Abstract
The woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) has been included in the transgene cassette of adeno-associated virus (AAV) in several gene therapy clinical trials, including those for inherited retinal diseases. However, the extent to which WPRE increases transgene expression in the retina is still unclear. To address this question, AAV2 vectors containing a reporter gene with and without WPRE were initially compared in vitro and subsequently in vivo by subretinal delivery in mice. In both instances, the presence of WPRE led to significantly higher levels of transgene expression as measured by fundus fluorescence, western blot, and immunohistochemistry. The two vectors were further compared in human retinal explants derived from patients undergoing clinically indicated retinectomy, where again the presence of WPRE resulted in an enhancement of reporter gene expression. Finally, an analogous approach using a transgene currently employed in a clinical trial for choroideremia delivered similar results both in vitro and in vivo, confirming that the WPRE effect is transgene independent. Our data fully support the inclusion of WPRE in ongoing and future AAV retinal gene therapy trials, where it may allow a therapeutic effect to be achieved at an overall lower dose of vector.
Highlights
Inherited retinal dystrophies (IRDs) are monogenic diseases caused by mutations in genes crucial for the function of retinal cells, most commonly photoreceptors and/or the retinal pigment epithelium (RPE)
Our results show for the first time that the presence of the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) significantly increases the expression of GFP in vivo following AAV2 subretinal delivery
The efficacy of an associated virus (AAV) retinal gene therapy approach is mainly dependent on three factors: the expression cassette, the delivery route, and the dose administered.[34]
Summary
Inherited retinal dystrophies (IRDs) are monogenic diseases caused by mutations in genes crucial for the function of retinal cells, most commonly photoreceptors and/or the retinal pigment epithelium (RPE). Recombinant AAV strategies have been the prime choice for retinal gene therapy due to their favorable toxicity profile and benign immune response.[2,3] Since the finding that AAV can transduce photoreceptor cells following subretinal injection,[4] several groups have tested both wild-type and mutant AAV capsids of various serotypes to maximize simultaneous transduction of RPE and photoreceptors.[5,6,7,8] The demonstration of safety and efficacy of serotype 2 in a canine model of Leber congenital amaurosis (LCA)[9] justified its used in the first AAV gene therapy trials in the human eye.[10,11,12] Other diseases followed, and currently, there are several ongoing clinical trials delivering wild-type AAV2 by subretinal injection.[13,14,15,16]
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