Age-dependent effects of RPE65 gene therapy for Leber's congenital amaurosis: a phase 1 dose-escalation trial

Abstract

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 x 10(10) vector genomes), medium (4.8 x 10(10) vector genomes), or high dose (1.5 x 10(11) 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.

Figure 1. Area of retina exposed to adeno-associated virus-mediated delivery of wild-type retinal pigment epithelium (AAV2-hRPE65v2)

Column 1 was drawn over composite photographs of a normal retina, and columns 2 and 3 over the baseline and follow-up Goldmann visual fields, respectively, in the injected eyes. All follow-up visual fields are shown at day 30, except for patients NP01 (4·75 months) and NP02 (2·75 months). Stimuli used to measure Goldmann visual fields were V4e (red) and II4e (blue). Scotomas and the natural blind spot are shown in black. *Visual field data from these patients were reported previously1 but are presented here for completeness.

Figure 2. Visual acuity and full-field sensitivity and dark adaptometry changes after injection with adeno-associated virus-mediated delivery of wild-type retinal pigment epithelium (AAV2-hRPE65v2)

(A) Correlation of age with visual acuity in the injected eye. Visual acuity at baseline was compared with the mean visual acuity after injection (all timepoints included); a worsened visual acuity was noted in CH06. p values for Significant differences are reported. (B) Change in logarithm of the minimum angle of resolution (LogMAR) scores in the injected and contralateral non-injected eyes is indicated as a function of time for patients given low, medium, and high doses of vector. LogMAR score was normalised to 0 at baseline for each individual. (C) Most patients in the middle and high dose groups were tested for full-field sensitivity to white light before and after injection. LP=light perception. HM=hand motion. CF=counting fingers.

Figure 3. Objective evidence of improvement in pupillary light reflexes

(A) Improved pupillary light reflexes—as a function of time after injection and after alternating stimulation of the injected (i, red columns) and non-injected (n, blue columns) eyes—are shown in representative recordings from patients after injection of middle and high doses of the vector. Red and blue curves represent diameters of the right and left pupils, respectively; however, only one pupil is shown for patient NP15 (day 7 after surgery) because the other was atropinised. Recorded light intensity was 0·04 lux for patients NP15 and CH08, 0·4 lux for CH10, and 10·0 lux for CH13. Days after injection are indicated. Alternating stimuli were presented 2 s after recording was initiated. In the panel for patient NP15, each stimulus was presented in 200 ms with 1 s spaces between the flashes. In the panels for patients CH08, CH10, and CH13, stimuli were presented in 1 s with 600 ms spaces between the flashes. Traces in each panel are shifted vertically to compare responses obtained at different timepoints. Control pupillary light responses (actual pupil diameters) measured in normal-sighted individuals at 4 lux are shown for comparison. (B) Correlation of improvements in full-field sensitivity with age (and baseline retinal sensitivity). The light sensitivities are not shown for patient NP15 because his data were analysed at day 60. The intensity at which the pupillary light response was eliminated from the test eye before injection and at which the relative afferent pupillary defect developed after injection was identified as the lower limit of sensitivity. The mean and SD of sensitivity of normal-sighted individuals in the age range of the patients is indicated by a blue line and shading, respectively.