Ex vivo gene therapy using bone marrow-derived cells: combined effects of intracerebral and intravenous transplantation in a mouse model of niemann–pick disease

Ex vivo gene therapy for lysosomal storage disorders: future perspectives

INTRODUCTION

Lysosomal storage disorders (LSD) are a group of monogenic rare diseases caused by pathogenic variants in genes that encode proteins related to lysosomal function. These disorders are good candidates for gene therapy for different reasons: they are monogenic, most of lysosomal proteins are enzymes that can be secreted and cross-correct neighboring cells, and small quantities of these proteins are able to produce clinical benefits in many cases. Ex vivo gene therapy allows for autologous transplant of modified cells from different sources, including stem cells and hematopoietic precursors.

AREAS COVERED

Here, we summarize the main gene therapy and genome editing strategies that are currently being used as ex vivo gene therapy approaches for lysosomal disorders, highlighting important characteristics, such as vectors used, strategies, types of cells that are modified and main results in different disorders.

EXPERT OPINION

Clinical trials are already ongoing, and soon approved therapies for LSD based on ex vivo gene therapy approaches should reach the market.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

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.

Stem Cell Applications in Lysosomal Storage Disorders: Progress and Ongoing Challenges

Lysosomal storage disorders (LSDs) are rare inborn errors of metabolism caused by defects in lysosomal function. These diseases are characterized by accumulation of completely or partially degraded substrates in the lysosomes leading to cellular dysfunction of the affected cells. Currently, enzyme replacement therapies (ERTs), treatments directed at substrate reduction (SRT), and hematopoietic stem cell (HSC) transplantation are the only treatment options for LSDs, and the effects of these treatments depend strongly on the type of LSD and the time of initiation of treatment. However, some of the LSDs still lack a durable and curative treatment. Therefore, a variety of novel treatments for LSD patients has been developed in the past few years. However, despite significant progress, the efficacy of some of these treatments remains limited because these therapies are often initiated after irreversible organ damage has occurred.Here, we provide an overview of the known effects of LSDs on stem cell function, as well as a synopsis of available stem cell-based cell and gene therapies that have been/are being developed for the treatment of LSDs. We discuss the advantages and disadvantages of use of hematopoietic stem cell (HSC), mesenchymal stem cell (MSC), and induced pluripotent stem cell (iPSC)-related (gene) therapies. An overview of current research data indicates that when stem cell and/or gene therapy applications are used in combination with existing therapies such as ERT, SRT, and chaperone therapies, promising results can be achieved, showing that these treatments may result in alleviation of existing symptoms and/or prevention of progression of the disease. All together, these studies offer some insight in LSD stem cell biology and provide a hopeful perspective for the use of stem cells. Further development and improvement of these stem cell (gene) combination therapies may greatly improve the current treatment options and outcomes of patients with a LSD.

Effects of gene therapy on cardiovascular symptoms of lysosomal storage diseases

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

Experimental neurotransplantation treatment for hereditary cerebellar ataxias

Hereditary cerebellar degenerations are a heterogeneous group of diseases often having a detrimental impact on patients’ quality of life. Unfortunately, no sufficiently effective causal therapy is available for human patients at present. There are several therapies that have been shown to affect the pathogenetic process and thereby to delay the progress of the disease in mouse models of cerebellar ataxias. The second experimental therapeutic approach for hereditary cerebellar ataxias is neurotransplantation. Grafted cells might provide an effect via delivery of a scarce neurotransmitter, substitution of lost cells if functionally integrated and rescue or trophic support of degenerating cells. The results of cerebellar transplantation research over the past 30 years are reviewed here and potential benefits and limitations of neurotransplantation therapy are discussed.

Gene Therapy for the Treatment of Neurological Disorders: Metabolic Disorders

Metabolic disorders comprise a large group of heterogeneous diseases ranging from very prevalent diseases such as diabetes mellitus to rare genetic disorders like Canavan Disease. Whether either of these diseases is amendable by gene therapy depends to a large degree on the knowledge of their pathomechanism, availability of the therapeutic gene, vector selection, and availability of suitable animal models. In this book chapter, we review three metabolic disorders of the central nervous system (CNS; Canavan Disease, Niemann-Pick disease and Phenylketonuria) to give examples for primary and secondary metabolic disorders of the brain and the attempts that have been made to use adeno-associated virus (AAV) based gene therapy for treatment. Finally, we highlight commonalities and obstacles in the development of gene therapy for metabolic disorders of the CNS exemplified by those three diseases.

Mesenchymal stem cells as cellular vectors for pediatric neurological disorders

Lysosomal storage diseases are a heterogeneous group of hereditary disorders characterized by a deficiency in lysosomal function. Although these disorders differ in their etiology and phenotype those that affect the nervous system generally manifest as a profound deterioration in neurologic function with age. Over the past several decades implementation of various treatment regimens including bone marrow and cord blood cell transplantation, enzyme replacement, and substrate reduction therapy have proved effective for managing some clinical manifestations of these diseases but their ability to ameliorate neurologic complications remains unclear. Consequently, there exists a need to develop alternative therapies that more effectively target the central nervous system. Recently, direct intracranial transplantation of tissue-specific stem and progenitor cells has been explored as a means to reconstitute metabolic deficiencies in the CNS. In this chapter we discuss the merits of bone marrow-derived mesenchymal stem cells (MSCs) for this purpose. Originally identified as progenitors of connective tissue cell lineages, recent findings have revealed several novel aspects of MSC biology that make them attractive as therapeutic agents in the CNS. We relate these advances in MSC biology to their utility as cellular vectors for treating neurologic sequelae associated with pediatric neurologic disorders.

Using ASMase knockout mice to model human diseases

Acid sphingomyelinase (ASMase) is a key initiator of sphingomyelin/ceramide signal transduction activated by many stress stimuli. Over the past two decades, much progress has been made in defining the clinical relevance of sphingomyelin/ceramide signaling in numerous diseases using ASMase knockout mice. Organs that operate this pathway are numerous and the disease states regulated are diverse, with ceramide generation governing injury in tumor, gut, ovary, brain, lung, heart, liver, and during infection. This chapter emphasizes evolutionary conservation of sphingolipid stress signaling and mammalian adaptations that permit transduction of organotypic responses. Recognition that the sphingomyelin/ceramide transducer calibrates extent of tissue injury, ultimately acting as a molecular switch that determines organ fate, is driving development of new pharmacologic concepts and tools to intervene therapeutically.

Developing treatment options for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.

Gene and stem cell therapy: alone or in combination?

INTRODUCTION

Both gene and stem cell therapies hold great promise in the treatment of many genetic diseases and are currently focus of interest for many investigators. While both approaches are offering great and valuable treatment options for devastating and life-threatening diseases, they hold much greater promise in combination.

METHODS

As there are multiple options in selecting gene transfer vehicles among the non-viral and viral vectors, there are also many options among the different transplantable cell types ranging from lineage-restricted progenitor cells to multipotent and pluripotent stem cells. Here, combination of the gene therapy and stem cell therapy is discussed.

RESULTS

Several suc-cessful gene and stem cell therapies have been reported both in animal and human trials. Combination of the gene therapy and stem cell therapy can be carried out sequentially where the cell transplantation and the in vivo gene therapy are accomplished one after the other; or, as it is more commonly practiced, they can be carried out as ex vivo gene therapy where the transplantable cells are genetically modified outside the body before being transplanted into the body.

CONCLUSION

The combination of the stem-cell technology with gene therapy has the potential of providing both regenerative tissue and therapeutic material simultaneously; therefore, having the benefits of both technologies.

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.

Comparative analysis of acid sphingomyelinase distribution in the CNS of rats and mice following intracerebroventricular delivery

Niemann-Pick A (NPA) disease is a lysosomal storage disorder (LSD) caused by a deficiency in acid sphingomyelinase (ASM) activity. Previously, we reported that biochemical and functional abnormalities observed in ASM knockout (ASMKO) mice could be partially alleviated by intracerebroventricular (ICV) infusion of hASM. We now show that this route of delivery also results in widespread enzyme distribution throughout the rat brain and spinal cord. However, enzyme diffusion into CNS parenchyma did not occur in a linear dose-dependent fashion. Moreover, although the levels of hASM detected in the rat CNS were determined to be within the range shown to be therapeutic in ASMKO mice, the absolute amounts represented less than 1% of the total dose administered. Finally, our results also showed that similar levels of enzyme distribution are achieved across rodent species when the dose is normalized to CNS weight as opposed to whole body weight. Collectively, these data suggest that the efficacy observed following ICV delivery of hASM in ASMKO mice could be scaled to CNS of the rat.

Lysosomal storage diseases as differential diagnosis of hepatosplenomegaly

In adults, elevated transaminases and hepatomegaly, often mild, with moderate to massive idiopathic splenomegaly might hint to a lysosomal storage disease (LSD). In most of these cases, hepatosplenomegaly does not eventually lead to cirrhosis, hepatocellular carcinoma or cholestasis. Nevertheless, the hepatic clinical findings might be the incentive for the patient to present at the physician's office. Many of the currently known >50 lysosomal storage diseases might manifest in liver: out of these, the most important ones in adults are: Gaucher disease, cholesterol ester storage disease (CESD) and the Niemann-Pick diseases. An increase of plasma chitotriosidase should alert the physician for the presence of an LSD. For Gaucher's disease, enzyme supplementation and substrate deprivation constitute effective therapeutic options. Fabry's disease, the most prevalent lysosomal storage disease, does usually not affect the liver, but causes painful episodes of hands' or feet pain (acroparesthesias), left ventricular hypertrophy, renal failure, early stroke and decreased life expectancy. The emerging advent of effective therapeutic options and the cumulative prevalence of lysosomal storage diseases urge the hepatologist to add these diagnostic pathways to the clinical repertoire.

Human umbilical cord blood-derived mesenchymal stem cells improve neurological abnormalities of Niemann-Pick type C mouse by modulation of neuroinflammatory condition

Niemann-Pick type C (NP-C) disease is a devastating developmental disorder with progressive and fatal neurodegeneration. We have used a mouse model of Niemann-Pick type C (NP-C) disease to evaluate the effects of direct intracerebral transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) on the progression of neurological disease in this order. Here, we show that hUCB-MSCs transplantation into NP-C mice prevents the loss of Purkinje neurons and inhibits cerebellar apoptotic cell death. Interestingly, these effects were associated with the modulation of inflammatory responses, as evidenced by increased anti-inflammatory cytokine IL-10, and reduced abnormal astrocytic activation. Furthermore, our results show that the hUCB-MSCs transplantation reduced the cholesterol accumulation level in neurons in NP-C mice compared with sham-transplanted animals. This study provides the first evidence that hUCB-MSCs can improve neurological symptoms in NP-C disease, suggesting it as a potential therapeutic agent against neurodegenerative diseases.

Systemic neurotransplantation--a problem-oriented systematic review

Systemic neurotransplantation (SNT) was introduced in the laboratory in 2000 and currently it is being widely examined in animal models of neurological disorders. The aim of this systematic review was to evaluate the current state of knowledge in the field of experimental SNT and the premise for the introduction of clinical trials. PubMed was searched and 60 articles utilizing an SNT approach were found and subjected to analysis. The time window for cell transplantation was addressed in only two studies, with contradictory results. Immunosuppression was applied in 25% of studies. No study addressed the justification for immunosuppression. Bone marrow was the most frequent source of grafted cells, followed by cord blood and then by cells of embryonic origin. Studies investigating dose-dependency revealed no satisfactory results with transplantation of less than 10(6) cells/animal; the efficient dose most frequently ranged from 10(6)-10(7) cells/animal (mice and rats). The behavioral effects of cell transplantation were assessed in 75% of all studies; significant improvement was achieved in 95% of them. Morphological effect was evaluated in half of the studies; significant positive effect was achieved in 73% of them. Experimental attempts to elucidate the mechanisms mediating cell-dependent effect were not undertaken in half of the studies. In the other half, the most frequent mechanisms were growth factors, neurogenesis and immunomodulation. SNT still seems to be at the very initial stage of development. Many critical factors have not been sufficiently addressed in laboratory studies and they must be clarified before the introduction of clinical trials.

Intracerebroventricular infusion of acid sphingomyelinase corrects CNS manifestations in a mouse model of Niemann-Pick A disease

Niemann-Pick A (NPA) disease is a lysosomal storage disorder (LSD) caused by a deficiency in acid sphingomyelinase (ASM) activity. Previously, we showed that the storage pathology in the ASM knockout (ASMKO) mouse brain could be corrected by intracerebral injections of cell, gene and protein based therapies. However, except for instances where distal areas were targeted with viral vectors, correction of lysosomal storage pathology was typically limited to a region within a few millimeters from the injection site. As NPA is a global neurometabolic disease, the development of delivery strategies that maximize the distribution of the enzyme throughout the CNS is likely necessary to arrest or delay progression of the disease. To address this challenge, we evaluated the effectiveness of intracerebroventricular (ICV) delivery of recombinant human ASM into ASMKO mice. Our findings showed that ICV delivery of the enzyme led to widespread distribution of the hydrolase throughout the CNS. Moreover, a significant reduction in lysosomal accumulation of sphingomyelin was observed throughout the brain and also within the spinal cord and viscera. Importantly, we demonstrated that repeated ICV infusions of ASM were effective at improving the disease phenotype in the ASMKO mouse as indicated by a partial alleviation of the motor abnormalities. These findings support the continued exploration of ICV delivery of recombinant lysosomal enzymes as a therapeutic modality for LSDs such as NPA that manifests substrate accumulation within the CNS.

In vivo delivery of human acid ceramidase via cord blood transplantation and direct injection of lentivirus as novel treatment approaches for Farber disease

Farber disease is a rare lysosomal storage disorder (LSD) caused by a deficiency of acid ceramidase (AC) activity and subsequent accumulation of ceramide. Currently, there is no treatment for Farber disease beyond palliative care and most patients succumb to the disorder at a very young age. Previously, our group showed that gene therapy using oncoretroviral vectors (RV) could restore enzyme activity in Farber patient cells. The studies described here employ novel RV and lentiviral (LV) vectors that engineer co-expression of AC and a cell surface marking transgene product, human CD25 (huCD25). Transduction of Farber patient fibroblasts and B cells with these vectors resulted in overexpression of AC and led to a 90% and 50% reduction in the accumulation of ceramide, respectively. Vectors were also evaluated in human hematopoietic stem/progenitor cells (HSPCs) and by direct in vivo delivery in mouse models. In a xenotransplantation model using NOD/SCID mice, we found that transduced CD34(+) cells could repopulate irradiated recipient animals, as measured by CD25 expression. When virus was injected intravenously into mice, soluble CD25 was detected in the plasma and increased AC activity was present in the liver up to 14 weeks post-injection. These findings suggest that vector and transgene expression can persist long-term and offer the potential of a lasting cure. To our knowledge, this is the first report of in vivo testing of direct gene therapy strategies for Farber disease.

Central nervous system therapy for lysosomal storage disorders

✓ Most lysosomal storage disorders are characterized by progressive central nervous system impairment, with or without systemic involvement. Affected individuals have an array of symptoms related to brain dysfunction, the most devastating of which is neurodegeneration following a period of normal development. The blood–brain barrier has represented a significant impediment to developing therapeutic approaches to treat brain disease, but novel approaches—including enzyme replacement, small-molecule, gene, and cell-based therapies—have given children afflicted by these conditions and those who care for them hope for the future.

Age- and dose-related effects on MSC engraftment levels and anatomical distribution in the central nervous systems of nonhuman primates: identification of novel MSC subpopulations that respond to guidance cues in brain

Mesenchymal stem cells (MSCs) have demonstrated efficacy as therapeutic vectors in rodent models of neurological diseases, but few studies have evaluated their safety and efficacy in a relevant large animal model. Previously, we reported that MSCs transplanted to the central nervous systems (CNS) of adult rhesus macaques engrafted at low levels without adversely affecting animal health, behavior, or motor function. Herein, we injected MSCs intracranially into 10 healthy infant macaques and quantified their engraftment levels and mapped their anatomical distribution in brain by real-time polymerase chain reaction using an sry gene-specific probe. These analyses revealed that MSC engraftment levels in brain were on average 18-fold higher with a maximal observed difference of 180-fold in neonates as compared with that reported previously for young adult macaques. Moreover, engraftment levels were 30-fold higher after injection of a low versus high cell dose and engrafted MSCs were nonrandomly distributed throughout the infant brain and localized to specific anatomical regions. Identification of unique subpopulations of macaque and human MSCs that express receptor proteins known to regulate tangential migration of interneurons may explain their migration patterns in brain. Extensive monitoring of infant transplant recipients using a battery of age appropriate tests found no evidence of any long-term adverse effects on the health or social, behavioral, cognitive, or motor abilities of animals up to 6 months post-transplant. Therefore, direct intracranial injection represents a safe means to deliver therapeutic levels of MSCs to the CNS. Moreover, expressed guidance receptors on MSC subpopulations may regulate migration of cells in the host brain. Disclosure of potential conflicts of interest is found at the end of this article.

Combination brain and systemic injections of AAV provide maximal functional and survival benefits in the Niemann-Pick mouse

Niemann-Pick disease (NPD) is caused by the loss of acid sphingomyelinase (ASM) activity, which results in widespread accumulation of undegraded lipids in cells of the viscera and CNS. In this study, we tested the effect of combination brain and systemic injections of recombinant adeno-associated viral vectors encoding human ASM (hASM) in a mouse model of NPD. Animals treated by combination therapy exhibited high levels of hASM in the viscera and brain, which resulted in near-complete correction of storage throughout the body. This global reversal of pathology translated to normal weight gain and superior recovery of motor and cognitive functions compared to animals treated by either brain or systemic injection alone. Furthermore, animals in the combination group did not generate antibodies to hASM, demonstrating the first application of systemic-mediated tolerization to improve the efficacy of brain injections. All of the animals treated by combination therapy survived in good health to an investigator-selected 54 weeks, whereas the median lifespans of the systemic-alone, brain-alone, or untreated ASM knockout groups were 47, 48, and 34 weeks, respectively. These data demonstrate that combination therapy is a promising therapeutic modality for treating NPD and suggest a potential strategy for treating disease indications that cause both visceral and CNS pathologies.

Bone Marrow-Derived Mesenchymal Stem Cells Promote Neuronal Networks with Functional Synaptic Transmission After Transplantation into Mice with Neurodegeneration

Recent studies have shown that bone marrow-derived MSCs (BM-MSCs) improve neurological deficits when transplanted into animal models of neurological disorders. However, the precise mechanism by which this occurs remains unknown. Herein we demonstrate that BM-MSCs are able to promote neuronal networks with functional synaptic transmission after transplantation into Niemann-Pick disease type C (NP-C) mouse cerebellum. To address the mechanism by which this occurs, we used gene microarray, whole-cell patch-clamp recordings, and immunohistochemistry to evaluate expression of neurotransmitter receptors on Purkinje neurons in the NP-C cerebellum. Gene microarray analysis revealed upregulation of genes involved in both excitatory and inhibitory neurotransmission encoding subunits of the ionotropic glutamate receptors (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, AMPA) GluR4 and GABA(A) receptor beta2. We also demonstrated that BM-MSCs, when originated by fusion-like events with existing Purkinje neurons, develop into electrically active Purkinje neurons with functional synaptic formation. This study provides the first in vivo evidence that upregulation of neurotransmitter receptors may contribute to synapse formation via cell fusion-like processes after BM-MSC transplantation into mice with neurodegenerative disease. Disclosure of potential conflicts of interest is found at the end of this article.

Injection of mouse and human neural stem cells into neonatal Niemann–Pick A model mice

Cloned mouse C17.2 neural stem cells (NSCs) or human NSCs were injected into five CNS sites in very large numbers (100,000 cells/site, or a total of 500,000 cells) into 18 neonatal mice homozygous for a targeted deletion (knockout) of the acid sphingomyelinase (ASM) gene (called ASMKO mice), a faithful model of human Niemann-Pick type A (NP-A) disease, and into 10 wild-type mice, all on the C57BL/6J background. Injected mice were not immunosuppressed, and all survived to adulthood. Non-injected ASMKO controls had developed widespread neuronal and glial vacuolation and lysosomal accumulation of sphingomyelin and cholesterol when examined histologically at 16 weeks of age. Unlike children with NP-A disease, the ASMKO mice also lose cerebellar Purkinje neurons progressively, are ataxic, and show parallel progressive declines in rotorod performance. At 16 weeks NSC-injected mice showed a dramatic decrease in neuronal and glial vacuolation (by standard histological staining) and in cholesterol accumulation (by filipin fluorescence staining) throughout the cerebral neocortex, hippocampal formation, striatum and cerebellum, with lesser but clear improvement throughout the brainstem. Improvement was modestly but consistently better in human HFT13-injected than in mouse C17.2-injected ASMKO mice. Improvement in the ASMKO brains was more widespread than the distribution of NSCs, an indication that ASM must have been secreted and diffused at therapeutic concentrations beyond the territory occupied by NSCs. However, though Purkinje cell rescue has been achieved with NSCs in some other disease models, loss of Purkinje neurons and decline in rotorod performance were still present in injected ASMKO mice.

Enzyme, cell and gene-based therapies for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a demyelinating storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA). Lack of ARSA activity leads to the accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the central and peripheral nervous systems. Based on the age at onset, the disease is usually classified into three forms: the late-infantile form, which manifests in the second year of life; the juvenile variants (onset between 4 and 12 years), which are subdivided into early-juvenile (EJ, onset before 6 years) and late-juvenile (LJ, onset after 6 years); and the adult form (onset after 12 years of age). Currently, there is no efficient therapy for the late-infantile form of MLD (50% of the patients), death occurring within a few years after onset of neurological symptoms. Allogeneic haematopoietic cell transplantation (HCT), when performed at a very early stage of the disease, may improve selected patients with juvenile or adult forms of MLD. As with other lysosomal storage diseases, the physiopathology of MLD is poorly understood. Demyelination is the main pathological finding, but substantial storage of sulfatides in neurons also occurs, and may contribute to the clinical phenotype. The physiopathological process leading to neuronal and glial cell degeneration and apoptosis involves accumulation of undegraded sulfatides but also secondary abnormalities (storage/mislocalization of unrelated lipids, inflammatory processes). This review summarizes the recent advances in the understanding of the physiopathology of MLD and the new therapeutic perspectives currently under preclinical investigation, including enzyme replacement therapy, gene therapy and cell therapy.

Clinical response to persistent, low-level beta-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1-5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at approximately 5% and approximately 2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of alpha-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII.

AAV8-mediated expression of glucocerebrosidase ameliorates the storage pathology in the visceral organs of a mouse model of Gaucher disease

BACKGROUND

Gaucher disease is the most common of the lysosomal storage disorders. The primary manifestation is the accumulation of glucosylceramide (GL-1) in the macrophages of liver and spleen (Gaucher cells), due to a deficiency in the lysosomal hydrolase glucocerebrosidase (GC). A Gaucher mouse model (D409V/null) exhibiting reduced GC activity and accumulation of GL-1 was used to evaluate adeno-associated viral (AAV)-mediated gene therapy.

METHODS

A recombinant AAV8 serotype vector bearing human GC (hGC) was administered intravenously to the mice. The levels of hGC in blood and tissues were determined, as were the effects of gene transfer on the levels of GL-1. Histopathological evaluation was performed on liver, spleen and lungs.

RESULTS

Vector administration to pre-symptomatic Gaucher mice resulted in sustained hepatic secretion of hGC at levels that prevented GL-1 accumulation and the appearance of Gaucher cells in the liver, spleen and lungs. AAV administration to older mice with established disease resulted in normalization of GL-1 levels in the spleen and liver and partially reduced that in the lung. Analysis of the bronchoalveolar lavage fluid (BALF) from treated mice showed significant correction of the abnormal cellularity and cell differentials. No antibodies to the expressed hGC were detected following a challenge with recombinant enzyme suggesting the animals were tolerized to human enzyme.

CONCLUSIONS

These data demonstrate the effectiveness of AAV-mediated gene therapy at preventing and correcting the biochemical and pathological abnormalities in a Gaucher mouse model, and thus support the continued consideration of this vector as an alternative approach to treating Gaucher disease.

Preclinical Evaluation of Adult Stem Cell Engraftment and Toxicity in the CNS of Rhesus Macaques

Congenital neurodegenerative diseases exhibit progressive postnatal neurologic impairment leading to premature death and are intractable to systemic therapies such as bone marrow transplantation. We injected bone marrow-derived mesenchymal stem cells (MSCs) into the CNS of young adult rhesus macaques to evaluate their safety and feasibility as vectors for direct intervention of neurologic disorders. Levels of engrafted male, donor MSCs were quantified in the CNS of female transplant recipients by real-time PCR using an SRY gene-specific probe. Analysis of coronal brain slices encompassing one-third of the total brain volume revealed engraftment levels ranging from 0.026 x 10(-3) to 0.163 x 10(-3)% of the total DNA content of brain tissue. Fine-mapping revealed male DNA distributed within specific anatomic structures along the neuraxis where label-retaining MSCs were visualized in histological sections by immunohistochemistry. Double labeling of sections confirmed that engrafted donor cells lacked expression of the macrophage marker CD68, the astrocytes marker GFAP, and neuronal markers NeuN and MAP2. MSC engraftment had no adverse effects on animal health, behavior, postural and locomotor patterns, or upper limb motor performance evaluated over a 6-month period posttransplantation. Therefore, MSC-based therapies represent a safe alternative for clinical intervention of CNS disorders.

Potential of mesenchymal stem cells in gene therapy approaches for inherited and acquired diseases

The intriguing biology of stem cells and their vast clinical potential is emerging rapidly for gene therapy. Bone marrow stem cells, including the pluripotent haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and possibly the multipotent adherent progenitor cells (MAPCs), are being considered as potential targets for cell and gene therapy-based approaches against a variety of different diseases. The MSCs from bone marrow are a promising target population as they are capable of differentiating along multiple lineages and, at least in vitro, have significant expansion capability. The apparently high self-renewal potential makes them strong candidates for delivering genes and restoring organ systems function. However, the high proliferative potential of MSCs, now presumed to be self-renewal, may be more apparent than real. Although expanded MSCs have great proliferation and differentiation potential in vitro, there are limitations with the biology of these cells in vivo. So far, expanded MSCs have failed to induce durable therapeutic effects expected from a true self-renewing stem cell population. The loss of in vivo self-renewal may be due to the extensive expansion of MSCs in existing in vitro expansion systems, suggesting that the original stem cell population and/or properties may no longer exist. Rather, the expanded population may indeed be heterogeneous and represents several generations of different types of mesenchymal cell progeny that have retained a limited proliferation potential and responsiveness for terminal differentiation and maturation along mesenchymal and non-mesenchymal lineages. Novel technology that allows MSCs to maintain their stem cell function in vivo is critical for distinguishing the elusive stem cell from its progenitor cell populations. The ultimate dream is to use MSCs in various forms of cellular therapies, as well as genetic tools that can be used to better understand the mechanisms leading to repair and regeneration of damaged or diseased tissues and organs.

Genetic correction of the fetal brain increases the lifespan of mice with the severe multisystemic disease mucopolysaccharidosis type VII

Neurogenetic diseases typically have globally distributed lesions, and pathology usually develops early in life, requiring early diagnosis and treatment. We investigated the effects of transferring a corrective gene into the fetal brain before the onset of pathology in the mucopolysaccharidosis (MPS) type VII mouse, a model of a lysosomal storage disease. A single adeno-associated virus serotype 1 vector injection into the ventricle at 15.5 days of gestation resulted in widespread distribution and lifelong expression of the normal gene in the brain and spinal cord. The normal enzyme was distributed to neighboring cells (as expected) and completely prevented the development of storage lesions throughout the central nervous system (CNS). No vector transfer was found outside the CNS, including the gonads, but a small amount of enzyme was present in visceral tissues, consistent with transfer from cerebrospinal fluid to venous circulation. The enzyme was present peripherally in such low amounts that it did not result in the severe skeletal dysmorphology that occurs readily when systemic treatment is used in neonates. However, the survival probability of the treated animals was significantly increased. The results suggest that the nervous system disease may contribute to the overall physiologic health of the animal in this type of disease.

Treatment of the mouse model of mucopolysaccharidosis type IIIB with lentiviral-NAGLU vector

The Sanfilippo syndrome type B (mucopolysaccharidosis IIIB) is an autosomal recessive disorder due to mutations in the gene encoding NAGLU (alpha-N-acetylglucosaminidase), one of the enzymes required for the degradation of the GAG (glycosaminoglycan) heparan sulphate. No therapy exists for affected patients. We have shown previously the efficacy of lentiviral-NAGLU-mediated gene transfer in correcting in vitro the defect on fibroblasts of patients. In the present study, we tested the therapy in vivo on a knockout mouse model using intravenous injections. Mice (8-10 weeks old) were injected with one of the lentiviral doses through the tail vein and analysed 1 month after treatment. A single injection of lentiviral-NAGLU vector resulted in transgene expression in liver, spleen, lung and heart of treated mice, with the highest level reached in liver and spleen. Expression of 1% normal NAGLU activity in liver resulted in a 77% decrease in the GAG content; more remarkably, an expression of 0.16% normal activity in lung was capable of decreasing the GAG level by 29%. Long-term (6 months) follow up of the gene therapy revealed that the viral genome integration persisted in the target tissues, although the real-time PCR analysis showed a decrease in the vector DNA content with time. Interestingly, the decrease in GAG levels was maintained in liver, spleen, lung and heart of treated mice. These results show the promising potential and the limitations of lentiviral-NAGLU vector to deliver the human NAGLU gene in vivo.

Solid tissues can be manipulated ex vivo and used as vehicles for gene therapy

BACKGROUND

Organ fragments can be cultured for weeks in vitro if they are prepared of microscopic thickness and if the basic organ structure is preserved. Such organ fragments, which we termed micro-organs (MOs), express in culture endogenous tissue-specific gene products. We have exploited this methodology to engineer MOs ex vivo by gene transfer.

METHODS

MOs prepared from spleen, lung, colon and skin were infected using: herpes simplex type-1, adeno virus, vaccinia virus and murine leukemia virus (MuLV), carrying the reporter gene beta-galactosidase.

RESULTS

All four viral vectors infected MOs in culture, with adeno infection giving significantly higher values. After optimization, high levels of expression (> 15% positive cells), comparable to those obtained with the adeno construct, were also obtained using the MuLV construct both in vitro and after implantation into syngeneic hosts. After implantation, the engineered tissue was found to remain localized, become vascularized, and to express the transduced gene for several months.

CONCLUSIONS

The system can be used to study interactions between viruses and tissues both ex vivo and in vivo. Furthermore, the approach proposes a novel platform for ex vivo gene therapy. Such engineered structures could be used as autologous biological pumps for continuous secretion in vivo of gene products of clinical importance.

AAV8-Mediated Hepatic Expression of Acid Sphingomyelinase Corrects the Metabolic Defect in the Visceral Organs of a Mouse Model of Niemann–Pick Disease

Acid sphingomyelinase deficiency is a lysosomal storage disorder in which the defective lysosomal hydrolase fails to degrade sphingomyelin. The resulting accumulation of substrate in the lysosomes of histiocytic cells leads to hepatosplenomegaly and severe pulmonary inflammation. Administration of a recombinant AAV1 vector encoding human acid sphingomyelinase to acid sphingomyelinase knockout (ASMKO) mice effectively reduced the accumulated substrate in all of the affected visceral organs. However, more complete and rapid clearance of sphingomyelin was observed when an AAV8-based serotype vector was used in lieu of AAV1. Importantly, AAV8-mediated hepatic expression of higher and sustained levels of the enzyme also corrected the abnormal cellularity, cell differentials, and levels of the chemokine MIP-1alpha in the bronchoalveolar lavage fluids of the ASMKO mice. Treatment also reversed the morphological aberrations associated with the alveolar macrophages of ASMKO mice and restored their phagocytic activity. No antibodies to the expressed enzyme were detected when the viral vectors were used in conjunction with a transcription cassette harboring a liver-restricted enhancer/promoter. Together, these data support the continued development of AAV8-mediated hepatic gene transfer as an approach to treat the visceral manifestations observed in individuals with acid sphingomyelinase deficiency.

Neurodegeneration Augments the Ability of Bone Marrow-Derived Mesenchymal Stem Cells to Fuse with Purkinje Neurons in Niemann–Pick Type C Mice

After transplantation, adult bone marrow-derived mesenchymal stem cells (BM-MSCs) may undergo transdifferentiation and/or cell fusion in response to new environments. However, the mechanism(s) that govern these cell fate switches remain unknown. Here we demonstrate that the pathology associated with murine Niemann-Pick disease type C (NP-C) cerebellum augments the ability of BM-MSCs to fuse with Purkinje neurons. The results suggest that the degenerative microenvironment of Purkinje neurons in the NP-C cerebellum modulates the cell fate switch of BM-MSCs via cell fusion.

Intracerebral transplantation of adult mouse neural progenitor cells into the Niemann-Pick-A mouse leads to a marked decrease in lysosomal storage pathology

Niemann-Pick disease is caused by a genetic deficiency in acid sphingomyelinase (ASM) leading to the intracellular accumulation of sphingomyelin and cholesterol in lysosomes. In the present study, we evaluated the effects of direct intracerebral transplantation of neural progenitor cells (NPCs) on the brain storage pathology in the ASM knock-out (ASMKO) mouse model of Type A Niemann-Pick disease. NPCs derived from adult mouse brain were genetically modified to express human ASM (hASM) and were transplanted into multiple regions of the ASMKO mouse brain. Transplanted NPCs survived, migrated, and showed region-specific differentiation in the host brain up to 10 weeks after transplantation (the longest time point examined). In vitro, gene-modified NPCs expressed up to 10 times more and released five times more ASM activity into the culture media compared with nontransduced NPCs. In vivo, transplanted cells expressed hASM at levels that were barely detectable by immunostaining but were sufficient for uptake and cross-correction of host cells, leading to reversal of distended lysosomal pathology and regional clearance of sphingomyelin and cholesterol storage. Within the host brain, the area of correction closely overlapped with the distribution of the hASM-modified NPCs. No correction of pathology occurred in brain regions that received transplants of nontransduced NPCs. These results indicate that the presence of transduced NPCs releasing low levels of hASM within the ASMKO mouse brain is necessary and sufficient to reverse lysosomal storage pathology. Potentially, NPCs may serve as a useful gene transfer vehicle for the treatment of CNS pathology in other lysosomal storage diseases and neurodegenerative disorders.

Neuroglial activation in Niemann-Pick Type C mice is suppressed by intracerebral transplantation of bone marrow-derived mesenchymal stem cells

Glial activation is thought to play a key role in pathogenesis of neurodegenerative disorders. Here we show that direct transplantation of bone marrow-derived mesenchymal stem cells (BM-MSC) results in alleviation of inflammatory responses associated with the cerebellum of Niemann-Pick disease Type C (NP-C) model mice. Immunohistochemical examinations using glial fibrillary acidic protein (GFAP) and F4/80 antibodies revealed that BM-MSC transplantation reduced significantly both of astrocytic and microglial activations in the cerebellum of NP-C mice. Expression of macrophage colony stimulating factor (M-CSF), a microglial activator, was also considerably down-regulated by the BM-MSC transplantation. These findings suggest that BM-MSC transplantation may have potential for a therapeutic role in the treatment of NP-C and other neurodegenerative brain disorders.

Modification of the brain-derived neurotrophic factor gene: a portal to transform mesenchymal stem cells into advantageous engineering cells for neuroregeneration and neuroprotection

Multipotential mesenchymal stem cells (MSCs) are ideal seed cells for recruiting the loss of neural cells due to their strong proliferative capacity, easy acquisition, and considerable tolerance of genetic modifications. After transduction of brain-derived neurotrophic factor (BDNF) gene via recombinant retroviral vectors into the human MSCs, nearly 100% of cells expressed BDNF (which were therefore transformed into BNDF-MSCs) as detected by immunocytochemistry, and the quantity of BDNF in the culture medium was increased by approximately 20,000-fold. In spite of the genomic integration of an exogenous gene, BDNF-MSCs did not present any structural aberration in the chromosomes. All-trans-retinoic acid (RA) induction caused the BDNF-MSCs to differentiate into neural cells with significantly increased expressions of such neural-specific proteins as nestin, NeuN, O4, and glial fibrillary acidic protein (GFAP). The voltage-dependent K+/Ca2+ currents were recorded from the induced BDNF-MSCs using patch-clamp technique. Compared with the MSCs induced by both RA and BDNF, BDNF-MSCs survived in significantly greater number in the induction medium, and also more cells were induced into neuron-like cells (NeuN, P < 0.01) and oligodendrocyte-like cells (O4, P < 0.05). We suppose that, once engrafted into human central nervous system, the BDNF-MSCs would not only recruit the neuronal losses, but also provide, by way of paracrine, large quantities of BDNF that effectively perform the functions of neuroprotection and neuroregeneration, promoting the activation of endogenous neural stem/progenitor cells and their chemotactic migration. On the other hand, the BDNF-MSCs that can survive in the host environment and differentiate subsequently into functional mature cells may also serve as specifically targeting vectors for ex vivo gene therapy.

Comparative Effects of Recombinant Acid Sphingomyelinase Administration by Different Routes in Niemann-Pick Disease Mice

An inherited deficiency of acid sphingomyelinase (ASM) activity results in the Type A and B forms of Niemann-Pick disease (NPD). The aim of this study was to evaluate the effects of recombinant human ASM (rhASM) replacement therapy on the mouse model, by comparing different routes of administration. Eight NPD mice received rhASM via an intravenous injection (IV) administered at a dose of 1 mg/kg and another group of 8 NPD mice received the same dose by subcutaneous injection (SC). The plasma levels of ASM activity in intravenously administered mice were significantly elevated immediately after injection. In contrast, in the subcutaneously injected mice, the level of ASM activity was maximal 6 h after injection. The levels of ASM activity in both groups had declined substantially by 2 days after injection. It was concluded that rhASM administered by subcutaneous injection is completely absorbed, and offers a similar efficacy to intravenously administered recombinant enzyme.