Gene therapy for leber congenital amaurosis caused by RPE65 mutations: safety and efficacy in 15 children and adults followed up to 3 years.

OBJECTIVE: To determine the safety and efficacy of subretinal gene therapy in the RPE65 form of Leber congenital amaurosis using recombinant adeno-associated virus 2 (rAAV2) carrying the RPE65 gene. DESIGN: Open-label, dose-escalation phase I study of 15 patients (range, 11-30 years of age) evaluated after subretinal injection of the rAAV2- RPE65 vector into the worse-functioning eye. Five cohorts represented 4 dose levels and 2 different injection strategies. MAIN OUTCOME MEASURES: Primary outcomes were systemic and ocular safety. Secondary outcomes assayed visual function with dark-adapted full-field sensitivity testing and visual acuity with Early Treatment Diabetic Retinopathy Study charts. Further assays included immune responses to the vector, static visual fields, pupillometry, mobility performance, and optical coherence tomography. RESULTS: No systemic toxicity was detected; ocular adverse events were related to surgery. Visual function improved in all patients to different degrees; improvements were localized to treated areas. Cone and rod sensitivities increased significantly in the study eyes but not in the control eyes. Minor acuity improvements were recorded in many study and control eyes. Major acuity improvements occurred in study eyes with the lowest entry acuities and parafoveal fixation loci treated with subretinal injections. Other patients with better foveal structure lost retinal thickness and acuity after subfoveal injections. CONCLUSIONS: Gene therapy for Leber congenital amaurosis caused by RPE65 mutations is sufficiently safe and substantially efficacious in the extrafoveal retina. There is no benefit and some risk in treating the fovea. No evidence of age-dependent effects was found. Our results point to specific treatment strategies for subsequent phases. APPLICATION TO CLINICAL PRACTICE: Gene therapy for inherited retinal disease has the potential to become a future part of clinical practice. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00481546.

Human CRB1-associated retinal degeneration: comparison with the rd8 Crb1-mutant mouse model.

PURPOSE: To investigate the human disease due to CRB1 mutations and compare results with the Crb1-mutant rd8 mouse. METHODS: Twenty-two patients with CRB1 mutations were studied. Function was assessed with perimetry and electroretinography (ERG) and retinal structure with optical coherence tomography (OCT). Cortical structure and function were quantified with magnetic resonance imaging (MRI). Rd8 mice underwent ERG, OCT, and retinal histopathology. RESULTS: Visual acuities ranged from 20/25 to light perception. Rod ERGs were not detectable; small cone signals were recordable. By perimetry, small central visual islands were separated by midperipheral scotomas from far temporal peripheral islands. The central islands were cone mediated, whereas the peripheral islands retained some rod function. With OCT, there were small foveal islands of thinned outer nuclear layer (ONL) surrounded by thick delaminated retina with intraretinal hyperreflective lesions. MRI showed structurally normal optic nerves and only subtle changes to occipital lobe white and gray matter. Functional MRI indicated that whole-brain responses from patients were of reduced amplitude and spatial extent compared with those of normal controls. Rd8 mice had essentially normal ERGs; OCT and histopathology showed patchy retinal disorganization with pseudorosettes more pronounced in ventral than in dorsal retina. Photoreceptor degeneration was associated with dysplastic regions. CONCLUSIONS: CRB1 mutations lead to early-onset severe loss of vision with thickened, disorganized, nonseeing retina. Impaired peripheral vision can persist in late disease stages. Rd8 mice also have a disorganized retina, but there is sufficient photoreceptor integrity to produce largely normal retinal function. Differences between human and mouse diseases will complicate proof-of-concept studies intended to advance treatment initiatives.

Retinal disease in Rpe65-deficient mice: comparison to human leber congenital amaurosis due to RPE65 mutations.

PURPOSE: To quantify the retinal disease in Rpe65-deficient mice across a wide age span and compare the results to those in humans with Leber congenital amaurosis (LCA) caused by RPE65 mutations. METHODS: Full-field electroretinograms (ERGs) were recorded from wild-type (C57BL/6; Rpe65(+/+)) and Rpe65(-/-) mice at ages ranging from ∼1 month to 2 years. A physiologically based model of rod phototransduction activation was used to determine photoreceptor (P3) cell components of ERG photoresponses. A bipolar (P2) cell component was also derived. Photoreceptor and inner retinal thickness measurements were made by using optical coherence tomography in human RPE65-LCA. RESULTS: Age-related declines in ERG photoreceptor and bipolar amplitudes were present in the Rpe65(-/-) mouse. The loss of photoresponse amplitude with age in the mutant mice paralleled reported losses of photoreceptor nuclear layer thickness over the same age range. Unexpectedly, the early activation phase of photoresponses in Rpe65(-/-) mice accelerated with age as amplitude decreased; this was not a feature of Rpe65(+/+) mice. Inner retinal dysfunction increased with age in the mutant mice. Human RPE65-LCA patients had retinal degeneration and loss of photoreceptors in the first decade of life. Unlike the mouse model, there were no examples of a normal photoreceptor complement. Abnormal thickening of the inner retina occurred with increasing loss of photoreceptors. CONCLUSIONS: The differences in time course of murine and human RPE65-deficiency diseases suggests that preclinical efficacy testing of therapeutic modalities would be most informative when the murine disease becomes comparable to early human disease, toward the end of the first year of life in Rpe65(-/-) mice.