Targeted gene knockout mouse models have helped to identify roles of autophagy in many tissues. Here, we investigated the retinal pigment epithelium (RPE) of Atg7f/f Tyr-Cre mice (on a C57BL/6 background), in which Cre recombinase is expressed under the control of the tyrosinase promoter to delete the autophagy gene Atg7. In line with pigment cell-directed blockade of autophagy, the RPE and the melanocytes of the choroid showed strong accumulation of the autophagy adaptor and substrate, sequestosome 1 (Sqstm1)/p62, relative to the levels in control mice. Immunofluorescence and Western blot analysis demonstrated that the RPE, but not the choroid melanocytes, of Atg7f/f Tyr-Cre mice also had strongly increased levels of retinoid isomerohydrolase RPE65, a pivotal enzyme for the maintenance of visual perception. In contrast to Sqstm1, genes involved in retinal regeneration, i.e. Lrat, Rdh5, Rgr, and Rpe65, were expressed at higher mRNA levels. Sequencing of the Rpe65 gene showed that Atg7f/f and Atg7f/f Tyr-Cre mice carry a point mutation (L450M) that is characteristic for the C57BL/6 mouse strain and reportedly causes enhanced degradation of the RPE65 protein by an as-yet unknown mechanism. These results suggest that the increased abundance of RPE65 M450 in the RPE of Atg7f/f Tyr-Cre mice is, at least partly, mediated by upregulation of Rpe65 transcription; however, our data are also compatible with the hypothesis that the RPE65 M450 protein is degraded by Atg7-dependent autophagy in Atg7f/f mice. Further studies in mice of different genetic backgrounds are necessary to determine the relative contributions of these mechanisms.

Several approaches have been developed for gene therapy in RPE65-related Leber congenital amaurosis. To date, strategies that have reached the clinical stages rely on adeno-associated viral vectors and two of them documented limited long-term effect. We have developed a lentiviral-based strategy of RPE65 gene transfer that efficiently restored protein expression and cone function in RPE65-deficient mice. In this study, we evaluated the ocular and systemic tolerances of this lentiviral-based therapy (LV-RPE65) on healthy nonhuman primates (NHPs), without adjuvant systemic anti-inflammatory prophylaxis. For the first time, we describe the early kinetics of retinal detachment at 2, 4, and 7 days after subretinal injection using multimodal imaging in 5 NHPs. We revealed prolonged reattachment times in LV-RPE65-injected eyes compared to vehicle-injected eyes. Low- (n = 2) and high-dose (n = 2) LV-RPE65-injected eyes presented a reduction of the outer nuclear and photoreceptor outer segment layer thickness in the macula, that was more pronounced than in vehicle-injected eyes (n = 4). All LV-RPE65-injected eyes showed an initial perivascular reaction that resolved spontaneously within 14 days. Despite foveal structural changes, full-field electroretinography indicated that the overall retinal function was preserved over time and immunohistochemistry identified no difference in glial, microglial, or leucocyte ocular activation between low-dose, high-dose, and vehicle-injected eyes. Moreover, LV-RPE65-injected animals did not show signs of vector shedding or extraocular targeting, confirming the safe ocular restriction of the vector. Our results evidence a limited ocular tolerance to LV-RPE65 after subretinal injection without adjuvant anti-inflammatory prophylaxis, with complications linked to this route of administration necessitating to block this transient inflammatory event.

Purpose: Delivery of Advanced Therapy Medicinal Products to the submacular space is increasingly evolving into a therapeutic modality. Cell replacement for age-related macular degeneration (AMD) and gene therapy for RPE65 are recent successful examples. Herein, a nonhuman primate (NHP) model was used to investigate surgical means to detach the macula.

Methods: Sixteen eyes of 13 healthy macaques underwent a 25-gauge vitrectomy and subretinal injection of balanced salt solution monitored by microscope-integrated intraoperative optical coherence tomography (miOCT). The animals were followed with OCT and histology.

Results: The miOCT monitoring allowed a more precise definition of surgical trauma ranging from an initial full-thickness foveal tear, or induction of a cystoid macular edema (CME), until no foveal defect was discernible, as the technique improved. However, as the subretinal fluid wave detached the fovea, the aforementioned lesions formed, whereas persistent retinal adhesion reproducibly proved to remain in the distal parafoveal semi-annulus. Measures to reduce foveal trauma during submacular fluid injection included reducing intraocular pressure, injection volume, and velocity, as well as the retinal location for bleb initiation, use of a vitreous tamponade, and a dual-bore subretinal cannula.

Conclusions: A stable very low intraocular pressure and careful subretinal injection may avoid tangential macular stretching or mechanical CME formation, while vitreous tamponade may facilitate a more lamellar subretinal flow, all thereby reducing foveal trauma during submacular injection in NHP.

Translational relevance: These results can be relevant to any submacular surgery procedure used today, as they synergistically reduce the risk of compromising foveal integrity.

Keywords: Advanced Therapy Medicinal Products; fovea; intraoperative OCT; non-human primates; submacular surgery.

Development of a gene delivery system with high efficiency and a good safety profile is essential for successful gene therapy. Here we developed a targeted non-viral delivery system using a multifunctional lipid ECO for treating Leber's congenital amaurosis type 2 (LCA2) and tested this in a mouse model. ECO formed stable nanoparticles with plasmid DNA (pDNA) at a low amine to phosphate (N/P) ratio and mediated high gene transfection efficiency in ARPE-19 cells because of their intrinsic properties of pH-sensitive amphiphilic endosomal escape and reductive cytosolic release (PERC). All-trans-retinylamine, which binds to interphotoreceptor retinoid-binding protein (IRBP), was incorporated into the nanoparticles via a polyethylene glycol (PEG) spacer for targeted delivery of pDNA into the retinal pigmented epithelium. The targeted ECO/pDNA nanoparticles provided high GFP expression in the RPE of 1-month-old Rpe65-/- mice after subretinal injection. Such mice also exhibited a significant increase in electroretinographic activity, and this therapeutic effect continued for at least 120 days. A safety study in wild-type BALB/c mice indicated no irreversible retinal damage following subretinal injection of these targeted nanoparticles. All-trans-retinylamine-modified ECO/pDNA nanoparticles provide a promising non-viral platform for safe and effective treatment of RPE-specific monogenic eye diseases such as LCA2.

Vision research has often led to significant advances in our understanding of biology. There has also been particular success in translating basic research in the eye into breakthrough clinical therapies that mark important milestones for ophthalmology and also for medical research. Anti-VEGF therapy for age-related macular degeneration was named as one of the top ten science advancements of the year 2006. Only two years later, successful transfer of the RPE65 gene into retinal pigment epithelium of patients with Leber congenital amaurosis was noted as one of the most important clinical applications of gene therapy. The articles in this Review series outline current developments in vision research and highlight its continued importance in ophthalmology and medicine.

Oxidative stress is an important contributor to the pathogenesis of many retinal diseases including age-related macular degeneration and retinal dystrophies. Light-induced retinal degeneration (LIRD) can serve as a model in which to study the response of the retina to stress. Of note, many genetic mutant mice are in a C57BL/6 J background and are thus resistant to the usual LIRD models. We recently developed a new model of fundus camera-delivered light-induced retinal degeneration (FCD-LIRD) which is effective in strains of mice expressing the light-resistant variant of RPE65 (450Met), including C57BL/6 J. In this work we investigated whether FCD-LIRD would be useful as a model in which to test the effect of genetic mutations on the response of the retina to stress. Furthermore, we tested whether oxidative stress plays an important role in the setting of this new FCD-LIRD model. FCD-LIRD was applied to C57BL/6 J mice and to mice simultaneously deficient in three proteins that are important in the response of the retina to oxidative stress (SOD1, DJ-1 and Parkin). Using fundus photography, we found that retinal damage was dramatically increased in the SOD1/DJ-1/Parkin deficient mice compared to C57BL/6 J. Outer retinal OCT volume and RPE cell morphology analysis in ZO-1-stained flat mounts added support to these findings. Gene expression analysis confirmed a strong oxidative stress response after FCD-LIRD, which was differentially altered in the SOD1/DJ1/Parkin deficient mice. We conclude that FCD-LIRD is useful to study the effect of genetic mutations on the response of the retina to light stress in light-resistant strains of mice. Furthermore, oxidative stress seems to be an important component of FCD-LIRD. Finally, we have established protocols to quantify the effect of FCD-LIRD on the retina and RPE which will be useful for future studies. Further dissection of the mechanisms by which the retina responds to light-induced oxidative stress may result in new strategies to modulate this response, which could lead to a reduction in retinal and RPE damage.

Clinical trials are currently underway using gene therapy to treat retinal disease such as Leber congenital amaurosis (LCA). Viral vectors that have been utilized to target retinal cells include adenoviruses, lentiviruses, and recombinant adeno-associated viruses (rAAV). Of the three classes, rAAV vectors show the greatest promise for retinal gene therapy. Recent developments in virus technology such as the development of hybrid and capsid mutant rAAV vectors mean that specific retinal cells can be targeted and faster stronger transgene expression is now possible compared to that achieved with the first generation of vectors. Gene therapy trials in dogs have been very important in the development of therapy for RPE65 LCA which is currently in phase I/II clinical trials in humans. Recent successes in using gene therapy to treat canine achromatopsia, X-linked progressive retinal atrophy (PRA) and the more severe rapid degenerations such as rod-cone dysplasia type 3 may lead also to the translation to human clinical trials. Dogs have played and continue to play an important role as animal models for proof-of-concept studies of retinal gene therapy. As modifications and improvements in gene therapy protocols are made from experience gathered from human clinical trials perhaps gene therapy for the treatment of canine clinical patients will become available to veterinary ophthalmologists.

Over a decade of research and development culminated in the 2017 United States Food and Drug Administration (FDA) approval of voretigene neparvovec-rzyl (VN) for RPE65 mutation-associated inherited retinal dystrophy (IRD), the first approved gene therapy for a hereditary genetic disease in the US, and the first and only pharmacologic treatment for an IRD.Areas covered: VN serves as a model for the development of gene therapies to treat other IRDs. This review provides an overview of RPE65 mutation associated IRD, gene augmentation and viral vectors, along with phase 1 and phase 3 studies that led to VN's FDA approval. Subretinal injection of VN has resulted in improved performance on the novel multi-luminance mobility test (MLMT), light sensitivity and visual fields in patients with RPE65 mutation associated IRD, which predominantly impairs rod function. Additionally, the dosage, administration technique, pharmacokinetics, and safety data of VN are reviewed.Expert Opinion: As a model for development, special challenges associated with the introduction of this first gene therapy include limited genetic testing in clinical practice, novel surgical complexity of ocular gene therapy administration, new functional vision endpoints, as well as unique development, launch and reimbursement considerations associated with orphan therapies and one-time gene therapies.

Voretigene neparvovec (Luxturna^®), a recombinant adeno-associated virus vector-based gene therapy, delivers a functioning copy of the human retinal pigment epithelium-specific 65 kDa (RPE65) gene into retinal cells of patients with reduced or absent levels of RPE65 protein, providing the potential to restore the visual cycle. A single-dose subretinal injection of voretigene neparvovec administered in each eye is approved in several countries worldwide for the treatment of vision loss in adult and paediatric patients with confirmed biallelic RPE65 mutation-associated inherited retinal dystrophy (IRD) and with sufficient viable retinal cells. In the pivotal phase III trial, significant improvements from baseline were seen in the mean bilateral multi-luminance mobility test scores in the voretigene neparvovec group compared with the control group at 1 year. The beneficial effects of voretigene neparvovec treatment were maintained after up to 4 years of follow-up (with follow-up continuing for 15 years). Control recipients were eligible to receive voretigene neparvovec at 1 year, and showed improvements at subsequent follow-ups (≤ 3 years post injection) consistent with those in patients who received voretigene neparvovec at baseline. Most adverse reactions in voretigene neparvovec recipients were transient, asymptomatic and non-serious, and resolved without sequelae (may have been related to voretigene neparvovec, the subretinal injection procedure, concomitant corticosteroid use or a combination thereof). Retinal detachment occurred in one patient at year 4. Although ongoing additional long-term efficacy and safety data are required, voretigene neparvovec is an important novel gene therapy for patients with RPE65 mutation-associated IRD and sufficient viable retinal cells.

Until recently, there was no treatment for inherited retinal blindness. Late in 2017, Luxturna^TM became the first approved gene therapy product for a genetic disease in the USA and in the European Union, changing the situation. This article presents current considerations regarding the administration of this treatment in the clinic.

Objective: To determine whether functional vision and visual function improvements after voretigene neparvovec (VN; LUXTURNA®, Spark Therapeutics, Inc.) administration in subjects with biallelic RPE65 mutation-associated inherited retinal disease are maintained at 3-4 years, and to review safety outcomes.

Design: Open-label, randomized, controlled phase 3 trial.

Subjects: Thirty-one individuals were enrolled and randomized 2:1 to intervention (n=21) or control (n=10). One subject from each group withdrew before, or at, randomization.

Methods: Subjects in the original intervention (OI) group received bilateral subretinal VN injections. Delayed intervention (DI) subjects served as controls for 1 year, then received VN.

Main outcome measures: Change from injection baseline in bilateral performance on the multi-luminance mobility test (MLMT), a measure of ambulatory navigation, and change from injection baseline in full-field light sensitivity threshold (FST) white light, visual field (VF), and visual acuity (VA).

Results: Mean bilateral MLMT change scores at Year 4 for OI subjects and at Year 3 for DI subjects were 1.7 and 2.4 respectively, with 71% of subjects with a Year 3 visit able to pass MLMT at the lowest light level. Mean change in FST white light, averaged over both eyes at Year 4 for OI subjects, and at Year 3 for DI subjects, was -1.90 log₁₀(cd.s/m²) and -2.91 log₁₀(cd.s/m²), respectively. Mean change in Goldmann kinetic VF III4e sum total degrees, averaged across both eyes, was 197.7 at Year 4 for OI subjects and 157.9 at Year 3 for DI subjects. Mean change in VA (Holladay scale), averaged across both eyes, was -0.003 logMAR at Year 4 for OI subjects and -0.06 logMAR at Year 3 for DI subjects. One OI subject had a retinal detachment around Year 4, which impacted VA for the OI group. No product-related serious adverse events (SAEs) occurred, and there were no deleterious immune responses.

Conclusions: Improvements in ambulatory navigation, light sensitivity, and VF were consistent in both intervention groups. Overall, improvements were maintained up to 3-4 years, with ongoing observation. The safety profile of VN was consistent with vitrectomy and the subretinal injection procedure, and was similar between intervention groups, with no product-related SAEs reported.

Early attempts at gene therapy of inherited retinal diseases by recombinant adenovirus-vectored gene replacement in laboratory animals met with moderate success but the effect was transient. Recently, emphasis has shifted to less toxic vectors, namely recombinant adeno-associated (rAAV) viruses. Ribozymes, targeted to the P23H rhodopsin mutation in transgenic rats, significantly reduced photoreceptor loss and slowed attenuation of the electroretinogram (ERG) for 8 months. By gene replacement, rAAV-based photoreceptor rescue has been achieved in the rds-/- mouse and has restored vision in dogs carrying a RPE65 gene mutation. Minigenes for neurotrophins delivered by rAAV have been effective in achieving structural rescue of photoreceptors in rodent models of dominant disease, although this has not always been accompanied by functional rescue. One of the current challenges is the application of ribozyme therapy for dominant mutations coupled with wild-type gene augmentation to overcome haploinsufficiency. Other animal models are currently being utilized for preclinical studies as well. Spontaneously mutated Irish Setters and rd mice offer excellent subjects for the therapy of recessive mutations as do the RPE65 knockout mouse and RCS (rdy) rat. With burgeoning preclinical successes, the future looks bright for the treatment and cure of inherited retinal diseases in human patients.

OBJECTIVE

An update on heritable eye disease will allow informed patient counseling and improved patient care.

RESULTS

New loci and genes have been associated with identifiable heritable ocular traits. Molecular genetic analysis is available for many of these genes either as part of research or for clinical testing. The advent of gene array technologies has enabled screening of samples for known mutations in genes linked to various disorders. Exomic sequencing has proven to be particularly successful in research protocols in identifying the genetic causation of rare genetic traits by pooling patient resources and discovering new genes. Further, genetic analysis has led improvement in patient care and counselling, as exemplified by the continued advances in our treatment of retinoblastoma.

CONCLUSIONS

Patients and families are commonly eager to participate in either research or clinical testing to improve their understanding of the cause and heritability of an ocular condition. Many patients hope that testing will then lead to appropriate treatments or cures. The success of gene therapy in the RPE65 form of Leber congenital amaurosis has provided a brilliant example of this hope; that a similar trial may become available to other patients and families burdened by genetic disease.

Gene therapy (GT) has offered immense hope to individuals who are visually impaired because of RPE65 mutations. Although GT has shown great success in clinical trials enrolling these individuals, evidence for stability and durability of this treatment over time is still unknown. Herein we explored the value of functional magnetic resonance imaging (fMRI) as an objective measure to assess independently the longevity of retinal GT.

Individuals with RPE65 mutations who underwent GT in their worse-seeing eye in a phase 1 clinical trial received a second subretinal injection in their contralateral eye in a follow-on clinical trial. Functional magnetic resonance imaging (MRI) was performed longitudinally to assess brain responses of patients with RPE65 mutations after stimulation of their most recently treated eye before and 1 to 3 years after GT.

Seven participants with RPE65 mutations who were part of the follow-on clinical trial gave informed consent to participate in a longitudinal neuroimaging fMRI study.

All participants underwent fMRI using a 3-Tesla MRI system and a 32-channel head coil. Participants' cortical activations were assessed using a block design paradigm of contrast reversing checkerboard stimuli delivered using an MRI-compatible video system.

The primary parameters being measured in this study were the qualitative and quantitative fMRI cortical activations produced by our population in response to the visual task.

Functional MRI results showed minimal or no cortical responses before GT. Significant increase in cortical activation lasting at least 3 years after GT was observed for all participants. Repeated measures analysis showed significant associations between cortical activations and clinical measures such as full-field light sensitivity threshold for white, red, and blue colors; visual field; and pupillary light reflex.

Participants with RPE65 mutations showed intact visual pathways, which became responsive and strengthened after treatment. Functional MRI results independently revealed the efficacy and durability of a 1-time subretinal injection. The fMRI results paralleled those recently reported during the long-term clinical evaluations of the same patients. Results from this study demonstrated that fMRI may play an important role in providing complementary information to patients' ophthalmic clinical evaluation and has usefulness as an outcome measure for future retinal intervention studies.

A recent study published to screen RPE65 in 187 families with Leber Congenital Amaurosis (LCA) by Zilin Zhong in 2019. There are seven novel variants were identified in RPE65, which was associated with LCA, but among only five were missense mutations [(c.124C > T, p.(Leu42Phe), c.149T > C, p. (Phe50Ser), c.340A > C, p.(Asn114His), c.425A > G, p.(Asp142Gly) and c.1399C > G, p.(Pro467Ala)] in the Chinese population and potentially facilitates its clinical implementation. Further in-continuation of this study to the target of five novel missense mutations were the analysis of both structural and functional impact by the molecular dynamics and simulation. The result of five missense mutations might in critical structural alterations of RPE65 protein, disrupt its membrane association or rescue the activity of enzyme due to thermodynamics stability, and for this reason impair its isomerohydrolase activity, resulting in retinal dystrophy. These observations suggest that the reduced protein stability and altered subcellular localization of RPE65 might signify a mechanism for these mutations to lead to vision loss in LCA patients.

Successful treatment of early-onset sever retinal degeneration (EOSRD) in an animal model of the disease has provided the first proof-o-principle for retinal gene therapy of higher mammals. Currently, large sets of DNA samples are screened to identify patients with Leber's congenital amaurosis (LCA) carrying mutations in RPE65 as possible candidates for gene therapy trials. Research into EOSRD and LCA aims to identify the function of proteins involved or phenotypic changes upon mutation. These data will be used to describe the disease phenotype and identify parameters that can predict the outcome of gene therapy trials.

OBJECTIVE

To identify individual cone photoreceptors in a transgenic mouse line in vivo based on selective expression of green fluorescent protein (GFP) using cSLO (confocal scanning laser ophthalmoscopy) and to use this approach to monitor cone cell fate in mouse models of retinal degeneration.

METHODS

Transgenic mice expressing GFP under the control of a red-green opsin promoter (RG-GFP mice) were analyzed in vivo with respect to GFP expression in cone cells using cSLO and functional integrity using electroretinography (ERG). Histology was performed to correlate the pattern of GFP expression with light microscopic data. Longitudinal monitoring of cone survival was evaluated in crossbreds of RG-GFP mice with cpfl1 and Rpe65(-/-) mutant mice, respectively.

RESULTS

The authors found that RG-GFP transgenic mice had a stable GFP expression that did not interfere with retinal function up to at least 3 months of age. Thus, a longitudinal analysis of cone degeneration in individual RG cpfl1 and RG Rpe65(-/-) cross-bred mice in vivo was successfully performed and demonstrated distinct time frames of cone survival in the particular mouse model.

CONCLUSIONS

Monitoring GFP expression in cone photoreceptor cells, such as in the RG-GFP mouse, is a promising in vivo approach for the analysis of cone survival in mice.

RPE65 is a membrane-associated retinoid isomerase involved in the visual cycle responsible for sustaining vision. Many mutations in the human RPE65 gene are associated with distinct forms of retinal degenerative diseases. The pathogenic mechanisms for most of these mutations remain poorly understood. Here, we show that three Leber congenital amaurosis -associated RPE65 mutants (R91W, Y249C and R515W) undergo rapid proteasomal degradation mediated by the 26 S proteasome non-ATPase regulatory subunit 13 (PSMD13) in cultured human retinal pigment epithelium (RPE) cells. These mutant proteins formed cytosolic inclusion bodies or high molecular weight complexes via disulfide bonds. The mutations are mapped on non-active sites but severely reduced isomerase activity of RPE65. At 30°C, however, the enzymatic function and membrane-association of the mutant RPE65s are significantly rescued possibly due to proper folding. In addition, PSMD13 displayed a drastically decreased effect on degradation of the mutant proteins in the cells grown at 30°C. These results suggest that PSMD13 plays a critical role in regulating pathogenicity of the mutations and the molecular basis for the PSMD13-mediated rapid degradation and loss of function of the mutants is misfolding of RPE65.

Retinal epithelium-specific protein 65 kDa (RPE65)-deficient dogs are a valuable large animal model species that have been used to refine gene augmentation therapy for Leber congenital amaurosis type-2 (LCA2). Previous studies have suggested that retinal degeneration in the dog model is slower than that observed in humans. However, the area centralis of the dog retina is a cone and rod photoreceptor rich region comparable to the human macula, and the effect of RPE65 deficiency specifically on this retinal region, important for high acuity vision, has not previously been reported.

Spectral-domain optical coherence tomography, fundus photography, and immunohistochemistry of retinal wholemounts and sagittal frozen sections were used to define the time-course and cell-types affected in degeneration of the area centralis in affected dogs.

Area centralis photoreceptor degeneration was evident from 6 weeks of age, and progressed to involve the inner retina. Immunohistochemistry showed that RPE65-deficient dogs developed early loss of S-cone outer segments, with slower loss of L/M-cone outer segments and rods.

Early-onset severe photoreceptor degeneration in the area centralis of dogs with RPE65-deficiency offers a model of the early foveal/perifoveal degeneration in some patients with LCA2. This model could be used to refine interventions aiming to improve function and halt the progression of foveal/perifoveal photoreceptor degeneration.

OBJECTIVE

Retinal pigment epithelial (RPE) cells are capable of differentiating into retinal neurons when induced by the appropriate growth factors. Amniotic fluid contains a variety of growth factors that are crucial for the development of a fetus. In this study, the effects of human amniotic fluid (HAF) on primary RPE cell cultures were evaluated.

METHODS

RPE cells were isolated from the globes of postnatal human cadavers. The isolated cells were plated and grown in DMEM/F12 with 10% fetal bovine serum. To confirm the RPE identity of the cultured cells, they were immunocytochemically examined for the presence of the RPE cell-specific marker RPE65. RPE cultures obtained from passages 2-7 were treated with HAF and examined morphologically for 1 month. To determine whether retinal neurons or progenitors developed in the treated cultures, specific markers for bipolar (protein kinase C isomer α, PKCα), amacrine (cellular retinoic acid-binding protein I, CRABPI), and neural progenitor (NESTIN) cells were sought, and the amount of mRNA was quantified using real-time PCR.

RESULTS

Treating RPE cells with HAF led to a significant decrease in the number of RPE65-positive cells, while PKCα- and CRABPI-positive cells were detected in the cultures. Compared with the fetal bovine serum-treated cultures, the levels of mRNAs quantitatively increased by 2-, 20- and 22-fold for NESTIN, PKCα, and CRABPI, respectively. The RPE cultures treated with HAF established spheres containing both pigmented and nonpigmented cells, which expressed neural progenitor markers such as NESTIN.

CONCLUSIONS

This study showed that HAF can induce RPE cells to transdifferentiate into retinal neurons and progenitor cells, and that it provides a potential source for cell-based therapies to treat retinal diseases.

Restored rod visual function after gene therapy can be established unequivocally by demonstrating that, after dark adaptation, spectral sensitivity has the shape characteristic of rods and that this shape collapses to a cone-like shape before rods have recovered after an intense bleach. We used these tests to assess retinal function in eight young adults and children with early-onset severe retinal dystrophy from Phase II of a clinical gene-therapy trial for RPE65 deficiency that involved the subretinal delivery of a recombinant adeno-associated viral vector carrying RPE65. We found substantial improvements in rod sensitivity in two participants: dark-adapted spectral sensitivity was rod-like after treatment and was cone-like before rods had recovered after a bleach. After 40 min of dark adaptation, one participant showed up to 1,000-fold sensitivity improvements 4 months after treatment and the second up to 100-fold improvements 6 months after treatment. The dark-adapted spectral sensitivities of the other six participants remained cone-like and showed little improvement in sensitivity.