Abstract
PurposeSafe and reproducible delivery of gene therapy vector into the subretinal space is essential for successful targeting of the retinal pigment epithelium (RPE) and photoreceptors. The success of surgery is critical for the clinical efficacy of retinal gene therapy. Iatrogenic detachment of the degenerate (often adherent) retina in patients with hereditary retinal degenerations and small volume (eg, 0.1 ml) subretinal injections pose new surgical challenges.MethodsOur subretinal gene therapy technique involved pre-operative planning with optical coherence tomography (OCT) and autofluorescence (AF) imaging, 23 G pars plana vitrectomy, internal limiting membrane staining with Membrane Blue Dual (DORC BV, Zuidland, Netherlands), a two-step subretinal injection using a 41 G Teflon tipped cannula (DORC) first with normal saline to create a parafoveal bleb followed by slow infusion of viral vector via the same self-sealing retinotomy. Surgical precision was further enhanced by intraoperative OCT (Zeiss Rescan 7000, Carl Zeiss Meditec AG, Jena, Germany). Foveal functional and structural recovery was evaluated using best-corrected Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity, microperimetry and OCT.ResultsTwo patients with choroideremia aged 29 (P1) and 27 (P2) years, who had normal and symmetrical levels of best-corrected visual acuity (BCVA) in both eyes, underwent unilateral gene therapy with the fellow eye acting as internal control. The surgeries were uncomplicated in both cases with successful detachment of the macula by subretinal vector injection. Both treated eyes showed recovery of BCVA (P1: 76–77 letters; P2: 84–88 letters) and mean threshold sensitivity of the central macula (P1: 10.7–10.7 dB; P2: 14.2–14.1 dB) to baseline within a month. This was accompanied by normalisation of central retinal thickness on OCT.ConclusionsHerein we describe a reliable technique for subretinal gene therapy, which is currently used in clinical trials to treat choroideremia using an adeno-associated viral (AAV) vector encoding the CHM gene. Strategies to minimise potential complications, such as avoidance of excessive retinal stretch, air bubbles within the injection system, reflux of viral vector and post-operative vitritis are discussed.
Highlights
Retinal gene therapy offers our best hope for treating inherited retinal dystrophies in the foreseeable future based on successful proofof-principle in animal models and promising data from human clinical trials
Intravitreal Adenoassociated viral (AAV) particles may stimulate an immune response to the viral capsids, which may further degrade the number of effective AAV particles in the subretinal space
We focus on the technique of subretinal gene therapy, which offers a targeted approach to treating outer retinal degenerations caused by genetic mutations in the retinal pigment epithelium (RPE) and photoreceptors
Summary
Retinal gene therapy offers our best hope for treating inherited retinal dystrophies in the foreseeable future based on successful proofof-principle in animal models and promising data from human clinical trials. Adenoassociated viral (AAV) vector based gene therapy for RPE65-associated Leber congenital amaurosis (LCA) and choroideremia (CHM) have entered Phase III and II clinical trials respectively In both cases, demonstrating long-term improvements in visual function in those patients in whom early treatment effects were observed.[1,2,3,4] AAV gene therapies for other monogenic retinal disorders are under investigation, eg MERTK-associated retinitis pigmentosa,[5] X-linked retinoschisis (XLRS), CNGA3-associated achromatopsia and ND4-associated Leber hereditary optic neuropathy (LHON).[6] In addition, gene therapy has been used to create sustained ectopic production of a secreted anti-vascular endothelial growth factor protein as an alternative way of treating wet age-related macular degeneration.[7]. The hydrostatic force of the subretinal injection will pump vector suspension into the extracellular space of the outer retina, thereby providing a potential reservoir of AAV particles for further transduction after the initial subretinal fluid has been reabsorbed
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