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Zhijian Wu, Suja Hiriyanna, Haohua Qian, Suddhasil Mookherjee, Kayleigh Kaneshiro, Maria M Campos, Robert N Fariss, Tiansen Li, Anand Swaroop, Peter Colosi; Preclinical Development of AAV Vectors for the Treatment of X-linked Retinitis Pigmentosa Caused by RPGR Mutations. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3305.
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Mutations in retinitis pigmentosa GTPase regulator (RPGR) account for over 70% of X-linked retinitis pigmentosa (RP) and 15% of all RP. To develop a clinical candidate for the disease, we evaluated dose-efficacy profiles of AAV vectors expressing mouse and human RPGRorf15 in an Rpgr knock-out (KO) mouse model.
AAV vectors carrying mouse or human RPGRorf15 full-length cDNA were generated using a human rhodopsin kinase promoter, a CMV/β-globin intron and the human β-globin polyadenylation site. The mouse RPGRorf15 vector was packaged in AAV8 or AAV9 capsids, while the human counterpart in AAV8 capsid. These vectors were injected subretinally into 6 to 8 week- or 12 month-old Rpgr-KO mice at doses ranging between 1e8 and 1e10 vector genomes (vg) per eye. The mice were monitored for retinal function and structural changes by electroretinography (ERG) and optical coherence tomography (OCT). The mice were sacrificed at 20-24 months for histological and immunohistochemical analyses.
Preservation of retinal function and structure in Rpgr-KO mice was achieved with either mouse or human RPGRorf15 vector administration. Among all tested doses, 3e8 vg or 1e9 vg per eye appeared to be optimal for the mouse or human RPGRorf15 vector injection, respectively. The mice receiving these vector doses showed significantly larger scotopic and photopic ERG amplitudes in their vector-injected eyes compared to fellow control eyes, at 18 months post-injection. OCT analyses revealed the preservation of outer nuclear layer (ONL) in the vector-injected retina, which was later confirmed by histology. Cone opsin mislocalization was partially corrected as well. Interestingly, the mice injected at 1 year of age also displayed larger ERG amplitude and a greater ONL thickness. The mice receiving other doses of the vectors generally exhibited suboptimal therapeutic effects, however very high doses, such as 1e10 vg of the mouse or human RPGRorf15 vector, produced pronounced retinal toxicity.
Both mouse and human RPGRorf15 AAV vectors are able to prevent photoreceptor degeneration and preserve rod and cone function in the Rpgr-KO mouse retina. Our studies suggest that retinal degeneration patients with RPGR mutations could benefit even when treated at an advanced age. The AAV8 human RPGRorf15 vector fits our criteria for further clinical development.
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