Cell-Based Therapy for Retinal Disease: The New Frontier

The availability of noninvasive high-resolution imaging technology, the immune-suppressive nature of the subretinal space, and the existence of surgical techniques that permit transplantation surgery to be a safe procedure all render the eye an ideal organ in which to begin cell-based therapy in the central nervous system. A number of early stage clinical trials are underway to assess the safety and feasibility of cell-based therapy for retinal blindness. Cell-based therapy using embryonic stem cell-derived differentiated cells (e.g., retinal pigment epithelium (RPE)), neural progenitor cells, photoreceptor precursors, and bone marrow-derived hematopoietic stem/progenitor cells has demonstrated successful rescue and/or replacement in preclinical models of human retinal degenerative disease. Additional research is needed to identify the mechanisms that control synapse formation/disjunction (to improve photoreceptor transplant efficacy), to identify factors that limit RPE survival in areas of geographic atrophy (to improve RPE transplant efficacy in eyes with age-related macular degeneration), and to identify factors that regulate immune surveillance of the subretinal space (to improve long-term photoreceptor and RPE transplant survival).

Restoring Vision Using Stem Cells and Transplantation

The replacement of retinal cells, or the support of surviving retinal neurons, in a degenerated retina presents a significant challenge in the fields of ophthalmology and regenerative medicine. Stem cell-based therapies are being explored as an approach for treating retinal dystrophies, such as retinitis pigmentosa (RP), Stargardt's disease, and age-related macular degeneration (AMD). This review provides an update on the recent progress made toward the restoration of vision lost to degenerative disease using stem cell-based transplantation strategies and the challenges that need to be overcome. Both retinal pigmented epithelium (RPE) and photoreceptor replacement therapies are discussed.

Pharmaceutical Development of AAV-Based Gene Therapy Products for the Eye

A resurgence of interest and investment in the field of gene therapy, driven in large part by advances in viral vector technology, has recently culminated in United States Food and Drug Administration approval of the first gene therapy product targeting a disease caused by mutations in a single gene. This product, LUXTURNA™ (voretigene neparvovec-rzyl; Spark Therapeutics, Inc., Philadelphia, PA), delivers a normal copy of the RPE65 gene to retinal cells for the treatment of biallelic RPE65 mutation–associated retinal dystrophy, a blinding disease. Many additional gene therapy programs targeting both inherited retinal diseases and other ocular diseases are in development, owing to an improved understanding of the genetic basis of ocular disease and the unique properties of the ocular compartment that make it amenable to local gene therapy. Here we review the growing body of literature that describes both the design and development of ocular gene therapy products, with a particular emphasis on target and vector selection, and chemistry, manufacturing, and controls.

Diagnosis and Treatment of Myopic Maculopathy

Visual impairment resulting from pathologic myopia is a serious issue worldwide. This is mainly due to the development of different types of myopic maculopathy. Despite being a major cause of visual impairment worldwide, myopic maculopathy was not consistently defined. To overcome this problem, in 2015 the Meta-Analysis for Pathologic Myopia Study Group proposed a simplified, uniform classification system for myopic maculopathy. Among several lesions of myopic maculopathy, myopic choroidal neovascularization (CNV) is one of the most common and severe vision-threatening complications. Recent large clinical trials have reported a good initial efficacy for visual acuity improvement by application of anti-vascular endothelial growth factor therapy for myopic CNVs. However, long-term clinical studies demonstrate a gradual decrease in the visual acuity gain and return to the baseline level due to the development of myopic CNV-related macular atrophy. Regarding visual impairment caused by advanced myopic chorioretinal atrophy, the only way to prevent blindness is to prevent myopia from developing or progressing at a young age before the axial length elongates extremely. As peripapillary diffuse atrophy in childhood may be an indicator of more advanced myopic chorioretinal atrophy in later life, some preventive measures should be considered in such children.

The assessment of retina in pregnant women with myopia

OBJECTIVES

Myopia is associated with increased frequency of retinal degenerative changes which are the risk factors of intra- and postpartal ophthalmological complications. Aim of this study was to analyze the degenerative lesions detected in opthalmological examination (including peripheral retinal lesions) as a potential risk factors for eyes' status in terms of delivery in myopic women.

MATERIAL AND METHODS

254 pregnant women affected with myopia underwent opthalmological examination as a screening method to examine retina. In case of any degenerative lesions, the qualification for laser photocoagulation treatment was performed. Furthermore, study group was divided into two subgroups due to presence or absence of the retinal lesions and opthalmological outcomes compared. Follow up examination was performed in every patient from the study group between 3 and 6 months after the delivery.

RESULTS

Among 508 eyes, retinal lesions were revealed in 69 women (121 eyes) what constituted for 23.8%. In remaining 185 patients results of the opthalmological examination were normal. Average maternal age was higher in group affected with degenerative lesions (p<0.001). Myopia in women with retinal lesions ranged between -0.25 and -12 dioptries (D), while in 43 cases of degenerative lesions qualified for laser photocoagulation this value ranged between -0.5 and -12.0 D (p=ns). Postpartal follow-up examination did not reveal any abnormalities in this group, as well.

CONCLUSION

Degenerative retinal lesions are present in one fourth of pregnant women. Both the severity and type of the lesions are not associated with severity of myopia. Among pregnant patients, retinal lesions occur in patients with more advanced maternal age. opthalmological examination remains an important prophylactic modality in retinal disorders, especially in primary retinal detachment due degenerative disorders.

CRISPR GENOME SURGERY IN THE RETINA IN LIGHT OF OFF-TARGETING

PURPOSE

Recent concerns regarding the clinical utilization of clustered regularly interspaced short palindromic repeats (CRISPR) involve uncertainties about the potential detrimental effects that many arise due to unintended genetic changes, as in off-target mutagenesis, during CRISPR genome surgery. This review gives an overview of off-targeting detection methods and CRISPR's place in the clinical setting, specifically in the field of ophthalmology.

RESULTS

As CRISPR utilization in the laboratory setting has increased, knowledge regarding CRISPR mechanisms including its off-target effects has also increased. Although a perfect method for achieving 100% specificity is yet to be determined, the past few years have seen many developments in off-targeting detection and in increasing efficacy of CRISPR tools.

CONCLUSION

The CRISPR system has high potential to be an invaluable therapeutic tool as it has the ability to modify and repair pathogenic retinal lesions. Although it is not yet a perfect system, with further efforts to improve its specificity and efficacy along with careful screening of off-target mutations, CRISPR-mediated genome surgery potential can become maximized and applied to patients.

Application of genome engineering for treatment of retinal diseases

Genome engineering with clustered regularly interspaced short palindromic repeats (CRISPR) system can be used as a tool to correct pathological mutations or modulate gene expression levels associated with pathogenesis of human diseases. Owing to well-established local administration methods including intravitreal and subretinal injection, it is relatively easy to administer therapeutic genome engineering machinery to ocular tissues for treating retinal diseases. In this context, we have investigated the potential of in vivo genome engineering as a therapeutic approach in the form of ribonucleoprotein or CRISPR packaged in viral vectors. Major issues in therapeutic application of genome engineering include specificity and efficacy according to types of CRISPR system. In addition to previous platforms based on ribonucleoprotein and CRISPRassociated protein 9 derived from Campylobacter jejuni, we evaluated the therapeutic effects of a CRISPR RNA-guided endonuclease derived from Lachnospiraceae bacterium ND2006 (LbCpf1) in regulating pathological angiogenesis in an animal model of wet-type age-related macular degeneration. LbCpf1 targeting Vegfa or Hif1a effectively disrupted the expression of genes in ocular tissues, resulting in suppression of choroidal neovascularization. It was also notable that there were no significant off-target effects in vivo. [BMB Reports 2018; 51(7): 315-316].

Use of hyperbaric oxygen therapy in quinine-associated visual disturbances

INTRODUCTION

Hyperbaric oxygen (HBO2 ) therapy is infrequently reported as a treatment for poison-induced retinal damage. We describe a case in which HBO2 therapy was used to treat suspected retinal toxicity induced by quinine.

CASE REPORT

We present a case in which HBO2 was used to treat visual disturbances thought to be caused by quinine-induced retinal damage. The patient intentionally ingested undisclosed amounts of citalopram and quinine. Following a complicated hospital course, including profound shock requiring treatment with four vasopressors and a peripheral left-ventricular assist device, the patient, once extubated, reported visual abnormalities consistent with those described from quinine-induced retinal toxicity. Visual disturbances seemed to show improvement following HBO2 treatment. Several months following hospitalization visual defects continued to be present on examination. However, with corrective lenses the patient's visual acuity was normal. No adverse events were attributed to the use of HBO2.

DISCUSSION

HBO2 for treatment of quinine-induced retinal damage is infrequently reported or studied. In the reported case, use of HBO2 appeared to be associated with substantial improvement in visual disturbances occurring in the setting of an overdose of quinine. The patient's improvement is remarkable, given her retinas were also jeopardized by her profound shock. Additional data are needed to understand the risks and benefits of this procedure, but due to limited treatment options for poison-induced retinal toxicity and the low likelihood for implementation of a controlled randomized trial of HBO2 in this population, the procedure may be considered in quinine-induced retinal toxicity.

Neuroprotective strategies for retinal disease

Diseases that affect the eye, including photoreceptor degeneration, diabetic retinopathy, and glaucoma, affect 11.8 million people in the US, resulting in vision loss and blindness. Loss of sight affects patient quality of life and puts an economic burden both on individuals and the greater healthcare system. Despite the urgent need for treatments, few effective options currently exist in the clinic. Here, we review research on promising neuroprotective strategies that promote neuronal survival with the potential to protect against vision loss and retinal cell death. Due to the large number of neuroprotective strategies, we restricted our review to approaches that we had direct experience with in the laboratory. We focus on drugs that target survival pathways, including bile acids like UDCA and TUDCA, steroid hormones like progesterone, therapies that target retinal dopamine, and neurotrophic factors. In addition, we review rehabilitative methods that increase endogenous repair mechanisms, including exercise and electrical stimulation therapies. For each approach, we provide background on the neuroprotective strategy, including history of use in other diseases; describe potential mechanisms of action; review the body of research performed in the retina thus far, both in animals and in humans; and discuss considerations when translating each treatment to the clinic and to the retina, including which therapies show the most promise for each retinal disease. Despite the high incidence of retinal diseases and the complexity of mechanisms involved, several promising neuroprotective treatments provide hope to prevent blindness. We discuss attractive candidates here with the goal of furthering retinal research in critical areas to rapidly translate neuroprotective strategies into the clinic.

Familial Exudative Vitreoretinopathy: Pathophysiology, Diagnosis, and Management

Familial exudative vitreoretinopathy (FEVR) is a heritable vitreoretinopathy characterized by anomalous retinal vascular development. The principal feature of the disease is an avascular peripheral retina. This in turn can cause further pathological changes including neovascularization, exudation, hemorrhage, and retinal detachment. The biological basis of the disease is thought to be from defects in the Wnt signaling pathway. Many gene mutations have been implicated, and these can be inherited in an autosomal dominant (most common), autosomal recessive, and X-linked recessive fashion. Examination with wide-field fluorescein angiography is essential and can identify the disease in its earlier stages, enabling timely treatment, in addition to helping identify asymptomatic family members. The current treatment paradigm involves laser photocoagulation of the avascular peripheral retina for neovascular sequelae and vitreoretinal surgery for progressive retinal detachment. Further studies are underway to better characterize this complex vitreoretinopathy.

[Purtscher-like retinopathy associated with antibiotic anaphylaxis]

We report a case of an 18-year-old woman with systemic antibiotic anaphylaxis who presented anasarca and bilateral visual loss two weeks after the intravenous use of pazufloxacin. Ancillary fundus tests revealed bilateral cotton-wool spots, Purtscher flecken, edema, and retinal arteriolar occlusion around the optic disc. After pulse corticosteroid, administration of anti-anaphylactic agent, and general support therapy for one month, the patient showed a favorable change, with the symptoms lessened or free systemically, except the continuous aggravation of fundus ischemic change. After two intravitreal injections of Ranibizumab, there were still a large area of capillary non-perfusion and neovacularizations in the binocular retina, resulting in vitreous hemorrhage. The patient's visual acuity had still light perception after right-eye vitrectomy and presented no improvement during the postoperative follow-up of two years. Literature review revealed that there were many causes associated with Purtscher-like retinopathy, and the consequent visual impairment varied significantly. Prompt management of the underlying condition is crucial in giving the patient the best chance to restore vision.

Clonazepam Associated Retinopathy

PURPOSE

To report a case of retinopathy associated with the longterm intake of the antiepileptic drug clonazepam.

METHODS

Case report.

RESULTS

A 36-year-old woman, with a history of long-term use of the antiepileptic drug clonazepam developed subtle visual disturbances. Funduscopy revealed areas of mild depigmentation of the retinal pigment epithelium throughout the posterior pole bilaterally corresponding to transmission hyperfluorescence on fluorescein angiography. There was no history of any inherited retinal degenerative disease and no other known agent responsible for retinal toxicity had been used.

CONCLUSIONS

The longstanding intake of the antiepileptic drug clonazepam may be associated with the development of toxic retinopathy.

Power-controlled temperature guided retinal laser therapy

Laser photocoagulation has been a treatment method for retinal diseases for decades. Recently, studies have demonstrated therapeutic benefits for subvisible effects. A treatment mode based on an automatic feedback algorithm to reliably generate subvisible and visible irradiations within a constant irradiation time is introduced. The method uses a site-individual adaptation of the laser power by monitoring the retinal temperature rise during the treatment using optoacoustics. This provides feedback to adjust the therapy laser power during the irradiation. The technique was demonstrated on rabbits in vivo using a 532-nm continuous wave Nd:YAG laser. The temperature measurement was performed with 523-nm Q-switched Nd:YLF laser pulses with 75-ns pulse duration at 1-kHz repetition rate. The beam diameter on the fundus was 200  μm for both lasers, respectively. The aim temperatures ranged from 50°C to 75°C in 11 eyes of 7 rabbits. The results showed ophthalmoscopically invisible effects below 55°C with therapy laser powers over a wide range. The standard deviation for the measured temperatures ranged from 2.1°C for an aim temperature of 50°C to 4.7°C for 75°C. The ED50 temperature value for ophthalmoscopically visible lesions in rabbits was determined as 65.3°C. The introduced method can be used for retinal irradiations with adjustable temperature elevations.

Laser and Anti-Vascular Endothelial Growth Factor Agent Treatments for Retinal Arterial Macroaneurysm

PURPOSE

To describe the efficacy of laser and intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) agents for patients with symptomatic retinal arterial macroaneurysm (RAM).

DESIGN

From 2009 to 2016, we collected patients with exudative or hemorrhagic RAM all treated by focal laser photocoagulation.

METHODS

Nd:YAG laser was performed in patients with subinternal limiting membrane (sub-ILM) hemorrhage. Intravitreal anti-VEGF agents were given in eyes with macular exudation as adjuncts. Changes of visual acuity and central foveal thickness before and after treatment were recorded and compared with Wilcoxon signed-rank test.

RESULTS

Thirty-five eyes that underwent a single session of laser photocoagulation for RAM resulted in macroaneurysm regression. The hemorrhagic group included 24 eyes having ruptured macroaneurysms without macular exudation. Five eyes with simultaneous sub-ILM hemorrhage receiving Nd:YAG laser membranotomy had resolution of preretinal hemorrhage. Exudative RAM having cystoid macular edema or submacular fluid with or without ruptured macroaneurysms was treated by focal laser photocoagulation alone in 3, or combined with single intravitreal anti-VEGF agent in 8 eyes. All patients had significantly improved vision when comparing visual acuity at baseline and final follow-up (P = 0.00016). Significant reduction of macular thickness was also observed after laser monotherapy or combined treatment in exudative RAM (P = 0.018).

CONCLUSIONS

Focal laser photocoagulation was helpful for the management of ruptured or leaky RAM. Combined focal laser and intravitreal anti-VEGF agents could better reduce macular exudation caused by RAM. Additionally, Nd:YAG laser was a safe and effective method to remove the sub-ILM hemorrhage caused by RAM.

Autoimmune Retinopathy: Current Concepts and Practices (An American Ophthalmological Society Thesis)

PURPOSE

To elicit and evaluate opinions in the diagnosis and management of nonparaneoplastic autoimmune retinopathy (npAIR) among members of the American Uveitis Society (AUS) and to further the development of consensus and criteria in the diagnosis and management of npAIR. We hypothesize that despite lack of any clear guidelines, a general consensus in the clinical diagnosis and treatment of npAIR exists among uveitis experts.

METHODS

A literature review was performed and a panel of uveitis experts was consulted to formulate a survey regarding the diagnosis and management of npAIR. An online survey of 10 questions was developed, and a link was distributed through the AUS membership discussion list. We defined "general consensus" as meaning that a majority (>50%) of the respondents provided the same answer to a question.

RESULTS

Fifty-four members of the AUS responded to the survey. Thirty-eight members (70.4%) see one to three AIR patients per year. Greater than 50% consensus was reached on most items, particularly items relating to diagnostic features and tests (up to 96% consensus).

CONCLUSIONS

The diagnosis and management of npAIR is challenging, as standardized clinical and laboratory diagnostic criteria have yet to be established. The results of this study support the presence of consensus regarding certain aspects of npAIR, but also indicate the need for developing clear clinical diagnostic criteria and treatment guidelines.

Stem Cells for Retinal Disease: A Perspective on the Promise and Perils

PURPOSE

To summarize key concepts, as well as early safety and efficacy signals from clinical trials, for stem/progenitor cell-based interventions for retinal disease.

DESIGN

Interpretive essay.

METHODS

Review and synthesis of selected recent reports of stem/progenitor cell-based approaches for retinal disease, with interpretation and perspective.

RESULTS

Stem/progenitor cell-based interventions represent a novel class of potential therapies for retinal diseases, such as age-related macular degeneration and inherited retinal dystrophies, aoong others. Sources include pluripotent stem cells and fetal and postnatal tissues. Two mechanisms of "rescue" have been proposed: regenerative or trophic. Although pluripotent and fetal sourced-cell types have been tested in preclinical animal models of retinal disease, many postnatal stem/progenitor cell populations currently in trial do not have preclinical safety or efficacy data. Some early-phase trials of cell therapies suggest acceptable safety profiles. Other reports, involving some types of autologous, nonocular cell sources, have been linked to severe, blinding complications. Larger trials will be needed to determine short-term and long-term safety and efficacy of these cell-based interventions.

CONCLUSIONS

Stem/progenitor cell-based interventions have the potential to address blinding retinal diseases that affect hundreds of millions worldwide. Yet no Food and Drug Administration-approved stem cell therapies for retinal disease exist. Although some early-phase trial data are promising, reports of blinding complications from cell interventions remain troubling. It is paramount to apply a strong level of scientific rigor toward a well-planned, step-wise sequence of preclinical and clinical studies, to determine whether this class of potential therapies will be safe and effective for individuals with retinal diseases.

Engrafted Neural Progenitor Cells Express a Tissue-Restricted Reporter Gene Associated with Differentiated Retinal Photoreceptor Cells

Neural progenitor cells (NPCs) have shown ability to repair injured CNS, and might provide precursors to retinal neurons. NPCs were isolated from the brains of 14 day murine embryos of transgenic mice that express β-galactosidase (β-gal) on the arrestin promoter, which specifically directs expression to retinal photoreceptor cells. NPCs were transferred to adult, syngeneic mice via inoculation into the anterior chamber of the eye, the peritoneal cavity, or the brain. At 14 weeks postgrafting, tissues were collected and examined to determine if differentiated NPC progeny were present in retina based on histochemical detection of β-gal. Four of six anterior chamber-inoculated recipients showed Bluo-gal-stained cells in retina, indicating the presence of transferred NPCs or their progeny. Because the progenitor cells do not express β-gal, positive staining indicates differentiation leading to activation of the arrestin promoter. Two recipients inoculated by the intraperitoneal route also exhibited Bluo-gal staining in retina. The NPCs did not express β-gal if inoculated into brain, but survived and dispersed. Most recipients, regardless of inoculation route, were PCR positive for β-gal DNA in extraocular tissues, but no Bluo-gal staining was found outside of the retina. Injury to the retina promoted, but was not required, for progenitor cell engraftment. β-Gal-positive cells were concentrated in the outer layers of the retina. In summary, a reporter gene specifically expressed in differentiated retinal photoreceptor cells due to the activity of the arrestin promoter was expressed in recipient mouse retina following transfer of NPCs prepared from the β-gal transgenic mice. The presence of β-gal DNA, but not Bluo-gal staining, in spleen and other tissues revealed that the cells also migrated elsewhere and took up residence in other organs, but did not undergo differentiation that led to β-gal expression.

[Guidance of Medical Care for Familial Exudative Vitreoretinopathy：Research on Rare and Intractable Diseases, Health and Labour Sciences Research Grants]

Familial exudative vitreoretinopathy is a hereditary insufficiency of retinal vascularture, which manifests a variety of vitreoretinal abnormalities, including nonvascularlized retina, abnormality of retinal vessel growing, dragged retina, retinal folds and total retinal detachment. While causative genes have been identified, cases are often sporadic. Periodic examination is necessary to find recurrence of the disease and late complications, including rhegmatogenous retinal detachment, cataract and glaucoma.

Bestrophinopathy: An RPE-photoreceptor interface disease

Bestrophinopathies, one of the most common forms of inherited macular degenerations, are caused by mutations in the BEST1 gene expressed in the retinal pigment epithelium (RPE). Both human and canine BEST1-linked maculopathies are characterized by abnormal accumulation of autofluorescent material within RPE cells and bilateral macular or multifocal lesions; however, the specific mechanism leading to the formation of these lesions remains unclear. We now provide an overview of the current state of knowledge on the molecular pathology of bestrophinopathies, and explore factors promoting formation of RPE-neuroretinal separations, using the first spontaneous animal model of BEST1-associated retinopathies, canine Best (cBest). Here, we characterize the nature of the autofluorescent RPE cell inclusions and report matching spectral signatures of RPE-associated fluorophores between human and canine retinae, indicating an analogous composition of endogenous RPE deposits in Best Vitelliform Macular Dystrophy (BVMD) patients and its canine disease model. This study also exposes a range of biochemical and structural abnormalities at the RPE-photoreceptor interface related to the impaired cone-associated microvillar ensheathment and compromised insoluble interphotoreceptor matrix (IPM), the major pathological culprits responsible for weakening of the RPE-neuroretina interactions, and consequently, formation of vitelliform lesions. These salient alterations detected at the RPE apical domain in cBest as well as in BVMD- and ARB-hiPSC-RPE model systems provide novel insights into the pathological mechanism of BEST1-linked disorders that will allow for development of critical outcome measures guiding therapeutic strategies for bestrophinopathies.