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Shannon E. Boye, Sanford L. Boye, Issam McDoom, Wei Chieh Huang, Sukanya Karan, Igor V. Peshenko, Alexander M. Dizhoor, Wolfgang Baehr, Samuel G. Jacobson, William W. Hauswirth; Establishing A Course For AAV-mediated Gene Therapy For Leber Congenital Amaurosis-1 (LCA1). Invest. Ophthalmol. Vis. Sci. 2012;53(14):1934.
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Ongoing clinical trials for RPE65 Leber congenital amaurosis (LCA2) have established that AAV can be used to safely deliver therapeutic transgene to the retinal pigment epithelium thereby restoring useful vision to patients. However, most retinal degenerations are caused by mutations in genes expressed in photoreceptors, a cell type yet to be targeted in clinical trials. Mutations in retinal guanylate cyclase-1 (GUCY2D) are the leading cause of another form of severe pediatric retinal dystrophy, LCA1. GUCY2D encodes GC1, a protein expressed in the outer segments of rod and cone photoreceptors which is involved in the recovery phase of phototransduction. Cones and rods of LCA1 patients lack function and degenerate over time. The purpose of this study was to test whether GUCY2D gene replacement would restore retinal function and preserve photoreceptors in the GC1/GC2 double knock-out (GCdko) mouse which is currently the only model with phenotypic fidelity to LCA1 (both cones and rods lack function and degenerate).
AAV8(Y733F) vector containing the human rhodopsin kinase (hGRK1) promoter was used to deliver murine GC1 (mGC1) to the subretinal space of GCdko mice at multiple postnatal time points (P18-108). Contralateral eyes served as uninjected controls. Retinal structure and function were monitored for at least 1 year with optical coherence tomography (OCT) and electroretinography (ERG), respectively. Visual behavior was assessed with Morris Water Maze. At 1 year, mice were sacrificed and retinas evaluated with IHC. Relevant proteins and RNA transcripts were isolated via immunoblot and RT-PCR, respectively. Treated and untreated GCdko eyes and wild type controls were compared for relative GC1 activity and calcium sensitivity.
Retinal function was restored and retinal structure (both rods and cones) preserved in GCdko mice treated with AAV8(Y733F)-mGC1 over the long term (at least 1 year). Behavioral and immunohistochemical analyses are underway.
This is the first demonstration that AAV-mediated GC1 expression is therapeutic over the long term in a true phenotypic model of LCA1. Together with the knowledge that LCA1 patients exhibit preservation of retinal structure for decades, these results strongly support the development of an AAV-based clinical vector for the treatment of this disease.
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