Gene Therapy and Transfection Efficiency Following Subretinal AAV Vector Delivery Is Not Affected by a Previous Intravitreal AAV Vector Administration

Abstract

Purpose: : In a parallel study we found normal AAV2-mediated GFP expression after intravitreal injection to one eye of normal C57 mice, and poor GFP expression if the other eye of the same mouse was injected intravitreally with the same vector one month after the first injection. We also found both injections worked well if they were subretinal. In this study we tested whether the efficiency of subretinal AAV vector transduction is altered by a previous intravitreal injection in the partner eye and whether therapeutic efficiency is altered in the rd12 mouse (with a recessive RPE65 mutation) after the same injection series.

Methods: : 1 µl of scAAV5-smCBA-GFP (2x10¹³ viral particles/ml) or scAAV5-smCBA-hRPE65 (1x10¹² viral particles/ml) was intravitreally injected into right eyes of C57 or rd12 mice, respectively. 4 weeks later the same vectors were subretinally injected into left eyes of either C57 or rd12 mice. AAV-mediated GFP expression in C57 and RPE65 expression/functional rescue in rd12 mice were evaluated one month after the second subretinal injection, including frozen section fluorescence analysis in C57 mice and dark-adapted ERGs plus RPE65 immunostaining in rd12 eyes.

Results: : In C57 mice, GFP positive cells was detected in eyes following the first intravitreal injection; strong GFP expression in both RPE and photoreceptor cells was detected in partner eyes following the second subretinal injection. In rd12 mice, dark-adapted ERGs were not recordable following the first intravitreal injection of scAAV5-smCBA-RPE65, but showed dramatic ERG restoration in the partner eye following second subretinal injection; immunostaining of retinal sections with anti-RPE65 antibody showed RPE65 expression mainly in RPE of subretinally injected eyes but not in intravitreally injected eyes except a little around the injection site.

Conclusions: : The results coupled with a parallel study showing that intravitreal AAV vector elicits only systemic vector capsid antibody indicate that circulating antibody following intravitreal injection of AAV vectors to one eye of a mouse does not influence AAV-mediated gene expression or related therapeutic effects in the other eye if vector is administered to the subretinal space. These data confirm that the subretinal space possesses a unique immune privilege relative to the vitreous cavity, and extend this idea not just to AAV vector mediated retinal gene expression but to therapeutic efficacy as well.

Keywords: gene transfer/gene therapy • immune tolerance/privilege • retinal degenerations: hereditary