Adenoviral gene therapy of the Tay-Sachs disease in hexosaminidase A-deficient knock-out mice

Gene therapy for the leukodystrophies: From preclinical animal studies to clinical trials

Leukodystrophies are progressive single gene disorders affecting the white matter of the brain. Several gene therapy trials are in progress to address the urgent unmet need for this patient population. We performed a comprehensive literature review of all gene therapy clinical trials listed in www.clinicaltrials.gov through August 2024, and the relevant preclinical studies that enabled clinical translation. Of the approximately 50 leukodystrophies described to date, only eight have existing gene therapy clinical trials: metachromatic leukodystrophy, X-linked adrenoleukodystrophy, globoid cell leukodystrophy, Canavan disease, giant axonal neuropathy, GM2 gangliosidoses, Alexander disease and Pelizaeus-Merzbacher disease. What led to the emergence of gene therapy trials for these specific disorders? What preclinical data or disease context was enabling? For each of these eight disorders, we first describe its pathophysiology and clinical presentation. We discuss the impact of gene therapy delivery route, targeted cell type, delivery modality, dosage, and timing on therapeutic efficacy. We note that use of allogeneic hematopoietic stem cell transplantation in some leukodystrophies allowed for an accelerated path to clinic even in the absence of available animal models. In other leukodystrophies, small and large animal model studies enabled clinical translation of experimental gene therapies. Human clinical trials for the leukodystrophies include ex vivo lentiviral gene delivery, in vivo AAV-mediated gene delivery, and intrathecal antisense oligonucleotide approaches. We outline adverse events associated with each modality focusing specifically on genotoxicity and immunotoxicity. We review monitoring and management of events related to insertional mutagenesis and immune responses. The data presented in this review show that gene therapy, while promising, requires systematic monitoring to account for the precarious disease biology and the adverse events associated with new technology.

Treating late-onset Tay Sachs disease: Brain delivery with a dual trojan horse protein

Tay-Sachs (TS) disease is a neurodegenerative disease resulting from mutations in the gene encoding the α-subunit (HEXA) of lysosomal β-hexosaminidase A (HexA). We report that (1) recombinant HEXA alone increased HexA activity and decreased GM2 content in human TS glial cells and peripheral mononuclear blood cells; 2) a recombinant chimeric protein composed of HEXA linked to two blood-brain barrier (BBB) entry elements, a transferrin receptor binding sequence and granulocyte-colony stimulating factor, associates with HEXB in vitro; reaches human cultured TS cells lysosomes and mouse brain cells, especially neurons, in vivo; lowers GM2 in cultured human TS cells; lowers whole brain GM2 concentration by approximately 40% within 6 weeks, when injected intravenously (IV) to adult TS-mutant mice mimicking the slow course of late-onset TS; and increases forelimbs grip strength. Hence, a chimeric protein equipped with dual BBB entry elements can transport a large protein such as HEXA to the brain, decrease the accumulation of GM2, and improve muscle strength, thereby providing potential treatment for late-onset TS.

Intrathecal delivery of a bicistronic AAV9 vector expressing β-hexosaminidase A corrects Sandhoff disease in a murine model: A dosage study

The pathological accumulation of GM2 ganglioside associated with Tay-Sachs disease (TSD) and Sandhoff disease (SD) occurs in individuals who possess mutant forms of the heterodimer β-hexosaminidase A (Hex A) because of mutation of the HEXA and HEXB genes, respectively. With a lack of approved therapies, patients experience rapid neurological decline resulting in early death. A novel bicistronic vector carrying both HEXA and HEXB previously demonstrated promising results in mouse models of SD following neonatal intravenous administration, including significant reduction in GM2 accumulation, increased levels of Hex A, and a 2-fold extension of survival. The aim of the present study was to identify an optimal dose of the bicistronic vector in 6-week-old SD mice by an intrathecal route of administration along with transient immunosuppression, to inform possible clinical translation. Three doses of the bicistronic vector were tested: 2.5e11, 1.25e11, and 0.625e11 vector genomes per mouse. The highest dose provided the greatest increase in biochemical and behavioral parameters, such that treated mice lived to a median age of 56 weeks (>3 times the lifespan of the SD controls). These results have direct implications in deciding a human equivalent dose for TSD/SD and have informed the approval of a clinical trial application (NCT04798235).

Life-Limiting Peripheral Organ Dysfunction in Feline Sandhoff Disease Emerges after Effective CNS Gene Therapy

OBJECTIVE

GM2 gangliosidosis is usually fatal by 5 years of age in its 2 major subtypes, Tay-Sachs and Sandhoff disease. First reported in 1881, GM2 gangliosidosis has no effective treatment today, and children succumb to the disease after a protracted neurodegenerative course and semi-vegetative state. This study seeks to further develop adeno-associated virus (AAV) gene therapy for human translation.

METHODS

Cats with Sandhoff disease were treated by intracranial injection of vectors expressing feline β-N-acetylhexosaminidase, the enzyme deficient in GM2 gangliosidosis.

RESULTS

Hexosaminidase activity throughout the brain and spinal cord was above normal after treatment, with highest activities at the injection sites (thalamus and deep cerebellar nuclei). Ganglioside storage was reduced throughout the brain and spinal cord, with near complete clearance in many regions. While untreated cats with Sandhoff disease lived for 4.4 ± 0.6 months, AAV-treated cats lived to 19.1 ± 8.6 months, and 3 of 9 cats lived >21 months. Correction of the central nervous system was so effective that significant increases in lifespan led to the emergence of otherwise subclinical peripheral disease, including megacolon, enlarged stomach and urinary bladder, soft tissue spinal cord compression, and patellar luxation. Throughout the gastrointestinal tract, neurons of the myenteric and submucosal plexuses developed profound pathology, demonstrating that the enteric nervous system was inadequately treated.

INTERPRETATION

The vector formulation in the current study effectively treats neuropathology in feline Sandhoff disease, but whole-body targeting will be an important consideration in next-generation approaches. ANN NEUROL 2023;94:969-986.

Efficacy of Adeno-Associated Virus Serotype 9-Mediated Gene Therapy for AB-Variant GM2 Gangliosidosis

GM2 gangliosidoses are a group of neurodegenerative lysosomal storage disorders that are characterized by the accumulation of GM2 gangliosides (GM2), leading to rapid neurological decline and death. The hydrolysis of GM2 requires the specific synthesis, processing, and combination of products of three genes-HEXA, HEXB, and GM2A-within the cell's lysosomes. Mutations in these genes result in Tay-Sachs disease, Sandhoff disease, or AB-variant GM2 gangliosidosis (ABGM2), respectively. ABGM2, the rarest of the three types, is characterized by a mutation in the GM2A gene, which encodes the GM2 activator (GM2A) protein. Being a monogenic disease, gene therapy is a plausible and likely effective method of treatment for ABGM2. This study aimed at assessing the effects of administering a one-time intravenous treatment of single-stranded Adeno-associated virus serotype 9 (ssAAV9)-GM2A viral vector at a dose of 1 × 1014 vector genomes (vg) per kilogram per mouse in an ABGM2 mouse model (Gm2a-/-). ssAAV9-GM2A was administered at 1-day (neonatal) or 6-weeks of age (adult-stage). The results demonstrated that, in comparison to Gm2a-/- mice that received a vehicle injection, the treated mice had reduced GM2 accumulation within the central nervous system and had long-term persistence of vector genomes in the brain and liver. This proof-of-concept study is a step forward towards the development of a clinically therapeutic approach for the treatment of patients with ABGM2.

Treatment of GM2 Gangliosidosis in Adult Sandhoff Mice using an Intravenous Self-Complementary Hexosaminidase Vector

BACKGROUND

GM2 gangliosidosis is a neurodegenerative, lysosomal storage disease caused by the deficiency of β-hexosaminidase A enzyme (HexA), an α/β-subunit heterodimer. A novel variant of the human hexosaminidase α-subunit, coded by HEXM, has previously been shown to form a stable homodimer, HexM, that hydrolyzes GM2 gangliosides (GM2) in vivo.

MATERIALS & METHODS

The current study assessed the efficacy of intravenous (IV) delivery of a self-complementary adeno-associated virus serotype 9 (scAAV9) vector incorporating the HEXM transgene, scAAV9/HEXM, including the outcomes based on the dosages provided to the Sandhoff (SD) mice. Six-week-old SD mice were injected with either 2.5E+12 vector genomes (low dose, LD) or 1.0E+13 vg (high dose, HD). We hypothesized that when examining the dosage comparison for scAAV9/HEXM in adult SD mice, the HD group would have more beneficial outcomes than the LD cohort. Assessments included survival, behavioral outcomes, vector biodistribution, and enzyme activity within the central nervous system.

RESULTS

Toxicity was observed in the HD cohort, with 8 of 14 mice dying within one month of the injection. As compared to untreated SD mice, which have typical survival of 16 weeks, the LD cohort and the remaining HD mice had a significant survival benefit with an average/median survival of 40.6/34.5 and 55.9/56.7 weeks, respectively. Significant behavioral, biochemical and molecular benefits were also observed. The second aim of the study was to investigate the effects of IV mannitol infusions on the biodistribution of the LD scAAV9/HEXM vector and the survival of the SD mice. Increases in both the biodistribution of the vector as well as the survival benefit (average/median of 41.6/49.3 weeks) were observed.

CONCLUSION

These results demonstrate the potential benefit and critical limitations of the treatment of GM2 gangliosidosis using IV delivered AAV vectors.

White Matter Pathology as a Barrier to Gangliosidosis Gene Therapy

The gangliosidoses are a family of neurodegenerative lysosomal storage diseases that have recently seen promising advances in gene therapy. White matter deficits are well established components of gangliosidosis pathology that are now receiving more attention because they are partially refractory to correction by gene therapy. After a brief synopsis of normal myelinogenesis, this review outlines current viewpoints on the origin of white matter deficits in the gangliosidoses and potential obstacles to treating them effectively by gene therapy. Dysmyelinogenesis (failure of myelin sheaths to form properly) is proposed as the predominant contributor to white matter pathology, but precise mechanistic details are not well understood. The involvement of neuronal storage deficits may extend beyond secondary demyelination (destruction of myelin due to axonal loss) and contribute to dysmyelinogenesis. Preclinical studies in animal models of the gangliosidoses have substantially improved lifespan and quality of life, leading to the initiation of several clinical trials. However, improvement of white matter pathology has lagged behind other metrics and few evidence-based explanations have been proposed to date. Research groups in the field are encouraged to include myelin-specific investigations in future gene therapy work to address this gap in knowledge.

Gene Therapy for Lysosomal Storage Disorders: Ongoing Studies and Clinical Development

Rare monogenic disorders such as lysosomal diseases have been at the forefront in the development of novel treatments where therapeutic options are either limited or unavailable. The increasing number of successful pre-clinical and clinical studies in the last decade demonstrates that gene therapy represents a feasible option to address the unmet medical need of these patients. This article provides a comprehensive overview of the current state of the field, reviewing the most used viral gene delivery vectors in the context of lysosomal storage disorders, a selection of relevant pre-clinical studies and ongoing clinical trials within recent years.

CRISPR-Cas9 for treating hereditary diseases

This chapter analyzes to use of the genome editing tool to the treatment of various genetic diseases. The genome editing method could be used to change the DNA in cells or organisms to understand their physiological response. Therefore, a key objective is to present general information about the use of the genome editing tool in a pertinent way. An emerging genome editing technology like a clustered regularly short palindromic repeats (CRISPR) is an extensively expended in biological sciences. CRISPR and CRISPR-associated protein 9 (CRISPR-Cas9) technique is being utilized to edit any DNA mutations associated with hereditary diseases to study in cells (in vitro) and animals (in vivo). Interestingly, CRISPR-Cas9 could be used to the investigation of treatments of various human hereditary diseases such as hemophila, β-thalassemia, cystic fibrosis, Alzheimer's, Huntington's, Parkinson's, tyrosinemia, Duchnene muscular dystrophy, Tay-Sachs, and fragile X syndrome disorders. Furthermore, CRISPR-Cas9 could also be used in other diseases to the improvement of human health. Finally, this chapter discuss current progress to treatment for hereditary diseases using CRISPR-Cas9 technology and highlights associated challenges and future prospects.

Metabolism of Glycosphingolipids and Their Role in the Pathophysiology of Lysosomal Storage Disorders

Glycosphingolipids (GSLs) are a specialized class of membrane lipids composed of a ceramide backbone and a carbohydrate-rich head group. GSLs populate lipid rafts of the cell membrane of eukaryotic cells, and serve important cellular functions including control of cell-cell signaling, signal transduction and cell recognition. Of the hundreds of unique GSL structures, anionic gangliosides are the most heavily implicated in the pathogenesis of lysosomal storage diseases (LSDs) such as Tay-Sachs and Sandhoff disease. Each LSD is characterized by the accumulation of GSLs in the lysosomes of neurons, which negatively interact with other intracellular molecules to culminate in cell death. In this review, we summarize the biosynthesis and degradation pathways of GSLs, discuss how aberrant GSL metabolism contributes to key features of LSD pathophysiology, draw parallels between LSDs and neurodegenerative proteinopathies such as Alzheimer's and Parkinson's disease and lastly, discuss possible therapies for patients.

Viral-Mediated Gene Replacement Therapy in the Developing Central Nervous System: Current Status and Future Directions

The past few years have witnessed rapid developments in viral-mediated gene replacement therapy for pediatric central nervous system neurogenetic disorders. Here, we provide pediatric neurologists with an up-to-date, comprehensive overview of these developments and note emerging trends for future research. This review presents the different types of viral vectors used in viral-mediated gene replacement therapy; the fundamental properties of viral-mediated gene replacement therapy; the challenges associated with the use of this therapy in the central nervous system; the pathway for therapy development, from translational basic science studies to clinical trials; and an overview of the therapies that have reached clinical trials in patients. Current viral platforms under investigation include adenovirus vectors, adeno-associated viral vectors, lentiviral/retroviral vectors, and herpes simplex virus type 1 vectors. This review also presents an in-depth analysis of numerous studies that investigated these viral platforms in cultured cells and in transgenic animal models for pediatric neurogenetic disorders. Viral vectors have been applied to clinical trials for many different pediatric neurogenetic disorders, including Canavan disease, metachromatic leukodystrophy, neuronal ceroid lipofuscinosis, mucopolysaccharidosis III, spinal muscular atrophy, and aromatic l-amino acid decarboxylase deficiency. Of these diseases, only spinal muscular atrophy has a viral-mediated gene replacement therapy approved for marketing. Despite significant progress in therapy development, many challenges remain. Surmounting these challenges is critical to advancing the current status of viral-mediated gene replacement therapy for pediatric central nervous system neurogenetic disorders.

New Approaches to Tay-Sachs Disease Therapy

Tay-Sachs disease belongs to the group of autosomal-recessive lysosomal storage metabolic disorders. This disease is caused by β-hexosaminidase A (HexA) enzyme deficiency due to various mutations in α-subunit gene of this enzyme, resulting in GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Tay-Sachs disease is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage and astrocyte activation along with inflammatory mediator production. In most cases, the disease manifests itself during infancy, the “infantile form,” which characterizes the most severe disorders of the nervous system. The juvenile form, the symptoms of which appear in adolescence, and the most rare form with late onset of symptoms in adulthood are also described. The typical features of Tay-Sachs disease are muscle weakness, ataxia, speech, and mental disorders. Clinical symptom severity depends on residual HexA enzymatic activity associated with some mutations. Currently, Tay-Sachs disease treatment is based on symptom relief and, in case of the late-onset form, on the delay of progression. There are also clinical reports of substrate reduction therapy using miglustat and bone marrow or hematopoietic stem cell transplantation. At the development stage there are methods of Tay-Sachs disease gene therapy using adeno- or adeno-associated viruses as vectors for the delivery of cDNA encoding α and β HexA subunit genes. Effectiveness of this approach is evaluated in α or β HexA subunit defective model mice or Jacob sheep, in which Tay-Sachs disease arises spontaneously and is characterized by the same pathological features as in humans. This review discusses the possibilities of new therapeutic strategies in Tay-Sachs disease therapy aimed at preventing neurodegeneration and neuroinflammation.

Efficacy of a Bicistronic Vector for Correction of Sandhoff Disease in a Mouse Model

G_M2 gangliosidoses are a family of severe neurodegenerative disorders resulting from a deficiency in the β-hexosaminidase A enzyme. These disorders include Tay-Sachs disease and Sandhoff disease, caused by mutations in the HEXA gene and HEXB gene, respectively. The HEXA and HEXB genes are required to produce the α and β subunits of the β-hexosaminidase A enzyme, respectively. Using a Sandhoff disease mouse model, we tested for the first time the potential of a comparatively lower dose (2.04 × 10¹³ vg/kg) of systemically delivered single-stranded adeno-associated virus 9 expressing both human HEXB and human HEXA cDNA under the control of a single promoter with a P2A-linked bicistronic vector design to correct the neurological phenotype. A bicistronic design allows maximal overexpression and secretion of the Hex A enzyme. Neonatal mice were injected with either this ssAAV9-HexB-P2A-HexA vector or a vehicle solution via the superficial temporal vein. An increase in survival of 56% compared with vehicle-injected controls and biochemical analysis of the brain tissue and serum revealed an increase in enzyme activity and a decrease in brain G_M2 ganglioside buildup. This is a proof-of-concept study showing the “correction efficacy” of a bicistronic AAV9 vector delivered intravenously for G_M2 gangliosidoses. Further studies with higher doses are warranted.

Genetics and Therapies for GM2 Gangliosidosis

Tay-Sachs disease, caused by impaired β-N-acetylhexosaminidase activity, was the first GM2 gangliosidosis to be studied and one of the most severe and earliest lysosomal diseases to be described. The condition, associated with the pathological build-up of GM2 ganglioside, has acquired almost iconic status and serves as a paradigm in the study of lysosomal storage diseases. Inherited as a classical autosomal recessive disorder, this global disease of the nervous system induces developmental arrest with regression of attained milestones; neurodegeneration progresses rapidly to cause premature death in young children. There is no effective treatment beyond palliative care, and while the genetic basis of GM2 gangliosidosis is well established, the molecular and cellular events, from diseasecausing mutations and glycosphingolipid storage to disease manifestations, remain to be fully delineated. Several therapeutic approaches have been attempted in patients, including enzymatic augmentation, bone marrow transplantation, enzyme enhancement, and substrate reduction therapy. Hitherto, none of these stratagems has materially altered the course of the disease. Authentic animal models of GM2 gangliodidosis have facilitated in-depth evaluation of innovative applications such as gene transfer, which in contrast to other interventions, shows great promise. This review outlines current knowledge pertaining the pathobiology as well as potential innovative treatments for the GM2 gangliosidoses.

Systemic Gene Transfer of a Hexosaminidase Variant Using an scAAV9.47 Vector Corrects GM2 Gangliosidosis in Sandhoff Mice

GM2 gangliosidosis is a group of neurodegenerative diseases caused by β-hexosaminidase A (HexA) enzyme deficiency. There is currently no cure. HexA is composed of two similar, nonidentical subunits, α and β, which must interact with the GM2 activator protein (GM2AP), a substrate-specific cofactor, to hydrolyze GM2 ganglioside. Mutations in either subunit or the activator can result in the accumulation of GM2 ganglioside within neurons throughout the central nervous system. The resulting neuronal cell death induces the primary symptoms of the disease: motor impairment, seizures, and sensory impairments. This study assesses the long-term effects of gene transfer in a Sandhoff (β-subunit knockout) mouse model. The study utilized a modified human β-hexosaminidase α-subunit (μ-subunit) that contains critical sequences from the β-subunit that enables formation of a stable homodimer (HexM) and interaction with GM2AP to hydrolyze GM2 ganglioside. We investigated a self-complementary adeno-associated viral (scAAV) vector expressing HexM, through intravenous injections of the neonatal mice. We monitored one cohort for 8 weeks and another cohort long-term for survival benefit, behavioral, biochemical, and molecular analyses. Untreated Sandhoff disease (SD) control mice reached a humane endpoint at approximately 15 weeks, whereas treated mice had a median survival age of 40 weeks, an approximate 2.5-fold survival advantage. On behavioral tests, the treated mice outperformed their knockout age-matched controls and perform similarly to the heterozygous controls. Through the enzymatic and GM2 ganglioside analyses, we observed a significant decrease in the GM2 ganglioside level, even though the enzyme levels were not significantly increased. Molecular analyses revealed a global distribution of the vector between brain and spinal cord regions. In conclusion, the neonatal delivery of a novel viral vector expressing the human HexM enzyme is effective in ameliorating the SD mouse phenotype for long-term. Our data could have implications not only for treatment of SD but also for Tay-Sachs disease (α-subunit deficiency) and similar brain disorders.

Novel Vector Design and Hexosaminidase Variant Enabling Self-Complementary Adeno-Associated Virus for the Treatment of Tay-Sachs Disease

GM2 gangliosidosis is a family of three genetic neurodegenerative disorders caused by the accumulation of GM2 ganglioside (GM2) in neuronal tissue. Two of these are due to the deficiency of the heterodimeric (α-β), "A" isoenzyme of lysosomal β-hexosaminidase (HexA). Mutations in the α-subunit (encoded by HEXA) lead to Tay-Sachs disease (TSD), whereas mutations in the β-subunit (encoded by HEXB) lead to Sandhoff disease (SD). The third form results from a deficiency of the GM2 activator protein (GM2AP), a substrate-specific cofactor for HexA. In their infantile, acute forms, these diseases rapidly progress with mental and psychomotor deterioration resulting in death by approximately 4 years of age. After gene transfer that overexpresses one of the deficient subunits, the amount of HexA heterodimer formed would empirically be limited by the availability of the other endogenous Hex subunit. The present study used a new variant of the human HexA α-subunit, μ, incorporating critical sequences from the β-subunit that produce a stable homodimer (HexM) and promote functional interactions with the GM2AP- GM2 complex. We report the design of a compact adeno-associated viral (AAV) genome using a synthetic promoter-intron combination to allow self-complementary (sc) packaging of the HEXM gene. Also, a previously published capsid mutant, AAV9.47, was used to deliver the gene to brain and spinal cord while having restricted biodistribution to the liver. The novel capsid and cassette design combination was characterized in vivo in TSD mice for its ability to efficiently transduce cells in the central nervous system when delivered intravenously in both adult and neonatal mice. This study demonstrates that the modified HexM is capable of degrading long-standing GM2 storage in mice, and it further demonstrates the potential of this novel scAAV vector design to facilitate widespread distribution of the HEXM gene or potentially other similar-sized genes to the nervous system.

Direct Intracranial Injection of AAVrh8 Encoding Monkey β-N-Acetylhexosaminidase Causes Neurotoxicity in the Primate Brain

GM2 gangliosidoses, including Tay-Sachs disease and Sandhoff disease, are lysosomal storage disorders caused by deficiencies in β-N-acetylhexosaminidase (Hex). Patients are afflicted primarily with progressive central nervous system (CNS) dysfunction. Studies in mice, cats, and sheep have indicated safety and widespread distribution of Hex in the CNS after intracranial vector infusion of AAVrh8 vectors encoding species-specific Hex α- or β-subunits at a 1:1 ratio. Here, a safety study was conducted in cynomolgus macaques (cm), modeling previous animal studies, with bilateral infusion in the thalamus as well as in left lateral ventricle of AAVrh8 vectors encoding cm Hex α- and β-subunits. Three doses (3.2 × 10¹² vg [n = 3]; 3.2 × 10¹¹ vg [n = 2]; or 1.1 × 10¹¹ vg [n = 2]) were tested, with controls infused with vehicle (n = 1) or transgene empty AAVrh8 vector at the highest dose (n = 2). Most monkeys receiving AAVrh8-cmHexα/β developed dyskinesias, ataxia, and loss of dexterity, with higher dose animals eventually becoming apathetic. Time to onset of symptoms was dose dependent, with the highest-dose cohort producing symptoms within a month of infusion. One monkey in the lowest-dose cohort was behaviorally asymptomatic but had magnetic resonance imaging abnormalities in the thalami. Histopathology was similar in all monkeys injected with AAVrh8-cmHexα/β, showing severe white and gray matter necrosis along the injection track, reactive vasculature, and the presence of neurons with granular eosinophilic material. Lesions were minimal to absent in both control cohorts. Despite cellular loss, a dramatic increase in Hex activity was measured in the thalamus, and none of the animals presented with antibody titers against Hex. The high overexpression of Hex protein is likely to blame for this negative outcome, and this study demonstrates the variations in safety profiles of AAVrh8-Hexα/β intracranial injection among different species, despite encoding for self-proteins.

Contemporary Animal Models For Human Gene Therapy Applications

Over the past three decades, gene therapy has been making considerable progress as an alternative strategy in the treatment of many diseases. Since 2009, several studies have been reported in humans on the successful treatment of various diseases. Animal models mimicking human disease conditions are very essential at the preclinical stage before embarking on a clinical trial. In gene therapy, for instance, they are useful in the assessment of variables related to the use of viral vectors such as safety, efficacy, dosage and localization of transgene expression. However, choosing a suitable disease-specific model is of paramount importance for successful clinical translation. This review focuses on the animal models that are most commonly used in gene therapy studies, such as murine, canine, non-human primates, rabbits, porcine, and a more recently developed humanized mice. Though small and large animals both have their own pros and cons as disease-specific models, the choice is made largely based on the type and length of study performed. While small animals with a shorter life span could be well-suited for degenerative/aging studies, large animals with longer life span could suit longitudinal studies and also help with dosage adjustments to maximize therapeutic benefit. Recently, humanized mice or mouse-human chimaeras have gained interest in the study of human tissues or cells, thereby providing a more reliable understanding of therapeutic interventions. Thus, animal models are of great importance with regard to testing new vector technologies in vivo for assessing safety and efficacy prior to a gene therapy clinical trial.

Construction of a hybrid β-hexosaminidase subunit capable of forming stable homodimers that hydrolyze GM2 ganglioside in vivo

Tay-Sachs or Sandhoff disease result from mutations in either the evolutionarily related HEXA or HEXB genes encoding respectively, the α- or β-subunits of β-hexosaminidase A (HexA). Of the three Hex isozymes, only HexA can interact with its cofactor, the GM2 activator protein (GM2AP), and hydrolyze GM2 ganglioside. A major impediment to establishing gene or enzyme replacement therapy based on HexA is the need to synthesize both subunits. Thus, we combined the critical features of both α- and β-subunits into a single hybrid µ-subunit that contains the α-subunit active site, the stable β-subunit interface and unique areas in each subunit needed to interact with GM2AP. To facilitate intracellular analysis and the purification of the µ-homodimer (HexM), CRISPR-based genome editing was used to disrupt the HEXA and HEXB genes in a Human Embryonic Kidney 293 cell line stably expressing the µ-subunit. In association with GM2AP, HexM was shown to hydrolyze a fluorescent GM2 ganglioside derivative both in cellulo and in vitro. Gene transfer studies in both Tay-Sachs and Sandhoff mouse models demonstrated that HexM expression reduced brain GM2 ganglioside levels.

Viral pre-challenge increases central nervous system inflammation after intracranial interleukin-1β injection

Introduction

Systemic inflammation has been shown to significantly worsen the outcome of neurological disease. However, after acute injuries to the brain both pre- and post-conditioning with bacterial endotoxin has been shown to reduce leukocyte recruitment to the CNS. Here, we sought to determine whether viral pre-challenge would have an effect on the outcome of acute CNS inflammation that was distinct from endotoxin.

Methods

Animals received a single intracranial microinjection of IL-1β in the presence or absence of a viral pre-challenge 24 hours prior to surgery. Liver and brain tissue were analysed for chemokine expression by qRT-PCR and leukocyte and monocyte infiltration 12 hours, 3 days and 7 days after the IL-1β injection.

Results

Here, a single injection of adenovirus prior to IL-1β injection resulted in adhesion molecule expression, chemokine expression and the recruitment of neutrophils to the injured CNS in significantly higher numbers than in IL-1β injected animals. The distribution and persistence of leukocytes within the CNS was also greater after pre-challenge, with neutrophils being found in both the ipsilateral and contralateral hemispheres. Thus, despite the absence of virus within the CNS, the presence of virus within the periphery was sufficient to exacerbate CNS disease.

Conclusions

These data suggest that the effect of a peripheral inflammatory challenge on the outcome of CNS injury or disease is not generic and will be highly dependent on the nature of the pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0178-3) contains supplementary material, which is available to authorized users.

Therapeutic response in feline sandhoff disease despite immunity to intracranial gene therapy

Salutary responses to adeno-associated viral (AAV) gene therapy have been reported in the mouse model of Sandhoff disease (SD), a neurodegenerative lysosomal storage disease caused by deficiency of β-N-acetylhexosaminidase (Hex). While untreated mice reach the humane endpoint by 4.1 months of age, mice treated by a single intracranial injection of vectors expressing human hexosaminidase may live a normal life span of 2 years. When treated with the same therapeutic vectors used in mice, two cats with SD lived to 7.0 and 8.2 months of age, compared with an untreated life span of 4.5 ± 0.5 months (n = 11). Because a pronounced humoral immune response to both the AAV1 vectors and human hexosaminidase was documented, feline cDNAs for the hexosaminidase α- and β-subunits were cloned into AAVrh8 vectors. Cats treated with vectors expressing feline hexosaminidase produced enzymatic activity >75-fold normal at the brain injection site with little evidence of an immune infiltrate. Affected cats treated with feline-specific vectors by bilateral injection of the thalamus lived to 10.4 ± 3.7 months of age (n = 3), or 2.3 times as long as untreated cats. These studies support the therapeutic potential of AAV vectors for SD and underscore the importance of species-specific cDNAs for translational research.

In cellulo examination of a beta-alpha hybrid construct of beta-hexosaminidase A subunits, reported to interact with the GM2 activator protein and hydrolyze GM2 ganglioside

The hydrolysis in lysosomes of GM2 ganglioside to GM3 ganglioside requires the correct synthesis, intracellular assembly and transport of three separate gene products; i.e., the alpha and beta subunits of heterodimeric beta-hexosaminidase A, E.C. # 3.2.1.52 (encoded by the HEXA and HEXB genes, respectively), and the GM2-activator protein (GM2AP, encoded by the GM2A gene). Mutations in any one of these genes can result in one of three neurodegenerative diseases collectively known as GM2 gangliosidosis (HEXA, Tay-Sachs disease, MIM # 272800; HEXB, Sandhoff disease, MIM # 268800; and GM2A, AB-variant form, MIM # 272750). Elements of both of the hexosaminidase A subunits are needed to productively interact with the GM2 ganglioside-GM2AP complex in the lysosome. Some of these elements have been predicted from the crystal structures of hexosaminidase and the activator. Recently a hybrid of the two subunits has been constructed and reported to be capable of forming homodimers that can perform this reaction in vivo, which could greatly simplify vector-mediated gene transfer approaches for Tay-Sachs or Sandhoff diseases. A cDNA encoding a hybrid hexosaminidase subunit capable of dimerizing and hydrolyzing GM2 ganglioside could be incorporated into a single vector, whereas packaging both subunits of hexosaminidase A into vectors, such as adeno-associated virus, would be impractical due to size constraints. In this report we examine the previously published hybrid construct (H1) and a new more extensive hybrid (H2), with our documented in cellulo (live cell- based) assay utilizing a fluorescent GM2 ganglioside derivative. Unfortunately when Tay-Sachs cells were transfected with either the H1 or H2 hybrid construct and then were fed the GM2 derivative, no significant increase in its turnover was detected. In vitro assays with the isolated H1 or H2 homodimers confirmed that neither was capable of human GM2AP-dependent hydrolysis of GM2 ganglioside.

Gene transfer corrects acute GM2 gangliosidosis--potential therapeutic contribution of perivascular enzyme flow

The GM2 gangliosidoses are fatal lysosomal storage diseases principally affecting the brain. Absence of β-hexosaminidase A and B activities in the Sandhoff mouse causes neurological dysfunction and recapitulates the acute Tay-Sachs (TSD) and Sandhoff diseases (SD) in infants. Intracranial coinjection of recombinant adeno-associated viral vectors (rAAV), serotype 2/1, expressing human β-hexosaminidase α (HEXA) and β (HEXB) subunits into 1-month-old Sandhoff mice gave unprecedented survival to 2 years and prevented disease throughout the brain and spinal cord. Classical manifestations of disease, including spasticity-as opposed to tremor-ataxia-were resolved by localized gene transfer to the striatum or cerebellum, respectively. Abundant biosynthesis of β-hexosaminidase isozymes and their global distribution via axonal, perivascular, and cerebrospinal fluid (CSF) spaces, as well as diffusion, account for the sustained phenotypic rescue-long-term protein expression by transduced brain parenchyma, choroid plexus epithelium, and dorsal root ganglia neurons supplies the corrective enzyme. Prolonged survival permitted expression of cryptic disease in organs not accessed by intracranial vector delivery. We contend that infusion of rAAV into CSF space and intraparenchymal administration by convection-enhanced delivery at a few strategic sites will optimally treat neurodegeneration in many diseases affecting the nervous system.

Efficient adenovirus-mediated gene transfer to gastric tissue by oral administration

BACKGROUND

Recombinant adenoviruses (rAd) are well-characterized viral vectors and have been studied in many human diseases. However, there are no detailed methods for transferring genes to the stomach using rAd.

METHODS

Gastric epithelial cells were infected with rAd encoding green fluorescence protein (AdGFP) for different times, or with AdGFP that had been incubated in artificial gastric juice at different pH values for 1 h. Gene expression was detected by fluorescence microscope and flow cytometry. Mice were infected via oral administration with rAd encoding red fluorescence protein and beta-galactosidase (AdRFP-lacZ) or rAd encoding mouse interleukin-17 (AdmIL-17), and tissues were collected at the indicated times after infection. LacZ expression in different tissues was detected by X-gal staining and IL-17 expression in the stomach was assessed by the real-time polymerase chain reaction and an enzyme-linked immunosorbent assay. Inflammation in the stomach was also assessed.

RESULTS

rAd could infect the gastric epithelial cells and tolerate pH 5 for 1 h in vitro. Adenovirus-mediated genes were specifically expressed in the gastrointestinal tract and transgene expression persisted in gastric tissue for up to 7 days after oral administration of AdRFP-lacZ. Oral administration of AdmIL-17 induced mIL-17 expression in gastric tissue at the mRNA and protein levels and protein level peaked on day 5 post-infection. IL-6, a target protein of IL-17, and gastric inflammation also increased in AdmIL-17-infected mice.

CONCLUSIONS

The present study has established a detailed method for transferring adenovirus-mediated gene to the stomach, which may provide a valuable approach for gene therapy or the study of the basic biology of gastric diseases.

Beyond the data deluge: Data integration and bio-ontologies

Biomedical research is increasingly a data-driven science. New technologies support the generation of genome-scale data sets of sequences, sequence variants, transcripts, and proteins; genetic elements underpinning understanding of biomedicine and disease. Information systems designed to manage these data, and the functional insights (biological knowledge) that come from the analysis of these data, are critical to mining large, heterogeneous data sets for new biologically relevant patterns, to generating hypotheses for experimental validation, and ultimately, to building models of how biological systems work. Bio-ontologies have an essential role in supporting two key approaches to effective interpretation of genome-scale data sets: data integration and comparative genomics. To date, bio-ontologies such as the Gene Ontology have been used primarily in community genome databases as structured controlled terminologies and as data aggregators. In this paper we use the Gene Ontology (GO) and the Mouse Genome Informatics (MGI) database as use cases to illustrate the impact of bio-ontologies on data integration and for comparative genomics. Despite the profound impact ontologies are having on the digital categorization of biological knowledge, new biomedical research and the expanding and changing nature of biological information have limited the development of bio-ontologies to support dynamic reasoning for knowledge discovery.

Inefficiency in GM2 Ganglioside Elimination by Human Lysosomal .BETA.-Hexosaminidase .BETA.-Subunit Gene Transfer to Fibroblastic Cell Line Derived from Sandhoff Disease Model Mice

Sandhoff disease (SD) is an autosomal recessive GM2 gangliosidosis caused by the defect of lysosomal beta-hexosaminidase (Hex) beta-subunit gene associated with neurosomatic manifestations. Therapeutic effects of Hex subunit gene transduction have been examined on Sandhoff disease model mice (SD mice) produced by the allelic disruption of Hexb gene encoding the murine beta-subunit. We demonstrate here that elimination of GM2 ganglioside (GM2) accumulated in the fibroblastic cell line derived from SD mice (FSD) did not occur when the HEXB gene only was transfected. In contrast, a significant increase in the HexB (betabeta homodimer) activity toward neutral substrates, including GA2 (asialo-GM2) and oligosaccharides carrying the terminal N-acetylglucosamine residues at their non-reducing ends (GlcNAc-oligosaccharides) was observed. Immunoblotting with anti-human HexA (alphabeta heterodimer) serum after native polyacrylamide gel electrophoresis (Native-PAGE) revealed that the human HEXB gene product could hardly form the chimeric HexA through associating with the murine alpha-subunit. However, co-introduction of the HEXA encoding the human alpha-subunit and HEXB genes caused significant corrective effect on the GM2 degradation by producing the human HexA. These results indicate that the recombinant human HexA could interspeciesly associate with the murine GM2 activator protein to degrade GM2 accumulated in the FSD cells. Thus, therapeutic effects of the recombinant human HexA isozyme but not human HEXB gene product could be evaluated by using the SD mice.

Mutation of the GM2 activator protein in a feline model of GM2 gangliosidosis

The G(M2) activator protein is required for successful degradation of G(M2) ganglioside by the A isozyme of lysosomal beta-N-acetylhexosaminidase (EC 3.2.1.52). Deficiency of the G(M2) activator protein leads to a relentlessly progressive accumulation of G(M2) ganglioside in neuronal lysosomes and subsequent fatal deterioration of central nervous system function. G(M2) activator deficiency has been described in humans, dogs and mice. This manuscript reports the discovery and characterization of a feline model of G(M2) activator deficiency that exhibits many disease traits typical of the disorder in other species. Cats deficient in the G(M2) activator protein develop clinical signs at approximately 14 months of age, including motor incoordination and exaggerated startle response to sharp sounds. Affected cats exhibit central nervous system abnormalities such as swollen neurons, membranous cytoplasmic bodies, increased sialic acid content and elevated levels of G(M2) ganglioside. As is typical of G(M2) activator deficiency, hexosaminidase A activity in tissue homogenates appears normal when assayed with a commonly used synthetic substrate. When the G(M2) activator cDNA was sequenced from normal and affected cats, a deletion of 4 base pairs was identified as the causative mutation, resulting in alteration of 21 amino acids at the C terminus of the G(M2) activator protein.

Storage solutions: treating lysosomal disorders of the brain

Many neurodegenerative diseases are characterized by the accumulation of undegradable molecules in cells or at extracellular sites in the brain. One such family of diseases is the lysosomal storage disorders, which result from defects in various aspects of lysosomal function. Until recently, there was little prospect of treating storage diseases involving the CNS. However, recent progress has been made in understanding these conditions and in translating the findings into experimental therapies. We review the developments in this field and discuss the similarities in pathological features between these diseases and some more common neurodegenerative disorders.

A direct gene transfer strategy via brain internal capsule reverses the biochemical defect in Tay-Sachs disease

Therapy for neurodegenerative lysosomal Tay-Sachs (TS) disease requires active hexosaminidase (Hex) A production in the central nervous system and an efficient therapeutic approach that can act faster than human disease progression. We combined the efficacy of a non-replicating Herpes simplex vector encoding for the Hex A alpha-subunit (HSV-T0alphaHex) and the anatomic structure of the brain internal capsule to distribute the missing enzyme optimally. With this gene transfer strategy, for the first time, we re-established the Hex A activity and totally removed the GM2 ganglioside storage in both injected and controlateral hemispheres, in the cerebellum and spinal cord of TS animal model in the span of one month's treatment. In our studies, no adverse effects were observed due to the viral vector, injection site or gene expression and on the basis of these results, we feel confident that the same approach could be applied to similar diseases involving an enzyme defect.

Bicistronic lentiviral vector corrects beta-hexosaminidase deficiency in transduced and cross-corrected human Sandhoff fibroblasts

Sandhoff disease is an autosomal recessive neurodegenerative disease characterized by a GM2 ganglioside intralysosomal accumulation. It is due to mutations in the beta-hexosaminidases beta-chain gene, resulting in a beta-hexosaminidases A (alphabeta) and B (betabeta) deficiency. Mono and bicistronic lentiviral vectors containing the HEXA or/and HEXB cDNAs were constructed and tested on human Sandhoff fibroblasts. The bicistronic SIV.ASB vector enabled a massive restoration of beta-hexosaminidases activity on synthetic substrates and a 20% correction on the GM2 natural substrate. Metabolic labeling experiments showed a large reduction of ganglioside accumulation in SIV.ASB transduced cells, demonstrating a correct recombinant enzyme targeting to the lysosomes. Moreover, enzymes secreted by transduced Sandhoff fibroblasts were endocytosed in deficient cells via the mannose 6-phosphate pathway, allowing GM2 metabolism restoration in cross-corrected cells. Therefore, our bicistronic lentivector supplying both alpha- and beta-subunits of beta-hexosaminidases may provide a potential therapeutic tool for the treatment of Sandhoff disease.

β-hexosaminidase lentiviral vectors: transfer into the CNS via systemic administration

Brain inflammation in GM2 gangliosidosis has been recently realized as a key factor in disease development. The aim of this study was to investigate the effects of a FIV beta-hexosaminidase vector in the brain of HexB-deficient (Sandhoff disease) mice following intraperitoneal administration to pups of neonatal age. Since brain inflammation, lysosomal storage and neuromuscular dysfunction are characteristics of HexB deficiency, these parameters were employed as experimental outcomes in our study. The ability of the lentiviral vector FIV(HEX) to infect murine cells was initially demonstrated with success in normal mouse fibroblasts and human Tay-Sachs cells in vitro. Furthermore, systemic transfer of FIV(HEX) to P2 HexB-/- knockout pups lead to transduction of peripheral and central nervous system tissues. Specifically, beta-hexosaminidase expressing cells were immunolocalized in periventricular areas of the cerebrum as well as in the cerebellar cortex. FIV(HEX) neonatal treatment resulted in reduction of GM2 storage along with attenuation of the brain inflammation and amelioration of the attendant neuromuscular deterioration. In conclusion, these results demonstrate the effective transfer of a beta-hexosaminidase lentiviral vector to the brain of Sandhoff mice and resolution of the GM2 gangliosidosis after neonatal intraperitoneal administration.

Late onset Tay–Sachs disease in mice with targeted disruption of the Hexa gene: behavioral changes and pathology of the central nervous system

Tay-Sachs disease is an autosomal recessive neurodegenerative disease resulting from a block in the hydrolysis of GM2 ganglioside, an intermediate in ganglioside catabolism. The mouse model of Tay-Sachs disease (Hexa -/-) has been described as behaviorally indistinguishable from wild type until at least 1 year of age due to a sialidase-mediated bypass of the metabolic defect that reduces the rate of GM2 ganglioside accumulation. In this study, we have followed our mouse model to over 2 years of age and have documented a significant disease phenotype that is reminiscent of the late onset, chronic form of human Tay-Sachs disease. Onset occurs at 11-12 months of age and progresses slowly, in parallel with increasing storage of GM2 ganglioside. The disease is characterized by hind limb spasticity, weight loss, tremors, abnormal posture with lordosis, possible visual impairment, and, late in the disease, muscle weakness, clasping of the limbs, and myoclonic twitches of the head. Immunodetection of GM2 ganglioside showed that storage varies widely in different regions, but is most intense in pyriform cortex, hippocampus (CA3 field, subiculum), amygdala, hypothalamus (paraventricular supraoptic, ventromedial and arcuate nuclei, and mammilary body), and the somatosensory cortex (layer V) in 1- to 2-year-old mutant mice. We suggest that the Tay-Sachs mouse model is a phenotypically valid model of disease and may provide for a reliable indicator of the impact of therapeutic strategies, in particular geared to the late onset, chronic form of human Tay-Sachs disease.

Systemic FIV vector administration: transduction of CNS immune cells and Purkinje neurons

The systemic effects of gene therapy have been previously described in a variety of peripheral organs following intravenous administration or intraperitoneal inoculation of viral vectors, as well as in the brain following intracranial administration. However, limited information is available on the ability of viral vectors to cross the blood-brain barrier and infect cells located within the central nervous system (CNS). We employed a VSV-G pseudotyped FIV(lacZ) vector capable of transducing dividing, growth-arrested, as well as post-mitotic cells with the reporter gene lacZ. Adult mice were injected intraperitoneally with FIV(lacZ), and the expression of beta-galactosidase was studied 5 weeks following treatment in the brain, liver, spleen and kidney by X-gal histochemistry and immunocytochemistry. Interestingly, relatively low doses of FIV(lacZ) administered intraperitoneally lead to beta-galactosidase detection in the brain and cerebellum. The identity of these cells was confirmed by double immunofluorescence, and included CD31-, CD3- and CD11b-positive cells. Fluorescent microspheres co-injected with FIV(lacZ) virus were identified within mononuclear cells in the brain parenchyma, suggesting infiltration of peripheral immune cells in the CNS. Cerebellar Purkinje neurons were also transduced in all adult-injected mice. Our observations indicate that relatively low doses of FIV(lacZ) administered intraperitoneally resulted in the transduction of immune cells in the brain, as well as a specific subset of cerebellar neurons.

Widespread distribution of beta-hexosaminidase activity in the brain of a Sandhoff mouse model after coinjection of adenoviral vector and mannitol

Sandhoff disease is a severe inherited neurodegenerative disorder resulting from deficiency of the beta-subunit of hexosaminidases A and B, lysosomal hydrolases involved in the degradation of G(M2) ganglioside and related metabolites. Currently, there is no viable treatment for the disease. Here, we show that adenovirus-mediated transfer of the beta-subunit of beta-hexosaminidase restored Hex A and Hex B activity after infection of Sandhoff fibroblasts. Gene transfer following intracerebral injection in a murine model of Sandhoff disease resulted in near-normal level of enzymatic activity in the entire brain at the different doses tested. The addition of hyperosmotic concentrations of mannitol to the adenoviral vector resulted in an enhancement of vector diffusion in the injected hemisphere. Adenoviral-induced lesions were found in brains injected with a high dose of the vector, but were not detected in brains injected with 100-fold lower doses, even in the presence of mannitol. Our data underline the advantage of the adjunction of mannitol to low doses of the adenoviral vector, allowing a high and diffuse transduction efficiency without viral cytotoxicity.

A highly efficient, stable, and rapid approach for ex vivo human liver gene therapy via a FLAP lentiviral vector

Allogenic hepatocyte transplantation or autologous transplantation of genetically modified hepatocytes has been used successfully to correct congenital or acquired liver diseases and can be considered as an alternative to orthotopic liver transplantation. However, hepatocytes are neither easily maintained in culture nor efficiently genetically modified and are very sensitive to dissociation before their reimplantation into the recipient. These difficulties have greatly limited the use of an ex vivo approach in clinical trials. In the present study, we have shown that primary human and rat hepatocytes can be efficiently transduced with a FLAP lentiviral vector without the need for plating and culture. Efficient transduction of nonadherent primary hepatocytes was achieved with a short period of contact with vector particles, without modifying hepatocyte viability, and using reduced amounts of vector. We also showed that the presence of the DNA FLAP in the vector construct was essential to reach high levels of transduction. Moreover, transplanted into uPA/SCID mouse liver, lentivirally transduced primary human hepatocytes extensively repopulated their liver and maintained a differentiated and functional phenotype as assessed by the stable detection of human albumin and antitrypsin in the serum of the animals for months. In conclusion, the use of FLAP lentiviral vectors allows, in a short period of time, a high transduction efficiency of human functional and reimplantable hepatocytes. This work therefore opens new perspectives for the development of human clinical trials based on liver-directed ex vivo gene therapy.

Gene therapy: prospects for glycolipid storage diseases

Lysosomal storage diseases comprise a group of about 40 disorders, which in most cases are due to the deficiency of a lysosomal enzyme. Since lysosomal enzymes are involved in the degradation of various compounds, the diseases can be further subdivided according to which pathway is affected. Thus, enzyme deficiencies in the degradation pathway of glycosaminoglycans cause mucopolysaccharidosis, and deficiencies affecting glycopeptides cause glycoproteinosis. In glycolipid storage diseases enzymes are deficient that are involved in the degradation of sphingolipids. Mouse models are available for most of these diseases, and some of these mouse models have been used to study the applicability of in vivo gene therapy. We review the rationale for gene therapy in lysosomal disorders and present data, in particular, about trials in an animal model of metachromatic leukodystrophy. The data of these trials are compared with those obtained with animal models of other lysosomal diseases.

Plasmid-based gene transfer ameliorates visceral storage in a mouse model of Sandhoff disease

Sandhoff disease is a severe neurodegenerative disorder with visceral involvement caused by mutations in the HEXB gene coding for the beta subunit of the lysosomal hexosaminidases A and B. HEXB mutations result in the accumulation of undegraded substrates such as GM2 and GA2 in lysosomes. We evaluated the efficacy of cationic liposome-mediated plasmid gene therapy using the Sandhoff disease mouse, an animal model of a human lysosomal storage disease. The mice received a single intravenous injection of two plasmids, encoding the human alpha and beta subunits of hexosaminidase cDNAs. As a result, 10-35% of normal levels of hexosaminidase expression, theoretically therapeutic levels, were achieved in most visceral organs, but not in the brain, 3 days after injection with decreased levels by day 7. Histochemical staining confirmed widespread enzyme activity in visceral organs. Both GA2 and GM2 were reduced by almost 10% and 50%, respectively, on day 3, and by 60% and 70% on day 7 compared with untreated age-matched Sandhoff disease mice. Consistent with the biochemical results, a reduction in GM2 was observed in liver cells histologically as well. These initial findings support further development of the plasmid gene therapy against lysosomal diseases with visceral pathology.

Serum hexosaminidase and beta-glucuronidase activities in infants: effects of age and sex

We investigated the effect of age and sex on the serum activity of hexosaminidase (HEX) and -glucuronidase (BGLU) in 275 normal term infants aged 12 h to 12 months. Up to six weeks of life, HEX was significantly higher in boys (P<=0.023). During the age period of 1-26 weeks, BGLU was also higher in boys, but differences were significant only at 2-6 and 7-15 weeks (P<=0.016). The developmental pattern of HEX and BGLU was sex dependent. HEX activity increased in both sexes from 4-7 days of life, reaching a maximum of 1.4-fold the birth value at 2-6 weeks of age in boys (P<0.001) and a maximum of 1.6-fold at 7-15 weeks in girls (P<0.001). HEX activity gradually decreased thereafter, reaching significantly lower levels at 27-53 weeks than during the first three days of life in boys (P = 0.002) and the same level of this age interval in girls. BGLU increased in both sexes from 4-7 days of age, showing a maximum increase at 7-15 weeks (3.3-fold in boys and 2.9-fold in girls, both P<0.001). Then BGLU decreased in boys to a value similar to that observed at 4-7 days of age. In girls, BGLU remained elevated until the end of the first year of life. These results indicate a variation of HEX and BGLU activities during the first year of life and a sex influence on their developmental pattern. This observation should be considered in the diagnosis of GM2 gangliosidosis and mucopolysaccharidosis type VII.

Restoration of the GM2 ganglioside metabolism in bone marrow-derived stromal cells from Tay-Sachs disease animal model

The therapeutic potential of bone marrow-derived stromal cells for the therapy of Tay-Sachs disease is primarily related to the restoration of their own GM2 ganglioside storage. With this aim, we produced bone marrow-derived stromal cells from the adult Tay-Sachs animal model and transduced them with a retroviral vector encoding for the alpha-subunit of the lysosomal enzyme beta-hexosaminidase A (E.C. 3.2.1.52). Our results demonstrate that transduced Tay-Sachs bone marrow-derived stromal cells have beta-hexosaminidase A comparable to that of bone marrow-derived stromal cells from wild-type mice. Moreover, beta-hexosaminidase A in transduced Tay-Sachs bone marrow-derived stromal cells was able to hydrolyze the GM2 ganglioside in a feeding experiment, thus demonstrating the correction of the altered phenotype.

Absence of metabolic cross-correction in Tay-Sachs cells: implications for gene therapy

We have investigated the ability of a receptor-mediated gene transfer strategy (cross-correction) to restore ganglioside metabolism in fibroblasts from Tay-Sachs (TS) patients in vitro. TS disease is a GM2 gangliosidosis attributed to the deficiency of the lysosomal enzyme beta-hexosaminidase A (HexA) (beta-N-acetylhexosaminidase, EC ). The hypothesis is that transduced cells overexpressing and secreting large amounts of the enzyme would lead to a measurable activity in defective cells via a secretion-recapture mechanism. We transduced NIH3T3 murine fibroblasts with the LalphaHexTN retroviral vector carrying the cDNA encoding for the human Hex alpha-subunit. The Hex activity in the medium from transduced cells was approximately 10-fold higher (up to 75 milliunits) than observed in non-transduced cells. TS cells were cultured for 72 h in the presence of the cell medium derived from the transduced NIH3T3 cells, and they were analyzed for the presence and catalytic activity of the enzyme. Although TS cells were able to efficiently uptake a large amount of the soluble enzyme, the enzyme failed to reach the lysosomes in a sufficient quantity to hydrolyze the GM2 ganglioside to GM3 ganglioside. Thus, our results showed that delivery of the therapeutic HexA was not sufficient to correct the phenotype of TS cells.

Interferon-alpha2b secretion by adenovirus-mediated gene delivery in rat, rabbit, and chimpanzee results in similar pharmacokinetic profiles

Gene delivery, with subsequent protein synthesis and secretion, in vivo has been proposed as an alternative way to deliver a therapeutic protein to the systemic circulation. Interferon-alpha (IFN) protein is effective in the treatment of viral and malignant diseases but has short serum half-life that requires frequent administration. An E1 region-deleted adenovirus vector encoding human IFN-alpha2b gene driven by the cytomegalovirus immediate early promoter (rAd-IFN) was generated to assess the serum concentration-time profiles of expressed IFN protein in animal models. Intravenous administration of rAd-IFN, normalized for body weight, resulted in dose-dependent serum IFN concentrations that persisted 8-40 days with similar concentration-time profiles in rats and rabbits. We sought to determine if serum concentration-time profiles in the rat and rabbit animal models would be predictive for a larger animal and would therefore be relevant models for potential dosing of human patients. Two chimpanzees (approximately 70 kg) dosed with rAd-IFN by intravenous administration normalized to body weight achieved serum IFN concentration-time profiles similar to those observed in rats and rabbits. The role of the immune response in limiting the persistence of transgene expression was highlighted by the persistence of serum IFN concentrations for over 200 days in beige/SCID immunodeficient mice. These studies suggest that serum concentration of secreted transgene products after gene delivery in small animal models may be highly predictive for larger species and will help define dosing strategies in human patients.

Learning cell biology as a team: a project-based approach to upper-division cell biology

To help students develop successful strategies for learning how to learn and communicate complex information in cell biology, we developed a quarter-long cell biology class based on team projects. Each team researches a particular human disease and presents information about the cellular structure or process affected by the disease, the cellular and molecular biology of the disease, and recent research focused on understanding the cellular mechanisms of the disease process. To support effective teamwork and to help students develop collaboration skills useful for their future careers, we provide training in working in small groups. A final poster presentation, held in a public forum, summarizes what students have learned throughout the quarter. Although student satisfaction with the course is similar to that of standard lecture-based classes, a project-based class offers unique benefits to both the student and the instructor.

Retrovirus-mediated transfer and expression of beta-hexosaminidase alpha-chain cDNA in human fibroblasts from G(M2)-gangliosidosis B1 variant

Mutations in the alpha-chain of lysosomal hexosaminidase (EC 3.2.1.52) underlie two distinct biochemical phenotypes known as variant B and variant B1 of G(M2) gangliosidosis. This paper shows that the transduction of human B1-type fibroblasts (producing catalytically inactive alpha-chains) with a retroviral vector encoding the human hexosaminidase alpha-chain leads to a complete correction of HexA (alpha beta dimer) activity with both synthetic and natural substrates. The alpha-subunit overexpression leads to a partial HexB (beta beta dimer) depletion corresponding to about 10% of control HexB activity. The newly synthesized enzyme is correctly processed and targeted to the lysosomes in transduced cells. The high levels of recombinant enzyme correctly produced the metabolic defect, enabling the cells efficiently to degrade the accumulated storage product present in lysosomes. The transduced fibroblasts are also able to secrete HexA efficiently into the culture medium. Moreover, transfer of the human transgene product to B1-type deficient fibroblasts lead to an increase of activity against 4MUGS, the alpha-chain specific synthetic substrate, up to 30% of the control mean activity level. This level of activity might be sufficient to restore the normal ganglioside G(M2) metabolism in recipient cells. The data obtained demonstrate that B1-type phenotype can be efficiently corrected by retrovirus-mediated gene transfer.

31Phosphorus magnetic resonance spectroscopy in late-onset Tay-Sachs disease

The late-onset form of GM2 gangliosidosis (Tay-Sachs disease) is an autosomal-recessive disorder with progressive neurologic disease, mainly characterized by motor neuron and spinocerebellar dysfunction. The majority of patients are of Ashkenazi Jewish origin. 31Phosphorus magnetic resonance spectroscopy of the brain was performed to study the metabolic changes of a 16-year-old patient with late-onset Tay-Sachs disease who had a heterozygous Gly269-->Ser mutation in the hexosaminidase A encoding gene in compound heterozygosity with another, yet unidentified mutation. Severe changes in phosphorus metabolism with a decreased amount of phosphodiesters and membrane-bound phosphates were demonstrated, suggesting an activation of phosphodiesterases by accumulating gangliosides. The clinical findings were well related to the changes in spectroscopically determined metabolites.

From gene transfer to gene therapy in lysosomal storage diseases affecting the central nervous system

Gene transfer into the central nervous system (CNS) is one of the foremost scientific challenges today. To give a brief survey of possible approaches to gene therapy in diseases affecting the CNS, we have selected the lysosomal storage diseases (LDS), which are an excellent model of both early-onset infantile neurological forms and late-onset adult psychiatric forms. Lysosomal storage diseases represent a group of about 50 monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. The clinical severity, including neuropsychiatric symptoms, and the absence of an efficient therapy for the majority of these disorders prompted the various trials of gene therapy now in progress. Most of the genes encoding the normal lysosomal enzymes have been cloned, and the size of the corresponding cDNAs is generally compatible with their transfer by recombinant vectors. New vectors with improved immunogenicity, transduction efficacy, insert capacity, and specificity of targeting are under development. Here we discuss several gene therapy strategies for the correction of LSD-induced anomalies in the CNS. Interesting results have been obtained by animal model brain, which raises hopes that large-scale clinical trials may soon be started.

Gene therapy in lysosomal diseases

Lysosomal storage diseases are monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. Various groups have been delineated according to the affected pathway and the accumulated substrate: mucopolysaccharidoses, lipidoses, glycoproteinoses and glycogenosis type II. Their clinical severity and the absence of efficient therapy for the majority of these disorders justify the development of gene transfer methods. Most of the genes encoding the normal lysosomal enzymes have been cloned and recently numerous animal models have been obtained for nearly all these diseases. Due to the clinical heterogeneity of lysosomal diseases, showing multivisceral involvement or affecting predominantly the reticuloendothelial system, muscle or central nervous system, various gene therapy strategies have to be developed. Vectors, ways of access, results and limits will be reviewed. Interesting results have already been obtained in the gene transfer for lysosomal diseases, but improvements are needed before a future application to humans.

Approach to gene therapy of glycogenosis type II (Pompe disease)

Pompe disease is a generalized lysosomal glycogenosis affecting essentially the skeletal muscles and the heart. It is due to the deficiency of acid alpha-glucosidase, also called acid maltase, involved in glycogen degradation by the cleavage of alpha-1,4 and alpha-1,6 glycosidic linkages. The severe infantile, milder juvenile, and late-onset or adult forms are associated under the generic name of glycogenoses type II. The clinical picture can differ according to these variants, forming a clinical spectrum from cardiorespiratory failure with early death in the infantile variant to late muscular weakness or respiratory problems in the adult variant. Enzymatic pre- and postnatal diagnoses and mutation characterization are available. Different therapeutic attempts have been conceived and some of them have come to clinical trials. Several pilot studies have demonstrated the feasibility of gene therapy and remarkable advances have been realized. Of particular interest, strategies for gene therapy in a generalized disease like Pompe disease must be accompanied by the secretion and uptake of the corrective enzyme by more distant cells or tissues in order to obtain efficient results. Preliminary positive results have been obtained in animal models, and new approaches with improvements in the access to muscle and heart, in the efficacy and innocuity of vectors, and in the clinical evolution are proposed. Gene therapy is a promising strategy for Pompe disease. However, several steps must be explored before this method becomes clinically successful.