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B. S. Pawlyk, O. V. Bulgakov, X. Liu, X. Xu, M. Adamian, X. Sun, S. C. Khani, E. L. Berson, M. A. Sandberg, T. Li; Replacement Gene Therapy With a Human RPGRIP1 Sequence Slows Photoreceptor Degeneration in a Murine Model of Leber Congenital Amaurosis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4497.
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RPGR-interacting protein 1 (RPGRIP1) is localized in the photoreceptor connecting cilium where it anchors the RPGR (retinitis pigmentosa GTPase regulator) protein. A genetic defect in RPGRIP1 is a known cause of Leber Congenital Amaurosis (LCA), a severe, early-onset form of retinal degeneration that leads to blindness in children. We evaluated the efficacy of replacement gene therapy using a human RPGRIP1 sequence in a murine model of LCA carrying a targeted disruption of RPGRIP1.
Cohorts of RPGRIP1 knockout (RPGRIP1-/-) mice up to 5 months of age were studied. At postnatal day 14, mice were given a subretinal injection in one eye of AAV8 vector carrying human RPGRIP1 cDNA under the transcriptional control of a human rhodopsin kinase promoter. Fellow eyes received a GFP vector as control.
As early as 2 weeks post-injection human RPGRIP1 was expressed specifically in photoreceptors and was localized correctly in the connecting cilia; it also restored the normal localization of RPGR. By immunoblotting analysis human RPGRIP1 (apparent molecular weight - 170 kDa) was found in the treated but not control retinas and matched precisely the endogenous RPGRIP1 protein from human donor retinas. Electroretinogram and histologic examinations showed improved rod and cone photoreceptor function and survival in the treated eyes. Overall, treatment led to a 2-fold improvement in rod function and a 4-fold improvement in cone function as measured by b-wave amplitudes at the final time point. At this stage of disease, control eyes had between 0-2 rows of remaining photoreceptor cells whereas treated eyes typically had between 4-5 rows.
These data demonstrate efficacy of gene replacement using a human RPGRIP1 cDNA driven by a photoreceptor-specific promoter and establish a prototype vector design for a potential gene therapy in future clinical trials in patients with LCA due to mutations in the gene encoding RPGRIP1.
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