Surgical Technique for Subretinal Gene Therapy in Humans with Inherited Retinal Degeneration

摘要

The technique draws on personal experience with gene augmentation therapy by subretinal injection in patients with choroideremia, RPE65 mutation-associated retinal dystrophy, and X-linked retinitis pigmentosa. Only 2 surgeons initially performed RPE65 gene therapy in the Phase 3 clinical trial leading to drug approval in the United States and the European Union.1 As new surgeons begin to use the commercially available product voretigene neparvovec-rzyl for RPE65 mutation–related inherited retinal dystrophy (IRD) or to participate in clinical trials, there is a need for education in best practices for subretinal injection. Clinical trials are currently listed on clinicaltrials.gov for choroideremia,2–5 X-linked retinitis pigmentosa (RPGR genotype), autosomal recessive retinitis pigmentosa (MERTK genotype), achromatopsia (CNGA3 and CNGB3), Stargardt disease (ABCA4), Leber congenital amaurosis (CEP290), and Usher syndrome type 1B (MY07A), with several additional subretinal gene therapies in the pipeline. There are few options with currently available technology for delivery of gene therapy for IRD other than subretinal injection. Intravitreal injection of gene therapy is simpler to perform but is predicted to be useful only for optic nerve or retinal diseases affecting primarily the retinal nerve fiber layer, ganglion cell layers, and inner retinal layers (e.g., Leber hereditary optic neuropathy and X-linked retinoschisis RS1) due to barriers presented by the internal limiting membrane and the retinal tissue.6,7 Microcatheters advanced into suprachoroidal space of rabbits achieved transfection with adeno-associated virus 2 (AAV2) vector as demonstrated by GFAP expression8; however, there is concern that therapy delivered to the suprachoroidal space would be more difficult to target, require higher doses, be more likely to disseminate to unwanted systemic sites, or fail to penetrate outer blood retinal barrier at the level of the retinal pigment epithelium and Bruch membrane. Therefore, subretinal injection is likely to remain the procedure of choice for the near future. Technological innovations may facilitate surgical delivery of vector to the subretinal space.9–12 Although previous publications discuss surgical technique for gene therapy surgery, they do not provide a complete, surgeon-oriented surgical plan that is easy to follow in the operating room. The surgeon's manual for administration of voretigene neparvovec-rzyl intentionally gives general instructions with few details to allow for surgical discretion. The current protocol may help experienced vitreoretinal surgeons new to gene therapy adapt their own procedures and operating room setting to facilitate safe and efficient surgery. Surgical Protocol Our methods of subretinal injection were refined during multiple surgeries at Bascom Palmer Eye Institute involving patients enrolled in Phase II to III clinical trials, but also patients treated with commercial products. Many steps are routine best practice procedures for vitreoretinal surgery adapted to a comprehensive plan for gene therapy surgery. The interventions described here were approved by the Human Subjects Research Office of the University of Miami when they involved patients enrolled in clinical trials. All patients signed standard consents for surgery as required by our hospital. Patient Selection and Preparation Select candidates by phenotype. Use CLIA-certified genetic testing to confirm the pathogenic genetic variant. Document retinal function with visual acuity, visual fields, and electrophysiology; retinal anatomy with fundus photography, optical coherence tomography (OCT), and autofluorescence. Use microperimetry to assess the favored fixation point. Obtain informed consent emphasizing risks of subretinal surgery including blindness, decreased vision, scarring, disease progression, injury to surrounding structures, inflammation, macular hole, and retinal detachment. Gene therapy surgery now may limit acc