe form. We developed up to clinical readiness a new hematopoietic stem cell (HSC) gene therapy approach for MPS II that benefits from a novel highly effective transduction protocol. We first provided proof of concept of efficacy of our approach aimed at enhanced IDS enzyme delivery to the CNS in a murine study of immediate translational value, employing a lentiviral vector (LV) encoding a codon-optimized human IDS cDNA. Then the therapeutic LV was tested for its ability to efficiently and safely transduce bona fide human HSCs in clinically relevant conditions according to a standard vs. a novel protocol that demonstrated superior ability to transduce bona fide long-term repopulating HSCs. Overall, these results provide strong proof of concept for the clinical translation of this approach for the treatment of Hunter syndrome.

Enhanced osteoblastic differentiation of parietal bone in a novel murine model of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II, OMIM 309900) is an X-linked disorder caused by a deficiency of lysosomal enzyme iduronate-2-sulfatase (IDS). The clinical manifestations of MPS II involve cognitive decline, bone deformity, and visceral disorders. These manifestations are closely associated with IDS enzyme activity, which catalyzes the stepwise degradation of heparan sulfate and dermatan sulfate. In this study, we established a novel Ids-deficient mice and further assessed the enzyme's physiological role. Using DNA sequencing, we found a genomic modification of the Ids genome, which involved the deletion of a 138-bp fragment spanning from intron 2 to exon 3, along with the insertion of an adenine at the 5' end of exon 3 in the mutated allele. Consistent with previous data, our Ids-deficient mice showed an attenuated enzyme activity and an enhanced accumulation of glycosaminoglycans. Interestingly, we noticed a distinct enlargement of the calvarial bone in both neonatal and young adult mice. Our examination revealed that Ids deficiency led to an enhanced osteoblastogenesis in the parietal bone, a posterior part of the calvarial bone originating from the paraxial mesoderm and associated with an enhanced expression of osteoblastic makers, such as Col1a and Runx2. In sharp contrast, cell proliferation of the parietal bone in these mice appeared similar to that of wild-type controls. These results suggest that the deficiency of Ids could be involved in an augmented differentiation of calvarial bone, which is often noticed as an enlarged head circumference in MPS II-affected individuals.

A novel CRISPR/Cas9-based iduronate-2-sulfatase (IDS) knockout human neuronal cell line reveals earliest pathological changes

Multiple complex intracellular cascades contributing to Hunter syndrome (mucopolysaccharidosis type II) pathogenesis have been recognized and documented in the past years. However, the hierarchy of early cellular abnormalities leading to irreversible neuronal damage is far from being completely understood. To tackle this issue, we have generated two novel iduronate-2-sulfatase (IDS) loss of function human neuronal cell lines by means of genome editing. We show that both neuronal cell lines exhibit no enzymatic activity and increased GAG storage despite a completely different genotype. At a cellular level, they display reduced differentiation, significantly decreased LAMP1 and RAB7 protein levels, impaired lysosomal acidification and increased lipid storage. Moreover, one of the two clones is characterized by a marked decrease of the autophagic marker p62, while none of the two mutants exhibit marked oxidative stress and mitochondrial morphological changes. Based on our preliminary findings, we hypothesize that neuronal differentiation might be significantly affected by IDS functional impairment.

Generation and characterization of an immunodeficient mouse model of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (Hunter syndrome, MPS II) is an inherited X-linked recessive disease caused by deficiency of iduronate-2-sulfatase (IDS), resulting in the accumulation of the glycosaminoglycans (GAG) heparan and dermatan sulfates. Mouse models of MPS II have been used in several reports to study disease pathology and to conduct preclinical studies for current and next generation therapies. Here, we report the generation and characterization of an immunodeficient mouse model of MPS II, where CRISPR/Cas9 was employed to knock out a portion of the murine IDS gene on the NOD/SCID/Il2rγ (NSG) immunodeficient background. IDS-/- NSG mice lacked detectable IDS activity in plasma and all analyzed tissues and exhibited elevated levels of GAGs in those same tissues and in the urine. Histopathology revealed vacuolized cells in both the periphery and CNS of NSG-MPS II mice. This model recapitulates skeletal disease manifestations, such as increased zygomatic arch diameter and decreased femur length. Neurocognitive deficits in spatial memory and learning were also observed in the NSG-MPS II model. We anticipate that this new immunodeficient model will be appropriate for preclinical studies involving xenotransplantation of human cell products intended for the treatment of MPS II.

Phenotypic Correction of Murine Mucopolysaccharidosis Type II by Engraftment of Ex Vivo Lentiviral Vector-Transduced Hematopoietic Stem and Progenitor Cells

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is an X-linked recessive lysosomal disease caused by deficiency of iduronate-2-sulfatase (IDS). The absence of IDS results in the accumulation of the glycosaminoglycans (GAGs) heparan sulfate and dermatan sulfate. Currently, the only approved treatment option for MPS II is enzyme replacement therapy (ERT), Elaprase. However, ERT is demanding for the patient and does not ameliorate neurological manifestations of the disease. Using an IDS-deficient mouse model that phenocopies the human disease, we evaluated hematopoietic stem and progenitor cells (HSPCs) transduced with a lentiviral vector (LVV) carrying a codon-optimized human IDS coding sequence regulated by a ubiquitous MNDU3 promoter (MNDU3-IDS). Mice treated with MNDU3-IDS LVV-transduced cells showed supraphysiological levels of IDS enzyme activity in plasma, peripheral blood mononuclear cells, and in most analyzed tissues. These enzyme levels were sufficient to normalize GAG storage in analyzed tissues. Importantly, IDS levels in the brains of MNDU3-IDS-engrafted animals were restored to 10-20% than that of wild-type mice, sufficient to normalize GAG content and prevent emergence of cognitive deficit as evaluated by neurobehavioral testing. These results demonstrate the potential effectiveness of ex vivo MNDU3-IDS LVV-transduced HSPCs for treatment of MPS II.

Gene editing strategies to treat lysosomal disorders: The example of mucopolysaccharidoses

Lysosomal storage disorders are a group of progressive multisystemic hereditary diseases with a combined incidence of 1:4,800. Here we review the clinical and molecular characteristics of these diseases, with a special focus on Mucopolysaccharidoses, caused primarily by the lysosomal storage of glycosaminoglycans. Different gene editing techniques can be used to ameliorate their symptoms, using both viral and nonviral delivery methods. Whereas these are still being tested in animal models, early results of phase I/II clinical trials of gene therapy show how this technology may impact the future treatment of these diseases. Hurdles related to specific hard-to-reach organs, such as the central nervous system, heart, joints, and the eye must be tackled. Finally, the regulatory framework necessary to advance into clinical practice is also discussed.

Mammalian Sulfatases: Biochemistry, Disease Manifestation, and Therapy

Sulfatases are enzymes that catalyze the removal of sulfate from biological substances, an essential process for the homeostasis of the body. They are commonly activated by the unusual amino acid formylglycine, which is formed from cysteine at the catalytic center, mediated by a formylglycine-generating enzyme as a post-translational modification. Sulfatases are expressed in various cellular compartments such as the lysosome, the endoplasmic reticulum, and the Golgi apparatus. The substrates of mammalian sulfatases are sulfolipids, glycosaminoglycans, and steroid hormones. These enzymes maintain neuronal function in both the central and the peripheral nervous system, chondrogenesis and cartilage in the connective tissue, detoxification from xenobiotics and pharmacological compounds in the liver, steroid hormone inactivation in the placenta, and the proper regulation of skin humidification. Human sulfatases comprise 17 genes, 10 of which are involved in congenital disorders, including lysosomal storage disorders, while the function of the remaining seven is still unclear. As for the genes responsible for pathogenesis, therapeutic strategies have been developed. Enzyme replacement therapy with recombinant enzyme agents and gene therapy with therapeutic transgenes delivered by viral vectors are administered to patients. In this review, the biochemical substrates, disease manifestation, and therapy for sulfatases are summarized.

A novel preclinical model of mucopolysaccharidosis type II for developing human hematopoietic stem cell gene therapy

A hematopoietic stem cell (HSC) gene therapy (GT) using lentiviral vectors has attracted interest as a promising treatment approach for neuropathic lysosomal storage diseases. To proceed with the clinical development of HSC-GT, evaluation of the therapeutic potential of gene-transduced human CD34+ (hCD34+) cells in vivo is one of the key issues before human trials. Here, we established an immunodeficient murine model of mucopolysaccharidosis type II (MPS II), which are transplantable human cells, and demonstrated the application of those mice in evaluating the therapeutic efficacy of gene-modified hCD34+ cells. NOG/MPS II mice, which were generated using CRISPR/Cas9, exhibited a reduction of disease-causing enzyme iduronate-2-sulfatatase (IDS) activity and the accumulation of glycosaminoglycans in their tissues. When we transplanted hCD34+ cells transduced with a lentiviral vector carrying the IDS gene into NOG/MPS II mice, a significant amelioration of biochemical pathophenotypes was observed in the visceral and neuronal tissues of those mice. In addition, grafted cells in the NOG/MPS II mice showed the oligoclonal integration pattern of the vector, but no obvious clonal dominance was detected in the mice. Our findings indicate the promising application of NOG/MPS II mice to preclinical study of HSC-GT for MPS II using human cells.

Hematopoietic stem cell gene therapy ameliorates CNS involvement in murine model of GM1-gangliosidosis

GM1-gangliosidosis is a progressive neurodegenerative glycosphingolipidosis resulting from a GLB1 gene mutation causing a deficiency of the lysosomal enzyme β-galactosidase, which leads to the abnormal accumulation of GM1 ganglioside in the central nervous system. In the most severe early infantile phenotype, excessive ganglioside accumulation results in a rapid decline in neurological and psychomotor functions, and death occurs within 2 years of age. Currently, there is no effective therapy for GM1-gangliosidosis. In this study, we evaluated the therapeutic efficacy of ex vivo gene therapy targeting hematopoietic stem cells using a lentiviral vector to increase enzyme activity, reduce substrate accumulation, and improve astrocytosis and motor function. Transplanting GLB1-transduced hematopoietic stem cells in mice increased β-galactosidase enzyme activity in the central nervous system and visceral organs. Specifically, this gene therapy significantly decreased GM1 ganglioside levels in the brain, especially in the cerebrum. More important, this gene therapy rectified astrocytosis in the cerebrum and improved motor function deficits. Furthermore, the elevation of serum β-galactosidase activity in secondary-transplanted mice suggested the ability of transduced hematopoietic stem cells to repopulate long term. These data indicate that ex vivo gene therapy with lentiviral vectors is a promising approach for the treatment of brain deficits in GM1 gangliosidosis.

Promoter considerations in the design of lentiviral vectors for use in treating lysosomal storage diseases

More than 50 lysosomal storage diseases (LSDs) are associated with lysosomal dysfunctions with the frequency of 1:5,000 live births. As a result of missing enzyme activity, the lysosome dysfunction accumulates undegraded or partially degraded molecules, affecting the entire body. Most of them are life-threatening diseases where patients could die within the first or second decade of life. Approximately 20 LSDs have the approved treatments, which do not provide the cure for the disorder. Therefore, the delivery of missing genes through gene therapy is a promising approach for LSDs. Over the years, ex vivo lentiviral-mediated gene therapy for LSDs has been approached using different strategies. Several clinical trials for LSDs are under investigation.Ex vivo lentiviral-mediated gene therapy needs optimization in dose, time of delivery, and promoter-driven expression. Choosing suitable promoters seems to be one of the important factors for the effective expression of the dysfunctional enzyme. This review summarizes the research on therapy for LSDs that has used different lentiviral vectors, emphasizing gene promoters.

Delivering gene therapy for mucopolysaccharide diseases

Mucopolysaccharide diseases are a group of paediatric inherited lysosomal storage diseases that are caused by enzyme deficiencies, leading to a build-up of glycosaminoglycans (GAGs) throughout the body. Patients have severely shortened lifespans with a wide range of symptoms including inflammation, bone and joint, cardiac, respiratory and neurological disease. Current treatment approaches for MPS disorders revolve around two main strategies. Enzyme replacement therapy (ERT) is efficacious in treating somatic symptoms but its effect is limited for neurological functions. Haematopoietic stem cell transplant (HSCT) has the potential to cross the BBB through monocyte trafficking, however delivered enzyme doses limit its use almost exclusively to MPSI Hurler. Gene therapy is an emerging therapeutic strategy for the treatment of MPS disease. In this review, we will discuss the various vectors that are being utilised for gene therapy in MPS as well as some of the most recent gene-editing approaches undergoing pre-clinical and clinical development.

Production of therapeutic iduronate-2-sulfatase enzyme with a novel single-stranded RNA virus vector

The Sendai virus vector has received a lot of attention due to its broad tropism for mammalian cells. As a result of efforts for genetic studies based on a mutant virus, we can now express more than 10 genes of up to 13.5 kilo nucleotides in a single vector with high protein expression efficiency. To prove this benefit, we examined the efficacy of the novel ribonucleic acid (RNA) virus vector harboring the human iduronate-2-sulfatase (IDS) gene with 1,653 base pairs, a causative gene for mucopolysaccharidosis type II, also known as a disorder of lysosomal storage disorders. As expected, this novel RNA vector with the human IDS gene exhibited its marked expression as determined by the expression of enhanced green fluorescent protein and IDS enzyme activity. While these cells exhibited a normal growth rate, the BHK-21 transformant cells stably expressing the human IDS gene persistently generated an active human IDS enzyme extracellularly. The human IDS protein produced failed to be incorporated into the lysosome when cells were pretreated with mannose-6-phosphate, demonstrating that this human IDS enzyme has potential for therapeutic use by cross-correction. These results suggest that our novel RNA vector may be applicable for further clinical settings.

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Gene Therapy for Mucopolysaccharidosis Type II-A Review of the Current Possibilities

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder based on a mutation in the IDS gene that encodes iduronate 2-sulphatase. As a result, there is an accumulation of glycosaminoglycans-heparan sulphate and dermatan sulphate-in almost all body tissues, which leads to their dysfunction. Currently, the primary treatment is enzyme replacement therapy, which improves the course of the disease by reducing somatic symptoms, including hepatomegaly and splenomegaly. The enzyme, however, does not cross the blood-brain barrier, and no improvement in the function of the central nervous system has been observed in patients with the severe form of the disease. An alternative method of treatment that solves typical problems of enzyme replacement therapy is gene therapy, i.e., delivery of the correct gene to target cells through an appropriate vector. Much progress has been made in applying gene therapy for MPS II, from cellular models to human clinical trials. In this article, we briefly present the history and basics of gene therapy and discuss the current state of knowledge about the methods of this therapy in mucopolysaccharidosis type II.