Retroviral mediated transfer of the cDNA for human glucocerebrosidase into hematopoietic stem cells of patients with Gaucher disease. A phase I study

Gene Therapy of Sphingolipid Metabolic Disorders

Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.

Gene Editing for Inherited Red Blood Cell Diseases

Today gene therapy is a real therapeutic option to address inherited hematological diseases that could be beneficial for thousands of patients worldwide. Currently, gene therapy is used to treat different monogenic hematological pathologies, including several red blood cell diseases such as β-thalassemia, sickle cell disease and pyruvate kinase deficiency. This approach is based on addition gene therapy, which consists of the correction of hematopoietic stem cells (HSCs) using lentiviral vectors, which integrate a corrected version of the altered gene. Lentivirally-corrected HSCs generate healthy cells that compensate for the deficiency caused by genetic mutations. Despite its successful results, this approach lacks both control of the integration of the transgene into the genome and endogenous regulation of the therapeutic gene, both of which are important aspects that might be a cause for concern. To overcome these limitations, gene editing is able to correct the altered gene through more precise and safer approaches. Cheap and easy-to-design gene editing tools, such as the CRISPR/Cas9 system, allow the specific correction of the altered gene without affecting the rest of the genome. Inherited erythroid diseases, such as thalassemia, sickle cell disease and Pyruvate Kinase Deficiency, have been the test bed for these gene editing strategies, and promising results are currently being seen. CRISPR/Cas9 system has been successfully used to manipulate globin regulation to re-activate fetal globin chains in adult red blood cells and to compensate for hemoglobin defects. Knock-in at the mutated locus to express the therapeutic gene under the endogenous gene regulatory region has also been accomplished successfully. Thanks to the lessons learned from previous lentiviral gene therapy research and trials, gene editing for red blood cell diseases is rapidly moving from its proof-of-concept to its first exciting results in the clinic. Indeed, patients suffering from β-thalassemia and sickle cell disease have already been successfully treated with gene editing, which will hopefully inspire the use of gene editing to cure erythroid disorders and many other inherited diseases in the near future.

Stem Cell Research Tools in Human Metabolic Disorders: An Overview

Metabolic disorders are very common in the population worldwide and are among the diseases with the highest health utilization and costs per person. Despite the ongoing efforts to develop new treatments, currently, for many of these disorders, there are no approved therapies, resulting in a huge economic hit and tension for society. In this review, we recapitulate the recent advancements in stem cell (gene) therapy as potential tools for the long-term treatment of both inherited (lysosomal storage diseases) and acquired (diabetes mellitus, obesity) metabolic disorders, focusing on the main promising results observed in human patients and discussing the critical hurdles preventing the definitive jump of this approach from the bench to the clinic.

Current Clinical Applications of In Vivo Gene Therapy with AAVs

Hereditary diseases are caused by mutations in genes, and more than 7,000 rare diseases affect over 30 million Americans. For more than 30 years, hundreds of researchers have maintained that genetic modifications would provide effective treatments for many inherited human diseases, offering durable and possibly curative clinical benefit with a single treatment. This review is limited to gene therapy using adeno-associated virus (AAV) because the gene delivered by this vector does not integrate into the patient genome and has a low immunogenicity. There are now five treatments approved for commercialization and currently available, i.e., Luxturna, Zolgensma, the two chimeric antigen receptor T cell (CAR-T) therapies (Yescarta and Kymriah), and Strimvelis (the gammaretrovirus approved for adenosine deaminase-severe combined immunodeficiency [ADA-SCID] in Europe). Dozens of other treatments are under clinical trials. The review article presents a broad overview of the field of therapy by in vivo gene transfer. We review gene therapy for neuromuscular disorders (spinal muscular atrophy [SMA]; Duchenne muscular dystrophy [DMD]; X-linked myotubular myopathy [XLMTM]; and diseases of the central nervous system, including Alzheimer’s disease, Parkinson’s disease, Canavan disease, aromatic l-amino acid decarboxylase [AADC] deficiency, and giant axonal neuropathy), ocular disorders (Leber congenital amaurosis, age-related macular degeneration [AMD], choroideremia, achromatopsia, retinitis pigmentosa, and X-linked retinoschisis), the bleeding disorder hemophilia, and lysosomal storage disorders.

Adipocytes as a vehicle for ex vivo gene therapy: Novel replacement therapy for diabetes and other metabolic diseases

Because of its availability and recent advances in cell biology, adipose tissue is now considered an ideal target site for the preparation of recipient cells and for the transplantation of gene‐transduced cells for supplementation of therapeutic proteins. Inherited or acquired serum protein deficiencies are the ideal targets for gene therapy. However, to develop an effective ex vivo gene therapy‐based protein replacement treatment, the requirements for the recipient cells are different from those for standard gene therapy that is intended to correct the function of the recipient cells themselves. To meet the requirements for such a therapeutic strategy, recent in vitro and animal model studies have developed new methods for the preparation, culture, expansion and manipulation of adipose cells using advanced gene transduction methods and transplantation scaffolds. In this short review, we introduce the progress made in novel adipose tissue‐based therapeutic strategies for the treatment of protein deficiencies by our group and other investigators, and describe their future applications for diabetes and other metabolic diseases. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00133.x, 2011)

Synthesis of an Aminooxy Derivative of the Trisaccharide Globotriose Gb3

The synthesis of α-aminooxy trisaccharide moiety [α-d-Gal-(1,4)-β-d-Gal-(1,4)-β-d-Glc-α-aminooxy], related to the cell surface globotriaosylceramide (Gb3) receptor of the B subunit of the AB₅ Shiga toxin of Shigella dysenteriae, has been synthesized for the first time in 11 steps with a 15% overall isolated yield. A highlight of this work entails utilizing chemically compatible synthetic transformations, including those related to glycosylation, incorporative of the succinimidyl moiety as a precursor to the aminooxy Gb3 derivative. The fully deprotected trisaccharide aminooxy compound was reacted with a carbonyl compound leading to oxime formation in quantitative yield underscoring the importance for future glyco-conjugations.

Minimum requirement of donor cells to reduce the glycolipid storage following bone marrow transplantation in a murine model of Fabry disease

BACKGROUND

Fabry disease (FD) is a lysosomal storage disorders characterized by a deficiency of the lysosomal enzyme, α-galactosidase A. This results in the accumulation of glycolipids, mainly globotriaosylceramide (GL-3), in the lysosomes of various organs. Although bone marrow transplantation and hematopoietic stem cell-based gene therapy can offer the potential of a curative therapeutic outcome for FD, the minimum requirement of donor cells or gene-corrected cells to reduce GL-3 levels is not known.

METHODS

Lethally-irradiated FD mice were transplanted intravenously with normal bone marrow cells (Ly5.1 positive) mixed with those of FD mice (Ly5.2 positive) at various ratios to investigate the level of engraftment and enzyme activity necessary to effect a reduction in GL-3 storage.

RESULTS

Chimerism of whole white blood cells of recipients' peripheral blood remained stable at 8 weeks after transplantation, and chimerism of granulocytes, monocytes, B cells and T cells was equal to that of white blood cells. GL-3 levels were significantly reduced in the lung and heart of animals with a 30% and 50% chimera, respectively. The extent of reduction in these mice was almost identical to that with 100% chimera.

CONCLUSIONS

In FD mice, reconstitution with 100% donor cells is not required to obtain a therapeutic effect following bone marrow transplantation. These results suggest that a 30% gene correction might be sufficient to reverse disease manifestations in FD.

Review of the safety and efficacy of imiglucerase treatment of Gaucher disease

Most patients who suffer from symptomatic Gaucher disease will benefit from enzyme replacement therapy (ERT) with imiglucerase. The safety profile is excellent, only a small percentage of those exposed developing antibodies; similarly, very few patients require pre-medication for allergic reactions. Within 3 to 5 years of imiglucerase therapy, best documented at doses of 30 to 60 units/kg/infusion, hepatosplenomegaly can be expected to be reduced so that the liver volume will be maintained at 1 to 1.5 times normal (30% to 40% reduction from advent of ERT) and spleen volume to </= 2 to 8 times normal (50% to 60% reduction from advent of ERT). For anemic and thrombocytopenic patients, with 2 to 5 years of imiglucerase, hemoglobin levels are expected to be >/= 11 g/dL for women and children and >/= 12 g/dL for men; and platelet counts in patients with an intact spleen, depending on the baseline value, should approximately be doubled. Bone crises and bone pain but not irreversible skeletal damage will improve in most patients. Nonetheless, some features and some symptomatic patients apparently do not respond equally well and/or perhaps inadequately. The benefit for patients with the neuronopathic forms is primarily in improved visceral and hematological signs and symptoms. There are still several unresolved issues, the high per-unit cost being an important one, which have spurred the development of biosimilar enzymes as well as chaperone therapies currently in clinical trials.

Review of the safety and efficacy of imiglucerase treatment of Gaucher disease

Most patients who suffer from symptomatic Gaucher disease will benefit from enzyme replacement therapy (ERT) with imiglucerase. The safety profile is excellent, only a small percentage of those exposed developing antibodies; similarly, very few patients require pre-medication for allergic reactions. Within 3 to 5 years of imiglucerase therapy, best documented at doses of 30 to 60 units/kg/infusion, hepatosplenomegaly can be expected to be reduced so that the liver volume will be maintained at 1 to 1.5 times normal (30% to 40% reduction from advent of ERT) and spleen volume to </= 2 to 8 times normal (50% to 60% reduction from advent of ERT). For anemic and thrombocytopenic patients, with 2 to 5 years of imiglucerase, hemoglobin levels are expected to be >/= 11 g/dL for women and children and >/= 12 g/dL for men; and platelet counts in patients with an intact spleen, depending on the baseline value, should approximately be doubled. Bone crises and bone pain but not irreversible skeletal damage will improve in most patients. Nonetheless, some features and some symptomatic patients apparently do not respond equally well and/or perhaps inadequately. The benefit for patients with the neuronopathic forms is primarily in improved visceral and hematological signs and symptoms. There are still several unresolved issues, the high per-unit cost being an important one, which have spurred the development of biosimilar enzymes as well as chaperone therapies currently in clinical trials.

Liposomes from a new chiral cationic lipid based on iridoidic template

A new cationic polyhydroxylated lipid, characterized by a chiral template, was synthesized. It comes from an iridoid glucoside, as polyhydroxylated moiety. This lipid affords liposomes using cholesterol-like co-lipid. The liposomes had a spheroidal shape with a small size distribution.

Emerging Strategies for the Treatment of Hereditary Metabolic Storage Disorders

Metabolic storage disorders are caused by mutations in genes that result in insufficient activity of enzymes required for the catabolism of substances that arise from the turnover of senescent cells in the body. Among the most prevalent of these conditions are Gaucher disease and Fabry disease, which are caused by reduced activity of the housekeeping enzymes glucocerebrosidase and alpha-galactosidase A, respectively. Enzyme replacement therapy is extraordinarily effective for patients with Gaucher disease. It is under examination in patients with Fabry disease, and improvement of various clinical aspects in these patients has been documented. The blood-brain barrier prevents systemically administered enzymes from reaching the central nervous system. This limitation is a major impediment for the treatment of patients with enzyme deficiency disorders in whom the brain is involved. Alternatives to enzyme replacement therapy that have been initiated to treat systemic manifestations and brain involvement in patients with metabolic disorders include substrate reduction therapy, active site-specific chaperone therapy, and gene therapy. The present status and anticipated advances in the application of these therapeutic approaches are examined here.

Retrovirus producer cell line metabolism: implications on viral productivity

The production of retroviral vectors by human cell lines is still hampered by low titers making it relatively difficult to produce very large quantities of this vector of high interest for clinical gene therapy applications. Thus, to improve vector production, we studied the influence of different sugars alone or combinations of sugars on cell growth, vector titers, and metabolism of the producer cell. The use of fructose at 140 mM or a mixed medium (with glucose at 25 mM and fructose at 140 mM) improved the virus titer three- to fourfold, respectively, and the producer cell productivity by fivefold. The increase in the cell productivity was due to a 1.5-fold increase in the vector stability, the remaining increase being due to higher cell specific productivity. The increase in the productivity was associated with lower glucose oxidation and an increase in the lactate and alanine yield. In the mixed medium, an increase in fatty acids derived from the glucose was observed in parallel with a reduction of glutamate and glutamine synthesis via the tricarboxylic acid (TCA) cycle acetyl-CoA and alpha-ketoglutarate, respectively. Although the higher productivities were associated with severe changes in the glycolysis, TCA cycle, and glutaminolysis, the cell energetic status monitored by phosphocreatine and adenosine triphosphate levels was not significantly affected. The synthesis of fatty acids and phospholipids were enhanced in the fructose or mixed media and are possibly key parameters in retroviral vector production.

Effect of osmotic pressure on the production of retroviral vectors: Enhancement in vector stability

The use of Moloney murine leukaemia virus (MoMLV) derived retroviral vectors in gene therapy requires the production of high titer preparations. However, obtaining high titers of infective MoMLV retroviral vectors is difficult due to the vector inherent instability. In this work the effect of the cell culture medium osmotic pressure upon the virus stability was studied. The osmolality of standard medium was raised from 335 up to 500 mOsm/kg using either ionic (sodium chloride) or non-ionic osmotic agents (sorbitol and fructose). It was observed that, independently of the osmotic agent used, the infectious vector inactivation rate was inversely correlated with the osmolality used in the production media; therefore, the use of high medium osmolalities enhanced vector stability. For production purposes a balance must be struck between cell yield, cell productivity and retroviral stability. From the conditions tested herein sorbitol addition, ensuring osmolalities between 410 and 450 mOsm/kg, yields the best production conditions; NaCl hampered the viral infectious production while fructose originates lower cell yields. Lipid extractions were performed for cholesterol and phospholipid analyses showing that more stable viral vectors had a 10% reduction in the cholesterol content. A similar reduction in cholesterol was observed in the producer cells. A detailed analysis of the major phospholipids composition, type and fatty acid content, by mass spectrometry did not show significant changes, confirming the decrease in the cholesterol to phospholipids ratio in the viral membrane as the major reason for the increased vector stability.

Hematopoietic stem cell gene therapy with drug resistance genes: an update

Transfer of drug resistance genes into hematopoietic stem cells (HSCs) has promise for the treatment of a variety of inherited, that is, X-linked severe combined immune deficiency, adenosine deaminase deficiency, thalassemia, and acquired disorders, that is, breast cancer, lymphomas, brain tumors, and testicular cancer. Drug resistance genes are transferred into HSCs either for providing myeloprotection against chemotherapy-induced myelosuppression or for selecting HSCs that are concomitantly transduced with another gene for correction of an inherited disorder. In this review, we describe ongoing experimental approaches, observations from clinical trials, and safety concerns related to the drug resistance gene transfer.

Measurement of lysosomal glucocerebrosidase activity in mouse liver using a fluorescence-activated cell sorter assay

Lysosomal acid beta-glucocerebrosidase hydrolyzes glucocerebroside to glucose ceramide. Patients diagnosed with Gaucher disease, however, lack this enzyme, leading to the accumulation of glucocerebroside in tissue macrophages within multiple organs. Such patients can receive enzyme replacement therapy during which a human placental-derived or recombinant form of acid beta-glucocerebrosidase is targeted to the macrophages. As part of evaluating the effectiveness of such therapies, currently available methodologies for measuring acid beta-glucocerebrosidase activity are primarily conducted in cultured cell lines or tissue culture. However, these in vitro assays are limited by their ability to evaluate the efficacy of in vivo acid beta-glucocerebrosidase replacement therapy in animal models. In particular, there is an unmet need to simultaneously define cellular localization and evaluate enzyme activity following treatment in vivo. In addition, results of commonly used fluorescent-based assays for enzyme activity are difficult to compare day to day and/or across laboratories due to the variability inherent in flow cytometric measurement. In this article, we describe a reproducible and consistent quantitative method for the combined measurement of fluorescein intensity from enzyme-substrate conversion and cell localization by phenotype-specific phycoerythrin-antibody staining. Following infusion of recombinant human acid beta-glucocerebrosidase in mice, nonparenchymal cells are prepared from the livers of treated and control animals. Acid beta-glucocerebrosidase activity is measured in molecules of equivalent soluble fluorophore units within Kupffer cell populations as defined by phenotype-specific monoclonal antibodies. This assay should be applicable to investigations of other Gaucher disease treatments in both human and animal models.

Clinical gene therapy for nonmalignant disease

Gene therapy is envisioned as a potentially definitive treatment for a variety of diseases that have a genetic etiology. We reviewed trials of clinical gene therapy for nonmalignant, single-gene, and multifactorial disorders and infectious diseases, and found limited evidence suggesting that gene therapy may benefit patients who have severe, combined, immunodeficiency disorder; cystic fibrosis; coronary artery disease or peripheral arterial disease; or hemophilia. Effective gene therapy requires the targeted transfer of exogenous genetic material into human cells and the subsequent regulated expression of the corresponding gene product. Because no phase 3 randomized controlled trials have been completed that fulfill these criteria, it is difficult to correlate signs of clinical benefit with the administration of gene therapy in any disease. Additional clinical and basic research is needed to determine the future role of gene therapy.

Progress in the use of gene transfer methods to treat genetic blood diseases

A report by French physician-scientists suggests a successful application of gene transfer methods in the treatment of two children with severe combined immunodeficiency (SCID) due to defective interleukin 2 receptor common gamma chain. The protocol used in this clinical trial was derived from a number of preclinical and basic studies leading to improved transduction of hematopoietic stem and primitive progenitor cells using retrovirus vectors. These improvements have also been shown to impact transduction of a long-lived progenitor cell in a chemotherapy protocol in cancer patients. The improved results of these human trials come during a period of increased scrutiny and criticism of human gene therapy trials, due, in part, to significant toxicities in some trials using adenovirus-based vectors. The potential efficacy versus toxicity of phase I trials of human gene therapy is also under question. After many years of research, however, there appears to be real evidence that genetic diseases may be successfully treated by gene transfer techniques. Future clinical studies should be based on continued progress in the understanding of the toxicology of gene delivery systems, vector technology, and target cell manipulation.

Efficient retrovirus-mediated transfer of the multidrug resistance 1 gene into autologous human long-term repopulating hematopoietic stem cells

Pre-clinical studies indicate that efficient retrovirus-mediated gene transfer into hematopoietic stem cells and progenitor cells can be achieved by co-localizing retroviral particles and target cells on specific adhesion domains of fibronectin. In this pilot study, we used this technique to transfer the human multidrug resistance 1 gene into stem and progenitor cells of patients with germ cell tumors undergoing autologous transplantation. There was efficient gene transfer into stem and progenitor cells in the presence of recombinant fibronectin fragment CH-296. The infusion of these cells was associated with no harmful effects and led to prompt hematopoietic recovery. There was in vivo vector expression, but it may have been limited by the high rate of aberrant splicing of the multidrug resistance 1 gene in the vector. Gene marking has persisted more than a year at levels higher than previously reported in humans.

Novel series of non-glycerol-based cationic transfection lipids for use in liposomal gene delivery

A novel series of nontoxic and non-glycerol-based simple monocationic transfection lipids containing one or two hydroxyethyl groups directly linked to the positively charged nitrogen atom were synthesized. The in vitro transfection efficiencies of these new liposomal gene delivery reagents were better than that of lipofectamine, a widely used transfection agent in cationic lipid-mediated gene transfer. The most efficient transfection formulation was observed to be a 1:1:0.3 mol ratio of DHDEAB (N, N-di-n-hexadecyl-N,N-dihydroxyethylammonium bromide):cholesterol:HDEAB (N-n-hexadecyl-N,N-dihydroxyethylammonium bromide) using a DHDEAB-to-DNA charge ratio (+/-) of 0.3:1. Observation of good transfection at charge ratios lower than 1 suggests that the amphiphile-DNA complex may have net negative charge. Our results reemphasize the important point that in cationic lipid-mediated gene delivery, the overall charge of the lipid-DNA complex need not always be positive. In addition, our transfection results also imply that favorable hydrogen-bonding interactions between the lipid headgroups and the cell surface of biological membranes may have some role for improving the transfection efficiency in cationic lipid-mediated gene delivery.

Prospects for in utero human gene therapy

Gene therapy for the treatment of disease in children and adults is being actively pursued at many medical centers. However, a number of genetic disorders result in irreversible damage to the fetus before birth. In these cases, as well as for those with genetic diseases who may benefit from therapy before symptoms are manifested, in utero gene therapy (IUGT) could be beneficial. Although some successes with in utero gene transfer have been reported in animals, significant questions remain to be answered before IUGT clinical trials would be acceptable. This review analyzes the state of the art and delineates the studies that still need to be performed before it would be appropriate to consider human IUGT.

Isolation and transduction of CD34+ cells from small quantities of peripheral blood from HIV-1-infected patients not treated with hemopoietic growth factors

A proposed hemopoietic stem cell gene therapy for treatment for HIV infection would involve transduction of CD34+ hemopoietic stem cells with vectors encoding anti-HIV constructs. Peripheral blood has proved to be a useful source of these hemopoietic stem cells and this study exploits this finding. Small quantities of peripheral blood were obtained from HIV-negative patients and HIV-positive patients who were and were not receiving hemopoietic growth factors (HGFs). CD34+ cells were obtained from these samples using a simple technique and scored for frequency of colony type. This demonstrated that HIV-negative patients had the highest frequency of colony-forming units (CFUs). HIV-positive patients not treated with HGFs had a lower frequency of CFUs, but the same colony type distribution as HIV-negative patients. HIV-positive patients treated with HGFs had the lowest frequency of CFUs, but their colony type distribution demonstrated that they had responded to treatment. CD34+ cells selected in this way were also transduced with the murine retroviral MFG vector using a technique that demonstrated transduction efficiencies ranging from 2% to 16% (median, 11.5%). This study simplifies the experimental requirements for development of a hemopoietic stem cell gene therapy for HIV infection and offers the possibility that longitudinal studies could be performed on peripheral blood CD34+ cells from HIV-positive or HIV-negative patients without the need for granulocyte colony-stimulating factor mobilization.

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.

Mobilization and transduction of peripheral blood progenitor cells in patients with mucopolysaccharidosis I

Mucopolysaccharidosis type I (MPS I) results from a deficiency of alpha-L-iduronidase enzyme (IDUA), an enzyme responsible for the catabolism of glycosaminoglycans. Genetically modified progenitor cells may permit a therapeutic effect similar to that obtained from allogeneic BMT without the associated risks. To that end, CD34+ peripheral blood hematopoietic progenitor cells from patients with MPS I were mobilized using G-CSF, collected by apheresis, and enriched using avidin-biotin separation techniques. These cells were cultured in a hollow fiber bioreactor and transduced with a retroviral vector (LP1CD) containing the cDNA for human IDUA and a murine dihydrofolate reductase (DHFR) enzyme. Approximately 4%-16% of the colonies expressed methotrexate drug resistance. Expression of the IDUA enzyme in the progenitor cells was initially high and declined after approximately 10 days of culture. These results indicate that PBPC from patients with MPS I can be mobilized, isolated, enriched, and transduced with a therapeutic gene.

Retroviral transfer of the glucocerebrosidase gene into CD34+ cells from patients with Gaucher disease: in vivo detection of transduced cells without myeloablation

Retroviral gene transfer of the glucocerebrosidase gene to hematopoietic progenitor and stem cells has shown promising results in animal models and corrected the enzyme deficiency in cells from Gaucher patients in vitro. Therefore, a clinical protocol was initiated to explore the safety and feasibility of retroviral transduction of peripheral blood (PB) or bone marrow (BM) CD34+ cells with the G1Gc vector. This vector uses the viral LTR promoter to express the human glucocerebrosidase cDNA. Three adult patients have been entered with follow-up of 6-15 months. Target cells were G-CSF-mobilized and CD34-enriched PB cells or CD34-enriched steady state BM cells, and were transduced ex vivo for 72 hr. Patient 1 had PB cells transduced in the presence of autologous stromal marrow cells. Patient 2 had PB cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. Patient 3 had BM cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. At the end of transduction, the cells were collected and infused immediately without any preparative treatment of the patients. The transduction efficiency of the CD34+ cells at the end of transduction was approximately 1, 10, and 1 for patients 1, 2, and 3, respectively, as estimated by semiquantitative PCR on bulk samples and PCR analysis of individual hematopoietic colonies. Gene marking in vivo was demonstrated in patients 2 and 3. Patient 2 had vector-positive PB granulocytes and mononuclear bone marrow cells at 1 month postinfusion and positive PB mononuclear cells at 2 and 3 months postinfusion. Patient 3 had a positive BM sample at 1 month postinfusion but was negative thereafter. These results indicate that gene-marked cells can engraft and persist for at least 3 months postinfusion, even without myeloablation. However, the level of corrected cells (<0.02%) is too low to result in any clinical benefit, and glucocerebrosidase enzyme activity did not increase in any patient following infusion of transduced cells. Modifications of vector systems and transduction conditions, along with partial myeloablation to allow higher levels of engraftment, may be necessary to achieve beneficial levels of correction in patients with Gaucher disease.

Interfacial indazolization: novel chemical evidence for remarkably high exo-surface pH of cationic liposomes used in gene transfection

Cationic liposomes are used as the carriers of polyanionic genes for combating against hereditary diseases in gene therapy. Studies directed to careful biophysical characterizations of the cationic liposomes commonly used in gene delivery have just begun. Herein, we report on a novel liposomal exo-surface bound indazolization reaction of an amphiphilic arenediazonium salt as evidence for the existence of remarkably alkaline exo-surface of cationic liposomes commonly used in gene transfection. Our results demonstrate that formation of 5-hexadecyl-7-methylindazole in thermal indazolization of 2,6-dimethyl-4-hexadecylbenzenediazonium tetrafluoroborate bound to liposome surface is a strong indication for the existence of significantly high exo-surface pH for cationic liposomes commonly used in gene delivery. The present method can be used in determining the relative exo-surface basicities of various cationic liposomes used in gene transfection and subsequently to find any possible correlation between the transfection efficiencies of these liposomes and their exo-surface basicities.

Stable alteration of pre-mRNA splicing patterns by modified U7 small nuclear RNAs

In several forms of beta-thalassemia, mutations in the second intron of the beta-globin gene create aberrant 5' splice sites and activate a common cryptic 3' splice site upstream. As a result, the thalassemic beta-globin pre-mRNAs are spliced almost exclusively via the aberrant splice sites leading to a deficiency of correctly spliced beta-globin mRNA and, consequently, beta-globin. We have designed a series of vectors that express modified U7 snRNAs containing sequences antisense to either the aberrant 5' or 3' splice sites in the IVS2-705 thalassemic pre-mRNA. Transient expression of modified U7 snRNAs in a HeLa cell line stably expressing the IVS2-705 beta-globin gene restored up to 65% of correct splicing in a sequence-specific and dose-dependent manner. Cell lines that stably coexpressed IVS2-705 pre-mRNA and appropriately modified U7 snRNA exhibited up to 55% of permanent restoration of correct splicing and expression of full-length beta-globin protein. This novel approach provides a potential alternative to gene replacement therapies.

Human gene therapy

Human gene therapy and its application for the treatment of human genetic disorders, such as cystic fibrosis, cancer, and other diseases, are discussed. Gene therapy is a technique in which a functioning gene is inserted into a human cell to correct a genetic error or to introduce a new function to the cell. Many methods, including retroviral vectors and non-viral vectors, have been developed for both ex vivo and in vivo gene transfer into cells. Vectors need to be developed that efficiently transfer genes to target cells, and promoter systems are required that regulate gene expression according to physiologic needs of the host cell. There are several safety and ethical issues related to manipulating the human genome that need to be resolved. Current gene therapy efforts focus on gene insertion into somatic cells only. Gene therapy has potential for the effective treatment of genetic disorders, and gene transfer techniques are being used for basic research, for example, in cancer, to examine the underlying mechanism of disease. There are still many technical obstacles to be overcome before human gene therapy can become a routine procedure. The current human genome project provides the sequences of a vast number of human genes, leading to the identification, characterization, and understanding of genes that are responsible for many human diseases.

Cationic lipid-mediated gene delivery to murine lung: correlation of lipid hydration with in vivo transfection activity

A panel of lipidic tetraalkylammonium chlorides has been prepared and screened in studies of both lipid hydration and in vivo mouse transfection. The effect of cationic lipid structure on liposome surface hydration was determined using differential scanning calorimetry. Increases in headgroup steric bulk and the inclusion of cis-unsaturation in the hydrophobic domain led to greater lipid hydration, indicative of a decrease in lipid polar domain associations. Cationic lipids containing hydrogen-bonding functionality in the polar domain exhibited a corresponding decrease in observed lipid hydration, indicative of an increase in lipid polar domain associations. To explore a potential correlation of the hydration data with transfection activity, we examined the in vivo transfection activity of the lipid panel by direct intratracheal instillation of cationic liposome-DNA complexes into BALB/c mice. The more active transfection agents were the lipids that featured headgroup structures promoting close polar domain association in combination with fatty acyl cis-unsaturation. The hydration data suggest that the more effective transfection lipids for mouse lung delivery are those possessing the greatest imbalance between the cross-sectional areas occupied by the polar and hydrophobic domains.

Neuronopathic forms of Gaucher's disease

Neuronopathic Gaucher patients may have a wide variety of clinical manifestations and natural history, and can present with a range of degrees of severity of systemic disease and neurological deficit. The brain pathology of these patients has been well described, but the mechanism by which glucocerebrosidase deficiency leads to neuronal dysfunction is not yet understood. The almost 20 different mutations of the glucocerebrosidase gene that have been described in Type 2 and 3 Gaucher patients poorly predict the phenotype of individual patients. Enzyme replacement therapy (ERT), often at high doses, has been shown to reverse most of the systemic manifestations of this disease, but can rarely reverse the neurological deficits. Therefore, other forms of treatment, such as gene therapy or a more efficient and direct enzyme delivery to neurons, are being devised.