Development of an optimized AAV2/5 gene therapy vector for Leber congenital amaurosis owing to defects in RPE65

Abstract

Leber congenital amaurosis is a group of inherited retinal dystrophies that cause severe sight impairment in childhood; RPE65-deficiency causes impaired rod photoreceptor function from birth and progressive impairment of cone photoreceptor function associated with retinal degeneration. In animal models of RPE65 deficiency, subretinal injection of recombinant adeno-associated virus (AAV) 2/2 vectors carrying RPE65 cDNA improves rod photoreceptor function, and intervention at an early stage of disease provides sustained benefit by protecting cone photoreceptors against retinal degeneration. In affected humans, administration of these vectors has resulted to date in relatively modest improvements in photoreceptor function, even when retinal degeneration is comparatively mild, and the duration of benefit is limited by progressive retinal degeneration. We conclude that the demand for RPE65 in humans is not fully met by current vectors, and predict that a more powerful vector will provide more durable benefit. With this aim we have modified the original AAV2/2 vector to generate AAV2/5-OPTIRPE65. The new configuration consists of an AAV vector serotype 5 carrying an optimized hRPE65 promoter and a codon-optimized hRPE65 gene. In mice, AAV2/5-OPTIRPE65 is at least 300-fold more potent than our original AAV2/2 vector.

Inclusion of the Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element Enhances AAV2-Driven Transduction of Mouse and Human Retina

“…The results of a phase 1/2 trial of gene therapy for LCA showed improved retinal sensitivity; however, cases of inflammation and/or immune responses were reported,17, 18 highlighting the issue of AAV immunogenicity. Improving vector efficiency through inclusion of a posttranscriptional regulatory element (PRE) within the transgene cassette may help overcome this problem by allowing a lower dose of AAV to be delivered to achieve any given treatment effect.…”

Subretinal Injection: A Review on the Novel Route of Therapeutic Delivery for Vitreoretinal Diseases

“…In an LCA animal model, subretinal injection of recombinant AAV 2/5-OPTIRPE65 improved retinal function against retinal degeneration in Rpe65 knockout mice [48] , and long-term transduction of RPE cells and photoreceptors in rats and nonhuman primates was observed [49] . AAV2 delivery of the RPE65 gene subretinally to the retina showed restoration of vision, rescuing the numbers of remaining photoreceptors both in young and old RPE65-mutant/deficient dogs [50,51] .…”

Neuroprotection in Glaucoma: Towards Clinical Trials and Precision Medicine

“…Clinical trials using gene therapy to treat other debilitating genetic conditions such as spinal muscular atrophy, 57 which has also recently been granted FDA approval, and junctional epidermolysis bullosa 58 are also showing considerable promise with good safety profiles and functional improvement. Although evaluation is ongoing and the longer-term impact remains uncertain, with other trials for LCA (NCT00643747) reporting a decline in the degree of visual improvement 59 and the subsequent development of an optimised AAV5 viral vector and transgene expression cassette to improve retinal transduction and yield higher levels of RPE65, 60 these advances all lend strong support to the use of directly administered gene therapies forming a core part of a clinician's toolkit when treating intractable illnesses in the foreseeable future.…”