Gene therapy for RPE65-related retinal disease

Preclinical dose response study shows NR2E3 can attenuate retinal degeneration in the retinitis pigmentosa mouse model RhoP23H+/. Gene Ther 2024;31:255-262. [PMID: 38273095 DOI: 10.1038/s41434-024-00440-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Retinitis pigmentosa (RP) is a heterogeneous disease and the main cause of vision loss within the group of inherited retinal diseases (IRDs). IRDs are a group of rare disorders caused by mutations in one or more of over 280 genes which ultimately result in blindness. Modifier genes play a key role in modulating disease phenotypes, and mutations in them can affect disease outcomes, rate of progression, and severity. Our previous studies have demonstrated that the nuclear hormone receptor 2 family e, member 3 (Nr2e3) gene reduced disease progression and loss of photoreceptor cell layers in RhoP23H-/- mice. This follow up, pharmacology study evaluates a longitudinal NR2E3 dose response in the clinically relevant heterozygous RhoP23H mouse. Reduced retinal degeneration and improved retinal morphology was observed 6 months following treatment evaluating three different NR2E3 doses. Histological and immunohistochemical analysis revealed regions of photoreceptor rescue in the treated retinas of RhoP23H+/- mice. Functional assessment by electroretinogram (ERG) showed attenuated photoreceptor degeneration with all doses. This study demonstrates the effectiveness of different doses of NR2E3 at reducing retinal degeneration and informs dose selection for clinical trials of RhoP23H-associated RP.

Nucleic acid delivery to retinal cells using lipopeptides as a potential tool towards ocular gene therapies

We evaluated the use of lipopeptides capable to bind to nucleic acids towards plasmid DNA (pDNA) delivery. The investigations were particularly focused on arising retinal pigment epithelial cells (ARPE-19) as motivated by the considerable number of ocular disorders linked to gene aberrations. The lipopeptides comprised the artificial oligoamino acid succinyl-tetraethylene pentamine (Stp) as well as incorporated lysines, histidines, cysteines, fatty acids, and tyrosine trimers. Regardless of the structural differences, the lipopeptides demonstrated to efficiently condense pDNA at nitrogen-to-phosphate molar ratio (N/P) ≥ 6. Spheric nanoparticles were observed by cryo-TEM and dynamic light scattering determined hydrodynamic sizes ranging from 50 to 130 nm. The biological assays evidenced highly efficient pDNA delivery with a lower degree of cytotoxicity compared to the well-known transfecting agent linear polyethylenimine (LPEI). Although more efficient than LPEI, cysteine-containing carriers were demonstrated to be less efficient than the other counterparts possibly due to exceeding polyplex stabilization via disulfide cross links, which could hamper pDNA unpacking at the target site. Therefore, clearly a balance between complex stability and cargo release should be taken into account to optimize the transfection efficiency of the non-viral vectors. The gene transfer activity in ARPE-19 cells suggests the applicability of this kind of carrier for ocular treatments based on retinal gene delivery.

Innovative Genoceuticals in Human Gene Therapy Solutions: Challenges and Safe Clinical Trials of Orphan Gene Therapy Products

The success of gene therapy attempts is controversial and inconclusive. Currently, it is popular among the public, the scientific community, and manufacturers of Gene Therapy Medical Products. In the absence of any remedy or treatment options available for untreatable inborn metabolic orphan or genetic diseases, cancer, or brain diseases, gene therapy treatment by genoceuticals and T-cells for gene editing and recovery remains the preferred choice as the last hope. A new concept of "Genoceutical Gene Therapy" by using orphan 'nucleic acid-based therapy' aims to introduce scientific principles of treating acquired tissue damage and rare diseases. These Orphan Genoceuticals provide new scope for the 'genodrug' development and evaluation of genoceuticals and gene products for ideal 'gene therapy' use in humans with marketing authorization application (MAA). This perspective study focuses on the quality control, safety, and efficacy requirements of using 'nucleic acid-based and human cell-based new gene therapy' genoceutical products to set scientific advice on genoceutical-based 'orphan genodrug' design for clinical trials as per Western and European guidelines. The ethical Western FDA and European EMA guidelines suggest stringent legal and technical requirements on genoceutical medical products or orphan genodrug use for other countries to frame their own guidelines. The introduction section proposes lessknown 'orphan drug-like' properties of modified RNA/DNA, human cell origin gene therapy medical products, and their transgene products. The clinical trial section explores the genoceutical sources, FDA/EMA approvals for genoceutical efficacy criteria with challenges, and ethical guidelines relating to gene therapy of specific rare metabolic, cancer and neurological diseases. The safety evaluation of approved genoceuticals or orphan drugs is highlighted with basic principles and 'genovigilance' requirements (to observe any adverse effects, side effects, developed signs/symptoms) to establish their therapeutic use. Current European Union and Food and Drug Administration guidelines continuously administer fast-track regulatory legal framework from time to time, and they monitor the success of gene therapy medical product efficacy and safety. Moreover, new ethical guidelines on 'orphan drug-like genoceuticals' are updated for biodistribution of the vector, genokinetics studies of the transgene product, requirements for efficacy studies in industries for market authorization, and clinical safety endpoints with their specific concerns in clinical trials or public use.

AAV for Gene Therapy in Ocular Diseases: Progress and Prospects

Owing to the promising therapeutic effect and one-time treatment advantage, gene therapy may completely change the management of eye diseases, especially retinal diseases. Adeno-associated virus (AAV) is considered one of the most promising viral gene delivery tools because it can infect various types of tissues and is considered as a relatively safe gene delivery vector. The eye is one of the most popular organs for gene therapy, since its limited volume is suitable for small doses of AAV stably transduction. Recently, an increasing number of clinical trials of AAV-mediated gene therapy are underway. This review summarizes the biological functions of AAV and its application in the treatment of various ocular diseases, as well as the characteristics of different AAV delivery routes in clinical applications. Here, the latest research progresses in AAV-mediated gene editing and silencing strategies to modify that the genetic ocular diseases are systematically outlined, especially by base editing and prime editing. We discuss the progress of AAV in ocular optogenetic therapy. We also summarize the application of AAV-mediated gene therapy in animal models and the difficulties in its clinical transformation.

Direct optogenetic activation of upper airway muscles in an acute model of upper airway hypotonia mimicking sleep onset

STUDY OBJECTIVES

Obstructive sleep apnea (OSA), where the upper airway collapses repeatedly during sleep due to inadequate dilator muscle tone, is challenging to treat as current therapies are poorly tolerated or have variable and unpredictable efficacy. We propose a novel, optogenetics-based therapy, that stimulates upper airway dilator muscle contractions in response to light. To determine the feasibility of a novel optogenetics-based OSA therapy, we developed a rodent model of human sleep-related upper airway muscle atonia. Using this model, we evaluated intralingual delivery of candidate optogenetic constructs, notably a muscle-targeted approach that will likely have a favorable safety profile.

METHODS

rAAV serotype 9 viral vectors expressing a channelrhodopsin-2 variant, driven by a muscle-specific or nonspecific promoter were injected into rat tongues to compare strength and specificity of opsin expression. Light-evoked electromyographic responses were recorded in an acute, rodent model of OSA. Airway dilation was captured with ultrasound.

RESULTS

The muscle-specific promoter produced sufficient opsin expression for light stimulation to restore and/or enhance electromyographic signals (linear mixed model, F = 140.0, p < 0.001) and induce visible tongue contraction and airway dilation. The muscle-specific promoter induced stronger (RM-ANOVA, F(1,8) = 10.0, p = 0.013) and more specific opsin expression than the nonspecific promoter in an otherwise equivalent construct. Viral DNA and RNA were robust in the tongue, but low or absent in all other tissues.

CONCLUSIONS

Significant functional responses to direct optogenetic muscle activation were achieved following muscle-specific promoter-driven rAAV-mediated transduction, providing proof-of-concept for an optogenetic therapy for patients with inadequate dilator muscle activity during sleep.

Dual AAV-based PCDH15 gene therapy achieves sustained rescue of visual function in a mouse model of Usher syndrome 1F

Mutations in the PCDH15 gene, encoding protocadherin-15, are among the leading causes of Usher syndrome type 1 (USH1F), and account for up to 12% USH1 cases worldwide. A founder truncating variant of PCDH15 has a ∼2% carrier frequency in Ashkenazi Jews accounting for nearly 60% of their USH1 cases. Although cochlear implants can restore hearing perception in USH1 patients, presently there are no effective treatments for the vision loss due to retinitis pigmentosa. We established a founder allele-specific Pcdh15 knockin mouse model as a platform to ascertain therapeutic strategies. Using a dual-vector approach to circumvent the size limitation of adeno-associated virus, we observed robust expression of exogenous PCDH15 in the retinae of Pcdh15KI mice, sustained recovery of electroretinogram amplitudes and key retinoid oxime, substantially improved light-dependent translocation of phototransduction proteins, and enhanced levels of retinal pigment epithelium-derived enzymes. Thus, our data raise hope and pave the way for future gene therapy trials in USH1F subjects.

Use of Biologics and Stem Cells in Equine Ophthalmology

Regenerative therapy and biologics have the promise to treat equine ocular surface diseases, including corneal ulceration or immune-mediated keratitis, or intraocular diseases such as uveitis. The use of blood-derived products such as serum or platelet-rich plasma, mesenchymal stem cells, or amniotic membrane grafts may be beneficial for the treatment of ulcerative and chronic keratitis in horses. Furthermore, the use of stem cells or gene therapy has promise for the treatment of Intraocular diseases such as equine recurrent uveitis by providing efficacious, practical, and long-term therapy for these blinding diseases.

The Use of rAAV2-RB1-Mediated Gene Therapy in Retinoblastoma

Purpose

Retinoblastoma (RB) is a life-threatening malignancy that arises from the retina and is activated upon homozygous inactivation of the tumor suppressor RB1. Gene therapy targeting RB1 is an effective strategy to treat RB. However, it is difficult to target the RB1 gene by site-specific repair, with up to 3366 gene mutation sites identified in RB1. Thus, it is necessary to construct a promising and efficacious gene therapeutic strategy for patients with RB.

Methods

To recover the function of the RB1 protein, we constructed a recombinant adeno-associated virus 2 (rAAV2) expressing RB1 that can restore RB1 function and significantly inhibit RB progression. To confirm the clinical feasibility of rAAV2-RB1, the RB1 protein was validated in vitro and in vivo after transfection. To further evaluate the clinical efficacy, RB patient-derived xenograft models were established and applied. The biosafety of rAAV2-RB1 was also validated in immunocompetent mice.

Results

rAAV2-RB1 was a rAAV2 expressing the RB1 protein, which was validated in vitro and in vivo. In vitro, rAAV2-RB1 was effectively expressed in patient-derived RB cells. In mice, intravitreal administration of rAAV2-RB1 in a population-based patient-derived xenograft trial induced limited tumor growth. Moreover, after transfection of rAAV2-RB1 in immunocompetent mice, rAAV2-RB1 did not replicate and was expressed in other important organs, except retinas, inducing minor local side effects.

Conclusions

Our study suggested a promising efficacy gene therapeutic strategy, which might provide a chemotherapy-independent treatment option for RB.

Zellweger Spectrum Disorder: Ophthalmic Findings from a New Natural History Study Cohort and Scoping Literature Review

PURPOSE

Individuals with Zellweger spectrum disorder (ZSD) manifest a spectrum of clinical phenotypes but almost all have retinal degeneration leading to blindness. The onset, extent, and progression of retinal findings have not been well described. It is crucial to understand the natural history of vision loss in ZSD to define reliable endpoints for future interventional trials. Herein, we describe ophthalmic findings in the largest number of ZSD patients to date.

DESIGN

Retrospective review of longitudinal data from medical charts and review of cross-sectional data from the literature.

PARTICIPANTS

Sixty-six patients with ZSD in the retrospective cohort and 119 patients reported in the literature, divided into 4 disease phenotypes based on genotype or clinical severity.

METHODS

We reviewed ophthalmology records collected from the retrospective cohort (Clinicaltrials.gov NCT01668186) and performed a scoping review of the literature for ophthalmic findings in patients with ZSD. We extracted available ophthalmic data and analyzed by age and disease severity.

MAIN OUTCOME MEASURES

Visual acuity (VA), posterior and anterior segment descriptions, nystagmus, refraction, electroretinography findings, visual evoked potentials, and OCT results and images.

RESULTS

Visual acuity was worse at younger ages in those with severe disease compared with older patients with intermediate to mild disease for all 78 participants analyzed, with a median VA of 0.93 logarithm of the minimum angle of resolution (Snellen 20/320). Longitudinal VA data revealed slow loss over time and legal blindness onset at an average age of 7.8 years. Funduscopy showed retinal pigmentation, macular abnormalities, small or pale optic discs, and attenuated vessels with higher prevalence in milder severity groups and did not change with age. Electroretinography waveforms were diminished in 91% of patients, 46% of which were extinguished and did not change with age. OCT in milder patients revealed schitic changes in 18 of 23 individuals (age range 1.8 to 30 years), with evolution or stable macular edema.

CONCLUSIONS

In ZSD, VA slowly deteriorates and is associated with disease severity, serial electroretinography is not useful for documenting vision loss progression, and intraretinal schitic changes may be common. Multiple systematic measures are required to assess retinal dystrophy accurately in ZSD, including functional vision measures.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

An Optical Coherence Tomography-Based Measure as an Independent Estimate of Retinal Function in Retinitis Pigmentosa

BACKGROUND

With the clinical advances in the field of gene therapy, the development of objective measures of visual function of patients with inherited retinal dystrophies (IRDs) is of utmost importance. Here, we propose one such measure.

METHODS

We retrospectively analyzed data from a cohort of 194 eyes of 97 genetically diagnosed patients with retinitis pigmentosa (RP), the most common IRD, followed at the UPMC Vision Institute. The analyzed data included the reflectivity ratio (RR) of the retinal nerve fiber layer (RNFL) to that of the entire retina, visual acuity (VA) and the thickness of the retinal outer nuclear layer (ONL) and the RNFL.

RESULTS

There was a strong positive correlation between the RR and VA. Both VA and the RR were negatively correlated with disease duration; VA, but not the RR, was negatively correlated with age. The RR correlated with the ONL but not with the RNFL thickness or the intraocular pressure. Age, RR, disease duration and ONL thickness were found to be independent predictors of VA by multivariate analysis.

CONCLUSION

The OCT RR could serve as an independent predictor of visual acuity, and by extension of retinal function, in genetically diagnosed RP patients. Such objective measures can be of great value in patient selection for therapeutic trials.

Safety and Efficacy of Adeno-Associated Viral Gene Therapy in Patients With Retinal Degeneration: A Systematic Review and Meta-Analysis

Purpose

This systematic review evaluates the safety and efficacy of ocular gene therapy using adeno-associated virus (AAV).

Methods

MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov were searched systematically for controlled or non-controlled interventional gene therapy studies using key words related to retinal diseases, gene therapy, and AAV vectors. The primary outcome measure was safety, based on ocular severe adverse events (SAEs). Secondary outcome measures evaluated efficacy of the therapy based on best corrected visual acuity (BCVA) and improvements in visual sensitivity and systemic involvement following ocular delivery. Pooling was done using a DerSimonian Laird random effects model. Risk of bias was assessed using the Cochrane Risk of Bias Tool, version 1.

Results

Our search identified 3548 records. Of these, 80 publications met eligibility criteria, representing 28 registered clinical trials and 5 postmarket surveillance studies involving AAV gene therapy for Leber congenital amaurosis (LCA), choroideremia, Leber hereditary optic neuropathy (LHON), age-related macular degeneration (AMD), retinitis pigmentosa (RP), X-linked retinoschisis, and achromatopsia. Overall, AAV therapy vectors were associated with a cumulative incidence of at least one SAE of 8% (95% confidence intervals [CIs] of 5% to 12%). SAEs were often associated with the surgical procedure rather than the therapeutic vector itself. Poor or inconsistent reporting of adverse events (AEs) were a limitation for the meta-analysis. The proportion of patients with any improvement in BCVA and visual sensitivity was 41% (95% CIs of 31% to 51%) and 51% (95% CIs of 31% to 70%), respectively. Systemic immune involvement was associated with a cumulative incidence of 31% (95% CI = 21% to 42%).

Conclusions

AAV gene therapy vectors appear to be safe but the surgical procedure required to deliver them is associated with some risk. The large variability in efficacy can be attributed to the small number of patients treated, the heterogeneity of the population and the variability in dosage, volume, and follow-up.

Translational Relevance

This systematic review will help to inform and guide future clinical trials.

Successful large gene augmentation of USH2A with non-viral episomal vectors

USH2A mutations are a common cause of autosomal recessive retinitis pigmentosa (RP) and Usher syndrome, for which there are currently no approved treatments. Gene augmentation is a valuable therapeutic strategy for treating many inherited retinal diseases; however, conventional adeno-associated virus (AAV) gene therapy cannot accommodate cDNAs exceeding 4.7 kb, such as the 15.6-kb-long USH2A coding sequence. In the present study, we adopted an alternative strategy to successfully generate scaffold/matrix attachment region (S/MAR) DNA plasmid vectors containing the full-length human USH2A coding sequence, a GFP reporter gene, and a ubiquitous promoter (CMV or CAG), reaching a size of approximately 23 kb. We assessed the vectors in transfected HEK293 cells and USH2A patient-derived dermal fibroblasts in addition to ush2au507 zebrafish microinjected with the vector at the one-cell stage. pS/MAR-USH2A vectors drove persistent transgene expression in patient fibroblasts with restoration of usherin. Twelve months of GFP expression was detected in the photoreceptor cells, with rescue of Usher 2 complex localization in the photoreceptors of ush2au507 zebrafish retinas injected with pS/MAR-USH2A. To our knowledge, this is the first reported vector that can be used to express full-length usherin with functional rescue. S/MAR DNA vectors have shown promise as a novel non-viral retinal gene therapy, warranting further translational development.

Aldehyde Dehydrogenase and Aldo-Keto Reductase Enzymes: Basic Concepts and Emerging Roles in Diabetic Retinopathy

Diabetic retinopathy (DR) is a complication of diabetes mellitus that can lead to vision loss and blindness. It is driven by various biochemical processes and molecular mechanisms, including lipid peroxidation and disrupted aldehyde metabolism, which contributes to retinal tissue damage and the progression of the disease. The elimination and processing of aldehydes in the retina rely on the crucial role played by aldehyde dehydrogenase (ALDH) and aldo-keto reductase (AKR) enzymes. This review article investigates the impact of oxidative stress, lipid-derived aldehydes, and advanced lipoxidation end products (ALEs) on the advancement of DR. It also provides an overview of the ALDH and AKR enzymes expressed in the retina, emphasizing their growing importance in DR. Understanding the relationship between aldehyde metabolism and DR could guide innovative therapeutic strategies to protect the retina and preserve vision in diabetic patients. This review, therefore, also explores various approaches, such as gene therapy and pharmacological compounds that have the potential to augment the expression and activity of ALDH and AKR enzymes, underscoring their potential as effective treatment options for DR.

Progress and prospects of gene therapy in ophthalmology from 2000 to 2022: A bibliometric analysis

Background

Gene therapy is a treatment approach at the genetic level, which brings great advances in many diseases and develops rapidly in recent years. Currently, its mechanism of action is mainly through the replacement of missing or defective genes, or the reduction of harmful gene products. However, the application of gene therapy in ophthalmology remains limited.

Methods

A total of 1143 articles and reviews published in the field of ocular gene therapies were found in the Web of Science Core Collection database and used for the bibliometric analysis. CiteSpace was mainly applied to the network analysis of countries, institutions, keywords, and dual-map overlay of journals. The visual analysis of authors, journals, and references was used by VOSviewer. The geographical distribution of publications was conducted by R language.

Results

The annual publications are increasing in general. Currently, the USA and the UK are two main sources of publications in this field. Switzerland, Denmark, and Finland are the top 3 countries that establish the most cooperation and exchanges with other countries or regions. The most cited and co-cited journal in this field is Investigative Ophthalmology & Visual Science. Gene therapy studies for eye diseases are mainly focused on retinal dysfunctions by the analysis of references, keywords, and counting of original research, including Leber's congenital amaurosis and retinitis pigmentosa.

Conclusion

This study used bibliometrics to analyze overall characteristics and put forward prospects for the future in the field of gene therapy in ophthalmology. Ocular diseases, especially hereditary retinal diseases, will be the major focus of gene therapy in the future.

Delivery Systems in Ocular Retinopathies: The Promising Future of Intravitreal Hydrogels as Sustained-Release Scaffolds

Slow-release delivery systems are needed to ensure long-term sustained treatments for retinal diseases such as age-related macular degeneration and diabetic retinopathy, which are currently treated with anti-angiogenic agents that require frequent intraocular injections. These can cause serious co-morbidities for the patients and are far from providing the adequate drug/protein release rates and required pharmacokinetics to sustain prolonged efficacy. This review focuses on the use of hydrogels, particularly on temperature-responsive hydrogels as delivery vehicles for the intravitreal injection of retinal therapies, their advantages and disadvantages for intraocular administration, and the current advances in their use to treat retinal diseases.

Evaluation of CRISPR/Cas9 exon-skipping vector for choroideremia using human induced pluripotent stem cell-derived RPE

BACKGROUND

Exon-skipping is a powerful genetic tool, especially when delivering genes using an AAV-mediated full-length gene supplementation strategy is difficult owing to large length of genes. Here, we used engineered human induced pluripotent stem cells and artificial intelligence to evaluate clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9-based exon-skipping vectors targeting genes of the retinal pigment epithelium (RPE). The model system was choroideremia; this is an X-linked inherited retinal disease caused by mutation of the CHM gene.

METHODS

We explored whether artificial intelligence detected differentiation of human OTX2, PAX6 and MITF (hOPM) cells, in which OTX2, PAX6 and MITF expression was induced by doxycycline treatment, into RPE. Plasmid encoding CHM exon-skipping modules targeting the splice donor sites of exons 6 were constructed. A clonal hOPM cell line with a frameshift mutation in exon 6 was generated and differentiated into RPE. CHM exon 6-skipping was induced, and the effects of skipping on phagocytic activity, cell death and prenylation of Rab small GTPase (RAB) were evaluated using flow cytometry, an in vitro prenylation assay and western blotting.

RESULTS

Artificial intelligence-based evaluation of RPE differentiation was successful. Retinal pigment epithelium cells with a frameshift mutation in exon 6 showed increased cell death, reduced phagocytic activity and increased cytosolic unprenylated RABs only when oxidative stress was in play. The latter two phenotypes were partially rescued by exon 6-skipping of CHM.

CONCLUSIONS

CHM exon 6-skipping contributed to RPE phagocytosis probably by increasing RAB38 prenylation under oxidative stress.

Adeno-Associated Virus-Mediated Gene Therapy

Choice of vector is the most critical step in gene therapy. Adeno-associated viruses (AAV); third generation vectors, are getting much attention of scientists to be used as vehicles due to their non-pathogenicity, excellent safety profile, low immune responses, great efficiency to transduce non-dividing cells, large capacity to transfer genetic material and long-term expression of genetic payload. AAVs have multiple serotypes and each serotype shows tropism for a specific cell. Different serotypes are used to target liver, lungs, muscles, retina, heart, CNS, kidneys, etc. Furthermore, AAV based gene therapies have tremendous marketing applications that can be perfectly incorporated in the anticipated sites of the host target genome resulting in life long expression of transgenes. Some therapeutic products use AAV vectors that are used to treat lipoprotein lipase deficiency (LPLD) and it is injected intramuscularly, to treat mutated retinal pigment epithelium RPE65 (RPE65) that is introduced to subretinal space, an intravenous infusion to treat spinal muscular atrophy and rAAV2-CFTR vector is introduced into nasal epithelial cells to treat cystic fibrosis. AAV therapies and other such interdisciplinary methodologies can create the miracles for the generation of precision gene therapies for the treatment of most serious and sometimes fatal disorders.

Use of gene therapy for optic nerve protection: Current concepts

Gene therapy has become an essential treatment for optic nerve injury (ONI) in recent years, and great strides have been made using animal models. ONI, which is characterized by the loss of retinal ganglion cells (RGCs) and axons, can induce abnormalities in the pupil light reflex, visual field defects, and even vision loss. The eye is a natural organ to target with gene therapy because of its high accessibility and certain immune privilege. As such, numerous gene therapy trials are underway for treating eye diseases such as glaucoma. The aim of this review was to cover research progress made in gene therapy for ONI. Specifically, we focus on the potential of gene therapy to prevent the progression of neurodegenerative diseases and protect both RGCs and axons. We cover the basic information of gene therapy, including the classification of gene therapy, especially focusing on genome editing therapy, and then we introduce common editing tools and vector tools such as Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) -Cas9 and adeno-associated virus (AAV). We also summarize the progress made on understanding the roles of brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), phosphatase-tensin homolog (PTEN), suppressor of cytokine signal transduction 3 (SOCS3), histone acetyltransferases (HATs), and other important molecules in optic nerve protection. However, gene therapy still has many challenges, such as misalignment and mutations, immunogenicity of AAV, time it takes and economic cost involved, which means that these issues need to be addressed before clinical trials can be considered.

The Predicted Splicing Variant c.11+5G>A in RPE65 Leads to a Reduction in mRNA Expression in a Cell-Specific Manner

Pathogenic variants in RPE65 lead to retinal diseases, causing a vision impairment. In this work, we investigated the pathomechanism behind the frequent RPE65 variant, c.11+5G>A. Previous in silico predictions classified this change as a splice variant. Our prediction using novel software's suggested a 124-nt exon elongation containing a premature stop codon. This elongation was validated using midigenes-based approaches. Similar results were observed in patient-derived induced pluripotent stem cells (iPSC) and photoreceptor precursor cells. However, the splicing defect in all cases was detected at low levels and thereby does not fully explain the recessive condition of the resulting disease. Long-read sequencing discarded other rearrangements or variants that could explain the diseases. Subsequently, a more relevant model was employed: iPSC-derived retinal pigment epithelium (RPE) cells. In patient-derived iPSC-RPE cells, the expression of RPE65 was strongly reduced even after inhibiting a nonsense-mediated decay, contradicting the predicted splicing defect. Additional experiments demonstrated a cell-specific gene expression reduction due to the presence of the c.11+5G>A variant. This decrease also leads to the lack of the RPE65 protein, and differences in size and pigmentation between the patient and control iPSC-RPE. Altogether, our data suggest that the c.11+5G>A variant causes a cell-specific defect in the expression of RPE65 rather than the anticipated splicing defect which was predicted in silico.

Anatomical and functional correlates of cystic macular edema in retinitis pigmentosa

Cystoid macular edema (CME) is a major cause of central visual deterioration in retinitis pigmentosa. The exact reason for CME and its prognostic significance in this patient population is unknown. We seek to find clues to answer these questions by examining the anatomical correlations between retinal cysts and retinal morphometric parameters in a cohort of patients with retinitis pigmentosa and CME. For this reason, 103 patients (196 eyes) with untreated cystoid macular edema (CME) were identified from a pool of 578 genotyped patients with retinitis pigmentosa. Image analyses were conducted using three central horizontal OCT scans of these patients to calculate cross-sectional areas of the retinal nerve fiber layer, outer retinal, inner retinal, cysts, and total retinal areas. Lengths of the ellipsoid zone and outer limiting membrane were also measured. Best-fit curves were derived for analyzing the factors playing a role in the size of the retinal cysts and the patients’ visual acuity. Generalized Estimating Equation and multivariate linear regression analyses were conducted to determine the correlations between visual acuity, morphometric and clinical data, and the significant cyst size and visual acuity determinants. Twenty-five percent of the screened patients (103/578) had CME. Patients with autosomal dominant retinitis pigmentosa had the highest incidence of CME (43.6%, p<0.001) but also had the best visual acuity (20/34±20/30, p = 0.02). The total cyst area was 0.14±0.18 mm². Outer retinal area (B = 0.214; p = 0.008), age (B = -0.003; p<0.001) and retinal nerve fiber area (B = 0.411; p = 0.005) were main determinants of the (r = 0.44; p<0.001) cyst size. Cysts resolved with progressing retinal degeneration. Length of the intact ellipsoid zone (B = -5.16E-5; p<0.001), the inheritance pattern (B = 0.04; p = 0.028) and retinal nerve fiber area (B = 0.751; p<0.001) were the main determinants of visual acuity. In patients with retinitis pigmentosa and cystoid macular edema, retinal nerve fiber layer thickness is associated with decreasing visual acuity and cyst size. This finding suggests that intraretinal cysts may compress retinal axons and cause subsequent visual loss in retinitis pigmentosa.

Loss of Fas Receptor Function Preserves Photoreceptor Structure and Function in Two Mouse Models of Inherited Retinal Degeneration

Purpose

The genetic heterogeneity of inherited retinal degeneration (IRD) has limited the development of mutation-specific therapies, necessitating the development of therapeutic approaches targeting broadly shared pathophysiologic pathways. The Fas receptor has been reported as a contributor to retinal cell death and inflammation in a wide variety of ocular diseases. The purpose of this study was to assess targeting the Fas pathway as a novel mutation-independent approach to improve photoreceptor survival in IRD.

Methods

We examined the effects of genetic inactivation of the Fas receptor on retinal degeneration in two distinct IRD mouse models, P23H and rd10. The Fas-lpr mouse, which contains a functionally inactive Fas receptor, was crossed with the P23H and rd10 mice to generate P23H/Fas-lpr and rd10/Fas-lpr mice. Fas activation, photoreceptor survival and retinal function were assessed.

Results

We detected elevated levels of Fas receptor and microglial activation in the retinas of both P23H and rd10 mice. Inactivation of Fas in these two IRD models (P23H/Fas-lpr and rd10/Fas-lpr mice) resulted in reduced cell death, increased photoreceptor survival, improved retinal function, and reduced microglial activation and inflammatory cytokine production.

Conclusions

The protective effect of a nonfunctional Fas receptor in two different mouse models of retinal degeneration suggests that whereas the individual IRD mutation may be specific, the retina's response to the different stressors appears to be shared and driven by Fas. Reducing Fas activity might represent a potential mutation-independent therapeutic approach to preserve retinal structure and function in patients with IRD.

Foveolar thickness as potential standardized structural outcome measurement in studies of Bietti crystalline dystrophy

Bietti crystalline dystrophy (BCD) is an ultra-rare orphan disorder that can lead to blindness. Because of the variable rates of progression of the disease, it is necessary to identify suitable outcome measurements for tracking progression in BCD. A retrospective analysis of patients with a clinical and genetic diagnosis of BCD was conducted. Four measurements of spectral domain-optical coherence tomography were compared to patients’ best corrected visual acuity. We observed that patients with higher measurements of foveolar thickness, choroidal thickness in the foveolar region, ellipsoid zone band length and the outer nuclear layer + area, had on average better visual acuity. Future studies are needed to validate the structural–functional correlations we observed in BCD and to propose a sensitive and clinically meaningful outcome measurement for tracking this rare, variable disease.

Advancing precision medicines for ocular disorders: Diagnostic genomics to tailored therapies

Successful sequencing of the human genome and evolving functional knowledge of gene products has taken genomic medicine to the forefront, soon combining broadly with traditional diagnostics, therapeutics, and prognostics in patients. Recent years have witnessed an extraordinary leap in our understanding of ocular diseases and their respective genetic underpinnings. As we are entering the age of genomic medicine, rapid advances in genome sequencing, gene delivery, genome surgery, and computational genomics enable an ever-increasing capacity to provide a precise and robust diagnosis of diseases and the development of targeted treatment strategies. Inherited retinal diseases are a major source of blindness around the world where a large number of causative genes have been identified, paving the way for personalized diagnostics in the clinic. Developments in functional genetics and gene transfer techniques has also led to the first FDA approval of gene therapy for LCA, a childhood blindness. Many such retinal diseases are the focus of various clinical trials, making clinical diagnoses of retinal diseases, their underlying genetics and the studies of natural history important. Here, we review methodologies for identifying new genes and variants associated with various ocular disorders and the complexities associated with them. Thereafter we discuss briefly, various retinal diseases and the application of genomic technologies in their diagnosis. We also discuss the strategies, challenges, and potential of gene therapy for the treatment of inherited and acquired retinal diseases. Additionally, we discuss the translational aspects of gene therapy, the important vector types and considerations for human trials that may help advance personalized therapeutics in ophthalmology. Retinal disease research has led the application of precision diagnostics and precision therapies; therefore, this review provides a general understanding of the current status of precision medicine in ophthalmology.

Cost-effectiveness of voretigene neparvovec in the treatment of patients with inherited retinal disease with RPE65 mutation in Switzerland

Objective

We aimed to evaluate the cost-effectiveness of voretigene neparvovec (VN) compared with standard of care (SoC) for patients with inherited retinal disease (IRD) caused by a biallelic RPE65-mutation. VN is a live, non-replicating adeno-associated virus serotype 2 (AAV2). SoC is best supportive care provided to patients with visual impairment. Patients under SoC may experience progressive vision loss leading to complete blindness.

Methods

We adapted a previously published Markov cohort model for IRD. An annual cycle length, life-long time horizon, discount rate of 3% for cost and health outcomes, and Swiss health system perspective were used. Data from a randomised controlled phase III trial of VN versus SoC (ClinicalTrials.gov: NCT00999609) were used to estimate transitions between health states in the first year, after which VN patients were assumed to remain for 39 subsequent years in the health state they were in at the end of the first year. After the 40^th year for VN patients and 1^st year for SoC patients, visual decline was modelled based on observational data on the natural progression of the disease. Quality-adjusted life years (QALYs) were calculated based on an external study which elicited clinicians’ EQ-5D-5L-based utility estimates for IRD patients with a RPE65-mutation. Costs (Swiss Francs (CHF), year 2018-2019) included drug acquisition/ administration, adverse events, testing for sufficient viable retinal cells, and healthcare-related costs of blindness. Societal costs of blindness were added in a complementary analysis. Robustness of the model results were tested in sensitivity and scenario analyses.

Results

For the base-case, VN resulted in incremental costs per patient of CHF 764’402 (VN: CHF 901’654, SoC: CHF 137’252), incremental blindness-free years of 7.67 (VN: 28.32, SoC: 20.65) and incremental QALYs of 6.73 (VN: 18.35, SoC: 11.62), leading to an incremental cost-effectiveness ratio of CHF 113’526 per QALY gained. In probabilistic sensitivity analysis, the cost-effectiveness of VN was better than CHF 100,000 per QALY gained in 41% of iterations. For the scenario analysis in which a societal perspective was adopted and for which a 50% work-related productivity loss from blindness was assumed, incremental costs of CHF 423,837 and an ICER of CHF 62’947 per QALY gained were produced. The scenario assuming VN treatment effect lasts for 20 years produced an ICER of CHF 156’171 per QALY gained, whereas assuming a life-long VN treatment effect resulted in an ICER of CHF 96’384 per QALY gained.

Conclusion

The incremental cost-effectiveness ratio of VN compared to the SoC was estimated to be CHF 113’526 and CHF 62’947 per QALY gained, respectively, from a Swiss healthcare system, and societal perspective assuming a 50% productivity loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-022-08211-y.

AAV-CRISPR/Cas9 Gene Editing Preserves Long-Term Vision in the P23H Rat Model of Autosomal Dominant Retinitis Pigmentosa

Retinitis pigmentosa (RP) consists of a group of inherited, retinal degenerative disorders and is characterized by progressive loss of rod photoreceptors and eventual degeneration of cones in advanced stages, resulting in vision loss or blindness. Gene therapy has been effective in treating autosomal recessive RP (arRP). However, limited options are available for patients with autosomal dominant RP (adRP). In vivo gene editing may be a therapeutic option to treat adRP. We previously rescued vision in neonatal adRP rats by the selective ablation of the Rhodopsin S334ter transgene following electroporation of a CRISPR/Cas9 vector. However, the translational feasibility and long-term safety and efficacy of ablation therapy is unclear. To this end, we show that AAV delivery of a CRISPR/Cas9 construct disrupted the Rhodopsin P23H transgene in postnatal rats, which rescued long-term vision and retinal morphology.

Therapeutic Applications of Adeno-Associated Virus (AAV) Gene Transfer of HLA-G in the Eye

The purpose of this paper is to review human leukocyte antigen G (HLA-G) in the eye, its role in immune tolerance, and the potential therapeutic use of AAV gene transfer and expression of HLA-G in various ocular tissues. Several studies are reviewed that demonstrate efficacy in animal models of disease, including intracorneal delivery of AAV-HLA-G to treat corneal inflammation and prevent corneal graft rejection, subconjunctival injection of AAV-HLA-G for ocular graft vs. host disease and potentially dry eye disease, and intravitreal injection of AAV-HLA-G to inhibit uveitis. Furthermore, due to the anti-vascular function of HLA-G, AAV-HLA-G may be an effective therapy for posterior ocular diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and choroidal neovascularization. Therefore, AAV-mediated gene transfer of HLA-G may be an effective treatment for common immune-mediated, inflammatory, and neovascular diseases of the eye.

Correlating optical coherence tomography biomarkers with visual acuity in nigerian retinitis pigmentosa patients

Background

Spectral Domain Optical Coherence Tomography (SD-OCT) has been used for imaging retinitis pigmentosa (RP) eyes and provides useful information on microstructural changes.

Aim

To review SD-OCT findings and correlate the central foveal thickness (CFT), outer nuclear layer (ONL), external limiting membrane (ELM), and ellipsoid zone (EZ) with visual function in nonsyndromic RP eyes.

Patients and Methods

A multicenter, retrospective review of records from consecutive eyes diagnosed to have RP. Biodata, systemic disease, visual acuity, lens status, intraocular pressure, and SD-OCT images were examined. The CFT was categorized into normal (250-299 microns), atrophic (0-249 microns), and edematous (≥300 microns). The ONL, ELM, and EZ within the subfoveal area was assessed and rated as normal, reduced (if less than normal), or absent (if missing). The status of these biomarkers was correlated with visual acuity and statistical analysis performed using Pearson Chi², P < 0.05. In addition, the vitreomacular interface was examined for the presence of vitreomacular traction (VMT), vitreomacular adhesion (VMA), and epiretinal membrane (ERM).

Results

Fifty-two RP eyes of 27 patients had SD-OCT images that were used for study analysis. There were 17 males and 10 females; 52% of participants were between 31 and 50 years (age range: 22-77 years). An atrophic retina was the most common finding in 42 eyes (81%); the average CFT in the atrophic group was 175 microns (range: 111-245 microns). There were three eyes with cystoid macular edema, and seven eyes were normal. For the OCT biomarkers, a reduction in ONL and ELM occurred in 69% and 46% of eyes, respectively, while an absence was the most common EZ finding (in 50% of eyes). There was a significant correlation between the presence or absence of the three biomarkers and presenting vision: ONL, ELM, and EZ with P values of 0.000, 0.006, and 0.011, respectively. The CFT had no significant correlation with vision; P = 0.522. Other findings on OCT include ERM 17%, VMA 6%, and VMT 2%.

Conclusion

This report supports the notion that OCT image reporting on physical retinal structure in RP eyes can be used to predict disease effects on vision. A prospective study to better quantify the degree of structural change and correlate with the degree of functional loss is required for RP gene types in Nigerians and black Africans.

Retinal Organoids and Retinal Prostheses: An Overview

Despite the progress of modern medicine in the last decades, millions of people diagnosed with retinal dystrophies (RDs), such as retinitis pigmentosa, or age-related diseases, such as age-related macular degeneration, are suffering from severe visual impairment or even legal blindness. On the one hand, the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) and the progress of three-dimensional (3D) retinal organoids (ROs) technology provide a great opportunity to study, understand, and even treat retinal diseases. On the other hand, research advances in the field of electronic retinal prosthesis using inorganic photovoltaic polymers and the emergence of organic semiconductors represent an encouraging therapeutical strategy to restore vision to patients at the late onset of the disease. This review will provide an overview of the latest advancement in both fields. We first describe the retina and the photoreceptors, briefly mention the most used RD animal models, then focus on the latest RO differentiation protocols, carry out an overview of the current technology on inorganic and organic retinal prostheses to restore vision, and finally summarize the potential utility and applications of ROs.

Three-Year Safety Results of SAR422459 (EIAV-ABCA4) Gene Therapy in Patients With ABCA4-Associated Stargardt Disease: An Open-Label Dose-Escalation Phase I/IIa Clinical Trial, Cohorts 1-5

PURPOSE

To report on the safety of the first 5 cohorts of a gene therapy trial using recombinant equine infectious anemia virus expressing ABCA4 (EIAV-ABCA4) in adults with Stargardt dystrophy due to mutations in ABCA4.

DESIGN

Nonrandomized multicenter phase I/IIa clinical trial.

METHODS

Patients received a subretinal injection of EIAVABCA4 in the worse-seeing eye at 3 dose levels and were followed for 3 years after treatment.

MAIN OUTCOME MEASURES

The primary end point was ocular and systemic adverse events. The secondary end points were best-corrected visual acuity, static perimetry, kinetic perimetry, total field hill of vision, full field electroretinogram, multifocal ERG, color fundus photography, short-wavelength fundus autofluorescence, and spectral domain optical coherence tomography.

RESULTS

The subretinal injections were well tolerated by all 22 patients across 3 dose levels. There was 1 case of a treatment-related ophthalmic serious adverse event in the form of chronic ocular hypertension. The most common adverse events were associated with the surgical procedure. In 1 patient treated with the highest dose, there was a significant decline in the number of macular flecks as compared with the untreated eye. However, in 6 patients, hypoautofluorescent changes were worse in the treated eye than in the untreated eye. Of these, 1 patient had retinal pigment epithelium atrophy that was characteristic of tissue damage likely associated with bleb induction. No patients had any clinically significant changes in best-corrected visual acuity, static perimetry, kinetic perimetry, total field hill of vision, full field electroretinogram, or multifocal ERG attributable to the treatment.

CONCLUSIONS

Subretinal treatment with EIAV-ABCA4 was well tolerated with only 1 case of ocular hypertension. No clinically significant changes in visual function tests were found to be attributable to the treatment. However, 27% of treated eyes showed exacerbation of retinal pigment epithelium atrophy on fundus autofluorescence. There was a significant reduction in macular flecks in 1 treated eye from the highest dose cohort. Additional follow-up and continued investigation in more patients will be required to fully characterize the safety and efficacy of EIAV-ABCA4.

The Role of Vitamin A in Retinal Diseases

Vitamin A is an essential fat-soluble vitamin that occurs in various chemical forms. It is essential for several physiological processes. Either hyper- or hypovitaminosis can be harmful. One of the most important vitamin A functions is its involvement in visual phototransduction, where it serves as the crucial part of photopigment, the first molecule in the process of transforming photons of light into electrical signals. In this process, large quantities of vitamin A in the form of 11-cis-retinal are being isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal. Complex machinery of transporters and enzymes is involved in this process (i.e., the visual cycle). Any fault in the machinery may not only reduce the efficiency of visual detection but also cause the accumulation of toxic chemicals in the retina. This review provides a comprehensive overview of diseases that are directly or indirectly connected with vitamin A pathways in the retina. It includes the pathophysiological background and clinical presentation of each disease and summarizes the already existing therapeutic and prospective interventions.

Real-world outcomes of voretigene neparvovec treatment in pediatric patients with RPE65-associated Leber congenital amaurosis

PURPOSE

To investigate real-world safety and efficacy of voretigene neparvovec gene therapy administration in pediatric patients with biallelic RPE65 disease-causing variants.

METHODS

A retrospective study of 27 eyes of 14 patients with RPE65-associated Leber congenital amaurosis examined postoperative complications and longitudinal changes in photoreceptor function following treatment with subretinal injection of voretigene neparvovec. Full-field stimulus threshold testing (FST), Goldmann visual fields (GVF), best-corrected visual acuity (BCVA), and central subfield thickness (CST) on optical coherence tomography (OCT) scans were collected preoperatively and up to 12 months posttreatment.

RESULTS

Baseline through 6-12 month follow-up FST and GVF data were obtained for 13 eyes of 7 patients. FST improved for each eye after treatment with a mean improvement of 2.1 log-units (P < 0.001) and GVF improved for each eye with a mean improvement of 221 sum degrees (P < 0.001). BCVA improved from logMAR 0.98 at baseline to logMAR 0.83 at last follow-up (P < 0.001). Across 19 eyes of 10 patients included in CST analysis, there was a small but statistically significant 9-μ decrease in mean CST from baseline to last follow-up (P < 0.001). The most common postoperative issues included elevation in intraocular pressure (59%), persistent intraocular inflammation (15%), and vitreous opacities (26%) that resolved over a period of months.

CONCLUSIONS

This report provides some of the earliest longitudinal real-world evidence of the pediatric safety and efficacy of voretigene neparvovec using multiple functional and structural measures of the retina. Outcomes demonstrate significant improvements in visual function consistent with clinical trial results.

A practical approach to the genomics of kidney disorders

Rapid technological advances in genomic testing continue to increase our understanding of the genetic basis of a wide range of kidney disorders. Establishing a molecular diagnosis benefits the individual by bringing an end to what is often a protracted diagnostic odyssey, facilitates accurate reproductive counselling for families and, in the future, is likely to lead to the delivery of more targeted management and surveillance regimens. The selection of the most appropriate testing modality requires an understanding both of the technologies available and of the genetic architecture and heterogeneity of kidney disease. Whilst we are witnessing a far greater diagnostic yield with broader genetic testing, such approaches invariably generate variants of uncertain significance and secondary incidental findings, which are not only difficult to interpret but present ethical challenges with reporting and feeding back to patients and their families. Here, we review the spectrum of nephrogenetic disorders, consider the optimal approach to genetic testing, explore the clinical utility of obtaining a molecular diagnosis, reflect on the challenges of variant interpretation and look to the future of this dynamic field.

Stronger together: Analytical techniques for recombinant adeno associated virus

With recent FDA approval of two recombinant adeno‐associated virus (rAAV)‐based gene therapies, these vectors have proven that they are suitable to address monogenic diseases. However, rAAVs are relatively new modalities, and their production and therapy costs significantly exceed those of conventional biologics. Thus, significant efforts are made to improve the processes, methods, and techniques used in manufacturing and quality control (QC). Here, we evaluate transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), and two modes of capillary electrophoresis (CE) for their ability to analyze the DNA encapsidated by rAAVs. While TEM and AUC are well‐established methods for rAAV, capillary gel electrophoresis (CGE) has been just recently proposed for viral genome sizing. The data presented reflect that samples are very complex, with various DNA species incorporated in the virus, including small fragments as well as DNA that is larger than the targeted transgene. CGE provides a good insight in the filling of rAAVs, but the workflow is tedious and the method is not applicable for the determination of DNA titer, since a procedure for the absolute quantification (e.g., calibration) is not yet established. For estimating the genome titer, we propose a simplified capillary zone electrophoresis approach with minimal sample preparation and short separation times (<5 min/run). Our data show the benefits of using the four techniques combined, since each of them alone is prone to delivering ambiguous results. For this reason, a clear view of the rAAV interior can only be provided by using several analytical methods simultaneously.

Current trends in gene therapy for retinal diseases (Review)

The eye is considered an effective target for genetic therapy, as it has a privileged immune status, it is easily accessed for medication delivery and it is affected by a number of inherited disorders. In particular, the retina is considered for gene therapy due to the fact that it can be visualized with ease, it does not have lymphatic vessels, nor a direct blood network for the outer layers and its cells do not divide after birth, and thus transgene expression is not affected. As gene therapy is currently on a continuously progressive development trend, this emerging field of gene manipulation techniques has yielded promising results. This involves the development of treatments for a number of debilitating and blinding diseases, which were to date considered intractable. However, numerous unanswered questions remain as regards the long-term efficacy and safety profile of these treatments. The present review article discusses the current research status regarding genetic manipulation techniques aimed at addressing visual impairment related to retinal disorders, both inherited and degenerative.

Functional evaluation in inherited retinal disease

Functional assessments are a fundamental part of the clinical evaluation of patients with inherited retinal diseases (IRDs). Their importance and impact have become increasingly notable, given the significant breadth and number of clinical trials and studies investigating multiple avenues of intervention across a wide range of IRDs, including gene, pharmacological and cellular therapies. Moreover, the fact that many clinical trials are reporting improvements in vision, rather than the previously anticipated structural stability/slowing of degeneration, makes functional evaluation of primary relevance. In this review, we will describe a range of methods employed to characterise retinal function and functional vision, beginning with tests variably included in the clinic, such as visual acuity, electrophysiological assessment and colour discrimination, and then discussing assessments often reserved for clinical trials/research studies such as photoaversion testing, full-field static perimetry and microperimetry, and vision-guided mobility testing; addressing perimetry in greatest detail, given it is commonly a primary outcome metric. We will focus on how these tests can help diagnose and monitor particular genotypes, also noting their limitations/challenges and exploring analytical methodologies for better exploiting functional measurements, as well as how they facilitate patient inclusion and stratification in clinical trials and serve as outcome measures.

Intraperitoneal chromophore injections delay early-onset and rapid retinal cone degeneration in a mouse model of Leber congenital amaurosis

Highly expressed in the retinal pigment epithelium (RPE), the RPE-specific 65-kDa (RPE65) enzyme is indispensable to generate 11-cis-retinal (11cRAL), a chromophore for rhodopsin and cone photopigments. RPE65 deficiency can lead to Leber congenital amaurosis type 2 (LCA2), in which the isomerization of photobleached all-trans-retinal into photosensitive 11cRAL is blocked, ultimately causing severe retinal dysfunction and degeneration. The related mouse models, which are constructed through gene knockout or caused by spontaneous mutations, morphologically present with early-onset and rapid retinal cone cells degeneration, including loss of short-wavelength-sensitive cone opsins (S-opsins) and mislocalization of medium-wavelength-sensitive cone opsins (M-opsins). Studies have shown that routine Rpe65 gene replacement therapy, mediated by an adeno-associated virus (AAV) vector, can restore RPE65 protein. However, AAV transfection and Rpe65 transgene expression require at least one to two weeks, and the treatment cannot fully block the early-onset cone degeneration. To determine the feasibility of delaying cone degeneration before gene therapy, we investigated the impact of 11cRAL treatment in an early-age LCA2 retinal degeneration 12 (rd12) mouse model. Similar to human patients, the mouse model carries a spontaneous mutation in the Rpe65 gene, which results in disrupted endogenous 11cRAL regeneration. We found that RPE65 deficiency did not notably affect rodent retinal vessels. Under red light illumination, the rd12 mice were intraperitoneally injected with exogenous 11cRAL from postnatal day (P) 14 to P21. Three days after the last injection, a notable recovery of retinal function was observed using scotopic and photopic electroretinograms. Using optical coherence tomography and histological analyses of the deficient retinas, we found changes in the thickness of the photoreceptor outer segment (OS); this change could be rescued by early 11cRAL treatment. In addition, the treatment notably preserved M- and S-opsins, both of which maintained appropriate localization inside cone cells, as shown by the wild-type mice. In contrast, the age-matched untreated rd12 mice were characterized by retinal S-opsin loss and M-opsin mislocalization from the photoreceptor OS to the inner segment, outer nuclear layer, or outer plexiform layer. Notably, 11cRAL treatment could not maintain retinal function for a long time. Ten days after the last injection, the rod and M-cone electroretinograms significantly decreased, and S-cone responses almost extinguished. Our findings suggest that early 11cRAL treatment is useful for restoring retinal function and rescuing morphology in the rd12 mouse model, and the early-onset and rapid cone degeneration can be delayed before gene therapy.

Targeting vascular endothelial growth factor using retinal gene therapy

Pharmacotherapies targeting vascular endothelial growth factor (VEGF) have revolutionized the management for neovascular retinal disorders including diabetic retinopathy and neovascular age-related macular degeneration. However, the burden of frequent injections, high cost, and treatment resistance in some patients remain unresolved. To overcome these challenges, newer generations of anti-angiogenic biological therapies, engineered proteins, implantable delivery systems, and biopolymers are currently being developed to enable more sustained, longer-lasting treatments. The use of gene therapies for pathologic angiogenesis has garnered renewed interests since the first FDA-approval of a gene therapy to treat inherited retinal diseases associated with biallelic RPE65 mutations. Newer generations of viral vectors and novel methods of intraocular injections helped overcome ocular barriers, improving the efficiency of transduction as well as safety profile. In addition, unlike current anti-VEGF gene therapy strategies which employ a biofactory approach to mimic existing pharmacotherapies, novel genome editing strategies that target pro-angiogenic factors at the DNA level offer a unique and distinct mechanistic approach that can potentially be more precise and lead to a permanent cure. Here, we review current anti-VEGF therapies and newer pharmacologic agents under development, examine technologies and progress in adapting anti-VEGF gene therapies, and explore the future application of CRISPR-Cas9 technology to suppress ocular angiogenesis.

Gene Therapy for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked, muscle wasting disease that affects 1 in 5000 males. Affected individuals become wheelchair bound by the age of twelve and eventually die in their third decade due to respiratory and cardiac complications. The disease is caused by mutations in the DMD gene that codes for dystrophin. Dystrophin is a structural protein that maintains the integrity of muscle fibres and protects them from contraction-induced damage. The absence of dystrophin compromises the stability and function of the muscle fibres, eventually leading to muscle degeneration. So far, there is no effective treatment for deteriorating muscle function in DMD patients. A promising approach for treating this life-threatening disease is gene transfer to restore dystrophin expression using a safe, non-pathogenic viral vector called adeno-associated viral (AAV) vector. Whilst microdystrophin gene transfer using AAV vectors shows extremely impressive therapeutic success so far in large animal models of DMD, translating this advanced therapy medicinal product from bench to bedside still offers scope for many optimization steps. In this paper, the authors review the current progress of AAV-microdystrophin gene therapy for DMD and other treatment strategies that may apply to a subset of DMD patients depending on the mutations they carry.

Utilizing Advanced Technology to Facilitate Diagnosis of Rare Retinal Disorders: A Case of Bietti Crystalline Dystrophy

SIGNIFICANCE

Optometrists, as primary eye care providers, encounter patients with rare ocular disease such as Bietti crystalline dystrophy from time to time. Using advanced technologies, which are also useful in managing common ocular conditions, to facilitate a prompt diagnosis is highly recommended.

PURPOSE

This report describes a patient with clinically diagnosed Bietti crystalline dystrophy with findings on funduscopy, multimodal imaging, and visual electrophysiology.

CASE REPORT

A 41-year-old Chinese woman who had subjectively progressing dimmed vision (especially in the left eye) for 9 months was referred to our clinic to test for retinitis pigmentosa. Best-corrected visual acuities were 6/6 and 6/7.6 in the right and left eyes, respectively. Funduscopy revealed multiple crystalline deposits on the posterior pole in both eyes. The 30-2 perimetry displayed bi-inferotemporal scotoma (left > right eye). Scotopic flash electroretinogram (ERG) yielded a normal result, whereas photopic ERG was slightly attenuated. Electro-oculogram showed an abnormal adaptation time course of the retinal pigmented epithelium (RPE). Multifocal ERG revealed a decreased central retinal response, but paracentral responses were relatively better preserved. Optical coherence tomography showed multiple patches of RPE atrophy, with disruption of the left ellipsoid zone. Outer retinal tubulations, hyperreflective dots on RPE-Bruch's membrane interface, and intraretinal bright spots were also identified.

CONCLUSIONS

Rare ocular diseases like Bietti crystalline dystrophy can be encountered by optometrists. This case report shows the ophthalmic findings of a rare chorioretinal dystrophy and provides insight on how to better use advanced equipment in an optometric practice to facilitate prompt diagnoses.

Primary cilia in retinal pigment epithelium development and diseases

Retinal pigment epithelium (RPE) is a highly polarized epithelial monolayer lying between the photoreceptor layer and the Bruch membrane. It is essential for vision through participating in many critical activities, including phagocytosis of photoreceptor outer segments, recycling the visual cycle‐related compounds, forming a barrier to control the transport of nutrients, ions, and water, and the removal of waste. Primary cilia are conservatively present in almost all the vertebrate cells and acts as a sensory organelle to control tissue development and homeostasis maintenance. Numerous studies reveal that abnormalities in RPE lead to various retinal diseases, such as age‐related macular degeneration and diabetic macular oedema, but the mechanism of primary cilia in these physiological and pathological activities remains to be elucidated. Herein, we summarize the functions of primary cilia in the RPE development and the mutations of ciliary genes identified in RPE‐related diseases. By highlighting the significance of primary cilia in regulating the physiological and pathological processes of RPE, we aim to provide novel insights for the treatment of RPE‐related retinal diseases.

Artificial Intelligence-Assisted Early Detection of Retinitis Pigmentosa - the Most Common Inherited Retinal Degeneration

The purpose of this study was to detect the presence of retinitis pigmentosa (RP) based on color fundus photographs using a deep learning model. A total of 1670 color fundus photographs from the Taiwan inherited retinal degeneration project and National Taiwan University Hospital were acquired and preprocessed. The fundus photographs were labeled RP or normal and divided into training and validation datasets (n = 1284) and a test dataset (n = 386). Three transfer learning models based on pre-trained Inception V3, Inception Resnet V2, and Xception deep learning architectures, respectively, were developed to classify the presence of RP on fundus images. The model sensitivity, specificity, and area under the receiver operating characteristic (AUROC) curve were compared. The results from the best transfer learning model were compared with the reading results of two general ophthalmologists, one retinal specialist, and one specialist in retina and inherited retinal degenerations. A total of 935 RP and 324 normal images were used to train the models. The test dataset consisted of 193 RP and 193 normal images. Among the three transfer learning models evaluated, the Xception model had the best performance, achieving an AUROC of 96.74%. Gradient-weighted class activation mapping indicated that the contrast between the periphery and the macula on fundus photographs was an important feature in detecting RP. False-positive results were mostly obtained in cases of high myopia with highly tessellated retina, and false-negative results were mostly obtained in cases of unclear media, such as cataract, that led to a decrease in the contrast between the peripheral retina and the macula. Our model demonstrated the highest accuracy of 96.00%, which was comparable with the average results of 81.50%, of the other four ophthalmologists. Moreover, the accuracy was obtained at the same level of sensitivity (95.71%), as compared to an inherited retinal disease specialist. RP is an important disease, but its early and precise diagnosis is challenging. We developed and evaluated a transfer-learning-based model to detect RP from color fundus photographs. The results of this study validate the utility of deep learning in automating the identification of RP from fundus photographs.

The Lrat-/- Rat: CRISPR/Cas9 Construction and Phenotyping of a New Animal Model for Retinitis Pigmentosa

PURPOSE

We developed and phenotyped a pigmented knockout rat model for lecithin retinol acyltransferase (LRAT) using CRISPR/Cas9. The introduced mutation (c.12delA) is based on a patient group harboring a homologous homozygous frameshift mutation in the LRAT gene (c.12delC), causing a dysfunctional visual (retinoid) cycle.

METHODS

The introduced mutation was confirmed by DNA and RNA sequencing. The expression of Lrat was determined on both the RNA and protein level in wildtype and knockout animals using RT-PCR and immunohistochemistry. The retinal structure and function, as well as the visual behavior of the Lrat^-/- and control rats, were characterized using scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), electroretinography (ERG) and vision-based behavioral assays.

RESULTS

Wildtype animals had high Lrat mRNA expression in multiple tissues, including the eye and liver. In contrast, hardly any expression was detected in Lrat^-/- animals. LRAT protein was abundantly present in wildtype animals and absent in Lrat^-/- animals. Lrat^-/- animals showed progressively reduced ERG potentials compared to wildtype controls from two weeks of age onwards. Vison-based behavioral assays confirmed reduced vision. Structural abnormalities, such as overall retinal thinning, were observed in Lrat^-/- animals. The retinal thickness in knockout rats was decreased to roughly 80% by four months of age. No functional or structural differences were observed between wildtype and heterozygote animals.

CONCLUSIONS

Our Lrat^-/- rat is a new animal model for retinal dystrophy, especially for the LRAT-subtype of early-onset retinal dystrophies. This model has advantages over the existing mouse models and the RCS rat strain and can be used for translational studies of retinal dystrophies.

Perspectives of people with inherited retinal diseases on ocular gene therapy in Australia: protocol for a national survey

INTRODUCTION

Voretigene neparvovec-rzyl (Luxturna) was approved by the Australian Therapeutic Goods Administration on 4 August 2020 for the treatment of biallelic mutations in the RPE65 gene, a rare cause of congenital and adult-onset retinal dystrophy (predominantly Leber congenital amaurosis). Previous studies have shown that individuals who might participate in gene therapy trials overestimate clinical effect and underestimate risks. However, little is known about the perspectives of patients who may be offered approved gene therapy treatment for ocular conditions (as distinct from participating in clinical trials of gene therapy). The main objective of this study is to develop a tool to assess knowledge, attitudes and perceptions of approved and future genetic therapies among potential recipients of ocular gene therapy. In addition, we aim to assess the quality of life, attitudes towards clinical trials and vision-related quality of life among this cohort.

METHODS AND ANALYSIS

A new 'Attitudes to Gene Therapy for the Eye' tool will be developed following consultation with people with inherited retinal disease (IRD) and content matter experts. Australians with IRD or their guardians will be asked to complete an internet-based survey comprising existing quality of life and visual function instruments and items for the newly proposed tool. We expect to recruit 500 survey participants from patient support groups, the practices of Australian ophthalmologists who are specialists in IRD and Australian ophthalmic research institutions. Launch is anticipated early 2021. Responses will be analysed using item response theory methodology.

ETHICS AND DISSEMINATION

This study has received ethics approval from the University of Melbourne (#2057534). The results of the study will be published in a peer-reviewed journal and will be presented at relevant conferences. Organisations involved in recruitment, and the Patient Engagement Advisory committee will assist the research team with dissemination of the study outcomes.

Effect of Long-term Anti-VEGF Treatment on Viability and Function of RPE Cells

Purpose/Aim of the study: Vascular endothelial growth factor (VEGF)-antagonists are given over long time periods in the clinic, but the long-term effects on retinal pigment epithelium (RPE) cells are not fully investigated. This study aims to investigate these effects with two clinical relevant VEGF antagonists, bevacizumab and aflibercept, on the function of primary RPE cells.Materials and Methods: All tests were conducted with primary porcine RPE. Cells were stimulated with bevacizumab or aflibercept (both 250 µg/ml) for 1 day, 7 days or 4 weeks. Cell viability was tested in MTT Assay. Secretion of TGF-ß was tested in ELISA, phagocytosis in a microscopic assay, migration in a scratch assay, and expression of RPE65 in Western blot. Barrier function was tested for bevacizumab in transwell-cultured cells by measuring transepithelial electrical resistance for up to 3 days.Results: Viability was reduced by both antagonists at all time points tested. TGF-ß secretion was not altered by any treatment. Phagocytosis was not significantly reduced by any treatment. Wound healing ability was not significantly altered by any treatment. The expression of RPE65 was reduced by bevacizumab but not aflibercept after 4 weeks. Transepithelial electrical resistance was not altered.Conclusions: Long-term treatment with anti VEGF may affect viability of RPE cells, and treatment with bevacizumab may have effects on RPE function in long-term treatment.

Characterization of PROM1 p.Arg373Cys Variant in a Cohort of Chinese Patients: Macular Dystrophy Plus Peripheral Bone-Spicule Degeneration

Purpose

The PROM1 p.Arg373Cys variant has been reported to cause dominant Stargardt disease, cone-rod dystrophy, and occasionally retinitis pigmentosa. This study aimed to evaluate the common phenotype associated with this variant in Chinese patients.

Methods

Variants in PROM1 were collected from in-house exome data. Potential pathogenic variants were selected, verified, and then confirmed by Sanger sequencing and co-segregation analysis. Ocular phenotypes were reviewed and further clarified by ophthalmologic examinations.

Results

The heterozygous c.1117C>T (p.Arg373Cys) variant was identified in four unrelated families, and biallelic variants were detected in three families. Of the 10 patients from four families with the p.Arg373Cys variant, six patients from three families who underwent full fundus examination demonstrated various degrees of macular dystrophy, as well as typical bone-spicule pigment deposits in the peripheral retina. The remaining four patients did not undergo a full dilated fundus examination. A relatively preserved zone was observed between the macular and peripheral lesions. Electroretinography results showed cone and rod involvement in three patients.

Conclusions

Unlike Stargardt disease alone, which was considered to be the main phenotype of the p.Arg373Cys variant, all patients with full-field fundus examination in our study presented with macular dystrophy plus peripheral retinopathy resembling retinitis pigmentosa. Different phenotypes associated with the p.Arg373Cys variant may actually reflect different stages of the same disease: a predominant central cone phenotype at an early stage and peripheral rod involvement as degeneration progresses. Evaluation of the full fundus, especially the peripheral region in additional patients, is expected to confirm our findings.

[Implementation of a new gene therapy in ophthalmology: Regulatory and organizational issues]

Voretigene neparvovec (VN) is the first gene therapy in ophthalmology for patients with RPE65-mediated hereditary retinal dystrophy. It has recently obtained European market approval, which is subject to strict regulatory and organizational conditions for its use. Here, we analyze the main studies supporting the authorization of this new therapy and describe the necessary steps to take at a hospital level for optimal administration to patients following current regulations.

Subretinal Rather Than Intravitreal Adeno-Associated Virus-Mediated Delivery of a Complement Alternative Pathway Inhibitor Is Effective in a Mouse Model of RPE Damage

Purpose

The risk for age-related macular degeneration has been tied to an overactive complement system. Despite combined attempts by academia and industry to develop therapeutics that modulate the complement response, particularly in the late geographic atrophy form of advanced AMD, to date, there is no effective treatment. We have previously demonstrated that pathology in the smoke-induced ocular pathology (SIOP) model, a model with similarities to dry AMD, is dependent on activation of the alternative complement pathway and that a novel complement activation site targeted inhibitor of the alternative pathway can be delivered to ocular tissues via an adeno-associated virus (AAV).

Methods

Two different viral vectors for specific tissue targeting were compared: AAV5-VMD2-CR2-fH for delivery to the retinal pigment epithelium (RPE) and AAV2YF-smCBA-CR2-fH for delivery to retinal ganglion cells (RGCs). Efficacy was tested in SIOP (6 months of passive smoke inhalation), assessing visual function (optokinetic responses), retinal structure (optical coherence tomography), and integrity of the RPE and Bruch's membrane (electron microscopy). Protein chemistry was used to assess complement activation, CR2-fH tissue distribution, and CR2-fH transport across the RPE.

Results

RPE- but not RGC-mediated secretion of CR2-fH was found to reduce SIOP and complement activation in RPE/choroid. Bioavailability of CR2-fH in RPE/choroid could be confirmed only after AAV5-VMD2-CR2-fH treatment, and inefficient, adenosine triphosphate-dependent transport of CR2-fH across the RPE was identified.

Conclusions

Our results suggest that complement inhibition for AMD-like pathology is required basal to the RPE and argues in favor of AAV vector delivery to the RPE or outside the blood-retina barrier.

Novel BEST1 mutation in autosomal recessive bestrophinopathy in Japanese siblings

PURPOSE

Autosomal recessive bestrophinopathy (ARB) is a disease that results from the mutations in the BEST1 gene. It is characterized by multifocal yellowish lipofuscin deposits, cystoid macular edema, and subretinal fluid. Among approximately 270 BEST1 mutations, only 40 that include both heterozygous and homozygous mutations are associated with ARB. However, very few ARB-related mutations have been reported in the Japanese population. Therefore, in this study, we aimed to identify BEST1 mutations and describe the genotype-phenotype relationship in Japanese dizygotic twins presenting with ARB.

MATERIALS AND METHODS

We performed clinical examinations in Japanese dizygotic twin patients (male: 29 years) with ARB as well as whole-exome sequencing in seven family members of these twins.

RESULTS

In this study, we have reported on a novel BEST1 mutation, the p. Phe151Cys mutation, associated with ARB in Japanese dizygotic twins who had bi-allelic p. Ala160Pro mutations in BEST1. The clinical features observed were binocular abnormalities of the fundus, such as multifocal yellowish subretinal deposits, cystoid macular edema, and subretinal fluid. The full-field electroretinography results were subnormal.

CONCLUSION

It was indicated that the novel BEST1 mutations identified may be strongly correlated with binocular ARB. This study provides significant information of the genotype-phenotype association in Japanese ARB patients. Further, the genetic analysis that we performed was very useful for the differential diagnosis and might have implications in the development of future treatment modalities.

Leber congenital amaurosis/early-onset severe retinal dystrophy: current management and clinical trials

Leber congenital amaurosis (LCA) is a severe congenital/early-onset retinal dystrophy. Given its monogenic nature and the immunological and anatomical privileges of the eye, LCA has been particularly targeted by cutting-edge research. In this review, we describe the current management of LCA, and highlight the clinical trials that are on-going and planned. RPE65-related LCA pivotal trials, which culminated in the first Food and Drug Administration-approved and European Medicines Agency-approved ocular gene therapy, have paved the way for a new era of genetic treatments in ophthalmology. At present, multiple clinical trials are available worldwide applying different techniques, aiming to achieve better outcomes and include more genes and variants. Genetic therapy is not only implementing gene supplementation by the use of adeno-associated viral vectors, but also clustered regularly interspaced short palindromic repeats (CRISPR)-mediated gene editing and post-transcriptional regulation through antisense oligonucleotides. Pharmacological approaches intending to decrease photoreceptor degeneration by supplementing 11-cis-retinal and cell therapy’s aim to replace the retinal pigment epithelium, providing a trophic and metabolic retinal structure, are also under investigation. Furthermore, optoelectric devices and optogenetics are also an option for patients with residual visual pathway. After more than 10 years since the first patient with LCA received gene therapy, we also discuss future challenges, such as the overlap between different techniques and the long-term durability of efficacy. The next 5 years are likely to be key to whether genetic therapies will achieve their full promise, and whether stem cell/cellular therapies will break through into clinical trial evaluation.

Exome sequencing and electro-clinical features in pediatric patients with very early-onset retinal dystrophies: A cohort study

BACKGROUND AND OBJECTIVE

Inherited retinal dystrophies (IRDs) are a major cause of childhood blindness. Timely diagnosis requires a high level of clinical suspicion from both neurologists and ophthalmologists and is increasingly important given recent advancements in gene therapy. We focused our study on genotype-phenotype associations in very early-onset forms of retinal dystrophy, the least well characterized and most challenging diagnostic subgroup.

METHODS

From January 12, 2015 to March 31, 2017, we prospectively performed whole exome sequencing targeted on the phenotype of non-syndromic IRDs and phenotype characterization in a cohort of 68 children affected by very early-onset inherited retinal dystrophies, defined by the onset before five years of age. Phenotype parameters included age at onset, clinical presentation, ophthalmic evaluation, electrophysiological patterns and clinical course.

RESULTS

A genetically confirmed diagnosis was achieved in 50 out of 60 (83%) families. The median age at onset was 4 months (<6 m in 70%, < 2 y in 82% of the cases). Clinical presentation was associated with visual loss and nystagmus in the majority of patients. Three (CNGB3, CNGA3 and CACNA1F) out of 22 genes considered pathogenic in the cohort, accounted for 51% of all IRD's, all within the class of stationary IRDs.

CONCLUSIONS

This study reports on the largest cohort of very early-onset retinal dystrophies, including a description of electroretinography patterns. The electro-clinical phenotype coupled with genetic diagnosis provided additional clues for child neurologists dealing with low vision and nystagmus in infancy. A high level of clinical suspicion improves the diagnosis with important implications for the future of the affected child.