Technique of retinal gene therapy: delivery of viral vector into the subretinal space.

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.

Outcomes following cataract surgery in choroideremia.

PurposeTo present a case series of cataract surgery outcomes in choroideremia eyes with an emphasis on the safety of this common operation in advanced stages of the disease.MethodsA single centre retrospective interventional case series comprising six patients with varying degrees of visual loss secondary to choroideremia underwent cataract surgery at a single tertiary eye hospital. Pre- and post-operative best-corrected Snellen visual acuity, spectral domain optical coherence tomography (SD-OCT), and slit lamp examination were performed together with fundus autofluorescence (FAF) and colour fundus photographs.The prevalence of intra- or post-operative complications, post-operative visual outcome, and change in central macular thickness were recorded.ResultsThe pre-operative best-corrected Snellen visual acuity in the operated eyes ranged from 6/12 (20/40) to PL. All but one patient had either an objective or a subjective improvement in visual acuity. There was no evidence of retinal phototoxicity or post-operative cystoid macular oedema (CMO). Three patients developed early capsular fibrosis.ConclusionsAlthough the residual functioning retina in choroideremia patients may be potentially vulnerable, this report finds no evidence of iatrogenic vision loss after uncomplicated cataract surgery. This suggests that cataract surgery may be performed safely in choroideremia patients, although a guarded prognosis for visual improvement should be emphasized in the informed consent.

[Gene therapy for retinal dystrophies]. / Gentherapie bei Netzhautdystrophien.

Genetic mutations are the cause of inherited retinal dystrophies. The underlying genetic basis of these diseases suggests that a gene therapy approach is logical either to replace or reduce the expression of defective genes. The first proof-of-concept clinical studies in patients with Leber's congenital amaurosis have suggested that retinal gene therapy is safe and potentially effective, at least for specific disease entities. In contrast to pharmacological treatment gene therapy has the advantage of being able to express a protein within specific cell populations and is a potentially definitive therapy. Besides replacing deficient genes in inherited diseases, additional strategies that might broaden the application of retinal gene therapy are also being developed. These include the permanent expression of neuroprotective substances or photosensitive molecules (so-called optogenetics). This overview discusses the current clinical strategies and potential problems of retinal gene therapy.