In this study, recombinant AAV vectors pseudotyped with viral capsids derived from AAV serotypes 7 and 8 were evaluated for gene transfer in the murine striatum relative to vectors pseudotyped with AAV serotypes 2, 5, and 6. In comparison with rAAV serotype 2, pseudotyped vectors derived from AAV-7 and AAV-8 have increased transduction efficiency in the murine CNS, with the rank order rAAV-7 > rAAV-8 > rAAV-5 > rAAV-2 = rAAV-6, with all vectors demonstrating a marked tropism for neuronal transduction. Pseudotyped rAAV vector gene transfer in the brain after preimplantation of a murine 4C8 glioblastoma tumor was also evaluated. Efficiency of gene transfer to the orthotopic tumor was increased when using AAV-6, -7, and -8 capsid proteins in comparison with serotype 2, with the order rAAV-8 = rAAV-7 > rAAV-6 > rAAV-2 > rAAV-5. The increased gene transfer efficiency of rAAV vectors pseudotyped with the rAAV-8 capsid also provided enhanced therapeutic efficacy in a mouse model of glioblastoma multiforme, using vectors encoding an inhibitor of the vascular endothelial growth factor pathway. These studies demonstrate that rAAV vectors pseudotyped with capsids derived from AAV serotypes 7 and 8 provide enhanced gene transfer in the murine CNS and may offer increased therapeutic efficacy in the treatment of neurological disease.
"With the steady advances in vector development, we argue that the vector itself should also be considered a variable that can have major consequences on transduction success. For instance, AAV1 and AAV5 are more efficacious than AAV2 in transduction of the primate substantia nigra (SN) and caudate nucleus,31,32 and several other serotypes have shown far superior transduction efficiency than AAV2 in rodent models, with respect to both volume and density.33,34 Should this improved efficiency translate to the Parkinsonian brain, it might allow for reduction in viral dose to achieve the same or greater volume and density of therapeutic gene expression. "
[Show abstract][Hide abstract] ABSTRACT: Over the past decade, nine gene therapy clinical trials for Parkinson's disease (PD) have been initiated and completed. Starting with considerable optimism at the initiation of each trial, none of the programs has yet borne sufficiently robust clinical efficacy or found a clear path towards regulatory approval. Despite the immediately disappointing nature of the efficacy outcomes in these trials, the clinical data garnered from the individual studies nonetheless represent tangible and significant progress for the gene therapy field. Collectively, the clinical trials demonstrate that we have overcome the major safety hurdles previously suppressing CNS gene therapy, for none produced any evidence of untoward risk or harm after administration of various vector-delivery systems. More importantly, these studies also demonstrated controlled, highly persistent generation of biologically active proteins targeted to structures deep in the human brain. Therefore a renewed, focused emphasis must be placed on advancing clinical efficacy by improving clinical trial design, patient selection, and outcome measures, developing more predictive animal models to support clinical testing, carefully performing retrospective analyses, and most importantly moving forward - beyond our past limits.Molecular Therapy (2013); doi:10.1038/mt.2013.281.
"Therefore, use of an AAV serotype with a high tropism for the target tissue would be expected to produce efficiencies higher than reported here for AAV, in addition to providing a level of selectivity in terms of vector safety. " Cross packaging" strategies to generate pseudotyped AAV vectors, where AAV2 vector genome is packaged together with capsid proteins of a different serotype, have been shown to improve target specificity and efficiency (Harding et al. 2006; Nathwani et al. 2008). "
"While AAV vectors primarily transduce neurons making studies of glia difficult, the identification of multiple serotypes of AAV has expanded the tropism of AAV vectors. Neuronal transduction by serotypes 1, 2 and 5–9 (Kaplitt et al., 1994; Bartlett et al., 1998; Davidson et al., 2000; Burger et al., 2004; Paterna et al., 2004; Cearley and Wolfe, 2006; Harding et al., 2006; Taymans et al., 2007) and glial transduction by serotypes 2, 5, 7 and 8 (Kaplitt et al., 1994; Davidson et al., 2000; Harding et al., 2006) has been described. The efficiency and cell type specificity of transduction, however, appears to be specific to the brain area studied (Taymans et al., 2007). "
[Show abstract][Hide abstract] ABSTRACT: Chronic in vivo imaging studies of the brain require a labeling method that is fast, long-lasting, efficient, nontoxic, and cell-type specific. Over the last decade, adeno-associated virus (AAV) has been used to stably express fluorescent proteins in neurons in vivo. However, AAV's main limitation for many studies (such as those of neuronal development) is the necessity of second-strand DNA synthesis, which delays peak transgene expression. The development of double-stranded AAV (dsAAV) vectors has overcome this limitation, allowing rapid transgene expression. Here, we have injected different serotypes (1, 2, 6, 7, 8, and 9) of a dsAAV vector carrying the green fluorescent protein (GFP) gene into the developing and adult mouse visual cortex and characterized its expression. We observed labeling of both neurons and astrocytes with serotype-specific tropism. dsAAV-GFP labeling showed high levels of neuronal GFP expression as early as 2 days postinjection and as long as a month, surpassing conventional AAV's onset of expression and matching its longevity. Neurons labeled with dsAAV-GFP appeared structurally and electrophysiologically identical to nonlabeled neurons, suggesting that dsAAV-GFP is neither cytotoxic nor alters normal neuronal function. We also demonstrated that dsAAV-labeled cells can be imaged with subcellular resolution in vivo over multiple days. We conclude that dsAAV is an excellent vector for rapid labeling and long-term in vivo imaging studies of astrocytes and neurons on the single cell level within the developing and adult visual cortex.
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