Kanmin Xue

Visual Acuity after Retinal Gene Therapy for Choroideremia

In this study, the subfoveal injection of a gene-therapy vector carrying nonmutated CHM, the gene that, when mutated, causes a form of blindness called choroideremia, was followed by an improvement in visual acuity in two of six patients at 3.5 years after injection.

Correlation of Optical Coherence Tomography and Autofluorescence in the Outer Retina and Choroid of Patients With Choroideremia.

Purpose To evaluate the relationships between RPE, photoreceptor, and choroidal degeneration in choroideremia. Methods Enhanced-depth imaging optical coherence tomography (EDI-OCT), scanning laser ophthalmoscopy (SLO), and autofluorescence (AF) were performed on 39 patients (78 eyes) with choroideremia. The edges of surviving outer retina on OCT and residual AF were aligned. The distribution of outer retinal tubulations was mapped over a range of ages (16–71 years), and comparison made between pre- and postsubretinal gene therapy. Subfoveal choroidal thickness (SFCT) was compared between 23 choroideremia patients (42 eyes) and 20 age- and refraction-matched male controls (40 eyes). Results The edges of RPE AF aligned with a reduction in outer nuclear layer thickness (Spearmans rho = 0.9992). Correlation was also found between the quality of AF and integrity of ellipsoid zone within islands of surviving retina. Tubulations existed in 71 of 78 (91%) eyes with choroideremia and remained stable following gene therapy. Subfoveal choroidal thickness was reduced at baseline in choroideremia (179.7 ± 17.2 μm) compared with controls (302.0 ± 4.8 μm; P < 0.0001), but did not undergo significant thinning until end-stage retinal degeneration (43.1 ± 6.5 μm). Conclusions The data suggest that RPE loss is the primary cause of photoreceptor degeneration in choroideremia. The choroid is thinner than controls from early stages, in keeping with a mild developmental defect. Photoreceptors appear to lose outer segments following loss of underlying RPE and form tubulations at the edges of degeneration. The preservation of tubulations over time and after subretinal injection would be consistent with these structures maintaining attachment to the inner retina and hence being potentially light responsive (ClinicalTrials.gov, NCT01461213).

The Spectrum of CHM Gene Mutations in Choroideremia and Their Relationship to Clinical Phenotype.

Purpose We report the underlying genotype and explore possible genotypic-phenotypic correlations in a large cohort of choroideremia patients. Methods We studied prospectively a cohort of 79 patients diagnosed within a tertiary referral service for patients with retinal dystrophies. Phenotypic evaluation consisted of clinical examination, including visual acuity and residual retinal area by fundus autofluorescence (FAF). Genotype was established by sequencing. We also investigated whether particular genotypes were associated with more severe phenotypes by performing analysis of covariance (ANCOVA), with visual acuity and FAF as the dependent variables and age as the covariant. Results A total of 74 (94%) of patients in our cohort had causative mutations by sequencing, the majority of which were anticipated to be null. Of these, 35 (47%) had insertions and deletions, 13 (18%) had mutations predicted to affect splicing, and 26 (35%) had single point mutations. In the latter case, 13 of 21 (62%) pedigrees with single point mutations were C to T transitions at C-phosphate-G (CpG) dinucleotides. These mutations were spread across 5 of only 24 CpG dinucleotides in the entire CHM cDNA. Furthermore, these 5 locations are the only sites at which C to T transitions result in a stop codon. No clear evidence was found for genotype–phenotype correlation except in the instance of a patient with a large deletion involving neighbouring sequences. Conclusions In patients with a diagnosis of choroideremia made by a specialty service, there is a high likelihood of establishing a genetic diagnosis. The majority of causative mutations appear to be null and, therefore, may benefit from gene replacement therapy. A disproportionate number of single point mutations observed were C to T transitions, consistent with the evolutionary decay of CpG dinucleotides through methylation and subsequent deamination. Hence, the development of choroideremia in such patients may represent the unwanted consequence of human evolution; de novo mutations are predicted to arise at these sites in future generations. (ClinicalTrials.gov number, NCT01461213.)

Structural and Functional Recovery Following Limited Iatrogenic Macular Detachment for Retinal Gene Therapy

Importance The early decline and recovery of retinal structure and function following iatrogenic macular detachment for retinal gene therapy is not well characterized in those with relatively preserved central visual function. Here, the recovery of retinal structure and function over the first month following iatrogenic retinal detachment for the delivery of adeno-associated viral vector encoding Rab Escort Protein 1 is described as a part of gene therapy for choroideremia. Objective To study changes in both retinal structure and function during the first month following iatrogenic macular detachment surgery. Design, Setting, and Participants This prospective interocularly controlled study was conducted between February 1 and December 31, 2015. Treatment consisted of a subretinal injection of 0.1 mL of a gene therapy solution containing 1 × 1011 viral particles performed unilaterally. The participants were 5 males, aged 23 to 71 years, with a clinical and genetic diagnosis of choroideremia. Main Outcomes and Measures Retinal structure and function were assessed at baseline, 1 week, and 1 month using optical coherence tomography, logMAR visual acuity, microperimetry, the Farnsworth-Munsell (FM) 100-hue test, and the Rayleigh match. Results Five white male patients aged 23 to 71 years underwent unilateral subretinal gene therapy for genetically confirmed choroidermeia. Optical coherence tomographic images demonstrated a complete resolution of the resulting iatrogenic retinal detachment by 1 week in all 5 patients. At 1 month, the mean (SE) change in central foveal thickness was +9.6 (7.2) &mgr;m in treated eyes and +8.8 (12.6) &mgr;m in control eyes. The mean (SE) change in visual acuity was +5.4 (3.3) letters in treated eyes and +0.8 (3.1) letters in control eyes. At 1 month, the mean (SE) threshold sensitivity changes were −1.2 (2.1) dB in treated eyes and −1.0 (1.2) dB in control eyes. Color discrimination at the FM 100-hue changed little at 1 month (mean [SE] change in C-index, −0.2 [0.4] in treated eyes and 0.1 [0.2] in control eyes). Rayleigh matches in 1 patient were consistent with a diagnosis of pseudoprotanomaly, suggesting decreased effective optical density of the cone photopigments. Conclusions and Relevance Retinal structural recovery—as assessed by optical coherence tomography—occurs soon after iatrogenic detachment. Similarly, visual acuity recovers or improves within 1 month of the procedure and may not be accompanied by improvements in threshold sensitivity or color discrimination. Changes in color matching in 1 patient suggest decreased optical density of the cone photopigments in the early postoperative period.

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.

Retinal Degeneration in Choroideremia follows an Exponential Decay Function

Fundus autofluorescence (AF) arises from lipofuscin, which is derived from retinoid byproducts of the visual cycle and accumulates within retinal pigment epithelial cells. Alterations in AF pattern are seen in a wide range of retinal degenerations. Choroideremia is an X-linked retinal dystrophy caused by loss-of-function mutations within the CHM gene, encoding Rab escort protein-1. It is uniquely characterized by a central “island” of residual AF that undergoes gradual shrinkage with disease progression. The decrease in AF area is correlated precisely with loss of overlying photoreceptors, leading to progressive visual field restriction and blindness around the fifth decade. Retinal gene replacement therapy using an adeno-associated viral vector could potentially slow down or stop disease progression in choroideremia. Although visual acuity may be improved by gene therapy, it is affected relatively late in the disease; therefore, the area of residual AF may provide an alternative anatomic biomarker for monitoring progression at earlier stages. A previous cross-sectional study suggested an exponential decrease in AF area with age in choroideremia. However, longitudinal data on natural disease progression is lacking. For instance, it is uncertain whether individuals progressed at different rates depending on genetic, epigenetic, or environmental factors, and whether the rate of progression varied between early and late stages of the disease.

Assessment of the Electronic Retinal Implant Alpha AMS in Restoring Vision to Blind Patients with End-Stage Retinitis Pigmentosa.

Purpose To report the initial efficacy results of the Retina Implant Alpha AMS (Retina Implant AG, Reutlingen, Germany) for partial restoration of vision in end-stage retinitis pigmentosa (RP). Design Prospective, single-arm, investigator-sponsored interventional clinical trial. Within-participant control comprising residual vision with the retinal implant switched ON versus OFF in the implanted eye. Participants The Retina Implant Alpha AMS was implanted into the worse-seeing eye of 6 participants with end-stage RP and no useful perception of light vision. Eligibility criteria included previous normal vision for ≥12 years and no significant ocular or systemic comorbidity. Methods Vision assessments were scheduled at 1, 2, 3, 6, 9, and 12 months postimplantation. They comprised tabletop object recognition tasks, a self-assessment mobility questionnaire, and screen-based tests including Basic Light and Motion (BaLM), grating acuity, and greyscale contrast discrimination. A full-field stimulus test (FST) was also performed. Main Outcome Measures Improvement in activities of daily living, recognition tasks, and assessments of light perception with the implant ON compared with OFF. Results All 6 participants underwent successful implantation. Light perception and temporal resolution with the implant ON were achieved in all participants. Light localization was achieved with the implant ON in all but 1 participant (P4) in whom the chip was not functioning optimally because of a combination of iatrogenic intraoperative implant damage and incorrect implantation. Implant ON correct grating detections (which were at chance level with implant OFF) were recorded in the other 5 participants, ranging from 0.1 to 3.33 cycles/degree on 1 occasion. The ability to locate high-contrast tabletop objects not seen with the implant OFF was partially restored with the implant ON in all but 1 participant (P4). There were 2 incidents of conjunctival erosion and 1 inferotemporal macula-on retinal detachment, which were successfully repaired, and 2 incidents of inadvertent damage to the implant during surgery (P3 and P4). Conclusions The Alpha AMS subretinal implant improved visual performance in 5 of 6 participants and has exhibited ongoing function for up to 24 months. Although implantation surgery remains challenging, new developments such as OCT microscope guidance added refinements to the surgical technique.

Characterizing the Natural History of Visual Function in Choroideremia Using Microperimetry and Multimodal Retinal Imaging.

Purpose Centripetal retinal degeneration in choroideremia (CHM) leads to early visual field restriction and late central vision loss. The latter marks an acute decline in quality of life but visual prognostication remains challenging. We investigated visual function in CHM by correlating best-corrected visual acuity (BCVA), microperimetry and multimodal imaging. Methods Fifty-six consecutive CHM patients attending Oxford Eye Hospital were examined with BCVA, 10–2 microperimetry, optical coherence tomography, and fundus autofluorescence (AF). Microperimetry was repeated in 21 eyes and analyzed with Bland-Altman. Kaplan-Meier survival plots of eyes retaining 20/20 BCVA were created. Intereye symmetry was assessed. Results Microperimetry coefficient of repeatability was 1.45 dB. Survival analysis showed an indistinguishable pattern between eyes (median survival 39 years). Macular sensitivity showed a similar decline in right and left eyes, with half-lives of 13.6 years. Zonal analysis showed faster decline nasal to the fovea. Intereye symmetry was more consistent for microperimetry sensitivity (r = 0.95, P < 0.001) than BCVA (r = 0.42, P = 0.0006). Near normal foveal sensitivity was maintained when the fovea was at least 2500 μm from the advancing edge of AF. Conclusions BCVA is a marker of central degeneration and can provide valuable information about the position of the remaining retina as well as a measure of the impact on daily living. Microperimetry represents the global macular region. Both visual functions showed a high degree of intereye symmetry, particularly in early stages, indicating the fellow eye can provide a suitable control for assessing interventions to one eye. The findings may help to tailor visual prognosis and interpret outcomes of trials.

Effects of pupil dilation on MAIA microperimetry.

Macular Integrity Assessment microperimetry assesses macular sensitivity to projected point light sources and maps eye movements to assess fixation stability. Although microperimetry is gaining prominence as an assessment tool in clinical and research settings, there is no consensus on whether it should be performed before or after pupil dilation. No studies to date have examined the effect of pupil dilation on results. The aim of this project was to elucidate the effect of pupil dilation on microperimetry outcomes.

First-in-human study of the safety and viability of intraocular robotic surgery

Microsurgery of the retina would be dramatically improved by instruments that offer supra-human precision. Here, we report the results of a first-in-human study of remotely controlled robot-assisted retinal surgery performed through a telemanipulation device. Specifically, 12 patients that required dissection of the epiretinal or inner limiting membrane over the macula were randomly assigned to either undergo robot-assisted surgery or manual surgery, under general anaesthesia. We evaluated surgical success, the duration of surgery and the amount of retinal microtrauma as a proxy for safety. Surgical outcomes were equally successful in the robotic surgery and manual surgery groups. Differences in the amount of retinal microtrauma between the two groups were statistically insignificant, yet dissection took longer with robotic surgery (median time: 4 min 55 s) than with manual surgery (1 min 20 s). We also show the feasibility of using the robot to inject recombinant tissue plasminogen activator under the retina to displace sight-threatening haemorrhage in three patients under local anaesthesia. A safe and viable robotic system for intraocular surgery would enable precise and minimally traumatic delivery of gene therapy or cell therapy to the retina.A first-in-man study of robotic-assisted intraocular surgery shows the feasibility and safety of the robotic device for the peeling of retinal membranes and for the injection of a therapeutic under the retina.