Recombinant adeno-associated viral (AAV) vectors have become powerful gene delivery tools for the treatment of retinal degeneration in a variety of animal models that mimic corresponding human diseases. AAV vectors possess a number of features that render them ideally suited for retinal gene therapy, including a lack of pathogenicity, minimal immunogenicity, and the ability to transduce postmitotic cells in a stable and efficient manner. In the sheltered environment of the retina, AAV vectors are able to maintain high levels of transgene expression in the retinal pigmented epithelium (RPE), photoreceptors, or ganglion cells for long periods of time after a single treatment. Each cell type can be specifically targeted by choosing the appropriate combination of AAV serotype, promoter, and intraocular injection site. The focus of this review is on examples of AAV-mediated gene therapy in those animal models of inherited retinal degeneration caused by mutations directly affecting the interacting unit formed by photoreceptors and the RPE. In each case discussed, expression of the therapeutic gene resulted in significant recovery of retinal structure and/or visual function. Because of the key role of the vasculature in maintaining a healthy retina, a summary of AAV gene therapy applications in animal models of retinal neovascular diseases is also included.
"We confirmed that GFP is efficiently expressed following subretinal injection of AAV2/8/GFP in mice, and that the GFP expression was localized to photoreceptor cells and RPE cells. Some groups have reported that exogenous gene expression is limited to the bleb area following subretinal injection [38,39], while others reported that the area of expression extended over the entire retina [40,41]. We recently reported that the average relative area of GFP expression (the expression area/the whole area) following subretinal injection of AAV type 8 GFP was 18.0±18.9% in the neural retina and 29.3±25.8% in the RPE cells . "
[Show abstract][Hide abstract] ABSTRACT: To assess the feasibility of a gene therapeutic approach to treating choroidal neovascularization (CNV), we generated an adeno-associated virus type 8 vector (AAV2/8) encoding an siRNA targeting vascular endothelial growth factor (VEGF), and determined the AAV2/8 vector's ability to inhibit angiogenesis.
We initially transfected 3T3 cells expressing VEGF with the AAV2/8 plasmid vector psiRNA-VEGF using the H1 promoter and found that VEGF expression was significantly diminished in the transfectants. We next injected 1 μl (3 × 10(14) vg/ml) of AAV2/8 vector encoding siRNA targeting VEGF (AAV2/8/SmVEGF-2; n = 12) or control vector encoding green fluorescent protein (GFP) (AAV2/8/GFP; n = 14) into the subretinal space in C57BL/6 mice. One week later, CNV was induced by using a diode laser to make four separate choroidal burns around the optic nerve in each eye. After an additional 2 weeks, the eyes were removed for flat mount analysis of the CNV surface area.
Subretinal delivery of AAV2/8/SmVEGF-2 significantly diminished CNV at the laser lesions, compared to AAV8/GFP (1597.3±2077.2 versus 5039.5±4055.9 µm(2); p<0.05). Using an enzyme-linked immunosorbent assay, we found that VEGF levels were reduced by approximately half in the AAV2/8/SmVEGF-2 treated eyes.
These results suggest that siRNA-VEGF can be expressed across the retina and that long-term suppression of CNV is possible through the use of stable AAV2/8-mediated siRNA-VEGF expression. In vivo gene therapy may thus be a feasible approach to the clinical management of CNV in conditions such as age-related macular degeneration.
"To formally assess the ability of NPs to function as a relevant therapeutic option for monogenic ocular diseases, we here conducted side-by-side studies comparing reporter gene (GFP) expression from self-complementary AAV2 (the serotype currently being used in clinical trials , , ) and self-complementary AAV5 (highly efficient for ocular delivery , ) with that from CK30PEG NPs generated from the same ITR plasmids. We chose to test two different promoters, the ubiquitously expressed chicken β-actin (CBA) promoter and the photoreceptor-specific (rod and cone , , ) mouse opsin promoter (MOP) since both have been used successfully in a variety of gene therapy studies , , , , , , . "
[Show abstract][Hide abstract] ABSTRACT: Gene therapy is a critical tool for the treatment of monogenic retinal diseases. However, the limited vector capacity of the current benchmark delivery strategy, adeno-associated virus (AAV), makes development of larger capacity alternatives, such as compacted DNA nanoparticles (NPs), critical. Here we conduct a side-by-side comparison of self-complementary AAV and CK30PEG NPs using matched ITR plasmids. We report that although AAVs are more efficient per vector genome (vg) than NPs, NPs can drive gene expression on a comparable scale and longevity to AAV. We show that subretinally injected NPs do not leave the eye while some of the AAV-injected animals exhibited vector DNA and GFP expression in the visual pathways of the brain from PI-60 onward. As a result, these NPs have the potential to become a successful alternative for ocular gene therapy, especially for the multitude of genes too large for AAV vectors.
PLoS ONE 12/2012; 7(12):e52189. DOI:10.1371/journal.pone.0052189 · 3.23 Impact Factor
"This genetic heterogeneity is associated with differences in rate and the extent of the degeneration. Accounting for 30%–40% of all cases of retinitis pigmentosa, autosomal dominant retinitis pigmentosa (ADRP) is the most common mode of inheritance and is the consequence of mutations in 24 known genes (Table 1) . "
[Show abstract][Hide abstract] ABSTRACT: Gene therapy for dominantly inherited genetic disease is more difficult than gene-based therapy for recessive disorders, which can be treated with gene supplementation. Treatment of dominant disease may require gene supplementation partnered with suppression of the expression of the mutant gene either at the DNA level, by gene repair, or at the RNA level by RNA interference or transcriptional repression. In this review, we examine some of the gene delivery approaches used to treat animal models of autosomal dominant retinitis pigmentosa, focusing on those models associated with mutations in the gene for rhodopsin. We conclude that combinatorial approaches have the greatest promise for success.
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