Early onset of lysosomal storage disease in a murine model of mucopolysaccharidosis type VII: undegraded substrate accumulates in many tissues in the fetus and very young MPS VII mouse

Non-cardiac Manifestations in Adult Patients With Mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are a heterogeneous group of disorders that results in the absence or deficiency of lysosomal enzymes, leading to an inappropriate storage of glycosaminoglycans (GAGs) in various tissues of the body such as bones, cartilage, heart valves, arteries, upper airways, cornea, teeth, liver and nervous system. Clinical manifestations can become progressively exacerbated with age and affect their quality of life. Developments in advanced supportive treatment options such as enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT) may have improved patients' life span. Adult MPS patients require specialist clinical surveillance long-term. In many cases, in addition to the MPS-related health problems, they may develop age-related complications. Considering the complexity of their clinical manifestations and lack of guidelines on the management of adult MPS disorders, multispecialty and multidisciplinary teams' care is essential to diagnose and treat health problems that are likely to be encountered. This review presents non-cardiac clinical manifestations, their pathophysiology, management and long-term outcomes in adult MPS patients.

Blood and bone marrow findings in two pups with mucopolysaccharidosis type VII

Routine blood smear findings in two of four 11-day-old mixed-breed dog littermates were suggestive of a lysosomal storage disease (LSD) that was documented to be mucopolysaccharidosis type VII (MPS VII) by molecular testing. In this condition, a functional β-glucuronidase deficiency results in the accumulation of glycosaminoglycans (GAGs) in cells and tissues where β-glucuronidase is important in GAG degradation. Most neutrophils and a moderate number of lymphocytes within the blood had atypical cytoplasmic magenta inclusions. The bone marrow assessment from one of the two affected pups at 24 days of age revealed similar magenta granulation in myeloid precursor cells that was most prominent in promyelocytes and myelocytes. Moreover, atypical magenta material was present within vacuoles as well as extracellularly in some osteoblasts and macrophages. Histologic bone marrow sections revealed prominent vacuolation of osteoblasts, and some osteoclasts appeared separated from the bone by layers of osteoblasts or hematopoietic cells. At 2 months of age, the second affected dog showed moderate growth retardation and had similar but more prominent hematologic findings that extended to monocytes, eosinophils, and eosinophil precursors. It had an increased number of bone marrow macrophages with many vacuoles that could be seen cytologically to contain magenta material, and there was mild nonselective phagocytosis of hemic cells. Of the hematologic cells, inclusions were most prominent in promyelocytes, myelocytes, and macrophages, cells with relatively high β-glucuronidase activity, and GAG exposure within lysosomes or lysosome-like primary granules of granulocyte precursors.

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Pain in Mucopolysaccharidoses: Analysis of the Problem and Possible Treatments

Mucopolysaccharidosis (MPS) are a group of lysosomal storage disorders that are caused by the deficiency of enzymes involving in the catabolism of glycosaminoglycan (GAGs). GAGs incompletely degraded accumulate in many sites, damaging tissues and cells, leading to a variety of clinical manifestations. Many of these manifestations are painful, but few data are available in the literature concerning the prevalence, etiology, and pathogenesis of pain in children with MPS. This review, through the analysis of the data available the in literature, underscores the relevant prevalence of pain in MPSs’ children, provides the instruments to discern the etiopathogenesis of the disease and of pain, illustrates the available molecules for the management of pain and the possible advantages of non-pharmacological pain therapy in MPSs’ patients.

Delayed development of ossification centers in the tibia of prenatal and early postnatal MPS VII mice

Short stature is a characteristic feature of most of the mucopolysaccharidoses, a group of inherited lysosomal storage disorders caused by a single enzyme deficiency. MPS patients present with progressive skeletal defects from an early age, including short stature due to impaired cartilage-to-bone conversion (endochondral ossification). The aim of this study was to determine which murine MPS model best reproduces the bone length reduction phenotype of human MPS and use this model to determine the earliest developmental stage when disrupted endochondral ossification first appears. Gus^mps/mps mice representing severe MPS VII displayed the greatest reduction in bone elongation and were chosen for histopathological analysis. Tibial development was assessed from E12.5 to 6 months of age. Chondrocytes in the region of the future primary ossification center became hypertrophic at a similar age to normal in the MPS VII mouse fetus, but a delay in bone deposition was observed with an approximate 1 day delay in the formation of the primary ossification centre. Likewise, chondrocytes in the region of the future secondary ossification center also became hypertrophic at the same age as normal in the MPS VII early postnatal mouse. Bone deposition in the secondary ossification centre was delayed by two days in the MPS VII proximal tibia (observed at postnatal day 14 (P14) compared to P12 in normal). The thickness of the tibial growth plate was larger in MPS VII mice from P9 onwards. Abnormal endochondral ossification starts in utero in MPS VII and worsens with age. It is characterized by a normal timeframe for chondrocyte hypertrophy but a delay in the subsequent deposition of bone in both the primary and secondary ossification centres, accompanied by an increase in growth plate thickness. This suggests that the signals for vascular invasion and bone deposition, some of which are derived from hypertrophic chondrocytes, are altered in MPS VII.

Pathogenesis and treatment of spine disease in the mucopolysaccharidoses

The mucopolysaccharidoses (MPS) are a family of lysosomal storage disorders characterized by deficient activity of enzymes that degrade glycosaminoglycans (GAGs). Skeletal disease is common in MPS patients, with the severity varying both within and between subtypes. Within the spectrum of skeletal disease, spinal manifestations are particularly prevalent. Developmental and degenerative abnormalities affecting the substructures of the spine can result in compression of the spinal cord and associated neural elements. Resulting neurological complications, including pain and paralysis, significantly reduce patient quality of life and life expectancy. Systemic therapies for MPS, such as hematopoietic stem cell transplantation and enzyme replacement therapy, have shown limited efficacy for improving spinal manifestations in patients and animal models. Therefore, there is a pressing need for new therapeutic approaches that specifically target this debilitating aspect of the disease. In this review, we examine how pathological abnormalities affecting the key substructures of the spine - the discs, vertebrae, odontoid process and dura - contribute to the progression of spinal deformity and symptomatic compression of neural elements. Specifically, we review current understanding of the underlying pathophysiology of spine disease in MPS, how the tissues of the spine respond to current clinical and experimental treatments, and discuss future strategies for improving the efficacy of these treatments.

Mucopolysaccharidosis VII in a Cat Caused by 2 Adjacent Missense Mutations in the GUSB Gene

BACKGROUND

Mucopolysaccharidoses (MPS) are common lysosomal storage disorders causing typically progressive skeletal and ocular abnormalities.

OBJECTIVES

To describe the clinic features, metabolic profile and a unique mutation in a domestic shorthair (DSH) kitten with MPS VII.

ANIMALS

Affected kitten and 80 healthy cats.

METHODS

Serum lysosomal enzyme activities and urinary glycosaminoglycan (GAG) accumulation were assessed. Exons of the β-glucuronidase gene (GUSB) were sequenced from genomic DNA and genotyping was conducted.

RESULTS

A 3-month-old DSH cat was presented for stunted growth, paresis, facial dysmorphia, multiple skeletal deformities, and corneal opacities. Evaluation of blood smears disclosed metachromatic granules in leukocytes and a urinary mucopolysaccharide spot test was positive. The proband had no GUSB activity but normal or increased activities for other lysosomal enzymes. Sequencing of the GUSB gene from the proband and comparison to the sequence of 2 healthy cats and the published feline genome sequence demonstrated 2 unique single base transitions (c.1421T>G and c.1424C>T) in exon 9, altering 2 adjacent codons (p.Ser475Ala and p.Arg476Trp). These amino acid changes are in a highly conserved domain of the GUSB protein and nontolerable to maintain function. Moreover, the p.Arg476Trp mutation previously has been identified in human patients. None of the other clinically healthy cats had these mutations.

CONCLUSIONS AND CLINIC IMPORTANCE

The diagnostic approach to MPS disorders is delineated. This is only the second mutation known to cause MPS VII in cats. Similarly, 2 different mutations have been described in MPS VII dogs, thereby showing the molecular heterogeneity of MPS VII in companion animals.

Enzyme replacement therapy in newborn mucopolysaccharidosis IVA mice: early treatment rescues bone lesions?

We treated mucopolysaccharidosis IVA (MPS IVA) mice to assess the effects of long-term enzyme replacement therapy (ERT) initiated at birth, since adult mice treated by ERT showed little improvement in bone pathology [1]. To conduct ERT in newborn mice, we used recombinant human N-acetylgalactosamine-6-sulfate sulfatase (GALNS) produced in a CHO cell line. First, to observe the tissue distribution pattern, a dose of 250units/g body weight was administered intravenously in MPS IVA mice at day 2 or 3. The infused enzyme was primarily recovered in the liver and spleen, with detectable activity in the bone and brain. Second, newborn ERT was conducted after a tissue distribution study. The first injection of newborn ERT was performed intravenously, the second to fourth weekly injections were intraperitoneal, and the remaining injections from 5th to 14th weeks were intravenous into the tail vein. MPS IVA mice treated with GALNS showed clearance of lysosomal storage in the liver and spleen, and sinus lining cells in bone marrow. The column structure of the growth plate was organized better than that in adult mice treated with ERT; however, hyaline and fibrous cartilage cells in the femur, spine, ligaments, discs, synovium, and periosteum still had storage materials to some extent. Heart valves were refractory to the treatment. Levels of serum keratan sulfate were kept normal in newborn ERT mice. In conclusion, the enzyme, which enters the cartilage before the cartilage cell layer becomes mature, prevents disorganization of column structure. Early treatment from birth leads to partial remission of bone pathology in MPS IVA mice.

Partial rescue of mucopolysaccharidosis type VII mice with a lifelong engraftment of allogeneic stem cells in utero

In utero hematopoietic cell transplantation (IUHCT) has been performed in Mucopolysaccharidosis Type VII (MPSVII) mice, but a lifelong engraftment of allogeneic donor cells has not been achieved. In this study, we sought to confirm a lifelong engraftment of allogeneic donor cells immunologically matched to the mother and to achieve partial rescue of phenotypes in the original MPSVII strain through IUHCT by intravenous injection. We performed in vitro fertilization in a MPSVII murine model and transferred affected embryos to ICR/B6-GFP surrogate mothers in cases where fetuses receiving IUHCT were all homozygous. Lineage-depleted cells from ICR/B6-GFP mice were injected intravenously at E14.5. Chimerism was confirmed by flow cytometry at 4 weeks after birth, and β-glucuronidase activity in serum and several phenotypes were assessed at 8 weeks of age or later. Donor cells in chimeric mice from ICR/B6-GFP mothers were detected at death, and were confirmed in several tissues including the brains of sacrificed chimeric mice. Although the serum enzyme activity of chimeric mice was extremely low, the engraftment rate of donor cells correlated with enzyme activity. Furthermore, improvement of bone structure and rescue of reproductive ability were confirmed in our limited preclinical study. We confirmed the lifelong engraftment of donor cells in an original immunocompetent MPSVII murine model using intravenous IUHCT with cells immunologically matched to the mother without myeloablation, and the improvement of several phenotypes.

Ataxia is the major neuropathological finding in arylsulfatase G-deficient mice: similarities and dissimilarities to Sanfilippo disease (mucopolysaccharidosis type III)

Deficiency of arylsulfatase G (ARSG) leads to a lysosomal storage disease in mice resembling biochemical and pathological features of the mucopolysaccharidoses and particularly features of mucopolysaccharidosis type III (Sanfilippo syndrome). Here we show that Arsg KO mice share common neuropathological findings with other Sanfilippo syndrome models and patients, but they can be clearly distinguished by the limitation of most phenotypic alterations to the cerebellum, presenting with ataxia as the major neurological finding. We determined in detail the expression of ARSG in the central nervous system and observed highest expression in perivascular macrophages (which are characterized by abundant vacuolization in Arsg KO mice) and oligodendrocytes. To gain insight into possible mechanisms leading to ataxia, the pathology in older adult mice (>12 months) was investigated in detail. This study revealed massive loss of Purkinje cells and gliosis in the cerebellum, and secondary accumulation of glycolipids like GM2 and GM3 gangliosides and unesterified cholesterol in surviving Purkinje cells, as well as neurons of some other brain regions. The abundant presence of ubiquitin and p62-positive aggregates in degenerating Purkinje cells coupled with the absence of significant defects in macroautophagy is consistent with lysosomal membrane permeabilization playing a role in the pathogenesis of Arsg-deficient mice and presumably Sanfilippo disease in general. Our data delineating the phenotype of mucopolysaccharidosis IIIE in a mouse KO model should help in the identification of possible human cases of this disease.

Mucopolysaccharidosis: cardiologic features and effects of enzyme-replacement therapy in 24 children with MPS I, II and VI

We determined the cardiologic features of children with MPS I, II and VI, and evaluated the effect of enzyme-replacement therapy (ERT) on cardiac disease. Twenty-four children aged 1-18 years with MPS I, II or VI were prospectively evaluated with echocardiogram and electrocardiogram from the start of enzyme-replacement therapy up to 6 years of treatment. At start of therapy, 66% had abnormal cardiac geometric features. Left-ventricular mass index (LVMI) was increased in half of the patients, due mainly to concentric hypertrophy in MPS I and II and to eccentric hypertrophy in MPS VI. Regurgitation was most severe in a subgroup of young MPS VI patients (<5 years) at the mitral valve. At baseline, all patients had abnormal valves. The ECG showed no clear rhythm or conduction abnormalities; neither, in most patients, did it reflect the hypertrophy. After ERT, the LVMI Z-score normalized in 70% of the patients who had a Z-score > 2. LVMI Z-scores decreased significantly in patients with MPS I and MPS II (p = 0.04 and p = 0.032). Despite ERT, valve regurgitation increased in 60% of the patients. We conclude that all our MPS patients have cardiac abnormalities. The most severe cardiac disease was observed in a subgroup of young MPS VI patients. While ERT had an effect on LVMI and IVSd, it apparently had little or none on valve regurgitation.

Long circulating enzyme replacement therapy rescues bone pathology in mucopolysaccharidosis VII murine model

Mucopolysaccharidosis (MPS) type VII is a lysosomal storage disease caused by deficiency of the lysosomal enzyme β-glucuronidase (GUS), leading to accumulation of glycosaminoglycans (GAGs). Enzyme replacement therapy (ERT) effectively clears GAG storage in the viscera. Recent studies showed that a chemically modified form of GUS (PerT-GUS), which escaped clearance by mannose 6-phosphate and mannose receptors and showed prolonged circulation, reduced CNS storage more effectively than native GUS. Clearance of storage in bone has been limited due to the avascularity of the growth plate. To evaluate the effectiveness of long-circulating PerT-GUS in reducing the skeletal pathology, we treated MPS VII mice for 12 weeks beginning at 5 weeks of age with PerT-GUS or native GUS and used micro-CT, radiographs, and quantitative histopathological analysis for assessment of bones. Micro-CT findings showed PerT-GUS treated mice had a significantly lower BMD. Histopathological analysis also showed reduced storage material and a more organized growth plate in PerT-GUS treated mice compared with native GUS treated mice. Long term treatment with PerT-GUS from birth up to 57 weeks also significantly improved bone lesions demonstrated by micro-CT, radiographs and quantitative histopathological assay. In conclusion, long-circulating PerT-GUS provides a significant impact to rescue of bone lesions and CNS involvement.

Skeletal response to lentiviral mediated gene therapy in a mouse model of MPS VII

Mucopolysaccharidosis VII (MPS VII) is an autosomal recessive, lysosomal storage disorder caused by β-glucuronidase (GUSB) deficiency, resulting in the accumulation of glycosaminoglycans (GAGs), in a variety of cell types. Severe, progressive skeletal pathology, termed dysostosis multiplex, is a prominent clinical feature of MPS VII. We have evaluated a gene therapy protocol for its efficacy in preventing the development and progression of bone pathology in MPS VII mice treated with a lentiviral vector at birth or at 7 weeks. Two weeks after injections, high levels of vector expression were observed in liver, spleen and bone marrow and to a lesser extent in kidney, lung and heart. Widespread clearance of GAG storage was observed in somatic tissues of both groups and some clearance of neuronal storage was observed in mice treated from birth. Micro-CT analysis demonstrated a significant decrease in vertebral and femoral bone mineral volume, trabecular number, bone surface density and cortical bone thickness in both treatment groups. Lumbar and femoral bone lengths were significantly decreased in untreated MPS VII mice, while growth plate heights were increased and these parameters did not change upon treatment. Small improvements in performance in the open field and rotarod behaviour tests were noted. Overall, systemic lentiviral-mediated gene therapy results in a measurable improvement in parameters of bone mass and architecture as well as biochemical and enzymatic correction. Conversely, growth plate chondrocytes were not responsive to treatment, as evidenced by the lack of improvement in vertebral and femoral bone length and growth plate height.

Canine fucosidosis: a neuroprogressive disorder

The lysosomal storage disease, canine fucosidosis, is caused by the absence of the lysosomal enzyme canine α-L-fucosidase with storage of undegraded fucose-rich material in different organs. Canine fucosidosis is a severe, progressive, fatal neurological disease which results in death or euthanasia and is the only available animal model for this human disease. We analysed the progressive neuropathology from birth to severe clinical disease and related this to the clinical signs. At birth no vacuolation was observed in fucosidosis brain; however, a complex storage presence with vacuolation was well established by 4 months of age, before the clinical signs of motor dysfunction which occurred at 10-12 months of age. Purkinje cell loss, neuronal loss, gliosis, perivascular storage and demyelination accompanied disease progression. Increased vacuolation (15.3-fold increase compared to controls) coincided with advanced motor and mental deterioration in late-stage disease. Significant loss of myelin commenced early, with greatest impact in the cerebellum, and was severe in late disease (1.6- to 1.9-fold decrease) compared to controls (p < 0.05) contributing to clinical signs of motor and mental dysfunction. This detailed description and quantification of the CNS pathology in canine fucosidosis will inform monitoring of the onset, progression and response of this disease to therapy.

Newborn screening for neuropathic lysosomal storage disorders

Interest in newborn screening (NBS) for lysosomal storage disorders (LSDs) has increased significantly due to newly developed enzyme replacement therapy (ERT), the need for early diagnosis, and advances in technical developments. Since the central nervous system cannot be treated by ERT, neuronopathic LSDs are generally not the primary target of NBS. An exception is Krabbe disease, in which hematopoietic stem cell transplantation before the onset of symptoms has benefits. However, NBS for LSD relies on measuring enzyme activities, so the most severely affected individuals (usually patients with neuronopathic subtypes) will be detected together with patients with less severe disease. In the near future, NBS is likely to be developed for diseases such as Gaucher, Niemann-Pick A/B, and certain mucopolysaccharidoses. The ability to predict phenotypes (neuronopathic or not) by enzyme activity and genotyping will therefore be critical for adequate patient management. This article reviews the status of LSD screening and issues concerning detection of neuronopathic LSDs by screening.

Altered lumbar spine structure, biochemistry, and biomechanical properties in a canine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disorder characterized by a deficiency in beta-glucuronidase activity, leading to systemic accumulation of poorly degraded glycosaminoglycans (GAG). Along with other morbidities, MPS VII is associated with pediatric spinal deformity. The objective of this study was to examine potential associations between abnormal lumbar spine matrix structure and composition in MPS VII, and spine segment and tissue-level mechanical properties, using a naturally occurring canine model with a similar clinical phenotype to the human form of the disorder. Segments from juvenile MPS VII and unaffected dogs were allocated to: radiography, gross morphology, histology, biochemistry, and mechanical testing. MPS VII spines had radiolucent lesions in the vertebral body epiphyses. Histologically, this corresponded to a GAG-rich cartilaginous region in place of bone and elevated GAG staining was seen in the annulus fibrosus. Biochemically, MPS VII samples had elevated GAG in the outer annulus fibrosus and epiphyses, low calcium in the epiphyses, and high water content in all regions except the nucleus pulposus. MPS VII spine segments had higher range of motion and lower stiffness than controls. Endplate indentation stiffness and failure loads were significantly lower in MPS VII samples, while annulus fibrosus tensile mechanical properties were normal. Vertebral body lesions in MPS VII spines suggest a failure to convert cartilage to bone during development. Low stiffness in these regions likely contributes to mechanical weakness in motion segments and is a potential factor in the progression of spinal deformity.

Widespread biochemical correction of murine mucopolysaccharidosis type VII pathology by liver hydrodynamic plasmid delivery

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by a deficiency of the acid hydrolase beta-glucuronidase. MPS VII mice develop progressive lysosomal accumulation of glycosaminoglycans (GAGs) within multiple organs, including the brain. Using this animal model, we compared two plasmid gene administration techniques: muscle electrotransfer and liver-directed transfer using hydrodynamic injection. We have evaluated both the expression kinetics and the biodistribution of beta-glucuronidase activity after gene transfer, as well as the correction of biochemical abnormalities in various organs. This study shows that MPS VII mice treated with a plasmid-bearing mouse beta-glucuronidase cDNA, acquire the ability to produce the beta-glucuronidase enzyme for an extended period of time. The liver seemed to be more appropriate than the muscle as a target organ to enable enzyme secretion into the systemic circulation. A beneficial effect on the MPS VII pathology was also observed, as liver-directed gene transfer led to the correction of secondary enzymatic elevations and to the reduction of GAGs storage in peripheral tissues and brain, as well as to histological correction in many tissues. This work is one of the first examples showing that non-viral plasmid DNA delivery can lead to improvements in both peripheral and brain manifestations of MPS VII disease. It confirms the potential of non-viral systemic gene transfer strategy in neurological lysosomal disorders.

The mucopolysaccharidoses: a success of molecular medicine

The mucopolysaccharidoses represent a devastating group of lysosomal storage diseases affecting approximately 1 in 25 000 individuals. Advances in biochemistry and genetics over the past 25 years have resulted in the identification of the key hydrolases underlying the mucopolysaccharidoses, with subsequent isolation and characterisation of the genes involved. Ultimately these advances have led to the recent development of specific treatment regimens for some of the mucopolysaccharidoses, in the form of direct enzyme replacement. Direct replacement of the defective gene product has been attempted for very few genetic disorders, and thus the experience gained in the lysosomal storage diseases by the development, evaluation and integration of treatment regimens into healthcare is instructive for other rare genetic disorders. This review focuses on the pathophysiology of the mucopolysaccharidoses and highlights the complex biochemical and physiological perturbations that underlie the disease phenotype.

Clinical response to persistent, low-level beta-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1-5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at approximately 5% and approximately 2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of alpha-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII.

Attenuation of murine lysosomal storage disease by allogeneic neonatal bone marrow transplantation using costimulatory blockade and donor lymphocyte infusion without myeloablation

Treatment of nonmalignant childhood disorders by bone marrow transplantation (BMT) is limited by toxicity from preparatory regimens and immune consequences associated with engraftment of allogeneic donor cells. Using costimulatory blockade (anti-CD40L mAb and CTLA-4Ig) combined with high-dose BMT in nonablated neonates, we obtained engraftment and established tolerance using both partially MHC mismatched (H2g7 into H2b) and fully mismatched BM (H2s into H2b). Recipients were mucopolysaccharidosis type VII (MPS VII) mice with lysosomal storage disease in order to assess therapeutic outcome. Recipients treated with donor lymphocyte infusion (DLI) amplified microchimerism to full donor. Recipients without DLI maintained long-term engraftment, tolerance, and had extended life spans. DLI increased donor cell mediated replacement of beta-glucuronidase (GUSB) activity in all tissues and maintained clearance of lysosomes better than in non-DLI-treated mice. DLI amplification of partially mismatched BM and fully mismatched BM caused late onset chronic GvHD in 56% and 100% of recipients, respectively.