Correction in trans for Fabry disease: expression, secretion and uptake of alpha-galactosidase A in patient-derived cells driven by a high-titer recombinant retroviral vector

Fabry disease: a rare disorder calling for personalized medicine

Fabry Disease (FD) is a genetic disease caused by a deficiency in the activity of lysosomal galactosidase A (α-GalA), an enzyme responsible for the catabolism of globotriaosylceramide (Gb3). Since lysosomes are present throughout the body and play a crucial role in catabolism and recycling of cytosolic compounds, FD can affect multiple organs and result in various symptoms, including renal, cardiovascular, neurological, cutaneous, and ophthalmic manifestations. Due to the nonspecific symptoms and the rarity of FD, it is often diagnosed late in life. However, introducing targeted therapies such as enzyme replacement therapy (ERT) and chaperone therapy has significantly improved FD's natural history and prognosis by restoring α-GalA enzyme activity. Despite the advancements, there are limitations to the currently available therapies, which has prompted research into new potential treatments for FD, including alternative forms of enzyme replacement therapy, substrate reduction therapy, mRNA therapy, and genetic therapy. In this review, we analyze the epidemiology, pathophysiology, and treatment of FD, with particular emphasis on promising therapeutic opportunities that could shift the treatment of this rare disease from a standardized to a personalized approach soon.

Cardiovascular Involvement in Fabry's Disease: New Advances in Diagnostic Strategies, Outcome Prediction and Management

Cardiovascular involvement is common in Fabry's disease and is the leading cause of morbidity and mortality. The research is focused on identifying diagnostic clues suggestive of cardiovascular involvement in the preclinical stage of the disease through clinical and imaging markers. Different pathophysiologically driven therapies are currently or will soon be available for the treatment of Fabry's disease, with the most significant benefit observed in the early stages of the disease. Thus, early diagnosis and risk stratification for adverse outcomes are crucial to determine when to start an aetiological treatment. This review describes the cardiovascular involvement in Fabry's disease, focusing on the advances in diagnostic strategies, outcome prediction and disease management.

Treatment of Fabry Disease: Established and Emerging Therapies

Fabry disease (FD) is a rare, X-linked inherited disorder of glycosphingolipid metabolism. It leads to the progressive accumulation of globotriaosylceramide within lysosomes due to a deficiency of α-galactosidase A enzyme. It involves multiple organs, predominantly the renal, cardiac, and cerebrovascular systems. Early diagnosis and treatment are critical to prevent progression to irreversible tissue damage and organ failure, and to halt life-threatening complications that can significantly reduce life expectancy. This review will focus on the established and emerging treatment options for FD.

In Vivo Delivery of Therapeutic Molecules by Transplantation of Genome-Edited Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (iPSCs) have already been used in transplantation therapies. Currently, cells from healthy people are transplanted into patients with diseases. With the rapid evolution of genome editing technology, genetic modification could be applied to enhance the therapeutic effects of iPSCs, such as the introduction of secreted molecules to make the cells a drug delivery system. Here, we addressed this possibility by utilizing a Fabry disease mouse model, as a proof of concept. Fabry disease is caused by the lack of α-galactosidase A (GLA). We previously developed an immunotolerant therapeutic molecule, modified α-N-acetylgalactosaminidase (mNAGA). We confirmed that secreted mNAGA from genome-edited iPSCs compensated for the GLA activity in GLA-deficient cells using an in vitro co-culture system. Moreover, iPSCs transplanted into Fabry model mice secreted mNAGA and supplied GLA activity to the liver. This study demonstrates the great potential of genome-edited iPSCs secreting therapeutic molecules.

Autologous, lentivirus-modified, T-rapa cell "micropharmacies" for lysosomal storage disorders

T cells are the current choice for many cell therapy applications. They are relatively easy to access, expand in culture, and genetically modify. Rapamycin‐conditioning ex vivo reprograms T cells, increasing their memory properties and capacity for survival, while reducing inflammatory potential and the amount of preparative conditioning required for engraftment. Rapamycin‐conditioned T cells have been tested in patients and deemed to be safe to administer in numerous settings, with reduced occurrence of infusion‐related adverse events. We demonstrate that ex vivo lentivirus‐modified, rapamycin‐conditioned CD4⁺ T cells can also act as next‐generation cellular delivery vehicles—that is, “micropharmacies”—to disseminate corrective enzymes for multiple lysosomal storage disorders. We evaluated the therapeutic potential of this treatment platform for Fabry, Gaucher, Farber, and Pompe diseases in vitro and in vivo. For example, such micropharmacies expressing α‐galactosidase A for treatment of Fabry disease were transplanted in mice where they provided functional enzyme in key affected tissues such as kidney and heart, facilitating clearance of pathogenic substrate after a single administration.

Gene therapy for Fabry disease: Progress, challenges, and outlooks on gene-editing

Gene therapy is the delivery of a therapeutic gene for endogenous cellular expression with the goal of rescuing a disease phenotype. It has been used to treat an increasing number of human diseases with many strategies proving safe and efficacious in clinical trials. Gene delivery may be viral or non-viral, performed in vivo or ex vivo, and relies on gene integration or transient expression; all of these techniques have been applied to the treatment of Fabry disease. Fabry disease is a genetic disorder of the α-galactosidase A gene, GLA, that causes an accumulation of glycosphingolipids in cells leading to cardiac, renal and cerebrovascular damage and eventually death. Currently, there are no curative treatments available, and the therapies that are used have significant drawbacks. These treatment concerns have led to the advent of gene therapies for Fabry disease. The first Fabry patients to receive gene therapy were treated with recombinant lentivirus targeting their hematopoietic stem/progenitor cells. Adeno-associated virus treatments have also begun. Alternatively, the field of gene-editing is a new and rapidly growing field. Gene-editing has been used to repair disease-causing mutations or insert genes into cellular DNA. These techniques have the potential to be applied to the treatment of Fabry disease provided the concerns of gene-editing technology, such as safety and efficiency, were addressed. This review focuses on the current state of gene therapy as it is being developed for Fabry disease, including progresses and challenges as well as an overview of gene-editing and how it may be applied to correct Fabry disease-causing mutations in the future.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Lentivirus-mediated gene therapy for Fabry disease

Enzyme and chaperone therapies are used to treat Fabry disease. Such treatments are expensive and require intrusive biweekly infusions; they are also not particularly efficacious. In this pilot, single-arm study (NCT02800070), five adult males with Type 1 (classical) phenotype Fabry disease were infused with autologous lentivirus-transduced, CD34⁺-selected, hematopoietic stem/progenitor cells engineered to express alpha-galactosidase A (α-gal A). Safety and toxicity are the primary endpoints. The non-myeloablative preparative regimen consisted of intravenous melphalan. No serious adverse events (AEs) are attributable to the investigational product. All patients produced α-gal A to near normal levels within one week. Vector is detected in peripheral blood and bone marrow cells, plasma and leukocytes demonstrate α-gal A activity within or above the reference range, and reductions in plasma and urine globotriaosylceramide (Gb₃) and globotriaosylsphingosine (lyso-Gb₃) are seen. While the study and evaluations are still ongoing, the first patient is nearly three years post-infusion. Three patients have elected to discontinue enzyme therapy.

Treatments for Fabry disease, an inherited lysosomal disorder caused by the deficiency of the enzyme alpha-galactosidase A, are not fully efficacious. Here the authors report a single-arm phase I trial of gene therapy with autologous, lentivirus-transduced, hematopoietic cells that express alpha-galactosidase A to demonstrate that this approach is safe in five patients with Fabry disease.

Ion channels and pain in Fabry disease

Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A (α-Gal A) activity which results in progressive accumulation of globotriaosylceramide (Gb3) and related metabolites. One prominent feature of Fabry disease is neuropathic pain. Accumulation of Gb3 has been documented in dorsal root ganglia (DRG) as well as other neurons, and has lately been associated with the mechanism of pain though the pathophysiology is still unclear. Small fiber (SF) neuropathy in FD differs from other entities in several aspects related to the perception of pain, alteration of fibers as well as drug therapies used in the practice with patients, with therapies far from satisfying. In order to develop better treatments, more information on the underlying mechanisms of pain is needed. Research in neuropathy has gained momentum from the development of preclinical models where different aspects of pain can be modelled and further analyzed. This review aims at describing the different in vitro and FD animal models that have been used so far, as well as some of the insights gained from their use. We focus especially in recent findings associated with ion channel alterations -that apart from the vascular alterations-, could provide targets for improved therapies in pain.

Developments in the treatment of Fabry disease

Enzyme replacement therapy (ERT) with recombinant α-galactosidase A (r-αGAL A) for the treatment of Fabry disease has been available for over 15 years. Long-term treatment may slow down disease progression, but cardiac, renal, and cerebral complications still develop in most patients. In addition, lifelong intravenous treatment is burdensome. Therefore, several new treatment approaches have been explored over the past decade. Chaperone therapy (Migalastat; 1-deoxygalactonojirimycin) is the only other currently approved therapy for Fabry disease. This oral small molecule aims to improve enzyme activity of mutated α-galactosidase A and can only be used in patients with specific mutations. Treatments currently under evaluation in (pre)clinical trials are second generation enzyme replacement therapies (Pegunigalsidase-alfa, Moss-aGal), substrate reduction therapies (Venglustat and Lucerastat), mRNA- and gene-based therapy. This review summarises the knowledge on currently available and potential future options for the treatment of Fabry disease.

Inhibition of Mitochondrial Complex I Impairs Release of α-Galactosidase by Jurkat Cells

Fabry disease (FD) is caused by mutations in the GLA gene that encodes lysosomal α-galactosidase-A (α-gal-A). A number of pathogenic mechanisms have been proposed and these include loss of mitochondrial respiratory chain activity. For FD, gene therapy is beginning to be applied as a treatment. In view of the loss of mitochondrial function reported in FD, we have considered here the impact of loss of mitochondrial respiratory chain activity on the ability of a GLA lentiviral vector to increase cellular α-gal-A activity and participate in cross correction. Jurkat cells were used in this study and were exposed to increasing viral copies. Intracellular and extracellular enzyme activities were then determined; this in the presence or absence of the mitochondrial complex I inhibitor, rotenone. The ability of cells to take up released enzyme was also evaluated. Increasing transgene copies was associated with increasing intracellular α-gal-A activity but this was associated with an increase in Km. Release of enzyme and cellular uptake was also demonstrated. However, in the presence of rotenone, enzyme release was inhibited by 37%. Excessive enzyme generation may result in a protein with inferior kinetic properties and a background of compromised mitochondrial function may impair the cross correction process.

Lentivector Iterations and Pre-Clinical Scale-Up/Toxicity Testing: Targeting Mobilized CD34+ Cells for Correction of Fabry Disease

Fabry disease is a rare lysosomal storage disorder (LSD). We designed multiple recombinant lentivirus vectors (LVs) and tested their ability to engineer expression of human α-galactosidase A (α-gal A) in transduced Fabry patient CD34⁺ hematopoietic cells. We further investigated the safety and efficacy of a clinically directed vector, LV/AGA, in both ex vivo cell culture studies and animal models. Fabry mice transplanted with LV/AGA-transduced hematopoietic cells demonstrated α-gal A activity increases and lipid reductions in multiple tissues at 6 months after transplantation. Next we found that LV/AGA-transduced Fabry patient CD34⁺ hematopoietic cells produced even higher levels of α-gal A activity than normal CD34⁺ hematopoietic cells. We successfully transduced Fabry patient CD34⁺ hematopoietic cells with “near-clinical grade” LV/AGA in small-scale cultures and then validated a clinically directed scale-up transduction process in a GMP-compliant cell processing facility. LV-transduced Fabry patient CD34⁺ hematopoietic cells were subsequently infused into NOD/SCID/Fabry (NSF) mice; α-gal A activity corrections and lipid reductions were observed in several tissues 12 weeks after the xenotransplantation. Additional toxicology studies employing NSF mice xenotransplanted with the therapeutic cell product demonstrated minimal untoward effects. These data supported our successful clinical trial application (CTA) to Health Canada and opening of a “first-in-the-world” gene therapy trial for Fabry disease.

Altered dynamics of a lipid raft associated protein in a kidney model of Fabry disease

Accumulation of globotriaosylceramide (Gb3) and other neutral glycosphingolipids with galactosyl residues is the hallmark of Fabry disease, a lysosomal storage disorder caused by deficiency of the enzyme alpha-galactosidase A (α-gal A). These lipids are incorporated into the plasma membrane and intracellular membranes, with a preference for lipid rafts. Disruption of raft mediated cell processes is implicated in the pathogenesis of several human diseases, but little is known about the effects of the accumulation of glycosphingolipids on raft dynamics in the context of Fabry disease. Using siRNA technology, we have generated a polarized renal epithelial cell model of Fabry disease in Madin-Darby canine kidney cells. These cells present increased levels of Gb3 and enlarged lysosomes, and progressively accumulate zebra bodies. The polarized delivery of both raft-associated and raft-independent proteins was unaffected by α-gal A knockdown, suggesting that accumulation of Gb3 does not disrupt biosynthetic trafficking pathways. To assess the effect of α-gal A silencing on lipid raft dynamics, we employed number and brightness (N&B) analysis to measure the oligomeric status and mobility of the model glycosylphosphatidylinositol (GPI)-anchored protein GFP-GPI. We observed a significant increase in the oligomeric size of antibody-induced clusters of GFP-GPI at the plasma membrane of α-gal A silenced cells compared with control cells. Our results suggest that the interaction of GFP-GPI with lipid rafts may be altered in the presence of accumulated Gb3. The implications of our results with respect to the pathogenesis of Fabry disease are discussed.

Gene therapy for fabry disease: a review of the literature

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal enzyme, α-galactosidase A. The lack of adequate enzymatic activity results in a systemic accumulation of neutral glycosphingolipids, predominantly globotriaosylceramide, in the lysosomes of, especially, endothelial and smooth muscle cells of blood vessels. Enzyme replacement therapy is at present the only available specific treatment for Fabry disease; however, this therapy has important drawbacks. Gene-mediated enzyme replacement is a reasonable and highly promising approach for the treatment of Fabry disease. It corresponds to a single gene disorder in which moderately low levels of enzyme activity should be sufficient for clinical efficacy and, thanks to cross-correction mechanisms, the transfection of a small number of cells will potentially correct distant cells too. This article summarizes the studies that have been carried out concerning gene therapy for the treatment of Fabry disease. We briefly review the literature from earlier studies in the 1990s to the current achievements.

Lysosomal delivery of therapeutic enzymes in cell models of Fabry disease

The success of enzymatic replacement in Gaucher disease has stimulated development of targeted protein replacement for other lysosomal disorders, including Anderson-Fabry disease, which causes fatal cardiac, cerebrovascular and renal injury: deficiency of lysosomal α-Galactosidase A induces accumulation of glycosphingolipids. Endothelial cell storage was the primary endpoint in a clinical trial that led to market authorization. Two α-Galactosidase A preparations are licensed worldwide, but fatal outcomes persist, with storage remaining in many tissues. We compare mechanisms of uptake of α -Galactosidase A into cells relevant to Fabry disease, in order to investigate if the enzyme is targeted to the lysosomes in a mannose-6-phosphate receptor dependent fashion, as generally believed. α -Galactosidase A uptake was examined in fibroblasts, four different endothelial cell models, and hepatic cells in vitro. Uptake of europium-labeled human α -Galactosidase A was measured by time-resolved fluorescence. Ligand-specific uptake was quantified in inhibitor studies. Targeting to the lysosome was determined by precipitation and by confocal microscopy. The quantity and location of cation-independent mannose-6-phosphate receptors in the different cell models were investigated using confocal microscopy. Uptake and delivery of α -Galactosidase A to lysosomes in fibroblasts is mediated by the canonical mannose-6-phosphate receptor pathway, but in endothelial cells in vitro this mechanism does not operate. Moreover, this observation is supported by a striking paucity of expression of cation independent mannose-6-phosphate receptors on the plasma membrane of the four endothelial cell models and by little delivery of enzyme to lysosomes, when compared with fibroblasts. If these observations are confirmed in vivo, alternative mechanisms will be needed to explain the ready clearance of storage from endothelial cells in patients undergoing enzyme replacement therapy.

Lentivector transduction improves outcomes over transplantation of human HSCs alone in NOD/SCID/Fabry mice

Fabry disease is a lysosomal storage disorder caused by a deficiency of α-galactosidase A (α-gal A) activity that results in progressive globotriaosylceramide (Gb(3)) deposition. We created a fully congenic nonobese diabetic (NOD)/severe combined immunodeficiency (SCID)/Fabry murine line to facilitate the in vivo assessment of human cell-directed therapies for Fabry disease. This pure line was generated after 11 generations of backcrosses and was found, as expected, to have a reduced immune compartment and background α-gal A activity. Next, we transplanted normal human CD34(+) cells transduced with a control (lentiviral vector-enhanced green fluorescent protein (LV-eGFP)) or a therapeutic bicistronic LV (LV-α-gal A/internal ribosome entry site (IRES)/hCD25). While both experimental groups showed similar engraftment levels, only the therapeutic group displayed a significant increase in plasma α-gal A activity. Gb(3) quantification at 12 weeks revealed metabolic correction in the spleen, lung, and liver for both groups. Importantly, only in the therapeutically-transduced cohort was a significant Gb(3) reduction found in the heart and kidney, key target organs for the amelioration of Fabry disease in humans.

Engineered human Tmpk fused with truncated cell-surface markers: versatile cell-fate control safety cassettes

Cell-fate control gene therapy (CFCGT)-based strategies can augment existing gene therapy and cell transplantation approaches by providing a safety element in the event of deleterious outcomes. Previously, we described a novel enzyme/prodrug combination for CFCGT. Here, we present results employing novel lentiviral constructs harboring sequences for truncated surface molecules (CD19 or low-affinity nerve growth factor receptor) directly fused to that CFCGT cDNA (TmpkF105Y). This confers an enforced one-to-one correlation between cell marking and eradication functions. In-vitro analysis demonstrated the full functionality of the fusion product. Next, low-dose 3'-azido-3'-deoxythymidine (AZT) administration to non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice injected with transduced clonal K562 cells suppressed tumor growth; furthermore, one integrated vector on average was sufficient to mediate cytotoxicity. Further, in a murine xenogeneic leukemia-lymphoma model we also demonstrated in-vivo control over transduced Raji cells. Finally, in a proof-of-principle study to examine the utility of this cassette in combination with a therapeutic cDNA, we integrated this novel CFCGT fusion construct into a lentivector designed for treatment of Fabry disease. Transduction with this vector restored enzyme activity in Fabry cells and retained AZT sensitivity. In addition, human Fabry patient CD34(+) cells showed high transduction efficiencies and retained normal colony-generating capacity when compared with the non-transduced controls. These collective results demonstrated that this novel and broadly applicable fusion system may enhance general safety in gene- and cell-based therapies.

Combination therapies for lysosomal storage disease: is the whole greater than the sum of its parts?

Lysosomal storage diseases (LSDs), as a group, are among the most common inherited diseases affecting children. The primary defect is typically a genetic deficiency of one of the lysosomal enzymes, often causing accumulation of undegraded substrates within the lysosome. This accumulation causes numerous secondary effects that contribute to the disease phenotype. Viral-mediated gene therapy (GT) can supply a persistent source of the deficient enzyme. However, with some notable exceptions, GT has been only modestly successful as a single approach. Recently, various therapies have been combined in order to more effectively target the diverse pathogenic mechanisms at work in LSDs. One strategy that has shown promise involves providing a persistent source of the deficient enzyme (GT, stem cell transplantation) while targeting a secondary consequence of disease with a more transient approach (substrate reduction, anti-inflammatories, pharmacological mimetic, etc.). This general strategy has resulted in both additive and synergistic effects. Interestingly, some therapeutic approaches by themselves provide essentially no clinical benefit but contribute greatly to the overall efficacy when used in combination with other treatments. Unfortunately, no therapeutic combination is universally effective. This adds to the difficulty in predicting and identifying combinations that will be most effective for individual LSDs. A better understanding of both pathogenic and therapeutic mechanisms is necessary in order to identify potentially successful combinations. While a single treatment would be ideal, the complex nature of these diseases may unavoidably limit the efficacy of single therapies. In order to more successfully treat LSDs, a shift in focus towards a combination therapy may be necessary.

α-Galactosidase A expressed in the salivary glands partially corrects organ biochemical deficits in the fabry mouse through endocrine trafficking

Fabry disease is caused by an X-linked deficiency of the lysosomal enzyme α-galactosidase A (GLA) and has been treated successfully with enzyme replacement therapy (ERT). Gene therapy has been proposed as an alternative to ERT due to the presumed advantages of continuous, endogenous production of the therapeutic enzyme. GLA production in the liver and its therapeutic efficacy in the Fabry mouse have been demonstrated previously with various viral vector systems. In consideration of the potential advantages of using the salivary glands as endogenous GLA biosynthesis sites, we explored the feasibility of this approach in the Fabry mouse. GLA -/0 or -/- mice received an adenoviral vector (2 × 10(10) or 1 × 10(9) viral particles) expressing GLA to the right submandibular gland via oral cannulation of the submandibular duct. Four days later, animals were sacrificed; saliva, plasma, kidney, liver, and brain were collected and assayed using ELISA, Western blot, and a GLA enzymatic activity assay using both traditional fluorescence methods and isotope dilution mass spectrometry by following the U.S. EPA Method 6800. GLA activity was significantly elevated in the serum and liver of both treatment groups, and improvement in the kidney was marginally significant (P < 0.069) in the high-dose group. Notably, we found that liver and salivary gland produce different glycoforms of the GLA transgene. Only small numbers of adenoviral genomes were observed in the livers of treated animals, but in four of 14 in the high-dose groups, liver levels of adenovirus exceeded 20 copies/μg, indicating that the sequestration in the salivary gland was imperfect at high doses. Taken together, these results indicate that the salivary gland-based gene therapy for Fabry disease is promising, and further studies with advanced viral vector gene delivery systems (e.g., adeno-associated virus) for long-term treatment appear to be warranted.

Gene therapy, gene targeting and induced pluripotent stem cells: applications in monogenic disease treatment

Monogenic diseases are often severe, life-threatening disorders for which lifelong palliative treatment is the only option. Over the last two decades, a number of strategies have been devised with the aim to treat these diseases with a genetic approach. Gene therapy has been under development for many years, yet suffers from the lack of an effective and safe vector for the delivery of genetic material into cells. More recently, gene targeting by homologous recombination has been proposed as a safer treatment, by specifically correcting disease-causing mutations. However, low efficiency is a major drawback. The emergence of two technologies could overcome some of these obstacles. Terminally differentiated somatic cells can be reprogrammed, using defined factors, to become induced pluripotent stem cells (iPSCs), which can undergo efficient gene mutation correction with the aid of fusion proteins known as zinc finger nucleases (ZFNs). The amalgamation of these two technologies has the potential to break through the current bottleneck in gene therapy and gene targeting.

Alpha-galactosidase A-Tat fusion enhances storage reduction in hearts and kidneys of Fabry mice

The protein transduction domain from human immunodeficiency virus (HIV) Tat allows proteins to penetrate the cell membrane. Enhanced cellular uptake of therapeutic proteins could benefit a number of disorders. This is especially true for lysosomal storage disorders (LSDs) where enzyme replacement therapy (ERT) and gene therapy have been developed. We developed a novel recombinant lentiviral vector (LV) that engineers expression of alpha-galactosidase A (alpha-gal A)-Tat fusion protein for correction of Fabry disease, the second-most prevalent LSD with manifestations in the brain, kidney and heart. In vitro experiments confirmed mannose-6-phosphate independent uptake of the fusion factor. Next, concentrated therapeutic LV was injected into neonatal Fabry mice. Analysis of tissues at 26 wks demonstrated similar alpha-gal A enzyme activities but enhanced globotriaosylceramide (Gb3) reduction in hearts and kidneys compared with the alpha-gal A LV control. This strategy might advance not only gene therapy for Fabry disease and other LSDs, but also ERT, especially for cardiac Fabry disease.

Sequencing and characterization of the porcine α-galactosidase A gene: towards the generation of a porcine model for Fabry disease

Fabry disease is an inherited lysosomal disorder caused by a deficiency of alpha-galactosidase A (α-gal A). The systemic accumulation of substrate, mainly globotriaosylceramide (Gb3), results in organ failure. Although Gb3 accumulation has been observed in an α-gal A-deficient mouse model, important clinical manifestations were not seen. The pursuit of effective treatment for Fabry disease through gene therapy, for example, has been hampered by the lack of a relevant large animal model to assess the efficacy and safety of novel therapies. Towards assembling the tools to generate an alternative animal model, we have sequenced and characterized the porcine ortholog of the α-gal A gene. When compared to the human α-gal A, the porcine α-gal A showed a high level of homology in the coding regions and located at chromosome Xq22. Cell lysate and supernatants from Fabry patient-derived fibroblasts transduced with a lentiviral vector (LV) carrying the porcine α-gal A cDNA (LV/porcine α-gal A), showed high levels of α-gal A activity and its enzymological stability was similar to that of human α-gal A. Uptake of secreted porcine α-gal A was observed into non-transduced cells and was partially inhibited by soluble mannose-6-phosphate. Furthermore, Gb3 accumulation was reduced in Fabry patient-derived fibroblasts transduced with the LV/porcine α-gal A. In conclusion, we elucidated and characterized the porcine α-gal A gene and enzyme. Similarity in enzymatic profile and chromosomal location between α-gal A of porcine and human origins may be of great advantage for the development of a large animal model for Fabry disease.

Vascular endothelial growth factor broadens lentivector distribution in the heart after neonatal injection

For some applications, the success of gene therapy depends on the efficiency of gene transfer into target organs, however, delivery to many tissues is limited. Efforts have been made to improve the efficiency of gene transfer into target organs such as the brain by using mannitol or vascular endothelial growth factor (VEGF) prior to gene delivery, since these treatments have been reported to increase vascular permeability in experimental animals. Here, we investigated the effect of VEGF pretreatment of neonatal mice on the ability of injected lentivirus (LV)--engineering expression of firefly luciferase (luc)--to enhance the transduction of various organs, including the brain and heart. LV/luc was delivered to VEGF-treated neonatal mice via the temporal vein. Whole-body bioluminescence imaging (WBLI) of luciferase expression showed that VEGF pretreatment does not diminish transgene expression over time since it remained steady for up to 12 weeks. Ex vivo imaging of the organs and assessments of organ luciferase activity showed that VEGF pretreatment resulted in significantly increased luciferase expression not only in the heart, but also in the brain, lung, and kidney. This study shows that VEGF may have therapeutic importance to enhance the efficiency of viral gene delivery to the heart, as well as to other target organs.

An approach to achieve long-term expression in skin gene therapy

For gene therapy purposes, the skin is an attractive organ to target for systemic delivery of therapeutic proteins to treat systemic diseases, skin diseases, or skin cancer. To achieve long-term stable expression of a therapeutic gene in keratinocytes (KC), we have developed an approach using a bicistronic retroviral vector expressing the desired therapeutic gene linked to a selectable marker (multidrug resistant gene, MDR) that is then introduced into KC and fibroblasts (FB) to create genetically modified human skin equivalent (HSE). After grafting the HSE onto immunocompromised mice, topical colchicine treatment is used to select and enrich for genetically modified keratinocyte stem cells (KSC) that express MDR and are resistant to colchicine's antimitotic effects. Both the apparatus for topical colchicine delivery and the colchicine doses have been optimized for application to human skin. This approach can be validated by systemic delivery of therapeutic factors such as erythropoietin and the antihypertensive atrial natriuretic peptide.

Anti-CD25 Targeted Killing of Bicistronically Transduced Cells: A Novel Safety Mechanism Against Retroviral Genotoxicity

Gene therapy for Fabry disease, a deficiency in alpha-galactosidase A (alpha-gal A) activity, has the potential to provide a cure for the disorder with a single treatment. Despite modifications to existing vectors, concerns have arisen regarding the risk of genotoxicity associated with the use of retroviruses. To address safety concerns, we propose that expression of a cell surface protein, human CD25 (huCD25) in a bicistronic format, with any therapeutic gene such as alpha-gal A can provide a target that can be used to kill transduced cells selectively should transformative events occur. We show that an anti-CD25 antibody and immunotoxin can specifically target and eliminate transduced leukemia cells expressing CD25. In a murine leukemia model, antibody treatment reduced tumor burden 32-fold and increased survival compared with untreated mice. Furthermore, after a bone marrow transplant of therapeutically transduced cells into Fabry mice, antibody treatment reduced the number of retrovirally transduced huCD25-expressing cells in the peripheral blood. A systemic loss of transduced cells with functional consequences was also evident in the liver and spleen. This proof-of-principle study demonstrates that a targeted antibody can reduce tumor burden and selectively clear bicistronically transduced hematopoietic cells that express a target antigen, thus acting as a built-in safety mechanism.

Novel therapeutic targets for the treatment of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder resulting from deficient activity of alpha-galactosidase A. The traditional concept that is used to explain the complications of the disease involves progressive accumulation of globotriaosylceramide in endothelial and smooth muscle cells, resulting in vascular damage. Clinically, progressive renal insufficiency, cardiac involvement and brain pathology evolves. Two pharmaceutical companies have developed enzyme replacement therapy in Fabry disease. Although the first clinical trials showed great promise, it is clear that long-term effects are not as robust as was anticipated. Stabilisation of renal function and decreases in cardiac hypertrophy has been observed, but some patients may experience progressive complications. As there are recent indications that serum components contribute to the pathophysiology of Fabry disease, fundamental studies are needed to unravel the precise role and identity of these factors. Combination of these basic studies with clinical follow up may ultimately reveal when the 'point of no return' is reached. Advanced renal insufficiency seems to be a clinical indicator of lack of response, but other signs and symptoms are probably related to adverse outcome. It is anticipated that in the future controlled studies in early symptomatic or presymptomatic patients will be required. In addition, alternative strategies such as substrate reduction or chaperone therapy, either alone or in combination with enzyme replacement therapy, should be explored. Because Fabry disease is rare, collaborative efforts should be undertaken and openness of data should be strived for.

Multiple Reduced-intensity Conditioning Regimens Facilitate Correction of Fabry Mice After Transplantation of Transduced Cells

Hematopoietic cell transplantation can impact lysosomal storage disorders (LSDs) and will be enhanced by gene therapy. Transduced cells in LSDs often secrete the therapeutic hydrolase, which can be used by bystander cells. However, toxicity associated with myeloablative transplant preparative regimens limits many applications of this approach in gene therapy. We hypothesized that reduced-intensity (RI) conditioning regimens would allow stable engraftment of therapeutically transduced cells and allow correction of Fabry disease. We transplanted transduced cells into Fabry mice receiving eight different clinically relevant chemotherapy- and/or radiotherapy-based RI conditioning regimens generating modest and transient lymphoid/myeloid cell depletion. Two comprehensive transplantation Protocols were performed. Firstly, transplantation of 0.38 x 10(6) gene-modified stem/progenitor cells was nominally effective; none of the RI regimens led to stable alpha-galactosidase A (alpha-gal A) correction. Secondly, transduced cells were preselected for functional transgene expression and transplanted at a higher dose (0.72 x 10(6) cells). Each RI regimen yielded engraftment of functional transgene-positive cells through 180 days along with increased plasma alpha-gal A activity. Importantly, the RI regimens mediated broad organ enzyme correction and were not associated with immune responses against alpha-gal A. RI conditioning thus has an important role in gene therapy for LSDs; a variety of regimens can be effective in this context.

Correction of cardiac abnormalities in fabry mice by direct intraventricular injection of a recombinant lentiviral vector that engineers expression of alpha-galactosidase A

BACKGROUND

Recombinant lentiviral vectors (LVs) offer the possibility of stable, long-term expression of transgenes even in non-dividing cells. In the present study this vector system was applied to a clinically relevant cardiovascular problem.

METHODS AND RESULTS

Fabry disease results from deficient activity of alpha-galactosidase A (alpha-gal A) and cardiac abnormalities are a common and an important cause of death in patients with the disease. A therapeutic LV that delivers the alpha-gal A cDNA has been synthesized. In vitro studies established efficient transduction of the H9c2 rat cardiomyocytes and showed overexpression of enGFP (control) and alpha-gal A. In in vivo studies, the enGFP cDNA was transferred into C57BL/6 mouse hearts by direct intraventricular injection. Next, in a mouse model of Fabry disease, the recombinant therapeutic construct was delivered analogously. In cardiac tissue, alpha-gal A activity rose to 23% of normal levels at day 7 after LV injection, which is encouraging because levels of correction approximating 5% of normal may be curative for this disorder. There was also a corresponding reduction in globotriaosylceramide accumulation. Other organs assayed showed no detectable changes in alpha-gal A activity levels in injected animals.

CONCLUSION

A localized benefit of directly injecting a therapeutic LV into the heart has been shown, confirming the utility of this delivery system for research and therapy for a variety of cardiovascular disorders.

Efficient correction of Fabry mice and patient cells mediated by lentiviral transduction of hematopoietic stem/progenitor cells

A deficiency in alpha-galactosidase A (alpha-gal A) activity causes Fabry disease. Virus-based delivery of genes can correct cells and establish a sustained supply of therapeutic proteins. Recombinant lentiviral vectors (LVs) show promise in this context. We first demonstrate LV-mediated marking of peripheral blood (PB) cells by transduction/transplantation of hematopoietic stem/progenitor cells. Stable enGFP expression was observed in PB for 37 weeks. Next, we transplanted Fabry mice with bone marrow mononuclear cells (BMMNCs) transduced a single time with a LV encoding the human alpha-gal A cDNA. Sustained expression of functional alpha-gal A in Fabry mice was observed over 24 weeks. Plasma alpha-gal A activity from treated Fabry mice was two-fold higher than wild-type controls. Increased alpha-gal A activity, often to supra-normal levels, and reduction of globotriaosylceramide, a glycolipid that accumulates in Fabry disease, was observed in all organs assessed. In secondary bone marrow transplantations, Fabry mice showed multilineage marking of PB, splenocytes and BMMNCs, along with therapeutic levels of alpha-gal A activity in plasma and organs over 20 weeks. Lastly, we transduced mobilized PB CD34(+) cells from a Fabry patient and observed corresponding enzymatic increases. Thus a single LV-mediated transduction of primitive hematopoietic cells can result in sustained correction for Fabry disease.

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.

Bioluminescent imaging of a marking transgene and correction of Fabry mice by neonatal injection of recombinant lentiviral vectors

Successful therapy for many inherited disorders could be improved if the intervention were initiated early. This is especially true for lysosomal storage disorders. Earlier intervention may allow metabolic correction to occur before lipid buildup has irreversible consequences and/or before the immune system mounts limiting responses. We have been developing gene therapy to treat lysosomal storage disorders, especially Fabry disease. We describe studies directed toward metabolic correction in neonatal animals mediated by recombinant lentiviral vectors. To develop this method, we first injected a marking lentiviral vector that engineers expression of luciferase into the temporal vein of recipient neonatal animals. The use of a cooled charged-coupled device camera allowed us to track transgene expression over time in live animals. We observed intense luciferase expression in many tissues, including the brain, that did not diminish over 24 weeks. Next, we injected neonatal Fabry mice a single time with a therapeutic lentiviral vector engineered to express human alpha-galactosidase A. The injection procedure was well tolerated. We observed increased plasma levels of alpha-galactosidase A activity starting at our first plasma collection point (4 weeks). Levels of alpha-galactosidase A activity were found to be significantly elevated in many tissues even after 28 weeks. No immune response was observed against the corrective transgene product. Increased levels of enzyme activity also led to significant reduction of globotriaosylceramide in the liver, spleen, and heart. This approach provides a method to treat lysosomal storage disorders and other disorders before destructive manifestations occur.

AAV2 Vector Harboring a Liver-Restricted Promoter Facilitates Sustained Expression of Therapeutic Levels of α-Galactosidase A and the Induction of Immune Tolerance in Fabry Mice

The successful application of gene therapy for the treatment of genetic diseases such as Fabry is reliant on the development of vectors that are safe and that facilitate sustained expression of therapeutic levels of the transgene product. Here, we report that intravenous administration of a recombinant AAV2 vector encoding human alpha-galactosidase A under the transcriptional control of a liver-restricted enhancer/promoter (AAV2/DC190-alphagal) generated significantly higher levels of expression in BALB/c and Fabry mice than could be realized using the ubiquitous CMV promoter (AAV2/CMVHI-alphagal). Moreover, AAV2/DC190-alphagal-mediated hepatic expression of alpha-galactosidase A was sustained for 12 months in BALB/c mice and was associated with a significantly reduced immune response to the expressed enzyme. Subsequent challenge of the AAV2/DC190-alphagal-treated animals with recombinant human alpha-galactosidase A at 6 months failed to elicit the production of anti-alpha-galactosidase A antibodies, suggesting the induction of immune tolerance in these animals. The levels of expression attained with AAV2/DC190-alphagal in the Fabry mice were sufficient to reduce the abnormal accumulation of globotriaosylceramide in the liver, spleen, and heart to basal levels and in the kidney by approximately 40% at 8 weeks. Together, these results demonstrate that AAV2-mediated gene transfer that limits the expression of alpha-galactosidase A to the liver may be a viable strategy for treating Fabry disease.

Specific hammerhead ribozymes reduce synthesis of cation-independent mannose 6-phosphate receptor mRNA and protein

Storage diseases because of lysosomal enzyme deficiencies may be treated by the transplantation of cells that secrete the enzyme which is deficient in patients. One can expect that increasing the amount of secreted enzymes will improve the therapy efficacy. Secretion of lysosomal enzymes can be enhanced by reducing the mannose 6-phosphate receptor involved in the lysosomal sorting of newly synthesized lysosomal enzymes. For this purpose, we have constructed hammerhead ribozymes targeting the mRNA of the large murine mannose 6-phosphate receptor (M6PR300). In vitro ribozymes cleave M6PR300 RNA fragments efficiently with cleavage rates of 69-93% after 3 h of incubation. Ribozymes were cloned into an expression vector in which they are integrated into the VaI adenovirus RNA to increase stability and in which they are transcribed from an RNA polymerase III promoter. These plasmids were transiently transfected into BHK cells to investigate in vivo activity. Two ribozymes reduce efficiently the levels of murine M6PR300 mRNA in transient transfection experiments to 42-45%. This correlates with the reduction of M6PR300 biosynthesis, which is reduced also to 37% of normal. We can also demonstrate that the reduction in M6PR300 is sufficient to increase a lysosomal enzyme secretion.

Fabry disease--a metabolic disorder with a challenge for endocrinologists?

OBJECTIVE

To revisit Fabry disease, a rare X-linked metabolic glycosphingolipid storage disease caused by a deficiency of the lysosomal enzyme alpha-galactosidase A (alpha-gal A).

METHOD

Summary of the existing knowledge of Fabry disease including the clinical feature of Fabry disease and the recent breakthrough in the treatment of Fabry patients with the development of recombinant human alpha-gal A.

CONCLUSION

The diffuse organ manifestations of Fabry disease resemble medical endocrinological diseases, and medical endocrinology might be an appropriate speciality to manage the treatment in collaboration with other specialists and clinical geneticists.

Long-term correction of globotriaosylceramide storage in Fabry mice by recombinant adeno-associated virus-mediated gene transfer

Fabry disease is an X-linked recessive inborn metabolic disorder characterized by systemic and vascular accumulation of globotriaosylceramide (Gb(3)) caused by a deficiency of the lysosomal enzyme alpha-galactosidase A (alpha-gal A). The condition is associated with an increased morbidity and mortality due to renal failure, cardiac disease, and early onset of stroke. Hemizygous males are primarily affected clinically with variable expression in heterozygous females. Gene-therapy trials have been initiated recently in alpha-gal A knockout mouse models of Fabry disease by using a variety of viral vectors. In the present investigation we administered single i.v. injections of 1 x 10(10) genomes of recombinant adeno-associated virus (rAAV) encoding the human alpha-gal A gene driven by a modified chicken beta-actin (CAG) promoter to alpha-gal A knockout (Fabry) mice. Transgenic mice were analyzed for expression of alpha-gal A activity and Gb(3) levels in liver, kidney, heart, spleen, small intestine, lung, and brain. Administration of the rAAV-CAG-hAGA vector resulted in stable expression of alpha-gal A in organs of the Fabry mice for >6 months. alpha-Gal A activity in the organs became equal to or higher than that of wild-type mice. Accumulated Gb(3) in the liver, heart, and spleen was reduced to that of wild-type mice with lesser but significant reductions in kidney, lung, and small intestine. Injection of the rAAV-CAG-hAGA construct into skeletal muscle did not result in expression of alpha-gal A in it or in other tissues. This study provides a basis for a simple and efficient gene-therapy approach for patients with Fabry disease and is indicative of its potential for the treatment of other lysosomal storage disorders.

Reduction of alpha-Gal expression by relocalizing alpha-galactosidase to the trans-Golgi network and cell surface

Historically, the most effective means of modifying cell surface carbohydrates has required the intracellular overexpression of glycosyltransferases or glycosidases and is dependent on the enzymes occupying a cellular localization close to the carbohydrate structures they modify. We report on relocalizing the lysosomal resident glycosidase human alpha-galactosidase to other regions of the cell, Golgi and cell surface, where it is in closer proximity for cleaving the carbohydrate structure Galalpha(1,3)Gal. Relocalization of alpha-galactosidase was achieved by using the transmembrane and cytoplasmic domains from the human protein furin, which is known to localize in the trans-Golgi network (TGN) and cell surface. Two chimeric forms of alpha-galactosidase were generated, one directing it to the TGN of the cell and the other to the cell surface, as shown by confocal microscopy. The relocalized enzymes have the ability to cleave terminal alpha-galactose as detected by expression on the cell surface. Furthermore, when expressed as a transgene in mice, the TGN form of alpha-galactosidase was more effective at decreasing cell surface terminal alpha-galactose than was the native lysosomal form. When expressed in conjunction with the alpha1,2fucosyltransferase that also decreases Galalpha(1,3)Gal, the reduction was additive. The ability to relocalize enzymes that modify cell surface carbohydrate structures has far-reaching implications in biology and may be useful in such fields as xenotransplantation and treatment of glycosidase disorders.

Long-term systemic therapy of Fabry disease in a knockout mouse by adeno-associated virus-mediated muscle-directed gene transfer

Fabry disease is a systemic disease caused by genetic deficiency of a lysosomal enzyme, alpha-galactosidase A (alpha-gal A), and is thought to be an important target for enzyme replacement therapy. We studied the feasibility of gene-mediated enzyme replacement for Fabry disease. The adeno-associated virus (AAV) vector containing the alpha-gal A gene was injected into the right quadriceps muscles of Fabry knockout mice. A time course study showed that alpha-gal A activity in plasma was increased to approximately 25% of normal mice and that this elevated activity persisted for up to at least 30 weeks without development of anti-alpha-gal A antibodies. The alpha-gal A activity in various organs of treated Fabry mice remained 5-20% of those observed in normal mice. Accumulated globotriaosylceramide in these organs was completely cleared by 25 weeks after vector injection. Reduction of globotriaosylceramide levels was also confirmed by immunohistochemical and electronmicroscopic analyses. Echocardiographic examination of treated mice demonstrated structural improvement of cardiac hypertrophy 25 weeks after the treatment. AAV vector-mediated muscle-directed gene transfer provides an efficient and practical therapeutic approach for Fabry disease.

Adenovirus-transduced lung as a portal for delivering alpha-galactosidase A into systemic circulation for Fabry disease

Gene therapy efforts have focused primarily on the use of either the liver or skeletal muscle as depot organs for the production of a variety of therapeutic proteins that act systemically. Here we examined the lung to determine whether it could function as yet another portal for the secretion of proteins into the circulation. Fabry disease is caused by a deficiency of the lysosomal hydrolase alpha-galactosidase A, resulting in the abnormal deposition of the glycosphingolipid globotriaosylceramide (GL-3) in vascular lysosomes. Pulmonary instillation of a recombinant adenoviral vector (Ad2/CMVHI-alpha(gal)) encoding human alpha-galactosidase A into Fabry mice resulted in high-level transduction and expression of the enzyme in the lung. Importantly, enzymatic activity was also detected in the plasma, liver, spleen, heart, and kidneys of the Fabry mice. The detection of enzymatic activity outside of the lung, along with the finding that viral DNA was limited to the lung, indicates that the enzyme crossed the air/blood barrier, entered the systemic circulation, and was internalized by the distal visceral organs. The levels of alpha-galactosidase A attained in these tissues were sufficient to reduce GL-3 to basal levels in the lung, liver, and spleen and to approximately 50% of untreated levels in the heart. Together, these results suggest that the lung may be a viable alternate depot organ for the production and systemic secretion of alpha-galactosidase A for Fabry disease.

Correction of the nonlinear dose response improves the viability of adenoviral vectors for gene therapy of Fabry disease

Systemic administration of recombinant adenoviral vectors for gene therapy of chronic diseases such as Fabry disease can be limited by dose-dependent toxicity. Because administration of a high dose of Ad2/CMVHI-alpha gal encoding human alpha-galactosidase A results in expression of supraphysiological levels of the enzyme, we sought to determine whether lower doses would suffice to correct the enzyme deficiency and lysosomal storage abnormality observed in Fabry mice. Reducing the dose of Ad2/CMVHI-alpha gal by 10-fold (from 10(11) to 10(10) particles/mouse) resulted in a greater than 200-fold loss in transgene expression. In Fabry mice, the reduced expression of alpha-galactosidase A, using the lower dose of Ad2/CMVHI-alpha gal, was associated with less than optimal clearance of the accumulated glycosphingolipid (GL-3) from the affected lysosomes. It was determined that this lack of linearity in dose response was not due to an inability to deliver the recombinant viral vectors to the liver but rather to sequestration, at least in part, of the viral vectors by the Kupffer cells. This lack of correlation between dose and expression levels could be obviated by supplementing the low dose of Ad2/CMVHI-alpha gal with an unrelated adenoviral vector or by depleting the Kupffer cells before administration of Ad2/CMVHI-alpha gal. Prior removal of the Kupffer cells, using clodronate liposomes, facilitated the use of a 100-fold lower dose of Ad2/CMVHI-alpha gal (10(9) particles/mouse) to effect the nearly complete clearance of GL-3 from the affected organs of Fabry mice. These results suggest that practical strategies that minimize the interaction between the recombinant adenoviral vectors and the reticuloendothelial system (RES) may improve the therapeutic window of this vector system. In this regard, we showed that pretreatment of mice with gamma globulins also resulted in significantly enhanced adenovirus-mediated transduction and expression of alpha-galactosidase A in the liver.

Preselective gene therapy for Fabry disease

Fabry disease is a lipid storage disorder resulting from mutations in the gene encoding the enzyme alpha-galactosidase A (alpha-gal A; EC ). We previously have demonstrated long-term alpha-gal A enzyme correction and lipid reduction mediated by therapeutic ex vivo transduction and transplantation of hematopoietic cells in a mouse model of Fabry disease. We now report marked improvement in the efficiency of this gene-therapy approach. For this study we used a novel bicistronic retroviral vector that engineers expression of both the therapeutic alpha-gal A gene and the human IL-2Ralpha chain (huCD25) gene as a selectable marker. Coexpression of huCD25 allowed selective immunoenrichment (preselection) of a variety of transduced human and murine cells, resulting in enhanced intracellular and secreted alpha-gal A enzyme activities. Of particular significance for clinical applicability, mobilized CD34(+) peripheral blood hematopoietic stem/progenitor cells from Fabry patients have low-background huCD25 expression and could be enriched effectively after ex vivo transduction, resulting in increased alpha-gal A activity. We evaluated effects of preselection in the mouse model of Fabry disease. Preselection of transduced Fabry mouse bone marrow cells elevated the level of multilineage gene-corrected hematopoietic cells in the circulation of transplanted animals and improved in vivo enzymatic activity levels in plasma and organs for more than 6 months after both primary and secondary transplantation. These studies demonstrate the potential of using a huCD25-based preselection strategy to enhance the clinical utility of ex vivo hematopoietic stem/progenitor cell gene therapy of Fabry disease and other disorders.

Gene therapy for Fabry disease

Fabry disease is an X-linked metabolic disorder caused by a deficiency of alpha-galactosidase A (alpha-Gal A). Lack of this lysosomal hydrolase results in the accumulation of galactose-terminal glycosphingolipids in a number of tissues, including vascular endothelial cells. Premature death is predominantly associated with vascular conditions of the heart, kidneys and brain. Historically, treatment has largely been palliative. Alternative treatments for many lysosomal storage diseases have been developed, including allogeneic organ and bone marrow transplantation, enzyme replacement therapy, and gene therapy. Significant clinical risks still exist with allogeneic transplantations. Alpha-Gal A enzyme replacement therapy has been implemented in clinical trials. This approach has been effective but may have limitations for long-term systemic or cost-effective correction. As an alternative, gene therapy approaches, involving a variety of gene delivery systems, have been pursued for the amelioration of Fabry disease. Fabry disease is a compelling disorder for gene therapy, as target cells are readily accessible and relatively low levels of enzyme correction may suffice to reduce storage. Importantly, metabolic cooperativity effects are also manifested in Fabry disease, wherein corrected cells secrete alpha-Gal A that can correct bystander cells. In addition, a broad therapeutic window probably exists, and mouse models of Fabry disease have been generated to assist studies. As an example, in vitro and in vivo studies using alpha-Gal A-transduced haematopoietic cells from Fabry mice have demonstrated enzymatic correction of recipient cells and dissemination of alpha-Gal A upon transplantation, leading to reduced lipid storage in a number of clinically relevant organs. This corrective enzymatic effect has recently been shown to be even further enhanced upon pre-selection of therapeutically transduced cells prior to transplantation. This review will briefly detail current gene delivery methods and summarize results to date in the context of gene therapy for Fabry disease.

[Fabry disease. Clinical and genetic aspects. Therapeutic perspectives]

INTRODUCTION

This review presents the clinical and genetic aspects of Fabry disease, along with recent advances in research.

CURRENT KNOWLEDGE AND KEY POINTS

Fabry disease is an X-linked inborn error of metabolism due to a deficient activity of the lysosomal enzyme alpha-galactosidase A. The enzymatic defect leads to the systemic accumulation of neutral glycosphingolipids in plasma and tissues. Clinical manifestations in affected hemizygous males are primarily due to progressive disease of small vessels, including angiokeratoma, autonomic dysfunction, and lifelong debilitating pain. Renal failure and vasculopathy of the heart and brain lead to early demise in adulthood. Demonstration of alpha-galactosidase A deficiency in leukocytes or plasma is the definitive method for the diagnosis of affected hemizygous males. Most female carriers are clinically symptomatic, they may present isolated acroparesthesia, cardiac symptoms, or the characteristic benign corneal dystrophy. Due to random X-chromosomal inactivation, enzymatic detection of carriers is often inconclusive. A reliable molecular test for detection of heterozygosity is therefore highly desirable for accurate genetic counselling. The GLA gene has been mapped to chromosome Xq22, and cloned. Several studies have shown the molecular heterogeneity of the disease. Currently, no standard treatment exists for Fabry disease. Symptomatic treatment is provided as appropriate. In addition, renal transplantation or dialysis is available for patients experiencing end-stage renal failure.

FUTURE PROSPECTS AND PROJECTS

The ability to produce high doses of recombinant alpha-galactosidase A in vitro has opened the way to preclinical studies in the mouse model and led to the development of the first clinical trials with enzyme replacement therapy in patients with Fabry disease.

Long-term enzyme correction and lipid reduction in multiple organs of primary and secondary transplanted Fabry mice receiving transduced bone marrow cells

Fabry disease is a compelling target for gene therapy as a treatment strategy. A deficiency in the lysosomal hydrolase alpha-galactosidase A (alpha-gal A; EC ) leads to impaired catabolism of alpha-galactosyl-terminal lipids such as globotriaosylceramide (Gb3). Patients develop vascular occlusions that cause cardiovascular, cerebrovascular, and renal disease. Unlike for some lysosomal storage disorders, there is limited primary nervous system involvement in Fabry disease. The enzyme defect can be corrected by gene transfer. Overexpression of alpha-gal A by transduced cells results in secretion of this enzyme. Secreted enzyme is available for uptake by nontransduced cells presumably by receptor-mediated endocytosis. Correction of bystander cells may occur locally or systemically after circulation of the enzyme in the blood. In this paper we report studies on long-term genetic correction in an alpha-gal A-deficient mouse model of Fabry disease. alpha-gal A-deficient bone marrow mononuclear cells (BMMCs) were transduced with a retrovirus encoding alpha-gal A and transplanted into sublethally and lethally irradiated alpha-gal A-deficient mice. alpha-gal A activity and Gb3 levels were analyzed in plasma, peripheral blood mononuclear cells, BMMCs, liver, spleen, heart, lung, kidney, and brain. Primary recipient animals were followed for up to 26 weeks. BMMCs were then transplanted into secondary recipients. Increased alpha-gal A activity and decreased Gb3 storage were observed in all recipient groups in all organs and tissues except the brain. These effects occurred even with a low percentage of transduced cells. The findings indicate that genetic correction of bone marrow cells derived from patients with Fabry disease may have utility for phenotypic correction of patients with this disorder.

Glycosphingolipid depletion in fabry disease lymphoblasts with potent inhibitors of glucosylceramide synthase

BACKGROUND

Fabry disease is an inherited X-linked disorder resulting in the loss of activity of the lysosomal hydrolase alpha-galactosidase A and causing the clinical manifestations of renal failure, cerebral vascular disease, and myocardial infarction. The phenotypic expression of this disorder is manifest by the accumulation of glycosphingolipids containing alpha-galactosyl linkages, most prominently globotriaosylceramide.

METHODS

Based on quantitative structure activity studies, we recently reported two newly designed glucosylceramide synthase inhibitors based on 1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (P4). These inhibitors, 4'-hydroxy-P4 and ethylenedioxy-P4, were evaluated for their ability to deplete globotriaosylceramide and other glucosylceramide-based lipids in Fabry lymphocytes and were compared with N-butyldeoxynojirimycin, another reported glucosylceramide synthase inhibitor.

RESULTS

Concentrations as low as 10 nmol/L of 4'-hydroxy-P4 and ethylenedioxy-P4 resulted in 70 and 80% depletion, respectively, of globotriaosylceramide, with maximal depletion occurring at three days of treatment. There was no impairment of cell growth. In contrast, N-butyldeoxynojirimycin only minimally lowered globotriaosylceramide levels, even at concentrations as high as 10 micromol/L. Globotriaosylceramide depletion was confirmed by the loss of binding of FITC-conjugated verotoxin B subunit to the lymphoblasts.

CONCLUSIONS

These findings suggest that selective glucosylceramide synthase inhibitors are highly effective in the depletion of globotriaosylceramide from Fabry cell lines. We suggest that these compounds have potential therapeutic utility in the treatment of Fabry disease.