Retroviral-mediated transfer of the iduronate-2-sulfatase gene into lymphocytes for treatment of mild Hunter syndrome (mucopolysaccharidosis type II)

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

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

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

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

Current and Emerging Therapies for Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are caused by deficiencies of specific lysosomal enzymes that affect the degradation of mucopolysaccharides or glycosaminoglycans (GAGs). Enzyme replacement therapies are available for an increasing number of MPSs since more than 15 years. Together with hematopoietic stem cell transplantation, these enzyme therapies are currently the gold standard of causal treatment in MPS. Both treatments can improve symptoms and prognosis, but they do not cure these severe conditions. The limitations of intravenous enzyme replacement and cell therapy can be summarized as the development of immune reactions against the therapeutic molecules/cells and failure to restore enduring and sufficient drug exposures in all relevant tissues. Thus innovative approaches include small molecules and encapsulated cells that do not induce immune reactions, gene therapy approaches that aim for sustained enzyme expression, and new enzymes that are able to penetrate barriers to drug distribution like the blood-brain barrier. This chapter provides an update on the state of development of these new therapies and highlights current challenges.

Effects of gene therapy on cardiovascular symptoms of lysosomal storage diseases

Lysosomal storage diseases (LSDs) are inherited conditions caused by impaired lysosomal function and consequent substrate storage, leading to a range of clinical manifestations, including cardiovascular disease. This may lead to significant symptoms and even cardiac failure, which is an important cause of death among patients. Currently available treatments do not completely correct cardiac involvement in the LSDs. Gene therapy has been tested as a therapeutic alternative with promising results for the heart disease. In this review, we present the results of different approaches of gene therapy for LSDs, mainly in animal models, and its effects in the heart, focusing on protocols with cardiac functional analysis.

Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives

Lysosomes and lysosomal enzymes play a central role in numerous cellular processes, including cellular nutrition, recycling, signaling, defense, and cell death. Genetic deficiencies of lysosomal components, most commonly enzymes, are known as "lysosomal storage disorders" or "lysosomal diseases" (LDs) and lead to lysosomal dysfunction. LDs broadly affect peripheral organs and the central nervous system (CNS), debilitating patients and frequently causing fatality. Among other approaches, enzyme replacement therapy (ERT) has advanced to the clinic and represents a beneficial strategy for 8 out of the 50-60 known LDs. However, despite its value, current ERT suffers from several shortcomings, including various side effects, development of "resistance", and suboptimal delivery throughout the body, particularly to the CNS, lowering the therapeutic outcome and precluding the use of this strategy for a majority of LDs. This review offers an overview of the biomedical causes of LDs, their socio-medical relevance, treatment modalities and caveats, experimental alternatives, and future treatment perspectives.

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.

Characterization of a novel mucopolysaccharidosis type II mouse model and recombinant AAV2/8 vector-mediated gene therapy

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is an X-linked inherited disorder caused by a deficiency of the enzyme iduronate-2-sulfatase (IDS), which results in the lysosomal accumulation of glycosaminoglycans (GAG) such as dermatan and heparan sulfate. Here, we report the generation of IDS knockout mice, a model of human MPS II, and an analysis of the resulting phenotype. We also evaluated the effect of gene therapy with a pseudotyped, recombinant adeno-associated virus 2/8 vector encoding the human IDS gene (rAAV-hIDS) in IDS-deficient mice. IDS activity and GAG levels were measured in serum and tissues after therapy. Gene therapy completely restored IDS activity in plasma and tissue of the knockout mice. The rescued enzymatic activity completely cleared the accumulated GAGs in all the tissues analyzed. This model can be used to explore the therapeutic potential of IDS replacement and other strategies for the treatment of MPS II. Additionally, AAV2/8 vectors have promising future clinical applications for the treatment of patients with MPS II.

Gene therapy of Hunter syndrome: evaluation of the efficiency of muscle electro gene transfer for the production and release of recombinant iduronate-2-sulfatase (IDS)

Mucopolysaccharidosis type II (MPSII) is an inherited disorder due to a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). The disease is characterized by a considerable deposition of heparan- and dermatan-sulfate, causing a general impairment of physiological functions. Most of the therapeutic protocols proposed so far are mainly based upon enzyme replacement therapy which is very expensive. There is a requirement for an alternative approach, and to this aim, we evaluated the feasibility of muscle electro gene transfer (EGT) performed in the IDS-knockout (IDS-ko) mouse model. EGT is a highly efficient method of delivering exogenous molecules into different tissues. More recently, pre-treatment with bovine hyaluronidase has shown to further improve transfection efficiency of muscle EGT. We here show that, by applying such procedure, IDS was very efficiently produced inside the muscle. However, no induced IDS activity was measured in the IDS-ko mice plasma, in contrast to matched healthy controls. In the same samples, an anticipated and rapidly increasing immune response against the recombinant protein was observed in the IDS-ko vs control mice, although reaching the same levels at 5 weeks post-injection. Additional experiments performed on healthy mice showed a significant contribution of hyaluronidase pre-treatment in increasing the immune response.

Endogenous heparan sulfate and heparin modulate bone morphogenetic protein-4 signaling and activity

Bone morphogenetic proteins (BMPs) and their endogenous antagonists are important for brain and bone development and tumor initiation and progression. Heparan sulfate (HS) proteoglycans (HSPG) modulate the activities of BMPs and their antagonists. How glycosaminoglycans (GAGs) influence BMP activity in various malignancies and in inherited abnormalities of GAG metabolism, and the structural features of GAGs essential for modulation of BMP signaling, remain incompletely defined. We examined whether chemically modified soluble heparins, the endogenous HS in malignant cells and the HS accumulated in Hurler syndrome cells influence BMP-4 signaling and activity. We show that both exogenous (soluble) and endogenous GAGs modulate BMP-4 signaling and activity, and that this effect is dependent on specific sulfate residues of GAGs. Our studies suggest that endogenous sulfated GAGs promote the proliferation and impair differentiation of malignant human cells, providing the rationale for investigating whether pharmacological agents that inhibit GAG synthesis or function might reverse this effect. Our demonstration of impairment of BMP-4 signaling by GAGs in multipotent stem cells in human Hurler syndrome identifies a mechanism that might contribute to the progressive neurological and skeletal abnormalities in Hurler syndrome and related mucopolysaccharidoses.

Reduction of GAG storage in MPS II mouse model following implantation of encapsulated recombinant myoblasts

BACKGROUND

Hunter syndrome, mucopolysaccharidosis type II (MPS II), is a X-linked inherited disorder caused by the deficiency of the enzyme iduronate-2-sulfatase (IDS), involved in the lysosomal catabolism of the glycosaminoglycans (GAG) dermatan and heparan sulfate. Such a deficiency leads to the intracellular accumulation of undegraded GAG and eventually to a progressive severe clinical pattern. Many attempts have been made in the last two to three decades to identify possible therapeutic strategies for the disorder, including gene therapy and somatic cell therapy.

METHODS

In this study we evaluated the intraperitoneal implantation of allogeneic myoblasts over-expressing IDS, enclosed in alginate microcapsules, in the MPS II mouse model. Animals were monitored for 8 weeks post-implantation, during which plasma and tissue IDS levels, as well as tissue and urinary GAG contents, were measured.

RESULTS AND CONCLUSIONS

Induced enzyme activity occurred both in the plasma and in the different tissues analyzed. A significant decrease in urinary undegraded GAG between the fourth and the sixth week of treatment was observed. Moreover, a biochemical reduction of GAG deposits was measured 8 weeks after treatment in the liver and kidney, on average 30 and 38%, respectively, while in the spleen GAG levels were almost normalized. Finally, the therapeutic effect was confirmed by histolochemical examination of the same tissues. Such effects were obtained following implantation of about 1.5 x 10(6) recombinant cells/animal. Taken together, these results represent a clear evidence of the therapeutic efficacy of this strategy in the MPS II mouse model, and encourage further evaluation of this approach for potential treatment of human beings.

Gene therapy for lysosomal storage diseases

The lysosomal storage diseases are a family of inherited disorders usually caused by a deficiency in a single lysosomal enzyme, and are characterised by progressive intralysosomal storage in multiple cell types. Although individual syndromes can be uncommon, as a whole this family of diseases affects approximately 1 in 3,000 live births. The severity of disease can be variable, ranging from minimal evidence of lysosomal storage to widespread multi-system involvement and early mortality. Although the enzymatic defects responsible for most of these diseases are known, treatment options for the majority of these disorders are limited to supportive care and genetic counselling. Knowledge of the genetic defects underlying these diseases, coupled with advances in the fields of gene transfer and expression, provide an opportunity to utilise gene therapy strategies in order to treat these disorders. Here we provide a description of the biochemical and molecular basis of gene therapy for lysosomal storage diseases, as well as an overview of some of the in vitro and in vivo studies that have been performed.

Biodistribution and efficacy of donor T lymphocytes in a murine model of lysosomal storage disease

Lymphocyte-directed gene transfer has been proposed as potential therapy to treat certain congenital immunological deficiencies as well as other genetic diseases such as lysosomal storage diseases (LSDs). To understand better the extent to which adoptively transferred peripheral T lymphocytes (PTLs) are able to ameliorate LSDs we utilized the beta-glucuronidase-deficient mouse as a model system. PTLs (1 x 10(7)) isolated from the spleen of syngeneic mice overexpressing ( approximately 8-fold) human beta-glucuronidase (GUSB) were injected intravenously into young adult beta-glucuronidase-deficient mice without myeloablative conditioning. Using biochemical and histochemical assays, we were able to track the donor lymphocytes in vivo. Donor lymphocytes were detected in relatively high numbers in liver, spleen, small intestine, mesenteric lymph node, and thymus for at least 5 months, the last time point of analysis. Although liver and spleen had the highest total GUSB activity, histopathologic analysis demonstrated minimal to no correction of lysosomal distention at all time points studied. By contrast, we have shown in earlier studies that administration of similar numbers of macrophages reduced lysosomal storage in several organs, including liver and spleen. To understand this difference in efficacy, we compared the relative level of GUSB released into the medium by nonactivated and activated PTLs as well as by macrophages. Macrophages released >50-fold excess enzyme compared to either activated or nonactivated PTLs. These data suggest that a LSD can be more effectively treated by directing a gene therapy approach to a hematopoietic lineage other than T lymphocytes.

Construction of a high efficiency retroviral vector for gene therapy of Hunter's syndrome

BACKGROUND

As an alternative method to the conventional therapies for Hunter's syndrome, which is a lethal lysosomal storage disorder, we have developed gene delivery vehicles using a series of retroviral vectors. The objective of this study was to develop a safe and efficient retroviral vector and to optimize conditions for efficient transduction of human bone marrow CD34+ stem cells using our vector.

METHODS

We constructed three types of MLV-based retroviral vectors expressing iduronate-2-sulfatase (IDS) which is deficient in patients suffering from Hunter's syndrome: MIN-IDS and MIM-IDS, which express IDS along with bacterial neo and human MDR genes, respectively, and MT-IDS lacking any selectable marker. Respective producer lines were derived from the packaging line, PG13, and compared for viral titer and levels of gene expression. After comparing, the retroviral vector, MT-IDS, was used to transduce human bone marrow CD34+ stem cells on fibronectin under various MOIs.

RESULTS

In comparison, MT-IDS not only produced the highest viral titer (close to 10(7) cfu/ml), but also showed the highest level of gene expression in various transduction assays and RNA analysis. When 1.5 x 10(5) human CD34+ bone marrow cells were transduced with MT-IDS under the most optimal MOIs, about 80% of total colony forming units were shown to contain the IDS cDNA.

CONCLUSIONS

Minimum-sized retroviral vector that contains no selective marker as well as a viral coding sequences could drive a high level of gene expression, be produced efficiently from the producer line, and enter hematopoietic cells at a high frequency. Our data suggest the great potential for using MT-based vector(s) in a gene therapy trial for Hunter's syndrome utilizing human CD34+ stem cells as target cells.

Various cells retrovirally transduced with N-acetylgalactosoamine-6-sulfate sulfatase correct Morquio skin fibroblasts in vitro

Gene therapy may provide a long-term approach to the treatment of mucopolysaccharidoses. As a first step toward the development of an effective gene therapy for mucopolysaccharidosis type IVA (Morquio syndrome), a recombinant retroviral vector, LGSN, derived from the LXSN vector, containing a full-length human wildtype N-acetylgalactosamine-6-sulfate sulfatase (GALNS) cDNA, was produced. Severe Morquio and normal donor fibroblasts were transduced by LGSN. GALNS activity in both Morquio and normal transduced cells was several fold higher than normal values. To measure the variability of GALNS expression among different transduced cells, we transduced normal and Morquio lymphoblastoid B cells and PBLs, human keratinocytes, murine myoblasts C2C12, and rabbit synoviocytes HIG-82 with LGSN. In all cases, an increase of GALNS activity after transduction was measured. In Morquio cells co-cultivated with enzyme-deficient transduced cells, we demonstrated enzyme uptake and persistence of GALNS activity above normal levels for up to 6 days. The uptake was mannose-6-phosphate dependent. Furthermore, we achieved clear evidence that LGSN transduction of Morquio fibroblasts led to correction of the metabolic defect. These results provide the first evidence that GALNS may be delivered either locally or systematically by various cells in an ex vivo gene therapy of MPS IVA.

"Supercharged Cells" for delivery of recombinant human iduronate-2-sulfatase

Expression of iduronate-2-sulfatase (IDS) from three different promoters in four retroviral vectors was studied in peripheral blood lymphocytes from patients with Hunter syndrome (PBL(MPS)), i.e., the LTR in vectors L2SN and L2, avian beta-actin promoter in LB2, and the CMV early promoter in LNC2. PBL(MPS) were exposed to packaging cell supernatant resulting in transduction frequencies ranging 10-fold from 5 to 49%. Surprisingly, IDS activities were equally high in all transduced lymphocyte populations: 515 U/mg/h in PBL(MPS)-L2SN, 734 in PBL(MPS)-LB2, 352 in PBL(MPS)-L2, and 389 in PBL(MPS)-LNC2 compared to controls (<10 in PBL(MPS)-LXSN or PBL(MPS)). The half-life of endocytosed IDS in PBL(MPS) was 1.9 days. However, the level of lymphocyte IDS activity from proviral expression was found to be only a fraction of the total, a large portion being derived from reuptake of enzyme from murine packaging cells, i.e., a "second source" of enzyme. Therefore, measurement of transgene lysosomal enzyme soon after exposure of target cells to vector supernatant may yield a gross overestimate of long-term transgene expression by transduced cells. Nevertheless, patient fibroblasts cocultured with transduced PBL(MPS) had reduced (35)SO(4)-GAG accumulation, levels similar to those of normal fibroblasts. These studies revealed a broadly applicable phenomenon: cells can be charged with a lysosomal enzyme to levels much higher than those found in nature. By "supercharging" cells with a lysosomal protein (or other molecule bearing the mannose-6-phosphate ligand), such cells may be exploited as vehicles for systemic delivery of therapeutic or diagnostic agents.

Hematopoietic cell transplantation for mucopolysaccharidosis IIB (Hunter syndrome)

Hunter syndrome is an X-linked metabolic storage disorder arising from deficiency of iduronate sulfatase enzyme activity. Despite the successful use of hematopoietic cell transplantation for a variety of lysosomal and peroxisomal storage diseases, limited benefit occurs following transplantation in either the severe or mild forms of Hunter syndrome. A brief ethical commentary is provided on the case of a boy with mucopolysaccharidosis IIB (ie the mild form) who received an unrelated umbilical cord blood transplant to improve his future quality of life. Bone Marrow Transplantation (2000).

Combined ultrafiltration-transduction in a hollow-fiber bioreactor facilitates retrovirus-mediated gene transfer into peripheral blood lymphocytes from patients with mucopolysaccharidosis type II

The process of growing and transducing large quantities of human primary peripheral blood lymphocytes (PBLs) with high gene transfer efficiency continues to be one of the major challenges for clinical and experimental gene therapy. Toward developing a clinical trial of lymphocyte gene therapy for mucopolysaccharidosis type II (i.e., Hunter syndrome), we investigated a novel method that exploited the innate capability of a hollow-fiber bioreactor system to filter large quantities of vector supernatant and facilitate transduction. An aliquot (5 x 10(7)) of PBL apheresis product was precultured in a gas-permeable culture bag or a bioreactor, and then transduced with a retroviral vector L2SN containing the iduronate-2-sulfatase (IDS) and neomycin resistance genes. We observed that the total number of PBLs could be expanded up to 187-fold, yielding up to 10(10) cells at the end of a 7-day culture period. The multiplicity of infection could be increased (up to 20-fold) by ultrafiltrating a large volume of vector supernatant through the semipermeable membrane of this system. A high level of transduction efficiency (up to 57%) was achieved, resulting in IDS enzyme activity as high as 1250 U/mg/hr in transduced PBL(MPS) 15 days after transduction. This level was markedly increased from that of nontransduced cells (<3 U/mg/hr) and was even greater than that of normal PBLs (mean, 809; n = 10). After 12 days of G418 selection, PBL(MPS) transductants exhibited a proviral IDS enzyme level approximately threefold higher than that in normal PBLs. These results indicated that the hollow-fiber bioreactor could be used to culture and transduce human primary PBLs in clinically useful quantities with relatively high gene transfer efficiency and transgene expression.

Real-time quantitative polymerase chain reaction to assess gene transfer

Accurate quantification of gene transfer (or gene correction) is a universal challenge in the field of gene therapy. In developing a clinical trial of lymphocyte gene therapy for Hunter syndrome (mucopolysaccharidosis type II), methods using Southern blot or automated DNA sequencing technology were employed, but found to be laborious and subject to considerable variation. As an alternative approach, we explored a real-time kinetic PCR assay appropriate to new instrumentation (PE Biosystems model 7700). A TaqMan probe was designed to hybridize directly across the exon 2-exon 3 junction of the iduronate-2-sulfatase transgene cDNA. In this assay system, cDNA from the retroviral vector L2SN generates a PCR product that is 84 nucleotides long and readily quantified by TaqMan probe binding and subsequent cleavage. Evaluation of this method demonstrated sensitivity over at least 5 logs with respect to the standard (vector plasmid pL2SN). There was no detectable signal from genomic DNA from nontransduced cells, thus indicating the specificity of this assay. The sample preparation method used to prepare specimens was a relatively simple cell lysis procedure, without DNA extraction, and represents a significant advancement over the more complex methods of DNA extraction that are typically used for such assays. This specific assay, and comparison to previous methods, illustrates the utility of a new method that is readily generalized to many gene therapy studies, and that has the potential to be extended to measure gene expression by means of quantitative RT-PCR.

Freezing characteristics of genetically modified lymphocytes for the treatment of MPS II

The freezing characteristics of genetically modified lymphocytes obtained from a donor with mucopolysaccharidosis type II (MPS II) were determined using cryomicroscopy and controlled rate freezing studies to determine postthaw viability. The cells from a donor with MPS II used in this investigation were cultured and transduced with a retroviral vector for the iduronate-2-sulfatase (IDS) enzyme for clinical studies for human gene therapy. The water transport and intracellular ice formation (IIF) characteristics of the cells were determined after completion of the culture and transduction protocol. The water transport parameters, I(pg) and E(lp), for the cultured and transduced cells were determined to be 4.4 +/- 1.3 x 10(-14) m3/Ns and 173 +/- 25 kJ/mol, respectively. The IIF nucleation parameters, kappa and omega, were 5.5 x 10(10) K5 and 3.5 x 10(11) (l/m2 s), respectively. The postthaw viability of the genetically modified cells was less than the viability of the freshly isolated cells from the same donor. The postthaw viability of the cultured and transduced cells from a donor with MPS II was also less than that observed with cells from a normal donor that were frozen and thawed under the same conditions. These studies are essential in understanding the biophysical changes resulting from the ex vivo culture of cells and the manner in which these changes influence the ability of the cells to be cryopreserved.

Retroviral transduction and expansion of peripheral blood lymphocytes for the treatment of mucopolysaccharidosis type II, Hunter's syndrome

BACKGROUND

Gene therapy using autologous peripheral blood lymphocytes (PBLs) has been used to produce adenosine deaminase with which to treat patients with severe combined immunodeficiency. Patients with mucopolysaccharidosis type II (MPS II) lack iduronate-2-sulfatase (IDS), and serial PBL gene therapy may benefit these patients.

STUDY DESIGN AND METHODS

The purpose of these studies was to develop a method to transduce PBLs from a patient with MPS II by using a retroviral vector, LS2N, containing the IDS gene. PBLs were collected by apheresis and cryopreserved in aliquots for the performance of multiple transductions and expansions. The PBLs were expanded in number and then transduced in a hollow-fiber bioreactor (HFBR). Additional culture allowed for further expansion.

RESULTS

Fresh PBLs (6.2 x 10(7)) from a patient with MPS II were transduced with L2SN and expanded in an HFBR with an extracapillary space of 11 mL. After 10 days of culture, 4.1 x 10(9) cells were harvested. Cryopreserved MPS II PBLs could not be reliably expanded if they were placed in the HFBR immediately after being thawed; however, cells were successfully transduced and expanded in the HFBR if they were first cultured in a bag. To increase the cell yield, PBLs were expanded in a 60-mL HFBR after transduction and expansion in an 11-mL HFBR. In four separate experiments, 2 x 10(8) cryopreserved PBL were cultured for 3 days in a bag and transferred to an 11-mL HFBR, where they were transduced daily with L2SN for 3 days and then expanded for 4 additional days. Cells were then transferred into a 60-mL HFBR and expanded for an additional 7 days. In the four experiments, 5.5 x 10(9), 7.4 x 10(9), 1.12 x 10(9), and 19.4 x 1(9) cells were produced. The vector was detected in the harvested cells, but the proportion of cells transduced was less than 2.5 percent, the lowest standard used in the assay. In two of the experiments, cells harvested from the HFBR were used in a gene therapy clinical trial.

CONCLUSION

Autologous cryopreserved PBLs can be transduced and expanded to produce >1 x 10(10) cells. This procedure is being used for a Phase I/II clinical trial of lymphocyte gene therapy.

Potential use of T cell receptor genes to modify hematopoietic stem cells for the gene therapy of cancer

The purpose of this review is to illustrate some of the technical and biological hurdles that need to be addressed when developing new gene therapy based clinical trials. Gene transfer approaches can be used to "mark" cells to monitor their persistence in vivo in patients, to protect cells from toxic chemotherapeutic agents, correct a genetic defect within the target cell, or to confer a novel function on the target cell. Selection of the most suitable vector for gene transfer depends upon a number of factors such as the target cell itself and whether gene expression needs to be sustained or transient. The TCR gene transfer approach described here represents one innovative strategy being pursued as a potential therapy for metastatic melanoma. Tumor reactive T cells can be isolated from the tumor infiltrating lymphocytes (TIL) of melanoma patients. A retroviral vector has been constructed containing the T cell receptor (TCR) alpha and beta chain genes from a MART-1-specific T cell clone (TIL 5). Jurkat cells transduced with this virus specifically release cytokine in response to MART-1 peptide pulsed T2 cells, showing that the virus can mediate expression of a functional TCR. HLA-A2 transgenic mice are being used to examine whether transduced bone marrow progenitor cells will differentiate in vivo into mature CD8+ T cells expressing the MART-1-specific TCR. Expression of the human TCR alpha and beta chain genes has been detected by RT-PCR in the peripheral blood of HLA-A2 transgenic mice reconstituted with transduced mouse bone marrow. Expression of the TIL 5 TCR genes in the peripheral blood of these mice was maintained for greater than 40 weeks after bone marrow reconstitution. TIL 5 TCR gene expression was also maintained following transfer of bone marrow from mice previously reconstituted with transduced bone marrow to secondary mouse recipients, suggesting that a pluripotent progenitor or lymphocyte progenitor cell has been transduced.

High-efficiency gene transfer into normal and adenosine deaminase-deficient T lymphocytes is mediated by transduction on recombinant fibronectin fragments

Primary human T lymphocytes are powerful targets for genetic modification, although the use of these targets in human gene therapy protocols has been hampered by low levels of transduction. We have shown previously that significant increases in the transduction of hematopoietic stem and progenitor cells with retroviral vectors can be obtained by the colocalization of the retrovirus and target cells on specific fibronectin (FN) adhesion domains (H. Hanenberg, X. L. Xiao, D. Dilloo, K. Hashino, I. Kato, and D. A. Williams, Nat. Med. 2:876-882, 1996). We studied the transfer of genes into primary T lymphocytes by using FN-assisted retroviral gene transfer. Activated T lymphocytes were infected for three consecutive days on the recombinant FN fragment CH-296 with a retroviral vector encoding the murine B7-1 protein. Transduced lymphocytes were analyzed for murine B7-1 expression, and it was found that under optimal conditions, 80 to 89% of the CD3+ lymphocytes were transduced. Gene transfer was predominantly augmented by the interaction between VLA-4 on the T lymphocytes and the FN adhesion site CS-1. Adenosine deaminase (ADA)-deficient primary T lymphocytes transduced on CH-296 with a retrovirus encoding murine ADA (mADA) exhibited levels of mADA activity severalfold higher than the levels of the endogenous human ADA protein observed in normal human T lymphocytes. Strikingly, the long-term expression of the transgene was dependent on the activation status of the lymphocytes. This approach will have important applications in human gene therapy protocols targeting primary T lymphocytes.

The sulfatase gene family

During the past few years, molecular analyses have provided important insights into the biochemistry and genetics of the sulfatase family of enzymes, identifying the molecular bases of inherited diseases caused by sulfatase deficiencies. New members of the sulfatase gene family have been identified in man and other species using a genomic approach. These include the gene encoding arylsulfatase E, which is involved in X-linked recessive chondrodysplasia punctata, a disorder of cartilage and bone development. Another important breakthrough has been the discovery of the biochemical basis of multiple sulfatase deficiency, an autosomal recessive disorder characterized by a severe of all sulfatase activities. These discoveries, together with the resolution of the crystallographic structure of sulfatases, have improved our understanding of the function and evolution of this fascinating family of enzymes.