Walter Flato Goodman Center for Comparative Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, and Division of Neurology, Stokes Research Institute, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA.
Neurogenetic disorders typically affect cells throughout the brain. Adeno-associated virus (AAV) vector-mediated transfer of a normal cDNA can correct the metabolic defects at the site of injection, but treatment of the entire brain requires widespread delivery of the normal gene and/or protein. Current methods require multiple injections for widespread distribution. However, some AAV vectors can be transported along neuronal pathways associated with the injected region. Thus, targeting widely dispersed systems in the CNS might be a pathway for gene dispersal from a limited number of sites. We tested this hypothesis in the ventral tegmental area (VTA), a region with numerous efferent and afferent projections. A single 1 mul injection resulted in transport of the vector genome to projection sites in distal parts of the brain. When compared with injections into the striatum, the VTA injection resulted in higher enzyme levels in more regions of the brain. The AAV-9 serotype vector was the most widely disseminated, but AAV-Rh.10 and AAV-1 were also transported after VTA injection. The effect on global lesions of a neurogenetic disease was tested in the mouse model of MPS VII (mucopolysaccharidosis VII), a lysosomal storage disorder. Widespread distribution of the vector genome after AAV-9 VTA injection resulted in even further distribution of the enzyme product, by secretion and uptake by surrounding cells, and complete correction of the storage lesions throughout the entire brain. This unprecedented level of correction from a single injection into the developed brain provides a potential strategy to correct a large volume of brain while minimizing the number of injections.
"On the other hand, N-terminal galactose binding AAV9 is one of the most efficient vectors for CNS gene transfer. AAV9 has been shown to perform extensive neuronal and glial transduction from different routes of injection in small and large animal models (Cearley and Wolfe, 2007; Foust et al., 2009; Bevan et al., 2011; Dayton et al., 2012; Ahmed et al., 2013; Benkhelifa-Ziyyat et al., 2013; Iwata et al., 2013; Yamashita et al., 2013). In addition to important features on the capsid surfaces, efficiency of AAV vector mediated gene transfer can be affected by several post-entry, trafficking and genome-related events within the CNS. "
[Show abstract][Hide abstract] ABSTRACT: Gene therapy is a promising approach for treating a spectrum of neurological and neurodegenerative disorders by delivering corrective genes to the central nervous system (CNS). In particular, adeno-associated viruses (AAVs) have emerged as promising tools for clinical gene transfer in a broad range of genetic disorders with neurological manifestations. In the current review, we have attempted to bridge our understanding of the biology of different AAV strains with their transduction profiles, cellular tropisms, and transport mechanisms within the CNS. Continued efforts to dissect AAV-host interactions within the brain are likely to aid in the development of improved vectors for CNS-directed gene transfer applications in the clinic.
"Another issue is the delivery of the therapeutic agent to the site of action. The delivery problem is compounded when the desired target is the entire brain and the therapeutic agent must cross the blood brain barrier or be delivered by intracranial injection [18,24,28]. Often, direct intracranial injection will only affect a small portion of the brain. "
[Show abstract][Hide abstract] ABSTRACT: Background
Angelman syndrome is a monogenic neurologic disorder that affects 1 in 15,000 children, and is characterized by ataxia, intellectual disability, speech impairment, sleep disorders, and seizures. The disorder is caused by loss of central nervous system expression of UBE3A, a gene encoding a ubiquitin ligase. Current treatments focus on the management of symptoms, as there have not been therapies to treat the underlying molecular cause of the disease. However, this outlook is evolving with advances in molecular therapies, including artificial transcription factors a class of engineered DNA-binding proteins that have the potential to target a specific site in the genome.
Here we review the recent progress and prospect of targeted gene expression therapies. Three main issues that must be addressed to advance toward human clinical trials are specificity, toxicity, and delivery.
Artificial transcription factors have the potential to address these concerns on a level that meets and in some cases exceeds current small molecule therapies. We examine the possibilities of such approaches in the context of Angelman syndrome, as a template for other single-gene, neurologic disorders.
"A proper combination of these factors improves therapeutic benefit while reducing unwanted complications. In this view, our group and others have shown that targeting highly interconnected brain regions facilitates vector and transgene dispersion from one or few injection sites, thus lowering vector load and reducing acute toxicity (12,19). "
[Show abstract][Hide abstract] ABSTRACT: Globoid Cell Leukodystrophy (GLD) is an inherited lysosomal storage disease caused by β-galactocerebrosidase (GALC) deficiency. Gene therapy (GT) should provide rapid, extensive and lifetime GALC supply in CNS tissues to prevent or halt irreversible neurologic progression. Here we used a lentiviral vector (LV) to transfer a functional GALC gene in the brain of Twitcher mice, a severe GLD model. A single injection of LV.GALC in the external capsule of Twitcher neonates resulted in robust transduction of neural cells with minimal and transient activation of inflammatory and immune response. Importantly, we documented a proficient transduction of proliferating and post-mitotic oligodendroglia, a relevant target cell type in GLD. GALC activity (30-50% of physiological levels) was restored in the whole CNS of treated mice as early as 8 days post-injection. The early and stable enzymatic supply ensured partial clearance of storage and reduction of psychosine levels, translating in amelioration of histopathology and enhanced lifespan. At 6 months post-injection in non-affected mice, LV genome persisted exclusively in the injected region, where transduced cells overexpressed GALC. Integration site analysis in transduced brain tissues showed no aberrant clonal expansion and preferential targeting of neural-specific genes. This study establishes neonatal LV-mediated intracerebral GT as a rapid, effective, and safe therapeutic intervention to correct CNS pathology in GLD and provides a strong rationale for its application in this and similar leukodystrophies, alone or in combination with therapies targeting the somatic pathology, with the final aim of providing an effective and timely treatment of these global disorders.
Human Molecular Genetics 01/2014; 23(12). DOI:10.1093/hmg/ddu034 · 6.39 Impact Factor
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