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Summary Background Gene therapy has the potential to reverse disease or prevent further deterioration of vision in patients with incurable inherited retinal degeneration. We therefore did a phase 1 trial to assess the effect of gene therapy on retinal and visual function in children and adults with Leber’s congenital amaurosis. Methods We assessed the retinal and visual function in 12 patients (aged 8–44 years) with RPE65-associated Leber’s congenital amaurosis given one subretinal injection of adeno-associated virus (AAV) containing a gene encoding a protein needed for the isomerohydrolase activity of the retinal pigment epithelium (AAV2-hRPE65v2) in the worst eye at low (1·5×1010 vector genomes), medium (4·8×1010 vector genomes), or high dose (1·5×1011 vector genomes) for up to 2 years. Findings AAV2-hRPE65v2 was well tolerated and all patients showed sustained improvement in subjective and objective measurements of vision (ie, dark adaptometry, pupillometry, electroretinography, nystagmus, and ambulatory behaviour). Patients had at least a 2 log unit increase in pupillary light responses, and an 8-year-old child had nearly the same level of light sensitivity as that in age-matched normal-sighted individuals. The greatest improvement was noted in children, all of whom gained ambulatory vision. The study is registered with ClinicalTrials.gov, number NCT00516477. Interpretation The safety, extent, and stability of improvement in vision in all patients support the use of AAV-mediated gene therapy for treatment of inherited retinal diseases, with early intervention resulting in the best potential gain. Funding Center for Cellular and Molecular Therapeutics at the Children’s Hospital of Philadelphia, Foundation Fighting Blindness, Telethon, Research to Prevent Blindness, F M Kirby Foundation, Mackall Foundation Trust, Regione Campania Convenzione, European Union, Associazione Italiana Amaurosi Congenita di Leber, Fund for Scientific Research, Fund for Research in Ophthalmology, and National Center for Research Resources.

The safety and efficacy of gene therapy for inherited retinal diseases is being tested in humans affected with Leber's congenital amaurosis (LCA), an autosomal recessive blinding disease. Three independent studies have provided evidence that the subretinal administration of adeno-associated viral (AAV) vectors encoding RPE65 in patients affected with LCA2 due to mutations in the RPE65 gene, is safe and, in some cases, results in efficacy. We evaluated the long-term safety and efficacy (global effects on retinal/visual function) resulting from subretinal administration of AAV2-hRPE65v2. Both the safety and the efficacy noted at early timepoints persist through at least 1.5 years after injection in the three LCA2 patients enrolled in the low dose cohort of our trial. A transient rise in neutralizing antibodies to AAV capsid was observed but there was no humoral response to RPE65 protein. The persistence of functional amelioration suggests that AAV-mediated gene transfer to the human retina does not elicit immunological responses which cause significant loss of transduced cells. The persistence of physiologic effect supports the possibility that gene therapy may influence LCA2 disease progression. The safety of the intervention and the stability of the improvement in visual and retinal function in these subjects support the use of AAV-mediated gene augmentation therapy for treatment of inherited retinal diseases.

Objective The aim of the current study is to show the clinical data of long-term (3 year) follow-up of five patients affected by Leber Congenital Amaurosis type 2 (LCA2) treated with a single unilateral injection of AAV2-hRPE65v2. Design clinical trial Participants five LCA2 patients with RPE65 gene mutations Methods After informed consent and confirmation of trial eligibility criteria, the eye with worse visual function was selected for subretinal delivery of Adeno-Associated Virus (AAV2-hRPE65v2). Subjects were evaluated before and after surgery at designated follow-up visits (1, 2, 3, 14, 30, 60, 90, 180, 270, 365 days, 1.5 years and 3 years) by complete ophthalmic examination. Efficacy for each subject was monitored with best corrected visual acuity, kinetic visual field, nystagmus testing and pupillary light reflex. Main Outcome Measures best corrected visual acuity, kinetic visual field, nystagmus testing and pupillary light reflex. Results The data showed a statistically significant improvement of best corrected visual acuity between baseline and 3 years after treatment in the treated eye (p<0.001). In all patients we observed an enlargement of the areas of visual field, which remained stable till 3 years post injection (average values: baseline 1058 deg2 vs 3 years post treatment: 4630 deg2) and a reduction of the nystagmus frequency compared to baseline at the 3 year time-point. Furthermore, a statistically significant difference was observed in the pupillary constriction of the treated eye (p<0.05) compared to the untreated eye in three patients at 1 and 3-year time-points. No patients suffered serious adverse events related to the vector in the 3 year post-injection period. Conclusions The long-term follow-up data (3 years) on the 5-patient Italian cohort involved in the LCA2 gene therapy clinical trial clearly showed a stability of improvement in visual and retinal function that had been achieved a few months after treatment. Longitudinal data analysis showed that the maximum improvement was achieved within six months after treatment, and the visual improvement was stable up to the last observed time-point.