Outer retinal transduction can be achieved after intravitreal delivery of adeno-associated virus serotype 2 vector with glycosidic enzymes

Abstract

BackgroundGene therapies for retinal disorders, including in current clinical trials, so far have relied on subretinal delivery of adeno-associated virus (AAV) vectors carrying therapeutic DNA into outer retinal cells. Subretinal injection has many limitations over the less-invasive route of administration into the vitreal cavity. However, at present only limited retinal transduction can be achieved after intravitreal delivery of AAV vectors. We hypothesise that the inner limiting membrane and extracellular matrix proteoglycans act as a barrier to AAV vector entry into and movement across the retina. Therefore, glycosidic enzymes, which degrade these extracellular barriers, can improve retinal gene therapy. In this study we investigated the effects of enzymatic digestion of extracellular matrices on the depth of vector penetration into the retina. MethodsThe green fluorescent protein (GFP)-expressing AAV serotype 2 (AAV2) vector was co-injected intravitreally with glycosidic enzymes at their optimum concentration. Efficacy of virus transduction was assessed by visualising fluorescence in histological cross-sections with fluorescence microscopy. We also analysed safety of these treatments and retinal function using electroretinography. FindingsGlycosidic enzymes led to a significant improvement in retinal transduction after intravitreal delivery of AAV2. These enzymes markedly improved transduction of the outer retina, including photoreceptor cells. Electroretinograms were unchanged (compared with controls) even at much higher doses of enzymes than were needed for optimum retinal transduction. InterpretationAAV2-mediated retinal transduction is improved by co-injection of glycosidic enzymes into the vitreous. Improved transduction efficiency may allow intravitreal injection to become the preferred route for delivering gene therapy to the inner and outer retina in both preclinical and clinical settings. FundingUK Medical Research Council.