Expression in blood cells may contribute to biochemical and pathological improvements after neonatal intravenous gene therapy for mucopolysaccharidosis VII in dogs

Neonatal cellular and gene therapies for mucopolysaccharidoses: the earlier the better?

Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders (LSDs). The increasing interest in newborn screening procedures for LSDs underlines the need for alternative cellular and gene therapy approaches to be developed during the perinatal period, supporting the treatment of MPS patients before the onset of clinical signs and symptoms. The rationale for considering these early therapies results from the clinical experience in the treatment of MPSs and other genetic disorders. The normal or gene-corrected hematopoiesis transplanted in patients can produce the missing protein at levels sufficient to improve and/or halt the disease-related abnormalities. However, these current therapies are only partially successful, probably due to the limited efficacy of the protein provided through the hematopoiesis. An alternative explanation is that the time at which the cellular or gene therapy procedures are performed could be too late to prevent pre-existing or progressive organ damage. Considering these aspects, in the last several years, novel cellular and gene therapy approaches have been tested in different animal models at birth, a highly early stage, showing that precocious treatment is critical to prevent long-term pathological consequences. This review provides insights into the state-of-art accomplishments made with neonatal cellular and gene-based therapies and the major barriers that need to be overcome before they can be implemented in the medical community.

Evaluation of AAV-mediated Gene Therapy for Central Nervous System Disease in Canine Mucopolysaccharidosis VII

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease arising from mutations in β-d-glucuronidase (GUSB), which results in glycosaminoglycan (GAG) accumulation and a variety of clinical manifestations including neurological disease. Herein, MPS VII dogs were injected intravenously (i.v.) and/or intrathecally (i.t.) via the cisterna magna with AAV9 or AAVrh10 vectors carrying the canine GUSB cDNA. Although i.v. injection alone at 3 days of age resulted in normal cerebrospinal fluid (CSF) GUSB activity, brain tissue homogenates had only ~1 to 6% normal GUSB activity and continued to have elevated GAG storage. In contrast, i.t. injection at 3 weeks of age resulted in CSF GUSB activity 44-fold normal while brain tissue homogenates had >100% normal GUSB activity and reduced GAGs compared with untreated dogs. Markers for secondary storage and inflammation were eliminated in i.t.-treated dogs and reduced in i.v.-treated dogs compared with untreated dogs. Given that i.t.-treated dogs expressed higher levels of GUSB in the CNS tissues compared to those treated i.v., we conclude that i.t. injection of AAV9 or AAVrh10 vectors is more effective than i.v. injection alone in the large animal model of MPS VII.

Gene therapy for neurologic manifestations of mucopolysaccharidoses

INTRODUCTION

Mucopolysaccharidoses (MPS) are a family of lysosomal disorders caused by mutations in genes that encode enzymes involved in the catabolism of glycoaminoglycans. These mutations affect multiple organ systems and can be particularly deleterious to the nervous system. At the present time, enzyme replacement therapy and hematopoietic stem-cell therapy are used to treat patients with different forms of these disorders. However, to a great extent, the nervous system is not adequately responsive to current therapeutic approaches.

AREAS COVERED

Recent advances in gene therapy show great promise for treating MPS. This article reviews the current state of the art for routes of delivery in developing genetic therapies for treating the neurologic manifestations of MPS.

EXPERT OPINION

Gene therapy for treating neurological manifestations of MPS can be achieved by intraventricular, intrathecal, intranasal and systemic administrations. The intraventricular route of administration appears to provide the most widespread distribution of gene therapy vectors to the brain. The intrathecal route of delivery results in predominant distribution to the caudal areas of the brain. The systemic route of delivery via intravenous infusion can also achieve widespread delivery to the CNS; however, the distribution to the brain is greatly dependent on the vector system. Intravenous delivery using lentiviral vectors appear to be less effective than adeno-associated viral (AAV) vectors. Moreover, some subtypes of AAV vectors are more effective than others in crossing the blood-brain barrier. In summary, the recent advances in gene vector technology and routes of delivery to the CNS will facilitate the clinical translation of gene therapy for the treatment of the neurological manifestations of MPS.

Neonatal bone marrow transplantation prevents bone pathology in a mouse model of mucopolysaccharidosis type I

Neonatal bone marrow transplantation (BMT) could offer a novel therapeutic opportunity for genetic disorders by providing sustainable levels of the missing protein at birth, thus preventing tissue damage. We tested this concept in mucopolysaccharidosis type I (MPS IH; Hurler syndrome), a lysosomal storage disorder caused by deficiency of α-l-iduronidase. MPS IH is characterized by a broad spectrum of clinical manifestations, including severe progressive skeletal abnormalities. Although BMT increases the life span of patients with MPS IH, musculoskeletal manifestations are only minimally responsive if the timing of BMT delays, suggesting already irreversible bone damage. In this study, we tested the hypothesis that transplanting normal BM into newborn MPS I mice soon after birth can prevent skeletal dysplasia. We observed that neonatal BMT was effective at restoring α-l-iduronidase activity and clearing elevated glycosaminoglycans in blood and multiple organs. At 37 weeks of age, we observed an almost complete normalization of all bone tissue parameters, using radiographic, microcomputed tomography, biochemical, and histological analyses. Overall, the magnitude of improvements correlated with the extent of hematopoietic engraftment. We conclude that BMT at a very early stage in life markedly reduces signs and symptoms of MPS I before they appear.

Effects of vector backbone and pseudotype on lentiviral vector-mediated gene transfer: studies in infant ADA-deficient mice and rhesus monkeys

Systemic delivery of a lentiviral vector carrying a therapeutic gene represents a new treatment for monogenic disease. Previously, we have shown that transfer of the adenosine deaminase (ADA) cDNA in vivo rescues the lethal phenotype and reconstitutes immune function in ADA-deficient mice. In order to translate this approach to ADA-deficient severe combined immune deficiency patients, neonatal ADA-deficient mice and newborn rhesus monkeys were treated with species-matched and mismatched vectors and pseudotypes. We compared gene delivery by the HIV-1-based vector to murine γ-retroviral vectors pseudotyped with vesicular stomatitis virus-glycoprotein or murine retroviral envelopes in ADA-deficient mice. The vesicular stomatitis virus-glycoprotein pseudotyped lentiviral vectors had the highest titer and resulted in the highest vector copy number in multiple tissues, particularly liver and lung. In monkeys, HIV-1 or simian immunodeficiency virus vectors resulted in similar biodistribution in most tissues including bone marrow, spleen, liver, and lung. Simian immunodeficiency virus pseudotyped with the gibbon ape leukemia virus envelope produced 10- to 30-fold lower titers than the vesicular stomatitis virus-glycoprotein pseudotype, but had a similar tissue biodistribution and similar copy number in blood cells. The relative copy numbers achieved in mice and monkeys were similar when adjusted to the administered dose per kg. These results suggest that this approach can be scaled-up to clinical levels for treatment of ADA-deficient severe combined immune deficiency subjects with suboptimal hematopoietic stem cell transplantation options.

Pathogenesis of mitral valve disease in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis VII (MPS VII) is due to the deficient activity of β-glucuronidase (GUSB) and results in the accumulation of glycosaminoglycans (GAGs) in lysosomes and multisystemic disease with cardiovascular manifestations. The goal here was to determine the pathogenesis of mitral valve (MV) disease in MPS VII dogs. Untreated MPS VII dogs had a marked reduction in the histochemical signal for structurally-intact collagen in the MV at 6 months of age, when mitral regurgitation had developed. Electron microscopy demonstrated that collagen fibrils were of normal diameter, but failed to align into large parallel arrays. mRNA analysis demonstrated a modest reduction in the expression of genes that encode collagen or collagen-associated proteins such as the proteoglycan decorin which helps collagen fibrils assemble, and a marked increase for genes that encode proteases such as cathepsins. Indeed, enzyme activity for cathepsin B (CtsB) was 19-fold normal. MPS VII dogs that received neonatal intravenous injection of a gamma retroviral vector had an improved signal for structurally-intact collagen, and reduced CtsB activity relative to that seen in untreated MPS VII dogs. We conclude that MR in untreated MPS VII dogs was likely due to abnormalities in MV collagen structure. This could be due to upregulation of enzymes that degrade collagen or collagen-associated proteins, to the accumulation of GAGs that compete with proteoglycans such as decorin for binding to collagen, or to other causes. Further delineation of the etiology of abnormal collagen structure may lead to treatments that improve biomechanical properties of the MV and other tissues.

Squeezers and leaf-cutters: differential diversification and degeneration of the venom system in toxicoferan reptiles

Although it has been established that all toxicoferan squamates share a common venomous ancestor, it has remained unclear whether the maxillary and mandibular venom glands are evolving on separate gene expression trajectories or if they remain under shared genetic control. We show that identical transcripts are simultaneously expressed not only in the mandibular and maxillary glands, but also in the enigmatic snake rictal gland. Toxin molecular frameworks recovered in this study were three-finger toxin (3FTx), CRiSP, crotamine (beta-defensin), cobra venom factor, cystatin, epididymal secretory protein, kunitz, L-amino acid oxidase, lectin, renin aspartate protease, veficolin, and vespryn. We also discovered a novel low-molecular weight disulfide bridged peptide class in pythonid snake glands. In the iguanian lizards, the most highly expressed are potentially antimicrobial in nature (crotamine (beta-defensin) and cystatin), with crotamine (beta-defensin) also the most diverse. However, a number of proteins characterized from anguimorph lizards and caenophidian snakes with hemotoxic or neurotoxic activities were recruited in the common toxicoferan ancestor and remain expressed, albeit in low levels, even in the iguanian lizards. In contrast, the henophidian snakes express 3FTx and lectin toxins as the dominant transcripts. Even in the constricting pythonid and boid snakes, where the glands are predominantly mucous-secreting, low-levels of toxin transcripts can be detected. Venom thus appears to play little role in feeding behavior of most iguanian lizards or the powerful constricting snakes, and the low levels of expression argue against a defensive role. However, clearly the incipient or secondarily atrophied venom systems of these taxa may be a source of novel compounds useful in drug design and discovery.

Effect of neonatal gene therapy on lumbar spine disease in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis VII (MPS VII) is due to deficient β-glucuronidase (GUSB) activity, which leads to accumulation of chondroitin, heparan, and dermatan sulfate glycosaminoglycans in various tissues including those of the spine. Associated spine disease can be due to abnormalities in the vertebrae, the intervertebral disks, or other spine tissues. The goal of this study was to determine if neonatal gene therapy could prevent lumbar spine disease in MPS VII dogs. MPS VII dogs were injected intravenously with a retroviral vector (RV) expressing canine GUSB at 2 to 3 days after birth, which resulted in transduction of hepatocytes that secreted GUSB into blood. Expression was stable for up to 11 years, and mean survival was increased from 0.4 years in untreated dogs to 6.1 years in treated dogs. Despite a profound positive clinical effect, 6-month-old RV-treated MPS VII dogs still had hypoplastic ventral epiphyses with reduced calcification in the lumbar spine, which resulted in a reduced stiffness and increased range of motion that were not improved relative to untreated MPS VII dogs. At six to 11 years of age, ventral vertebrae remained hypoplastic in RV-treated MPS VII dogs, and there was desiccation of the nucleus pulposus in some disks. Histochemical staining demonstrated that disks did not have detectable GUSB activity despite high serum GUSB activity, which is likely due to poor diffusion into this relatively avascular structure. Thus, neonatal gene therapy cannot prevent lumbar spine disease in MPS VII dogs, which predicts that enzyme replacement therapy (ERT) will similarly be relatively ineffective even if started at birth.

Neonatal gene therapy with a gamma retroviral vector in mucopolysaccharidosis VI cats

Mucopolysaccharidosis (MPS) VI is due to a deficiency in the activity of N-acetylgalactosamine 4-sulfatase (4S), also known as arylsulfatase B. Previously, retroviral vector (RV)-mediated neonatal gene therapy reduced the clinical manifestations of MPS I and MPS VII in mice and dogs. However, sulfatases require post-translational modification by sulfatase-modifying factors. MPS VI cats were injected intravenously (i.v.) with a gamma RV-expressing feline 4S, resulting in 5 ± 3 copies of RV per 100 cells in liver. Liver and serum 4S activity were 1,450 ± 1,720 U/mg (26-fold normal) and 107 ± 60 U/ml (13-fold normal), respectively, and were directly proportional to the liver 4S protein levels for individual cats. This study suggests that sulfatase-modifying factor (SUMF) activity in liver was sufficient to result in active enzyme despite overexpression of 4S. RV-treated MPS VI cats achieved higher body weights and longer appendicular skeleton lengths, had reduced articular cartilage erosion, and reduced aortic valve thickening and aortic dilatation compared with untreated MPS VI cats, although cervical vertebral bone lengths were not improved. This demonstrates that therapeutic expression of a functional sulfatase protein can be achieved with neonatal gene therapy using a gamma RV, but some aspects of bone disease remain difficult to treat.

Gene therapy in the cornea: 2005--present

Successful restoration of vision in human patients with gene therapy affirmed its promise to cure ocular diseases and disorders. The efficacy of gene therapy is contingent upon vector and mode of therapeutic DNA introduction into targeted cells/tissues. The cornea is an ideal tissue for gene therapy due to its ease of access and relative immune-privilege. Considerable progress has been made in the field of corneal gene therapy in last 5 years. Several new gene transfer vectors, techniques and approaches have evolved. Although corneal gene therapy is still in its early stages of development, the potential of gene-based interventions to treat corneal abnormalities has begun to surface. Identification of next generation viral and nanoparticle vectors, characterization of delivered gene levels, localization, and duration in the cornea, and significant success in controlling corneal disorders, particularly fibrosis and angiogenesis, in experimental animal disease models, with no major side effects have propelled gene therapy a step closer toward establishing gene-based therapies for corneal blindness. Recently, researchers have assessed the delivery of therapeutic genes for corneal diseases and disorders due to trauma, infections, chemical, mechanical, and surgical injury, and/or abnormal wound healing. This review provides an update on the developments in gene therapy for corneal diseases and discusses the barriers that hinder its utilization for delivering genes in the cornea.

The function of dog models in developing gene therapy strategies for human health

The domestic dog is of great benefit to humankind, not only through companionship and working activities cultivated through domestication and selective breeding, but also as a model for biomedical research. Many single-gene traits have been well-characterized at the genomic level, and recent advances in whole-genome association studies will allow for better understanding of complex, multigenic hereditary diseases. Additionally, the dog serves as an invaluable large animal model for assessment of novel therapeutic agents. Thus, the dog has filled a crucial step in the translation of basic research to new treatment regimens for various human diseases. Four well-characterized diseases in canine models are discussed as they relate to other animal model availability, novel therapeutic approach, and extrapolation to human gene therapy trials.

Perinatal gene transfer to the liver

The liver acts as a host to many functions hence raising the possibility that any one may be compromised by a single gene defect. Inherited or de novo mutations in these genes may result in relatively mild diseases or be so devastating that death within the first weeks or months of life is inevitable. Some diseases can be managed using conventional medicines whereas others are, as yet, untreatable. In this review we consider the application of early intervention gene therapy in neonatal and fetal preclinical studies. We appraise the tools of this technology, including lentivirus, adenovirus and adeno-associated virus (AAV)-based vectors. We highlight the application of these for a range of diseases including hemophilia, urea cycle disorders such as ornithine transcarbamylase deficiency, organic acidemias, lysosomal storage diseases including mucopolysaccharidoses, glycogen storage diseases and bile metabolism. We conclude by assessing the advantages and disadvantages associated with fetal and neonatal liver gene transfer.

Comparison of ventricular and intravenous lentiviral-mediated gene therapy for murine MPS VII

Mucopolysaccharidosis type VII (MPS VII) is caused by the deficiency of the lysosomal hydrolase β-glucuronidase. Symptoms include intellectual impairment, growth retardation, visual and hearing deficits and organ malfunction. The MPS VII mouse displays most of the symptoms variously associated with the MPS disorders, and has been widely used as a developmental paradigm for gene therapy. In this study, a lentiviral vector expressing murine β-glucuronidase was delivered to 6-week-old MPS VII affected mice, either by intravenous injection, or by ventricular infusion. Therapeutic outcomes were assessed 7 months after gene transfer. Intravenous vector delivery restored liver β-glucuronidase to normal levels. Consequently, most somatic pathology was corrected, and brain pathology was reduced. In mice that received ventricular vector most brain regions appeared biochemically and histologically normal. These animals showed significantly improved behavioural performance within the open-field test. An additional positive outcome of ventricular vector delivery was the significant reduction of lysosomal storage within the eye. The blood-brain barrier is not completely impervious to lysosomal enzymes, therefore, therapeutic enzyme can be distributed widely throughout the brain via the extensive cerebral vasculature. However, improvements in somatic gene delivery and expression are required for this to be completely successful. Ventricular vector delivery cleared lysosomal storage within the CNS making this a reasonable, albeit more challenging, therapeutic option for the MPS. The best therapeutic outcomes, with possible synergistic effects within the CNS, might be expected to occur when vector delivery to the brain is used in combination with somatic gene transfer.

Adeno-associated virus gene transfer in Morquio A disease - effect of promoters and sulfatase-modifying factor 1

Mucopolysaccharidosis (MPS) IVA is an autosomal recessive disorder caused by deficiency of the lysosomal enzyme N-acetylgalatosamine-6-sulfate sulfatase (GALNS), which leads to the accumulation of keratan sulfate and chondroitin 6-sulfate, mainly in bone. To explore the possibility of gene therapy for Morquio A disease, we transduced the GALNS gene into HEK293 cells, human MPS IVA fibroblasts and murine MPS IVA chondrocytes by using adeno-associated virus (AAV)-based vectors, which carry human GALNS cDNA. The effects of the promoter and the cotransduction with the sulfatase-modifying factor 1 gene (SUMF1) on GALNS activity levels was evaluated. Downregulation of the cytomegalovirus (CMV) immediate early enhancer/promoter was not observed for 10 days post-transduction. The eukaryotic promoters induced equal or higher levels of GALNS activity than those induced by the CMV promoter in HEK293 cells. Transduction of human MPS IVA fibroblasts induced GALNS activity levels that were 15-54% of those of normal human fibroblasts, whereas in transduced murine MPS IVA chondrocytes, the enzyme activities increased up to 70% of normal levels. Cotransduction with SUMF1 vector yielded an additional four-fold increase in enzyme activity, although the level of elevation depended on the transduced cell type. These findings suggest the potential application of AAV vectors for the treatment of Morquio A disease, depending on the combined choice of transduced cell type, selection of promoter, and cotransduction of SUMF1.

Neonatal intravenous injection of a gammaretroviral vector has a low incidence of tumor induction in mice

Neonatal intravenous injection of gammaretroviral vectors (gamma-RVs) with an intact long terminal repeat (LTR) and an internal liver promoter can result in long-term expression in liver cells and correction of mucopolysaccharidosis. Some expression also occurs in blood cells and brain, which likely derives from the LTR, and may contribute to clinical efficacy. The goal of this project was to determine whether neonatal gene therapy with an LTR-intact gamma-RV would induce tumors in mice. Fifty-one normal newborn C57BL/6 mice were injected intravenously at 10(10) transducing units/kg with a gamma-RV expressing canine beta-glucuronidase (GUSB) cDNA. This resulted in transduction of 23 +/- 9% of hepatocytes as determined by histochemical staining, and 0.24 +/- 0.20 copy of gamma-RV DNA per cell in liver as determined by real-time polymerase chain reaction. Serum GUSB activity was stable for 1.75 years after transduction at 705 +/- 119 units/ml. Ninety-six percent of mice survived for the duration of evaluation, which was similar to the survival rate for 65 control mice that were not injected with gamma-RV. One gamma-RV-treated mouse (2%) developed a small (diameter, 2 mm) liver adenoma, which was similar to the frequency of liver adenomas (2%) or hepatocellular carcinoma (2%) in untreated mice. Although 22% of gamma-RV-treated mice developed hematopoietic tumors, none contained high gamma-RV DNA copy numbers, and the frequency was similar to that in the control group (22%). We conclude that neonatal intravenous injection of an LTR-intact gamma-RV does not have a high risk of inducing cancer in mice.

A self-inactivating gamma-retroviral vector reduces manifestations of mucopolysaccharidosis I in mice

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to deficiency in alpha-L-iduronidase (IDUA) that results in accumulation of glycosaminoglycans (GAGs) throughout the body, causing numerous clinical defects. Intravenous administration of a gamma-retroviral vector (gamma-RV) with an intact long terminal repeat (LTR) reduced the clinical manifestations of MPS I, but could cause insertional mutagenesis. Although self-inactivating (SIN) gamma-RVs in which the enhancer and promoter elements in the viral LTR are absent after transduction reduces this risk, such vectors could be less effective. This report demonstrates that intravenous (i.v.) injection of a SIN gamma-RV expressing canine IDUA from the liver-specific human alpha(1)-antitrypsin promoter into adult or newborn MPS I mice completely prevents biochemical abnormalities in several organs, and improved bone disease, vision, hearing, and aorta to a similar extent as was seen with administration of the LTR-intact vector to adults. Improvements were less profound than when using an LTR-intact gamma-RV in newborns, which likely reflects a lower level of transduction and expression for the SIN vector-transduced mice, and might be overcome by using a higher dose of SIN vector. A SIN gamma-RV vector ameliorates clinical manifestations of MPS I in mice and should be safer than an LTR-intact gamma-RV.

Large animal models of neurological disorders for gene therapy

he development of therapeutic interventions for genetic disorders and diseases that affect the central nervous system (CNS) has proven challenging. There has been significant progress in the development of gene therapy strategies in murine models of human disease, but gene therapy outcomes in these models do not always translate to the human setting. Therefore, large animal models are crucial to the development of diagnostics, treatments, and eventual cures for debilitating neurological disorders. This review focuses on the description of large animal models of neurological diseases such as lysosomal storage diseases, Parkinsons disease, Huntingtons disease, and neuroAIDS. The review also describes the contributions of these models to progress in gene therapy research.

Development and use of DNA archives at veterinary teaching hospitals to investigate the genetic basis of disease in dogs

The DNA archives developed at veterinary medical teaching hospitals will be important resources for mapping disease loci and identifying underlying genes. The most important feature of a DNA archive is accurate identification or exclusion of diseases in each animal. Such archives will be complimentary resources to tissue banks that are currently available.

Improved retroviral vector design results in sustained expression after adult gene therapy in mucopolysaccharidosis I mice

BACKGROUND

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to alpha-L-iduronidase (IDUA) deficiency that results in the accumulation of glycosaminoglycans (GAG). Gene therapy can reduce most clinical manifestations, but mice that receive transfer as adults lose expression unless they receive immunosuppression. Increasing liver specificity of transgene expression has reduced immune responses to other genes.

METHODS

A gamma retroviral vector was generated with a liver-specific human alpha1-antitrypsin promoter and the canine IDUA cDNA inverted relative to the retroviral long-terminal repeat. Adult MPS I mice received the vector intravenously at 6 weeks of age and were assessed for expression via serial serum IDUA assays. Functional testing and organ analysis were performed at 8 months.

RESULTS

This vector resulted in high specificity of expression in liver, and serum IDUA activity was stable in 90% of animals. Although the average serum IDUA activity was relatively low at 12.6 +/- 8.1 units/ml in mice with stable expression, a relatively high percentage of enzyme contained the mannose 6-phosphorylation necessary for uptake by other cells. At 6.5 months after transduction, most organs had high IDUA activity and normalized GAG levels. There was complete correction of hearing and vision abnormalities and significant improvements in bone, although the aorta was refractory to treatment.

CONCLUSIONS

Stable expression of IDUA in adult MPS I mice can be achieved without immunosuppression by modifying the vector to reduce expression in the spleen. This approach may be effective in patients with MPS I or other lysosomal storage diseases.

Radiographic evaluation of bones and joints in mucopolysaccharidosis I and VII dogs after neonatal gene therapy

Mucopolysaccharidosis I (MPS I) and MPS VII are due to deficient activity of the glycosaminoglycan-degrading lysosomal enzymes alpha-L-iduronidase and beta-glucuronidase, respectively, and result in abnormal bones and joints. Here, the severity of skeletal disease in MPS I and MPS VII dogs and the effects of neonatal gene therapy were evaluated. For untreated MPS VII dogs, the lengths of the second cervical vertebrae (C2) and the femur were only 56% and 84% of normal, respectively, and bone dysplasia and articular erosions, and joint subluxation were severe. Previously, we reported that neonatal intravenous injection of a retroviral vector (RV) with the appropriate gene resulted in expression in liver and blood cells, and high serum enzyme activity. In this study, we demonstrate that C2 and femurs of RV-treated MPS VII dogs were longer at 82% and 101% of normal, respectively, and there were partial improvements of qualitative abnormalities. For untreated MPS I dogs, the lengths of C2 and femurs (91% and 96% of normal, respectively) were not significantly different from normal dogs. Qualitative changes in MPS I bones and joints were generally modest and were partially improved with RV treatment, although cervical spine disease was severe and was difficult to correct with gene therapy in both models. The greater severity of skeletal disease in MPS VII than in MPS I dogs may reflect accumulation of chondroitin sulfate in cartilage in MPS VII, or could relate to the specific mutations. Neonatal RV-mediated gene therapy ameliorates, but does not prevent, skeletal disease in MPS I and MPS VII dogs.

Long-term correction of inhibitor-prone hemophilia B dogs treated with liver-directed AAV2-mediated factor IX gene therapy

Preclinical studies and initial clinical trials have documented the feasibility of adenoassociated virus (AAV)-mediated gene therapy for hemophilia B. In an 8-year study, inhibitor-prone hemophilia B dogs (n = 2) treated with liver-directed AAV2 factor IX (FIX) gene therapy did not have a single bleed requiring FIX replacement, whereas dogs undergoing muscle-directed gene therapy (n = 3) had a bleed frequency similar to untreated FIX-deficient dogs. Coagulation tests (whole blood clotting time [WBCT], activated clotting time [ACT], and activated partial thromboplastin time [aPTT]) have remained at the upper limits of the normal ranges in the 2 dogs that received liver-directed gene therapy. The FIX activity has remained stable between 4% and 10% in both liver-treated dogs, but is undetectable in the dogs undergoing muscle-directed gene transfer. Integration site analysis by linear amplification-mediated polymerase chain reaction (LAM-PCR) suggested the vector sequences have persisted predominantly in extrachromosomal form. Complete blood count (CBC), serum chemistries, bile acid profile, hepatic magnetic resonance imaging (MRI) and computed tomography (CT) scans, and liver biopsy were normal with no evidence for tumor formation. AAV-mediated liver-directed gene therapy corrected the hemophilia phenotype without toxicity or inhibitor development in the inhibitor-prone null mutation dogs for more than 8 years.

Gene therapy for mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are due to deficiencies in activities of lysosomal enzymes that degrade glycosaminoglycans. Some attempts at gene therapy for MPS in animal models have involved intravenous injection of vectors derived from an adeno-associated virus (AAV), adenovirus, retrovirus or a plasmid, which primarily results in expression in liver and secretion of the relevant enzyme into blood. Most vectors can correct disease in liver and spleen, although correction in other organs including the brain requires high enzyme activity in the blood. Alternative approaches are to transduce hematopoietic stem cells, or to inject a vector locally into difficult-to-reach sites such as the brain. Gene therapy holds great promise for providing a long-lasting therapeutic effect for MPS if safety issues can be resolved.

Correction of clinical manifestations of canine mucopolysaccharidosis I with neonatal retroviral vector gene therapy

Mucopolysaccharidosis I (MPS I) (Hurler syndrome) is due to deficient alpha-L-iduronidase (IDUA) activity and is the most common of the MPS disorders. Neonatal MPS I dogs were injected intravenously (IV) with a gamma retroviral vector containing a complete long-terminal repeat (LTR) and an internal human alpha(1)-antitrypsin (hAAT) promoter upstream of the canine IDUA complementary DNA (cDNA). This resulted in stable serum IDUA activity of 366 +/- 344 units (U)/ml (28-fold normal) for up to 1.8 years, which likely derived primarily from secretion of IDUA by transduced liver cells. Retroviral vector (RV)-treated dogs had >18% of normal IDUA activity in organs and had decreased severity and/or incidence of hernias, chest deformities, joint disease, facial dysmorphia, corneal clouding, valvular heart disease, and aortic dilatation as compared with untreated MPS I dogs. The marked reduction that was observed in lysosomal storage in the brain of RV-treated dogs may have been due in part to expression from the LTR of the vector in cells in the brain. This possibility will be explored in future studies, because the potential for insertional mutagenesis has raised concerns about using vectors with an intact LTR. If proven safe, this gene therapy technique may be utilized in treating children with Hurler syndrome.

Animal models for mucopolysaccharidosis disorders and their clinical relevance

Progress in understanding how a particular genotype produces the phenotype of an inborn error of metabolism, such as a mucopolysaccharidosis, in human patients has been facilitated by the study of animals with mutations in the orthologous genes. These are not just animal models, but true orthologues of the human genetic disease, with defects involving the same evolutionarily conserved genes and the same molecular, biochemical, and anatomic lesions as in human patients. These animals are often domestic species because of the individual medical attention paid to them, particularly dogs and cats. In addition, naturally occurring mouse models have also been found in breeding colonies. Within the last several decades, advances in molecular biology have allowed the production of knockout mouse models of human genetic disease, including the lysosomal storage diseases. The ability to use both inbred strains of a small, prolific species together with larger out-bred animals found because of their disease phenotype provides a powerful combination with which to investigate pathogenesis, develop approaches to therapy, and define biomarkers to evaluate therapeutic success. This has been true for the inborn errors of metabolism and, in particular, the mucopolysaccharidoses.

CONCLUSION

Animal models of human genetic disease continue to play an important role in understanding the molecular and physiological consequences of lysosomal storage diseases and to provide an opportunity to evaluate the efficacy and safety of therapeutic interventions.

Improvements in mucopolysaccharidosis I mice after adult retroviral vector-mediated gene therapy with immunomodulation

Mucopolysaccharidosis I (MPS I) is caused by deficient alpha-L-iduronidase (IDUA) activity and results in the accumulation of glycosaminoglycans and multisystemic disease. Gene therapy could program cells to secrete mannose 6-phosphate-modified IDUA, and enzyme in blood could be taken up by other cells. Neonatal retroviral vector (RV)-mediated gene therapy has been shown to reduce the manifestations of murine MPS I; however, intravenous injection of RV into adults was ineffective owing to a cytotoxic T lymphocyte (CTL) response against transduced cells. In this study, prolonged inhibition of CD28 signaling with CTLA4-Ig, or transient administration of CTLA4-Ig with an anti-CD40 ligand antibody or with an anti-CD4 antibody, resulted in stable expression in most mice that received RV as adults. Mice with stable expression had 81 +/- 41U/ml IDUA activity in serum. This resulted in reductions in bone disease, improvements in hearing and vision, and reductions in biochemical and pathological evidence of lysosomal storage in most organs. Improvements in brain were likely due to diffusion of enzyme from blood. However, aortic disease was refractory to treatment. This demonstrates that most manifestations of MPS I can be prevented using adult gene therapy if an immune response is blocked.

Effect of neonatal administration of a retroviral vector expressing alpha-L-iduronidase upon lysosomal storage in brain and other organs in mucopolysaccharidosis I mice

Mucopolysaccharidosis I (MPS I) due to deficient alpha-L-iduronidase (IDUA) activity results in accumulation of glycosaminoglycans in many cells. Gene therapy could program cells to secrete IDUA modified with mannose 6-phosphate (M6P), and enzyme could be taken up by other cells via the M6P receptor. We previously reported that newborn MPS I mice that were injected intravenously with 10(9) (high-dose) or 10(8) (low-dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA achieved stable levels of IDUA activity in serum and had reduced disease in heart, eye, ear, and bone in a dose-dependent fashion. However, the dose required for improvement in manifestations of disease in other organs was not reported. High-dose and low-dose RV mice with an average serum IDUA activity of 1037+/-90 U/ml (471-fold normal) and 43+/-12 U/ml (20-fold normal), respectively, had complete correction of biochemical and pathological evidence of disease in the liver, spleen, kidney, and small intestines. Although mice that received high-dose RV had complete correction of lysosomal storage in thymus, ovary, lung, and testis, correction in these organs was only partial for those that received low-dose RV. Storage in brain was almost completely corrected with high-dose RV, but was not improved with low-dose RV. The correction of disease in brain may be due to diffusion of enzyme from blood. We conclude that high-dose RV prevents biochemical and pathological manifestations of disease in all organs in MPS I mice including brain.

Immune response after neonatal transfer of a human factor IX-expressing retroviral vector in dogs, cats, and mice

INTRODUCTION

Gene therapy could prevent bleeding in hemophilia. However, antibodies could inhibit coagulation, while cytotoxic T lymphocytes could destroy modified cells. The immaturity of the newborn immune system might prevent these immune responses from occurring after neonatal gene therapy.

MATERIALS AND METHODS

Newborn dogs, cats, or mice were injected intravenously with a retroviral vector expressing human Factor IX. Plasma was evaluated for antigen and anti-human Factor IX antibodies. Cytotoxic T lymphocyte responses were evaluated indirectly by analysis of retroviral vector RNA in liver. Lymphocytes were evaluated for cytokine secretion and the ability to suppress an immune response to human Factor IX in mice.

RESULTS AND CONCLUSIONS

Hemophilia B dogs that achieved 942+/-500 ng/ml (19% normal) or 5+/-0.4 ng/ml (0.1% normal) of human Factor IX in plasma only bled 0 or 1.2 times per year, respectively, and were tolerant to infusion of human Factor IX. Normal cats expressed human Factor IX at 118+/-29 ng/ml (2% normal) in plasma without antibody formation. However, plasma human Factor IX disappeared at late times in 1 of 4 cats, which was probably due to a cytotoxic T lymphocyte response that destroyed cells with high expression. C3H mice were tolerant to human Factor IX after neonatal gene therapy, which may involve clonal deletion of human Factor IX-responsive cells. These data demonstrate that neonatal gene therapy does not induce antibodies to human Factor IX in dogs, cats, or mice. The putative cytotoxic T lymphocyte response in one cat requires further study.

Mucopolysaccharidosis I cats mount a cytotoxic T lymphocyte response after neonatal gene therapy that can be blocked with CTLA4-Ig

Although gene therapy has reduced manifestations of genetic diseases, immune responses can abrogate the effect. One approach to inducing tolerance is to perform gene transfer in newborns when the immune system is immature. We demonstrate here that the dose of retroviral vector (RV) is important in mice, as mucopolysaccharidosis I (MPS I) mice that received neonatal intravenous gene therapy with a high dose of a canine alpha-L-iduronidase (cIDUA)-expressing RV had stable expression, while those that received a low dose did not. It was unclear, however, if neonatal transfer with any dose could induce tolerance in large animals. Therefore, newborn MPS I cats were injected intravenously with the RV expressing cIDUA. Although this resulted in high serum IDUA activity due to secretion by transduced cells, expression fell due to a CTL response. Cats that transiently received the immunosuppressive agent CTLA4-Ig did not develop a CTL response. In contrast, MPS I dogs, which can respond immunologically to canine IDUA, had stable serum IDUA activity after neonatal gene therapy. We conclude that cats, but not dogs, mount a potent CTL response to canine IDUA after neonatal gene therapy, which can be prevented with transient CTLA4-Ig.