Minicircle DNA-based gene therapy coupled with immune modulation permits long-term expression of α-L-iduronidase in mice with mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease characterized by mutations to the α-L-iduronidase (IDUA) gene resulting in inactivation of the IDUA enzyme. The loss of IDUA protein results in the progressive accumulation of glycosaminoglycans within the lysosomes resulting in severe, multi-organ system pathology. Gene replacement strategies have relied on the use of viral or nonviral gene delivery systems. Drawbacks to these include laborious production procedures, poor efficacy due to plasmid-borne gene silencing, and the risk of insertional mutagenesis. This report demonstrates the efficacy of a nonintegrating, minicircle (MC) DNA vector that is resistant to epigenetic gene silencing in vivo. To achieve sustained expression of the immunogenic IDUA protein we investigated the use of a tissue-specific promoter in conjunction with microRNA target sequences. The inclusion of microRNA target sequences resulted in a slight improvement in long-term expression compared to their absence. However, immune modulation by costimulatory blockade was required and permitted for IDUA expression in MPS I mice that resulted in the biochemical correction of pathology in all of the organs analyzed. MC gene delivery combined with costimulatory pathway blockade maximizes safety, efficacy, and sustained gene expression and is a new approach in the treatment of lysosomal storage disease.

Characterization of an MPS I-H knock-in mouse that carries a nonsense mutation analogous to the human IDUA-W402X mutation

Here we report the characterization of a knock-in mouse model for the autosomal recessive disorder mucopolysaccharidosis type I-Hurler (MPS I-H), also known as Hurler syndrome. MPS I-H is the most severe form of alpha-l-iduronidase deficiency. alpha-l-iduronidase (encoded by the IDUA gene) is a lysosomal enzyme that participates in the degradation of dermatan sulfate and heparan sulfate. Using gene replacement methodology, a nucleotide change was introduced into the mouse Idua locus that resulted in a nonsense mutation at codon W392. The Idua-W392X mutation is analogous to the human IDUA-W402X mutation commonly found in MPS I-H patients. We found that the phenotype in homozygous Idua-W392X mice closely correlated with the human MPS I-H disease. Homozygous W392X mice showed no detectable alpha-l-iduronidase activity. We observed a defect in GAG degradation as evidenced by an increase in sulfated GAGs excreted in the urine and stored in multiple tissues. Histology and electron microscopy also revealed evidence of GAG storage in all tissues examined. Additional assessment revealed bone abnormalities and altered metabolism within the Idua-W392X mouse. This new mouse will provide an important tool to investigate therapeutic approaches for MPS I-H that cannot be addressed using current MPS I-H animal models.

AGT-181: expression in CHO cells and pharmacokinetics, safety, and plasma iduronidase enzyme activity in Rhesus monkeys

Enzyme replacement therapy is not effective for the brain, owing to the lack of transport of the enzyme across the blood-brain barrier (BBB). Recombinant proteins such as the lysosomal enzyme, iduronidase, can penetrate the human BBB, following the re-engineering of the protein as an IgG fusion protein, where the IgG moiety targets an endogenous BBB transport system. The IgG acts as a molecular Trojan horse to ferry the fused protein into brain. AGT-181 is a genetically engineered fusion protein of human iduronidase and a chimeric monoclonal antibody against the human insulin receptor. Adult Rhesus monkeys were administered repeat intravenous doses of AGT-181 ranging from 0.2 to 20 mg/kg. Chronic AGT-181 dosing resulted in no toxicity at any dose, no changes in organ histology, no change in plasma or cerebrospinal fluid glucose, and no significant immune response. AGT-181 was rapidly removed from plasma, based on measurements of either plasma immunoreactive AGT-181 or plasma iduronidase enzyme activity. Plasma pharmacokinetics analysis showed a high systemic volume of distribution, and a clearance rate comparable to a small molecule. The safety pharmacology studies provide the basis for future drug development of AGT-181 as a new therapeutic approach to treatment of the brain in Hurler's syndrome.

Glycosaminoglycan-degrading enzymes in the varicose vein wall

AIM

Mechanical properties of the vein wall are determined by extracellular matrix components, including glycosaminoglycans (GAGs). The aim of the study was to evaluate the activity of enzymes involved in GAGs degradation pathway in the wall of varicose veins and varicose veins complicated by thrombophlebitis, when compared to the wall of normal ones.

METHODS

Normal, varicose veins and varicose veins complicated by thrombophlebitis were collected during surgical treatment of 10 patients. Activities of endoglycosidases, sulphatases and exoglycosidases were assessed according to colorimetric methods.

RESULTS

Activities of neutral endoglycosidases degrading chondroitin-4-sulphate (C4S) and heparan sulphate (HS) were decreased, whereas activities of neutral endoglycosidases degrading dermatan sulphate and hyaluronic acid were increased in varicose veins and varicose veins complicated by thrombophlebitis. Activities of acidic endoglycosidases degrading C4S and HS were decreased in varicose veins and varicose veins complicated by thrombophlebitis, whereas activity of acidic endoglycosidases degrading chondroitin-6-sulphate was decreased only in varicose veins complicated by thrombophlebitis. Furthermore increased activities of arylosulphatase B, beta-N-acetylhexosaminidase and alpha-L-iduronidase were demonstrated in varicose veins, as well as in varicose veins complicated by thrombophlebitis.

CONCLUSIONS

Changed activities of GAGs-degrading enzymes may contribute to previously reported changes in the content and molecular differentiation of GAGs in the wall of varicose veins that may play a role in the disease pathogenesis.

Enzyme replacement therapy in 12 patients with MPS I-H/S with homozygous p.Leu490Pro mutation

We describe a cohort of 14 Hurler-Scheie patients homozygous for the p.Leu490Pro missense mutation in the alpha-L-iduronidase gene. Now based in the UK, they are all of Pakistani/Kashmiri descent; 64% were female; 11/14 (79%) had a sibling or cousin with MPS I and the parents are consanguineous in all cases. The median age at diagnosis was 1.8 years (range from antenatal diagnosis to 16.5 years). Twelve were on ERT with recombinant human alpha-L-iduronidase (IDUA; Laronidase, Genzyme) for a median duration of 22.5 months (range 2-71 months) and median age at commencement of ERT was 8.6 years (range 0.4-23.1 years). There was clear improvement in the size of liver and spleen as well as reduction in urine glycosaminoglycans (GAGs). The mean (range) urine GAG levels in mg/mmol creatinine were 63.4 (28.9-105.6), 28.3 (10.9-41.4), 22.8 (12.1-43.1), 15.7 (9.2-24.8) and 16.3 (10.1-21.0) at commencement, 3 months post ERT, 6 months post ERT, 12 months post ERT and 24 months post ERT, respectively. Effects on growth were not clear as there does not seem to be an obvious trend of increase or decrease in height after commencement of ERT and this seems to be the case regardless of the age at which ERT was started.

Enzyme replacement therapy in two patients with an advanced severe (Hurler) phenotype of mucopolysaccharidosis I

Although offered, two of our Hurler patients (OMIM 607014) had not undergone bone marrow transplantation at an early stage of their disease. Rapid disease progression had resulted in a range of signs and symptoms representative of advanced neurodegeneration and debilitating somatic Hurler disease. As general palliative care had only little impact on the burden of disease, laronidase (Aldurazyme) treatment was introduced in an attempt to alleviate somatic symptoms and to improve the quality of their lives. Therapeutic benefits from enzyme replacement therapy included improvements in general physical condition and mood, as well as normalisation of the sleep patterns, disappearance of sleep apnoea syndrome and reduction of hepatosplenomegaly. Improvements in the joint mobility were mainly limited to the wrists and hips. In addition, improvements in cardiac function, stool habits, visual acuity, corneal clouding and hearing were observed in one or both patients. Irreversible skeletal changes did not deteriorate. The neurological outcome of these patients is likely not influenced as laronidase is believed not to pass the blood-brain barrier. Therefore, the decision to initiate this therapy in transplant-naïve Hurler patients with an advanced stage of the disease should be taken after careful consideration.

CONCLUSION

We are of the opinion that the option of enzyme therapy should not be excluded in severely affected Hurler patients who cannot undergo bone marrow transplantation. Stabilization or amelioration of somatic disease and improvement of the quality of their lives should be embraced as therapeutic goals.

Bone marrow transplantation for feline mucopolysaccharidosis I

Severe mucopolysaccharidosis type I (MPS I) is a fatal neuropathic lysosomal storage disorder with significant skeletal involvement. Treatment involves bone marrow transplantation (BMT), and although effective, is suboptimal, due to treatment sequelae and residual disease. Improved approaches will need to be tested in animal models and compared to BMT. Herein we report on bone marrow transplantation to treat feline mucopolysaccharidosis I (MPS I). Five MPS I stably engrafted kittens, transplanted with unfractionated bone marrow (6.3x10(7)-1.1x10(9) nucleated bone marrow cells per kilogram) were monitored for 13-37 months post-engraftment. The tissue total glycosaminoglycan (GAG) content was reduced to normal levels in liver, spleen, kidney, heart muscle, lung, and thyroid. Aorta GAG content was between normal and affected levels. Treated cats had a significant decrease in the brain GAG levels relative to untreated MPS I cats and a paradoxical decrease relative to normal cats. The alpha-l-iduronidase (IDUA) activity in the livers and spleens of transplanted MPS I cats approached heterozygote levels. In kidney cortex, aorta, heart muscle, and cerebrum, there were decreases in GAG without significant increases in detectable IDUA activity. Treated animals had improved mobility and decreased radiographic signs of disease. However, significant pathology remained, especially in the cervical spine. Corneal clouding appeared improved in some animals. Immunohistochemical and biochemical analysis documented decreased central nervous system ganglioside storage. This large animal MPS I study will serve as a benchmark of future therapies designed to improve on BMT.

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.

Potential treatment of liver-related disorders with in vitro expanded human liver precursors

Inherited deficiencies in critical components of metabolic pathways are the primary cause of many liver and lysosomal disorders, most of which are incurable. Stem cell transplantation may offer a new type of treatment for these diseases. We have isolated hepatocyte precursors from human fetal livers. These cells were highly proliferative in vitro in media with or without serum. Expanded hepatocyte precursors expressed endoderm and early hepatocyte markers. The precursors synthesized a large number of molecules related to human metabolic diseases and released some of them into the environment. In a homing test, these cells migrated preferentially into the liver. When transplanted into fetal sheep liver, they incorporated into the liver tissue and differentiated into hepatocytes. Transplantation of the liver precursors to alpha-l-iduronidase-deficient mice partially corrected the enzyme deficiency. Data from these studies suggest that in vitro expanded human liver precursor cells are a potential cell source for the treatment of liver- and lysosome-related disorders.

Ectopic expression of a conifer Abscisic Acid Insensitive3 transcription factor induces high-level synthesis of recombinant human alpha-L-iduronidase in transgenic tobacco leaves

We are examining various plant-based systems to produce enzymes for the treatment of human lysosomal storage disorders. Constitutive expression of the gene encoding the human lysosomal enzyme, alpha-L-iduronidase (IDUA; EC 3.2.1.76) in leaves of transgenic tobacco plants resulted in low-enzyme activity, and the protein appeared to be subject to proteolysis. Toward enhancing production of this recombinant enzyme in vegetative tissues, transgenic tobacco plants were generated to co-express a CaMV35S:Chamaecyparis nootkatensis Abscisic Acid Insensitive3 (CnABI3) gene construct, along with the human gene construct. The latter contained regulatory sequences of the Phaseolus vulgaris arcelin 5-I gene (5'-flanking, signal-peptide-encoding, and 3'-flanking regions). Ectopic synthesis of the CnABI3 protein led to the transactivation of the arcelin promoter and accordingly high activity (e.g., 25,000 pmol/min/mg total soluble protein) and levels of recombinant IDUA mRNA and protein were induced in leaves of transgenic tobacco, particularly in the presence of 150-200 microM S-(+)-ABA. Synthesis of human IDUA containing a carboxy-terminal ER retention (SEKDEL) sequence was also inducible by ABA in leaves co-transformed with the CnABI3 gene. As compared to the natural S-(+)-ABA, two persistent ABA analogues, (+)-8' acetylene ABA and (+)-8'methylene ABA, led to greater levels of beta-glucuronidase (GUS) reporter activities in leaves co-expressing the CnABI3 gene and a vicilin:GUS chimeric gene. In contrast, (+)-8' acetylene ABA and natural ABA appeared to be equally effective in stimulating the CnABI3-induced expression of an arcelin:GUS gene, and of the human IDUA gene, the latter also driven by arcelin-gene-regulatory sequences. Various stress-related treatments, particularly high concentrations of NaCl, had an even greater effect than ABA in promoting accumulation of human IDUA in co-transformed tobacco leaves. This strategy provides the means of enhancing the yields of recombinant proteins in transgenic plant vegetative tissues and potentially in cultured plant cells. The human recombinant protein can be readily induced in the presence of chemicals such as NaCl that can be added to cell cultures or even whole plants without a significant increase in production costs.

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.

Analysis of factors affecting development of carpal tunnel syndrome in patients with Hurler syndrome after hematopoietic cell transplantation

Children with Hurler syndrome (mucopolysaccharidosis type IH (MPSIH)) have skeletal, joint and soft tissue abnormalities that may persist or progress after hematopoietic stem cell transplantation (HSCT). We report our single center experience with development of carpal tunnel syndrome (CTS) in 43 children with MPSIH after HSCT. Twenty-three children (59%) developed CTS following HSCT; 19 of the 39 children with enzyme activity in the normal or heterozygous range developed CTS (49%), whereas all four children with low heterozygous or absent enzyme activity developed CTS after HSCT. Fourteen of 19 related donor marrow recipients, eight of 19 of those receiving an unrelated donor graft and one of five unrelated cord blood recipients developed CTS. The mean age at surgical release was 4.8 years. With each year increase in age at HSCT, there was a 55% increased risk. Age and enzyme activity after HSCT were significant factors in the development of CTS. Transplantation by 2 years of age reduced the risk of developing CTS by 46%; higher enzyme activity led to a 78% reduction in the risk of developing CTS. However, children transplanted for MPSIH remain at risk for the development of CTS, and should be monitored on an ongoing basis by nerve conduction velocity testing.

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.

A follow-up study of MPS I patients treated with laronidase enzyme replacement therapy for 6 years

Recombinant human alpha-L-iduronidase (Aldurazyme, laronidase) was approved as an enzyme replacement therapy for patients with the lysosomal storage disorder, mucopolysaccharidosis I (MPS I). In order to assess the long-term safety and efficacy of laronidase therapy, 5 of 10 patients in the original laronidase Phase 1/2 clinical trial were re-evaluated after 6 years of treatment. Lysosomal storage was further improved at 6 years (urinary glycosaminoglycans (GAG) excretion decreased 76%; mean liver size at 1.84% of body weight). Shoulder maximum range of motion was maintained or further increased and reached a mean 33.2 (R) and 25.0 (L) degrees gained in flexion and 34.0 (R) and 27.3 (L) degrees gained in extension. Sleep apnea was decreased in four of five patients and the airway size index improved. Cardiac disease evaluations showed no progression to heart failure or cor pulmonale but pre-existing significant valve disease did progress in some patients. Substantial growth was observed for the pre-pubertal patients, with a gain of 33 cm (27%) in height and a gain of 31 kg in weight (105%). In general, the evaluated patients reported an improved ability to perform normal activities of daily living. Overall these data represent the first evidence that laronidase can stabilize or reverse many aspects of MPS I disease during long-term therapy and that early treatment prior to the development of substantial cardiac and skeletal disease may lead to better outcomes.

Biochemical monitoring after haemopoietic stem cell transplant for Hurler syndrome (MPSIH): implications for functional outcome after transplant in metabolic disease

Hurler Syndrome is corrected by allogeneic BMT by the action of donor enzyme on recipient tissue. In this paper, we describe monitoring of 39 patients transplanted in two centres to determine donor chimerism, enzyme level and residual substrate - expressed as dermatan sulphate to chondroitin sulphate ratio. We show that in fully engrafted recipients, the enzyme level, expressed as mumol/g total protein/h, post-transplant is 24.2 from an unrelated donor and 10.2 from a heterozygote family donor (P<0.0001). There is a tight relationship between mean post-transplant enzyme level and residual substrate - Spearman's rank correlation coefficient (Rho) was -0.76 and -0.80 at 12 and 24 months, respectively (P<0.0001). We propose that these differences affect patient outcome. As unrelated donor transplant outcomes improve and especially given the higher levels of donor cell engraftment following cord transplants, our data might influence donor selection where only heterozygote-matched family members are available.

Intrathecal administration of AAV vectors for the treatment of lysosomal storage in the brains of MPS I mice

Mucopolysaccharidosis type I (MPS I) is caused by an inherited deficiency of alpha-L-iduronidase (IDUA). The result is a progressive, lysosomal storage disease with central nervous system (CNS) as well as systemic involvement. To target gene therapy to the CNS, recombinant adeno-associated virus (AAV) vectors carrying IDUA sequence were administered to MPS I mice via injection into cerebrospinal fluid. In contrast to intravenous administration, this intrathecal administration was effective in generating widespread IDUA activity in the brain, with the cerebellum and olfactory bulbs having highest activities. In general, IDUA levels correlated with vector dose, although this correlation was obscured in cerebellum by particularly high variability. High doses of vector (4 x 10(10) particles) provided IDUA levels approaching or exceeding normal levels in the brain. Histopathology indicated that the number of cells with storage vacuoles was reduced extensively or was eliminated entirely. Elimination of storage material in Purkinje cells was particularly dramatic. A lower vector dose (2 x 10(9) particles) reduced both the number of storage cells and the extent of storage per cell, but the effect was not complete. Some perivascular cells with storage persisted, and this cell type appeared to be more resistant to treatment than neurons or glial cells. We conclude that intrathecal administration of AAV-IDUA delivers vector to brain cells, and that this route of administration is both minimally invasive and effective.

Stabilising normal and mis-sense variant alpha-glucosidase

alpha-Glucosidase (EC 3.2.1.3) is a lysosomal enzyme that hydrolyses alpha-1,4- and alpha-1,6-linkages of glycogen to produce free glucose. A deficiency in alpha-glucosidase activity results in glycogen storage disorder type II (GSD II), also called Pompe disease. Here, d-glucose was shown to be a competitive inhibitor of alpha-glucosidase and when added to culture medium at 6.0 g/L increased the production of this protein by CHO-K1 expression cells and stabilised the enzyme activity. D-Glucose also prevented alpha-glucosidase aggregation/precipitation and increased protein yield in a modified purification scheme. In fibroblast cells, from adult-onset GSD II patients, D-glucose increased the residual level of alpha-glucosidase activity, suggesting that a structural analogue of d-glucose may be used for enzyme enhancement therapy.

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.

alpha-L-Iduronidase transport in neurites

Effective therapeutic strategies for mucopolysaccharidosis type I (MPSI) rely on mannose-6-phosphate receptor-mediated uptake of extracellular alpha-l-iduronidase (IDUA), the missing lysosomal enzyme in this disease, by deficient cells. Intravenously infused recombinant human IDUA does not reach the central nervous system, whereas neuropathology and neurological manifestations are prominent in Hurler syndrome, the most severe and most frequent form of MPSI. The creation of a single intracerebral source of IDUA by gene therapy was proved efficient to deliver enzyme throughout the brain of MPSI mice. IDUA spreading far beyond areas where the enzyme was synthesized suggested transport along neuronal processes. To examine the mechanisms of IDUA spreading in the brain, we constructed a chimeric protein in which GFP is fused at the C-terminus of IDUA. The fusion protein was expressed in rat primary neurons using lentivirus vectors. Fluorescent IDUA retained full catalytic activity including on natural substrates, interacted with mannose-6-phosphate receptors and was appropriately addressed to lysosomes. Fluorescent vesicles were broadly distributed over neuronal soma and processes. Time-lapse fluorescent video-microscopy showed that 54% of fluorescent vesicles exhibited either retrograde or anterograde displacements along neurites. Most moving organelles showed complex movements with frequent direction changes and arrests. Motility depended on microtubule integrity. Efficient axono-dendritic transport of IDUA provides a rationale for gene therapy based on the release of therapeutic enzyme at discrete locations within the central nervous system of patients with severe form of MPSI.

Epstein-Barr virus-induced transformation of B cells for the diagnosis of genetic metabolic disorders--enumerative conditions for cryopreservation

Epstein-Barr virus (EBV) infection in vitro causes transformation of B cells and generates B lymphoblastoid cell lines (LCLs). These LCLs have been widely used for the diagnostic of several genetic metabolic disorders. However, up to now, efficiency of LCL generation has been based on misleading subjective analysis. In this study, quantitative analyses have been performed to indicate efficiency of B-cell transformation to measuring human lysosomal acid hydrolases associated with: GM1-gangliosidosis type I, Gaucher disease and mucopolysaccharidosis type I. Peripheral blood mononuclear cells were isolated from 13 subjects, and LCLs were produced by culturing them with EBV for 12 days. Activities of the enzymes beta-galactosidase, beta-glucosidase and alpha-iduronidase were measured before and after cryopreservation in liquid nitrogen for 30 days. Efficiency of the B-cell transformation was screened every 4 days by the enumeration of cell proliferation, cell counts and changes in granularity estimated by flow cytometry. We observed the generation of 13 LCLs. Cell transformation was confirmed by the gradual increase of cellular clusters, cell size and granularity. In addition, we determined that the activity of the enzymes mentioned above did not change following cryopreservation. These data suggest that our enumerative approach for screening of EBV-LCLs is efficient for the enzymatic determination of human lysosomal acid hydrolases and may thus replace misleading subjective analyses.

Synthesis of enzymatically active human alpha-L-iduronidase in Arabidopsis cgl (complex glycan-deficient) seeds

As an initial step to develop plants as systems to produce enzymes for the treatment of lysosomal storage disorders, Arabidopsis thaliana wild-type (Col-0) plants were transformed with a construct to express human alpha-l-iduronidase (IDUA; EC 3.2.1.76) in seeds using the promoter and other regulatory sequences of the Phaseolus vulgaris arcelin 5-I gene. IDUA protein was easily detected on Western blots of extracts from the T(2) seeds, and extracts contained IDUA activity as high as 2.9 nmol 4-methylumbelliferone (4 MU)/min/mg total soluble protein (TSP), corresponding to approximately 0.06 microg IDUA/mg TSP. The purified protein reacted with an antibody specific for xylose-containing plant complex glycans, indicating its transit through the Golgi complex. In an attempt to avoid maturation of the N-linked glycans of IDUA, the same IDUA transgene was introduced into the Arabidopsis cgl background, which is deficient in the activity of N-acetylglucosaminyl transferase I (EC 2.4.1.101), the first enzyme in the pathway of complex glycan biosynthesis. IDUA activity and protein levels were significantly higher in transgenic cgl vs. wild-type seeds (e.g. maximum levels were 820 nmol 4 MU/min/mg TSP, or 18 microg IDUA/mg TSP). Affinity-purified IDUA derived from cgl mutant seeds showed a markedly reduced reaction with the antibody specific for plant complex glycans, despite transit of the protein to the apoplast. Furthermore, gel mobility changes indicated that a greater proportion of its N-linked glycans were susceptible to digestion by Streptomyces endoglycosidase H, as compared to IDUA derived from seeds of wild-type Arabidopsis plants. The combined results indicate that IDUA produced in cgl mutant seeds contains glycans primarily in the high-mannose form. This work clearly supports the viability of using plants for the production of human therapeutics with high-mannose glycans.

A picornaviral 2A-like sequence-based tricistronic vector allowing for high-level therapeutic gene expression coupled to a dual-reporter system

The 2A-like sequences from members of the picornavirus family were utilized to construct a tricistronic vector bearing the human iduronidase (IDUA) gene along with the firefly luciferase and DsRed2 reporter genes. The 2A-like sequences mediate a cotranslational cleavage event resulting in the release of each individual protein product. Efficient cleavage was observed and all three proteins were functional in vitro and in vivo, allowing for supratherapeutic IDUA enzyme levels and the coexpression of luciferase and DsRed2 expression, which enabled us to track gene expression.

Neonatal gene therapy of MPS I mice by intravenous injection of a lentiviral vector

Mucopolysaccharidosis type I (MPS I) is a lysosomal glycosaminoglycan (GAG) storage disorder caused by deficiency of alpha-l-iduronidase (IDUA). In this study, we evaluated the potential to perform gene therapy for MPS I by direct in vivo injection of a lentiviral vector, using an IDUA gene knockout murine model. We compared the efficacy in newborn versus young adult MPS I mice of a single intravenous injection of the lentiviral vector. The extent of transduction was dose-dependent, with the liver receiving the highest level of vector, but other somatic organs reaching almost the same level. The phenotypic manifestations of disease were partially improved in the mice treated as young adults, but were nearly normalized at every end-point measured in the mice treated as neonates. In the neonatally treated mice, the expressed IDUA activity resulted in decreased GAG storage, prevention of skeletal abnormalities, a more normal gross appearance, and improved survival. Most strikingly, significant levels of IDUA enzyme were produced in the brain of mice treated as neonates, with transduction of neurons at high levels. The sustained expression of enzymatically active IDUA in multiple organs had a significant beneficial effect on the phenotypic abnormalities of MPS I, which may be translated to clinical gene therapy of patients with Hurler disease.

Gene therapy for a mucopolysaccharidosis type I murine model with lentiviral-IDUA vector

Mucopolysaccharidosis type I is a lysosomal disease due to mutations in the IDUA gene, resulting in deficiency of alpha-L-iduronidase and accumulation of glycosaminoglycans (GAGs). Bone marrow transplantation and enzyme replacement are two therapies considered only moderately successful for affected patients, making the development of novel treatments necessary. We have previously shown the efficacy of lentivirus-mediated gene transfer to correct patient fibroblasts in vitro. Here we tested lentiviral-IDUA vector gene therapy in vivo on a murine MPS I model. Eight- to 10 week-old mice were injected with increasing lentiviral doses via the tail vein and analyzed 1 month after treatment. A single injection of lentiviral-IDUA vector resulted in transgene expression in several murine tissues, with the highest level reached in liver and spleen. Expression of 1% normal activity was sufficient in treated animals to normalize the GAG level in urine, liver, and spleen and was able to reduce the GAG level in kidney, heart, and lung. Polymerase chain reaction assays showed integration of the viral genome only in liver and spleen of treated animals, suggesting that the correction of the pathology in other tissues was due to secretion into the plasma by liver and spleen and uptake of corrective enzyme by distant tissues. Long-term (6 months) analysis showed the presence of enzyme-specific antibodies and the loss of enzyme activity and vector sequence in the target tissue, suggesting that the transgene-specific immune response interfered with long-term therapeutic correction and led to clearance of transduced cells. In conclusion, our results show the promising potential and the limitations of lentiviral-IDUA vector-mediated gene therapy in an in vivo model.

Liver-directed neonatal gene therapy prevents cardiac, bone, ear, and eye disease 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 liver to secrete enzyme with mannose 6-phosphate (M6P), and enzyme in blood could be taken up by other cells via the M6P receptor. Newborn MPS I mice were injected with 10(9) (high dose) or 10(8) (low dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA. Most animals achieved stable expression of IDUA in serum at 1240 +/- 147 and 110 +/- 31 units/ml, respectively. At 8 months, untreated MPS I mice had aortic insufficiency, increased bone mineral density (BMD), and reduced responses to sound and light. In contrast, MPS I mice that received high-dose RV had normal echocardiograms, BMD, auditory-evoked brain-stem responses, and electroretinograms. This is the first report of complete correction of these clinical manifestations in any model of mucopolysaccharidosis. Biochemical and pathologic evaluation confirmed that storage was reduced in these organs. Mice that received low-dose RV and achieved 30 units/ml of serum IDUA activity had no or only partial improvement. We conclude that high-dose neonatal gene therapy with an RV reduces some major clinical manifestations of MPS I in mice, but low dose is less effective.