Immunological aspects of RPE cell transplantation

Transplant of Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium Strips for Macular Degeneration and Retinitis Pigmentosa

Purpose

To explore the safety and efficacy of the allogeneic induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) strip transplantation for patients with RPE degeneration.

Design

Single-arm, open-label, interventional study.

Participants

Three eyes from 3 patients clinically diagnosed with RPE impairment disease; 1 patient had dry age-related macular degeneration (AMD), and remaining 2 patients had MERTK-associated retinitis pigmentosa.

Intervention

Allogeneic iPSC-derived RPE strip transplantation was performed by a 25-gauge pars plana vitrectomy. The RPE strips were prepared by incubating iPSC-derived RPE cells in 2-mm-wide grooves in the mold. Artificial retinal detachment was generated using a 38-gauge subretinal cannula, and the RPE strips were injected into the retinal bleb using a 31-gauge cannula with the maximum graft dose limited to 2 strips.

Main Outcome Measures

The reduction of RPE abnormal area by the engraftment of transplanted allogeneic iPSC-derived RPE cells, which was measured by analyzing fluorescein angiography with an automated evaluation program at pretransplantation and up to 52 weeks posttransplantation.

Results

The primary endpoint of reducing abnormal areas of RPE through the survival of the transplanted graft cells was achieved in all patients at 52 weeks posttransplantation. Visual function assessments confirmed significant vision-related quality of life improvement and potential retinal sensitivity restoration in 1 patient with dry AMD. The successful subretinal delivery of the iPSC-derived RPE strips was confirmed during and immediately after surgery. The engraftment of RPE cells migrated out from the strips was observed using polarization-sensitive OCT specifically and visualized as characteristic hexagonal cells via adaptive optics imaging in all patients. While no serious adverse events occurred, suspected immune reactions to graft cells and epiretinal membrane formation were observed in 1 patient each.

Conclusions

A decrease in the RPE abnormal area by reliable delivery of allogeneic iPSC-derived RPE strips was achieved in all 3 cases with no serious adverse events. Further long-term studies and larger cohorts with better preoperative vision are warranted to evaluate the safety and efficacy of RPE strip transplantation.

Financial Disclosures

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

hPSC-based treatment of retinal diseases - Current progress and challenges

Degenerative retinal diseases, such as age-related macular degeneration (AMD) and inherited retinal diseases (IRDs), cause visual impairment due to irreversible damage to the retinal pigment epithelium (RPE) and photoreceptor cells (PRCs). Currently, no definitive treatment exists. However, cell-based therapies using induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) offer potential solutions for restoring damaged retinal cells. This review summarizes recent advances in RPE and PRC transplantation, highlighting the benefits of each approach. For RPE transplantation, we focus on the outcomes of clinical studies involving three formulations: RPE sheets, RPE suspensions, and RPE strips. In the context of PRC transplantation, we trace the progress from fetal retinal transplantation to the latest studies. Additionally, we discuss our recent clinical work with retinal sheet transplantation and genome-edited retinal organoid sheets, which aim to improve functional integration by reducing bipolar cells in grafts. Finally, with the overall safety of the regenerative cell-based therapies demonstrated in past clinical applications, we explore future prospects for these therapies.

Advances in the Study of Age-Related Macular Degeneration Based on Cell or Cell-Biomaterial Scaffolds

Age-related macular degeneration (AMD), a progressive neurodegenerative disorder affecting the central retina, is pathologically defined by the irreversible degeneration of photoreceptors and retinal pigment epithelium (RPE), coupled with extracellular drusen deposition and choroidal neovascularization (CNV), and AMD constitutes the predominant etiological factor for irreversible vision impairment in adults aged ≥60 years. Cell-based or cell-biomaterial scaffold-based approaches have been popular in recent years as a major research direction for AMD; monotherapy with cell-based approaches typically involves subretinal injection of progenitor-derived or stem cell-derived RPE cells to restore retinal homeostasis. Meanwhile, cell-biomaterial scaffolds delivered to the lesion site by vector transplantation have been widely developed, and the implanted cell-biomaterial scaffolds can promote the reintegration of cells at the lesion site and solve the problems of translocation and discrete cellular structure produced by cell injection. While these therapeutic strategies demonstrate preliminary efficacy, rigorous preclinical validation and clinical trials remain imperative to validate their long-term safety, functional durability, and therapeutic consistency. This review synthesizes current advancements and translational challenges in cell-based and cell-biomaterial scaffold approaches for AMD, aiming to inform future development of targeted interventions for AMD pathogenesis and management.

Robotising vitreoretinal surgeries

The use of robotic surgery in ophthalmology has been shown to offer many potential advantages to current surgical techniques. Vitreoretinal surgery requires complex manoeuvres and high precision, and this is an area that exceeds manual human dexterity in certain surgical situations. With the advent of advanced therapeutics such as subretinal gene therapy, precise delivery and minimising trauma is imperative to optimize outcomes. There are multiple robotic systems in place for ophthalmology in pre-clinical and clinical use, and the Preceyes Robotic Surgical System (Preceyes BV) has also gained the CE mark and is commercially available for use. Recent in-vivo and in-human surgeries have been performed successfully with robotics systems. This includes membrane peeling, subretinal injections of therapeutics, and retinal vein cannulation. There is huge potential to integrate robotic surgery into mainstream clinical practice. In this review, we summarize the existing systems, and clinical implementation so far, and highlight the future clinical applications for robotic surgery in vitreo-retina.

PD-L1 Promotes Immunological Tolerance and Enhances Visual Protection of hESC-RPE Grafts in Retinal Degeneration

Immune rejection is a major barrier to the successful human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) transplantation for age-related macular degeneration (AMD). Traditional strategies to mitigate immune rejection involve ablating major histocompatibility complex (MHC) molecules on hESC-RPE. An alternative approach is immune checkpoint overexpression, avoiding natural killer (NK) cell-mediated destruction due to MHC-I deficiency. Our study highlights the benefits of PD-L1 overexpression without requiring MHC gene deletion, which preserved the immunosuppressive functions of hESC-RPE on NK cells. In Vivo experiments in retinal degeneration models showed that PD-L1-expressing hESC-RPE grafts exhibited significantly higher survival, reduced apoptosis and enhanced visual protection. Single-cell transcriptomics revealed reduced immune activation and oxidative stress in PD-L1-overexpressing grafts. PD-L1's protective role was further evidenced by improved light transduction in host photoreceptors. These findings support PD-L1 overexpression as a promising strategy to improve the efficiency of hESC-RPE-based therapy for AMD.

The impact of circadian rhythms on retinal immunity

The eye is an immune-protected organ, which is driven by factors such as cytokines, chemicals, light, and mechanical stimuli. The circadian clock is an intrinsic timing mechanism that influences the immune activities, such as immune cell count and activity, as well as inflammatory responses. Recent studies have demonstrated that the eye also possesses an intrinsic circadian rhythm, and this rhythmic regulation participates in ocular immune modulation. In this review, we discuss the immunoregulatory mechanisms of the circadian clock within the eye, and reveal new perspectives for the prevention and treatment of ocular diseases.

A review on eye diseases induced by blue light: pathology, model, active ingredients and mechanisms

Blue light induced eye damage (BLED) belongs to modern diseases. It is an ophthalmic disease caused by prolonged exposure to electronic devices or screens containing a large amount of high-energy short waves (blue light). Specific symptoms include dryness and discomfort in the eyes, blurred vision, headache, insomnia, and in severe cases, it may also cause various eye diseases such as cataracts and glaucoma. At present, the development of health products and drugs for eye blue light injury faces many difficulties. Therefore, further exploration and research are needed on the pathogenesis, pathophysiology, and pharmacological mechanisms of blue light injury. Natural medicine ingredients and preparations have unique advantages in targeting eye blue light injury fatigue products due to their multi-component synergistic effects, overall regulation, and mild and safe characteristics. Starting from the disease-related mechanisms and pathophysiological characteristics of eye blue light injury, this article elucidates the pharmacological mechanisms of various drugs for treating eye blue light injury. At the same time, it reviews the research on in vitro cultured cell and animal model conditions for blue light injury eyes, in order to provide reference for subsequent blue light injury modeling experiments. And explore future research directions to provide new ideas and methods for the prevention and treatment of BLED.

Retinitis Pigmentosa and Therapeutic Candidates

Retinitis pigmentosa (RP) is a class of inherited retinal dystrophies (IRDs) that involves the degeneration of retinal photoreceptor cells and results in progressive vision loss. It was identified and named in 1857. For over 100 years, treatment of RP was generally limited to modifications in diet, management of cystoid macular edema, and supportive care for low vision. Over the last several decades, advances in technology and our understanding of the human genome have led to a host of new therapeutic candidates for the treatment of RP. This includes gene and cell therapy, optogenetics, neuroprotective agents, and electronic retinal implants. In this article, we summarize both the traditional and novel therapeutic modalities for the treatment of retinitis pigmentosa.

Three-Dimensional Bioprinting for Retinal Tissue Engineering

Three-dimensional bioprinting (3DP) is transforming the field of regenerative medicine by enabling the precise fabrication of complex tissues, including the retina, a highly specialized and anatomically complex tissue. This review provides an overview of 3DP's principles, its multi-step process, and various bioprinting techniques, such as extrusion-, droplet-, and laser-based methods. Within the scope of biomimicry and biomimetics, emphasis is placed on how 3DP potentially enables the recreation of the retina's natural cellular environment, structural complexity, and biomechanical properties. Focusing on retinal tissue engineering, we discuss the unique challenges posed by the retina's layered structure, vascularization needs, and the complex interplay between its numerous cell types. Emphasis is placed on recent advancements in bioink formulations, designed to emulate retinal characteristics and improve cell viability, printability, and mechanical stability. In-depth analyses of bioinks, scaffold materials, and emerging technologies, such as microfluidics and organ-on-a-chip, highlight the potential of bioprinted models to replicate retinal disease states, facilitating drug development and testing. While challenges remain in achieving clinical translation-particularly in immune compatibility and long-term integration-continued innovations in bioinks and scaffolding are paving the way toward functional retinal constructs. We conclude with insights into future research directions, aiming to refine 3DP for personalized therapies and transformative applications in vision restoration.

Graft survival of major histocompatibility complex deficient stem cell-derived retinal cells

BACKGROUND

Gene editing of immunomodulating molecules is a potential transplantation strategy to control immune rejection. As we noticed the successful transplantation of retinal pigment epithelium (RPE) derived from embryonic stem cells of a cynomolgus monkey that accidentally lacked MHC class II (MHC-II) molecules, we hypothesized immune rejection could be evaded by suppressing MHC-II.

METHODS

Gene editing by the Crispr/Cas9 system was performed in induced pluripotent stem cells derived from a cynomolgus monkey (miPSCs) for targeted deletion of the gene coding class II MHC trans-activator (CIITA). Then the CIITA-knocked out miPSCs were differentiated into RPE cells to generate miPSC-derived MHC-II knockout RPE. The MHC-II knockout or wild-type RPEs were transplanted into the eyes of healthy cynomolgus monkeys. All monkeys used in this study were male.

RESULTS

Here we show when MHC-II knockout RPE are transplanted into monkey eyes, they show suppressed immunogenicity with no infiltration of inflammatory cells, leading to successful engraftment.

CONCLUSIONS

Our results reasonably evidence the efficacy of MHC-II knockout iPSC-RPE transplants for clinical application.

Sbno1 mediates cell-cell communication between neural stem cells and microglia through small extracellular vesicles

BACKGROUND

Neural stem cells (NSCs) play a crucial role in the progress of ischemic stroke. Research on zebrafish embryonic demonstrates an association between Strawberry Notch 1 (Sbno1) and central nervous system development. However, the regulation and underlying mechanism of Sbno1 in NSCs have not been studied yet. Here, we investigated the role and the mechanism of Sbno1 in NSCs development and the potential therapeutic value of Sbno1 in ischemic stroke.

METHODS

Adeno-associated virus (AAV) was used for overexpression or knockdown of Sbno1 in vitro or in vivo. A mouse model of MCAO was established to evaluate the neuroprotective effects of AAV-Sbno1, including balance beam test, rotarod test, and strength evaluation. H&E and immunofluorescence assessed neuronal impairment. Western blot and RT-qPCR were used to detect the expression of Sbno1 and its downstream target genes. RNA-seq and western blot were performed to explore further molecular mechanisms by which Sbno1 promoted endogenous repair of NSCs and macrophages M2 polarization. CCK8 was conducted to assess the effects of Sbno1 on NSCs proliferation. The impact of Sbno1 on NSCs apoptosis was evaluated by flow cytometry. NSCs derived from small extracellular vesicles (sEV) were obtained using ultracentrifugation and identified through nanoparticle tracking analysis (NTA) and western blot analysis.

RESULTS

Our results showed that Sbno1 is highly expressed in the central nervous system, which plays a crucial role in regulating the proliferation of NSCs through the PI3k-Akt-GSK3β-Wnt/β-catenin signaling pathway. In addition, with overexpression of Sbno1 in the hippocampus, post-stroke behavioral scores were superior to the wild-type mice, and immunofluorescence staining revealed an increased number of newly generated neurons. sEV released by NSCs overexpressing Sbno1 inhibited neuroinflammation, which mechanistically impaired the activation of the microglial NF-κB and MAPK signaling pathways.

CONCLUSIONS

Our studies indicate that sbno1 promotes the proliferation of NSCs and enhances endogenous repairing through the PI3k-Akt-GSK3β-Wnt/β-catenin signaling pathway. Additionally, NSCs overexpressing sbno1 improve ischemic stroke recovery and inhibit neuroinflammation after ischemia by sEV through the MAPK and NF-κB signaling pathways.

Tissue Engineering of Outer Blood Retina Barrier for Therapeutic Development

Age related macular degeneration and other retinal degenerative disorders are characterized by disruption of the outer blood retinal barrier (oBRB) with subsequent ischemia, neovascularization, and atrophy. Despite the treatment advances, there remains no curative therapy, and no treatment targeted at regenerating native-like tissue for patients with late stages of the disease. Here we present advances in tissue engineering, focusing on bioprinting methods of generating tissue allowing for safe and reliable production of oBRB as well as tissue reprogramming with induced pluripotent stem cells for transplantation. We compare these approaches to organ-on-a-chip models for studying the dynamic nature of physiologic conditions. Highlighted within this review are studies that employ good manufacturing practices and use clinical grade methods that minimize potential risk to patients. Lastly, we illustrate recent clinical applications demonstrating both safety and efficacy for direct patient use. These advances provide an avenue for drug discovery and ultimately transplantation.

Dielectrophoretic characterization of peroxidized retinal pigment epithelial cells as a model of age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is a prevalent ocular pathology affecting mostly the elderly population. AMD is characterized by a progressive retinal pigment epithelial (RPE) cell degeneration, mainly caused by an impaired antioxidative defense. One of the AMD therapeutic procedures involves injecting healthy RPE cells into the subretinal space, necessitating pure, healthy RPE cell suspensions. This study aims to electrically characterize RPE cells to demonstrate a possibility using simulations to separate healthy RPE cells from a mixture of healthy/oxidized cells by dielectrophoresis.

METHODS

BPEI-1 rat RPE cells were exposed to hydrogen peroxide to create an in-vitro AMD cellular model. Cell viability was evaluated using various methods, including microscopic imaging, impedance-based real-time cell analysis, and the MTS assay. Healthy and oxidized cells were characterized by recording their dielectrophoretic spectra, and electric cell parameters (crossover frequency, membrane conductivity and permittivity, and cytoplasm conductivity) were computed. A COMSOL simulation was performed on a theoretical microfluidic-based dielectrophoretic separation chip using these parameters.

RESULTS

Increasing the hydrogen peroxide concentration shifted the first crossover frequency toward lower values, and the cell membrane permittivity progressively increased. These changes were attributed to progressive membrane peroxidation, as they were diminished when measured on cells treated with the antioxidant N-acetylcysteine. The changes in the crossover frequency were sufficient for the efficient separation of healthy cells, as demonstrated by simulations.

CONCLUSIONS

The study demonstrates that dielectrophoresis can be used to separate healthy RPE cells from oxidized ones based on their electrical properties. This method could be a viable approach for obtaining pure, healthy RPE cell suspensions for AMD therapeutic procedures.

From theory to therapy: a bibliometric and visual study of stem cell advancements in age-related macular degeneration

BACKGROUND AIMS

Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, offer groundbreaking therapeutic potential for degenerative diseases and cellular repair. Despite their significance, a comprehensive bibliometric analysis in this field, particularly in relation to age-related macular degeneration (AMD), is yet to be conducted. This study aims to map the foundational and emerging areas in stem cell and AMD research through bibliometric analysis.

METHODS

This study analyzed articles and reviews on stem cells and AMD from 2000 to 2022, sourced from the Web of Science Core Collection. We used VOSviewer and CiteSpace for analysis and visualization of data pertaining to countries, institutions, authors, journals, references and key words. Statistical analyses were conducted using R language and Microsoft Excel 365.

RESULTS

In total, 539 publications were included, indicating an increase in global literature on stem cells and AMD from 2000 to 2022. The USA was the leading contributor, with 239 papers and the highest H-index, also the USA had the highest average citation rate per article (59.82). Notably, 50% of the top 10 institutions were from the USA, with the University of California system being the most productive. Key authors included Masayo Takahashi, Michiko Mandai, Dennis Clegg, Pete J. Coffey, Boris Stanzel, and Budd A. Tucker. Investigative Ophthalmology & Visual Science published the majority of relevant papers (n = 27). Key words like "clinical trial," "stem cell therapy," "retinal organoid," and "retinal progenitor cells" were predominant.

CONCLUSIONS

Research on stem cells and AMD has grown significantly, highlighting the need for increased global cooperation. Current research prioritizes the relationship between "ipsc," "induced pluripotent stem cell," "cell culture," and "human embryonic stem cell." As stem cell culture and safety have advanced, focus has shifted to prognosis and complications post-transplantation, signifying the movement of stem cell research from labs to clinical settings.

Human Pluripotent Stem Cells Derived Endothelial Cells Repair Choroidal Ischemia

Choroidal atrophy is a common fundus pathological change closely related to the development of age-related macular degeneration (AMD), retinitis pigmentosa, and pathological myopia. Studies suggest that choroidal endothelial cells (CECs) that form the choriocapillaris vessels are the first cells lost in choroidal atrophy. It is found that endothelial cells derived from human pluripotent stem cells (hPSC-ECs) through the MESP1+ mesodermal progenitor stage express CECs-specific markers and can integrate into choriocapillaris. Single-cell RNA-seq (scRNA-seq) studies show that hPSC-ECs upregulate angiogenesis and immune-modulatory and neural protective genes after interacting with ex vivo ischemic choroid. In a rat model of choroidal ischemia (CI), transplantation of hPSC-ECs into the suprachoroidal space increases choroid thickness and vasculature density. Close-up examination shows that engrafted hPSC-ECs integrate with all layers of rat choroidal vessels and last 90 days. Remarkably, EC transplantation improves the visual function of CI rats. The work demonstrates that hPSC-ECs can be used to repair choroidal ischemia in the animal model, which may lead to a new therapy to alleviate choroidal atrophy implicated in dry AMD, pathological myopia, and other ocular diseases.

Induction of human ESC-derived and adult primary multipotent limbal stem cells into retinal pigment epithelial cells and corneal stromal stem cells

Human embryonic stem cell (hESC)- and human induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (RPE) therapies are promising alternatives for the treatment of retinal degenerative diseases caused by RPE degeneration. The generation of autologous RPE cells from human adult donors, which has the advantage of avoiding immune rejection and teratoma formation, is an alternative cell resource to gain mechanistic insight into and test potential therapies for RPE degenerative diseases. Here, we found that limbal stem cells (LSCs) from hESCs and adult primary human limbus have the potential to produce RPE cells and corneal stromal stem cells (CSSCs). We showed that hESC-LSC-derived RPE cells (LSC-RPE) expressed RPE markers, had a phagocytic function, and synthesized tropical factors. Furthermore, during differentiation from LSCs to RPE cells, cells became pigmented, accompanied by a decrease in the level of LSC marker KRT15 and an increase in the level of RPE marker MITF. The Wnt signaling pathway plays a role in LSC-RPE fate transition, promotes MITF expression in the nucleus, and encourages RPE fate transition. In addition, we also showed that primary LSCs (pLSCs) from adult human limbus similar to hESC-LSC could generate RPE cells, which was supported by the co-expression of LSC and RPE cell markers (KRT15/OTX2, KRT15/MITF), suggesting the transition from pLSC to RPE cells, and typical polygonal morphology, melanization, RPE cell marker genes expression (TYR, RPE65), tight junction formation by ZO-1 expression, and the most crucial phagocytotic function. On the other hand, both hESC-LSCs and pLSCs also differentiated into CSSCs (LSC-CSSCs) that expressed stem cell markers (PAX6, NESTIN), presented MSC features, including surface marker expression and trilineage differentiation capability, like those in human CSSCs. Furthermore, the capability of pLSC-CSSC to differentiate into cells expressing keratocyte marker genes (ALDH3A1, PTGDS, PDK4) indicated the potential to induce keratocytes. These results suggest that the adult pLSC is an alternative cell resource, and its application provides a novel potential therapeutic avenue for preventing RPE dysfunction-related retinal degenerative diseases and corneal scarring.

Safety and stable survival of stem-cell-derived retinal organoid for 2 years in patients with retinitis pigmentosa

Transplantation of induced pluripotent stem cell (iPSC)-derived retinal organoids into retinal disease animal models has yielded promising results, and several clinical trials on iPSC-derived retinal pigment epithelial cell transplantation have confirmed its safety. In this study, we performed allogeneic iPSC-derived retinal organoid sheet transplantation in two subjects with advanced retinitis pigmentosa (jRCTa050200027). The primary endpoint was the survival and safety of the transplanted retinal organoid sheets in the first year post-transplantation. The secondary endpoints were the safety of the transplantation procedure and visual function evaluation. The grafts survived in a stable condition for 2 years, and the retinal thickness increased at the transplant site without serious adverse events in both subjects. Changes in visual function were less progressive than those of the untreated eye during the follow-up. Allogeneic iPSC-derived retinal organoid sheet transplantation is a potential therapeutic approach, and the treatment's safety and efficacy for visual function should be investigated further.

Co-cultivation of primary porcine RPE cells and neuroretina induces inflammation: a potential inflammatory AMD-model

One common aspect in the pathology of many retinal diseases like age-related macular degeneration (AMD) is the death of retinal pigment epithelium (RPE) cells. RPE cells are essential for photoreceptor survival as they recycle and remove compounds of the visual cycle and secrete protective cytokines. Studying RPE cells is crucial to improve our understanding of retinal pathologies, yet only a few retinal ex vivo models include them or do so only indirectly. Besides the positive effects in indirect co-cultivation models, also a slight inflammation was observed. In this study we developed an ex vivo model consisting of a primary porcine RPE monolayer directly co-cultured with porcine retinal organ cultures, to investigate and simulate inflammatory retinal diseases, such as (dry) AMD. The direct co-cultivation resulted in immune reactivity (enhanced expression of pro-inflammatory cytokines e.g., IL-1β, IL-6, IL-8) and cell death. These effects were evaluated for the retinal explant as well as for the RPE-monolayer to further understand the complex interactions between these two compartments. Taken together, this ex vivo model can be used to study inflammatory retinal diseases like AMD as well as the rejection observed after RPE-transplantation.

Replenishing Age-Related Decline of IRAK-M Expression in Retinal Pigment Epithelium Attenuates Outer Retinal Degeneration

Unchecked, chronic inflammation is a constitutive component of age-related diseases, including age-related macular degeneration (AMD). Here we identified interleukin-1 receptor-associated kinase (IRAK)-M as a key immunoregulator in retinal pigment epithelium (RPE) that declines with age. Rare genetic variants of IRAK-M increased the likelihood of AMD. IRAK-M expression in RPE declined with age or oxidative stress and was further reduced in AMD. IRAK-M-deficient mice exhibited increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M disrupted RPE cell homeostasis, including compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of AAV-expressing IRAK-M rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in IRAK-M-deficient mice. Our data support that replenishment of IRAK-M expression may redress dysregulated pro-inflammatory processes in AMD, thereby treating degeneration.

Factors Affecting Stem Cell-Based Regenerative Approaches in Retinal Degeneration

Inherited and age-associated vision loss is often associated with degeneration of the cells of the retina, the light-sensitive layer at the back of the eye. The mammalian retina, being a postmitotic neural tissue, does not have the capacity to repair itself through endogenous regeneration. There has been considerable excitement for the development of cell replacement approaches since the isolation and development of culture methods for human pluripotent stem cells, as well as the generation of induced pluripotent stem cells. This has now been combined with novel three-dimensional organoid culture systems that closely mimic human retinal development in vitro. In this review, we cover the current state of the field, with emphasis on the cell delivery challenges, role of the recipient immunological microenvironment, and challenges related to connectivity between transplanted cells and host circuitry both locally and centrally to the different areas of the brain.

A CASE OF RAPIDLY PROGRESSIVE RETINOPATHY ASSOCIATED WITH PEMBROLIZUMAB IMMUNOTHERAPY FOR METASTATIC UROTHELIAL CARCINOMA

PURPOSE

To describe a novel case of bilateral rapidly progressive retinopathy after immunotherapy with pembrolizumab for metastatic urothelial carcinoma.

METHODS

Case report.

RESULTS

A 64-year-old man undergoing pembrolizumab immunotherapy was referred to our hospital because of bilateral acute vision loss. His best-corrected visual acuity was 20/30 in the right eye and 20/320 in the left eye, and a visual field test revealed central and paracentral scotomas in the right eye and central scotoma in the left eye. We suspected immune-related retinopathy based on the progressive photoreceptor damage with abnormal electroretinogram findings, absence of overt intraocular inflammation, and presence of malignancy. Cessation of pembrolizumab and steroid pulse therapy followed by decreasing oral prednisolone improved visual function and photoreceptor damage, although there was recurrence after pembrolizumab was restarted.

CONCLUSION

We reported a case of rapidly progressive retinopathy that may have been triggered by pembrolizumab immunotherapy for metastatic urothelial carcinoma. High-dose corticosteroid pulse therapy was effective in reversing photoreceptor damage.

Single-cell RNA sequencing in dissecting microenvironment of age-related macular degeneration: Challenges and perspectives

Age-related macular degeneration (AMD) is the leading cause of blindness in individuals over the age of 50 years, yet its etiology and pathogenesis largely remain uncovered. Single-cell RNA sequencing (scRNA-seq) technologies are recently developed and have a number of advantages over conventional bulk RNA sequencing techniques in uncovering the heterogeneity of complex microenvironments containing numerous cell types and cell communications during various biological processes. In this review, we summarize the latest discovered cellular components and regulatory mechanisms during AMD development revealed by scRNA-seq. In addition, we discuss the main challenges and future directions in exploring the pathophysiology of AMD equipped with single-cell technologies. Our review underscores the importance of multimodal single-cell platforms (such as single-cell spatiotemporal multi-omics and single-cell exosome omics) as new approaches for basic and clinical AMD research in identifying biomarker, characterizing cellular responses to drug treatment and environmental stimulation.

The Role of Subretinal Injection in Ophthalmic Surgery: Therapeutic Agent Delivery and Other Indications

Subretinal injection is performed in vitreoretinal surgery with two main aims, namely, the subretinal delivery of therapeutic agents and subretinal injection of fluid to induce a controlled and localized macular detachment. The growing interest in this technique is mainly related to its suitability to deliver gene therapy in direct contact with target tissues. However, subretinal injection has been also used for the surgical management of submacular hemorrhage through the subretinal delivery of tissue plasminogen activator, and for the repair of full-thickness macular holes, in particular refractory ones. In the light of the increasing importance of this maneuver in vitreoretinal surgery as well as of the lack of a standardized surgical approach, we conducted a comprehensive overview on the current indications for subretinal injection, surgical technique with the available variations, and the potential complications.

Rethinking the potential and necessity of drug delivery systems in neovascular age-related macular degeneration therapy

Age-related macular degeneration (AMD) is the predominant threat to human vision and ultimately results in blindness. With the increase in the aging population, it has become a more crucial issue to human health. AMD is a multifactorial disease with the unique feature of uncontrollable angiogenesis during initiation and progression. Although increasing evidence indicates that AMD is largely hereditary, the predominant efficient treatment is antiangiogenesis, which mainly involves VEGF and HIF-α as therapeutic targets. The repeated administration of this treatment over the long term, generally through intravitreal injection, has called for the introduction of long-term drug delivery systems, which are expected to be achieved by biomaterials. However, the clinical results of the port delivery system indicate that the optimization of medical devices toward prolonging the activities of therapeutic biologics in AMD therapy seems more promising. These results indicate that we should rethink the possibility and potential of biomaterials as drug delivery systems in achieving long-term, sustained inhibition of angiogenesis in AMD therapy. In this review, the etiology, categorization, risk factors, pathogenesis, and current clinical treatments of AMD are briefly introduced. Next, the development status of long-term drug delivery systems is discussed, and the drawbacks and shortages of these systems are emphasized. By comprehensively considering the pathological aspect and the recent application of drug delivery systems in AMD therapy, we hope to find a better solution for the further development of long-term therapeutic strategies for AMD.

Stem cell sources and characterization in the development of cell-based products for treating retinal disease: An NEI Town Hall report

National Eye Institute recently issued a new Strategic Plan outlining priority research areas for the next 5 years. Starting cell source for deriving stem cell lines is as an area with gaps and opportunities for making progress in regenerative medicine, a key area of emphasis within the NEI Strategic Plan. There is a critical need to understand how starting cell source affects the cell therapy product and what specific manufacturing capabilities and quality control standards are required for autologous vs allogeneic stem cell sources. With the goal of addressing some of these questions, in discussion with the community-at-large, NEI hosted a Town Hall at the Association for Research in Vision and Ophthalmology annual meeting in May 2022. This session leveraged recent clinical advances in autologous and allogeneic RPE replacement strategies to develop guidance for upcoming cell therapies for photoreceptors, retinal ganglion cells, and other ocular cell types. Our focus on stem cell-based therapies for RPE underscores the relatively advanced stage of RPE cell therapies to patients with several ongoing clinical trials. Thus, this workshop encouraged lessons learned from the RPE field to help accelerate progress in developing stem cell-based therapies in other ocular tissues. This report provides a synthesis of the key points discussed at the Town Hall and highlights needs and opportunities in ocular regenerative medicine.

Immune Responses to Sequential Binocular Transplantation of Allogeneic Retinal Progenitor Cells to the Vitreous Cavity in Mice

Intravitreal transplantation of allogeneic human retinal progenitor cells (hRPCs) holds promise as a treatment for blinding retinal degenerations. Prior work has shown that neural progenitors are well-tolerated as allografts following single injections; however, sequential delivery of allogeneic cells raises the potential risk of host sensitization with subsequent immune rejection of grafts. The current study was designed to assess whether an immune response would be induced by repeated intravitreal transplants of allogeneic RPCs utilizing the mouse animal model. We injected murine retinal progenitor cells (gmRPCs), originally derived from donors with a C57BL/6 genetic background, into BALB/c recipient mice in order to provide safety data as to what might be expected following repeated treatment of patients with allogeneic human cell product. Immune responses to gmRPCs were mild, consisting of T cells, B cells, neutrophils, and natural killer cells, with macrophages clearly the predominating. Animals treated with repeat doses of gmRPCs did not show evidence of sensitization, nor was there immune-mediated destruction of the grafts. Despite the absence of immunosuppressive treatments, allogeneic gmRPC grafts survived following repeat dosing, thus providing support for the preliminary observation that repeated injection of allogeneic RPCs to the vitreous cavity is tolerated in patients with retinitis pigmentosa.

Network Pharmacology-Based Identification of Key Targets of Ziyin Mingmu Pills Acting on Age-Related Macular Degeneration

Objective

This study is designed to find out the molecular targets of effective Chinese medicine Ziyin Mingmu pills (ZMPs) in treating age-related macular degeneration (AMD) based on network pharmacology and experimental data.

Methods

A comprehensive network pharmacology strategy that consists of three sequential modules (drug-disease target molecular docking, enrichment analysis, and external verification) was carried out to identify potential targets of ZMPs acting on AMD.

Results

The active ingredients of ZMPs targeting 66 genes have effects on the process of AMD. GO and KEGG pathway enrichment analyses suggested that response to oxidative stress, regulation of angiogenesis, and lipid and atherosclerosis might serve as the most important signaling pathways in ZMPs for AMD treatment. Combined with the GSE29801 dataset for further analysis, two key genes, EGFR and VEGFA, were identified. Immune infiltration analysis showed that there was a strong association between EGFR and immune cell content. In addition, images were acquired following 24 h in the scratch experiment showed that ZMPs can reduce the percentage of wound healing distance. The Western blot assay found that ZMPs increased the expression of EGFR and decreased the expression of VEGFA.

Conclusion

This study sheds light on some mechanisms of ZMP therapy for AMD, particularly the effect of ZMP on the oxidative stress in RPE and cell survival and angiogenesis in AMD. We propound ZMPs as a promising strategy to intervene in the process of AMD.

Gene-agnostic therapeutic approaches for inherited retinal degenerations

Inherited retinal diseases (IRDs) are associated with mutations in over 250 genes and represent a major cause of irreversible blindness worldwide. While gene augmentation or gene editing therapies could address the underlying genetic mutations in a small subset of patients, their utility remains limited by the great genetic heterogeneity of IRDs and the costs of developing individualised therapies. Gene-agnostic therapeutic approaches target common pathogenic pathways that drive retinal degeneration or provide functional rescue of vision independent of the genetic cause, thus offering potential clinical benefits to all IRD patients. Here, we review the key gene-agnostic approaches, including retinal cell reprogramming and replacement, neurotrophic support, immune modulation and optogenetics. The relative benefits and limitations of these strategies and the timing of clinical interventions are discussed.

iPSC-based model of Vogt-Koyanagi-Harada disease for phenotype recapitulation and drug screening

Vogt-Koyanagi-Harada (VKH) disease, a major blinding eye disease, is characterized by an autoimmune response against melanocytes in multiple organs throughout the body. Currently, the aetiology and pathogenesis of VKH disease are unclear, and the treatment strategy needs to be further optimized. The retinal pigment epithelium (RPE), a monolayer of pigmented cells of the fundus, is essential for maintaining normal visual function and is involved in both the acute and chronic stages of VKH disease. Therefore, the functions of the RPE may play a critical role in the aetiology and treatment of VKH disease. Herein, we established a human induced pluripotent stem cell (hiPSC) RPE model of VKH disease by reprogramming peripheral blood mononuclear cells (PBMCs) into iPSCs and then differentiating them into RPE cells. Patient-derived RPE cells exhibited barrier disruption, impaired phagocytosis, and depigmentation compared with those from normal controls, which was consistent with the features of VKH disease. Furthermore, a small molecular compound targeting EGR2 was found to rescue the barrier and phagocytic functions of the hiPSC-RPE cells through high-throughput virtual screening and functional studies, suggesting a promising strategy for the treatment of VKH disease.

Stem cells for treating retinal degeneration

The mammalian retina lacks regenerative potency to replace damaged or degenerated cells. Therefore, traumatic or genetic insults that lead to the degeneration of retinal neurons or retinal pigment epithelium (RPE) cells alter visual perception and ultimately can lead to blindness. The advent of human stem cells and their exploitation for vision restoration approaches has boosted the field. Traditionally, animal models-mostly rodents-have been generated and used to mimic certain monogenetic hereditary diseases. Of note, some models were extremely useful to develop specific gene therapies, for example for Retinitis Pigmentosa, Leber congenital amaurosis and achromatopsia. However, complex multifactorial diseases are not well recapitulated in rodent models such as age-related macular degeneration (AMD) as rodents lack a macula. Here, human stem cells are extremely valuable to advance the development of therapies. Particularly, cell replacement therapy is of enormous importance to treat retinal degenerative diseases. Moreover, different retinal degenerative disorders require the transplantation of unique cell types. The most advanced one is to substitute the RPE cells, which stabilize the light-sensitive photoreceptors. Some diseases require also the transplantation of photoreceptors. Depending on the disease pattern, both approaches can also be combined. Within this article, I briefly feature the underlying principle of cell replacement therapies, demonstrate some successes and discuss certain shortcomings of these approaches for clinical application.

Pluripotent Stem Cells in Clinical Cell Transplantation: Focusing on Induced Pluripotent Stem Cell-Derived RPE Cell Therapy in Age-Related Macular Degeneration

Human pluripotent stem cells (PSCs), including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), represent valuable cell sources to replace diseased or injured tissues in regenerative medicine. iPSCs exhibit the potential for indefinite self-renewal and differentiation into various cell types and can be reprogrammed from somatic tissue that can be easily obtained, paving the way for cell therapy, regenerative medicine, and personalized medicine. Cell therapies using various iPSC-derived cell types are now evolving rapidly for the treatment of clinical diseases, including Parkinson's disease, hematological diseases, cardiomyopathy, osteoarthritis, and retinal diseases. Since the first interventional clinical trial with autologous iPSC-derived retinal pigment epithelial cells (RPEs) for the treatment of age-related macular degeneration (AMD) was accomplished in Japan, several preclinical trials using iPSC suspensions or monolayers have been launched, or are ongoing or completed. The evolution and generation of human leukocyte antigen (HLA)-universal iPSCs may facilitate the clinical application of iPSC-based therapies. Thus, iPSCs hold great promise in the treatment of multiple retinal diseases. The efficacy and adverse effects of iPSC-based retinal therapies should be carefully assessed in ongoing and further clinical trials.

Changes of a2-macroglobulin activity and endothelin-1 concentration in tears of rabbits after transplantation of retinal pigment epithelium cells derived from the induced pluripotent stem cells

Retinal diseases accompanied with the dysfunction or death of the retinal pigment epithelial (RPE) cells are widespread, hard to treat, and appear to be a leading case of visual loss and blindness among the persons older than 55 years. Transplantation of RPE cells derived from the induced pluripotent stem cells (IPSC-RPE) is a promising method of therapy for these diseases. To ensure the transplant survival instant follow-up is required. It can be based on biochemical analyses of tear fluid that can be easily non-invasively collected. For the post-transplantation process monitoring we have choosen such polyfunctional bioregulators as α2-macroglobulin (α2-MG) and endothelin-1 (ET-1). RPE atrophy in New Zealand Albino rabbits was modeled via the subretinal injection of bevacizumab. IPSC-RPE in suspension or as a monolayer on the scaffold were transplanted subretinally 1 month after the injection. α2-MG activity and ET-1 concentration in tears were estimated during the first month and after 2, 3 and 7 months after transplantation. On the 7-14 days after transplantation α2-MG activity increased in tears of the both operated and controlateral eye probably as a reaction on the corticosteroid therapy. In 50% rabbits there was one more increase after 2-3 months that could be due to the immune inflammation. Concentration of ET-1 in tears decreased dramatically on the 7-14 days and 7 months after transplantation, and it could have an influence upon the retinal vassal tone. The data obtained show that estimation of bioregulators in tears can help monitoring local metabolic processes after RPE transplantation that is necessary for the opportune, reasonable and focused medicamental correction of post-transplantation process.

Amniotic Membrane Enhances the Characteristics and Function of Stem Cell-Derived Retinal Pigment Epithelium Sheets by Inhibiting the Epithelial-Mesenchymal Transition

Human pluripotent stem cell-derived retinal pigment epithelium (iRPE) is an attractive cell source for disease modeling and cell replacement therapy of retinal disorders with RPE defects. However, there are still challenges to develop appropriate culture conditions close to in vivo microenvironment to generate iRPE sheets, which mimic more faithfully the characteristics and functions of the human RPE cells. Here, we developed a simple, novel platform to construct authentic iRPE sheets using human amniotic membrane (hAM) as a natural scaffold. The decellularized hAM (dAM) provided a Bruch's membrane (BM)-like bioscaffold, supported the iRPE growth and enhanced the epithelial features, polarity distribution and functional features of iRPE cells. Importantly, RNA-seq analysis was performed to compare the transcriptomes of iRPE cells cultured on different substrates, which revealed the potential mechanism that dAM supported and promoted iRPE growth was the inhibition of epithelial mesenchymal transition (EMT). The tissue-engineered iRPE sheets survived and kept monolayer when transplanted into the subretinal space of rabbits. All together, our results indicate that the dAM imitating the natural BM allows for engineering authentic human RPE sheets, which will provide valuable biomaterials for disease modeling, drug screening and cell replacement therapy of retinal degenerative diseases. STATEMENT OF SIGNIFICANCE: : Engineered RPE sheets have a great advantage over RPE cell suspension for transplantation as they support RPE growth in an intact monolayer which RPE functions are dependent on. The substrates for RPE culture play a critical role to maintain the physiological functions of the RPE in stem cell therapies for patients with retinal degeneration. In this study, we constructed engineered iRPE sheets on the decellularized human amniotic membrane (dAM) scaffolds, which contributed to enhancing epithelial features, polarity distribution and functional features of iRPE. dAM exhibited the ability of anti-epithelial mesenchymal transition (EMT) to support iRPE growth. Furtherly, the results of transplanted in vivo demonstrated the feasibility of iRPE sheets in retina regenerative therapy. Engineering RPE sheets on dAM is a promising strategy to facilitate the development of iRPE replacement therapy and retinal disease modeling.

[Optogenetics and cell replacement in retinology : Regenerative ophthalmology-What we can do!]

For many degenerative retinal diseases that progressively lead to blindness, no treatment options are available so far. In recent years, several innovative therapies have been experimentally explored, which are promising because they are independent of the genetic cause of the degenerative disease. One of these is optogenetics, which involves light-sensitive proteins that selectively act as ion channels or ion pumps to control the potential of the treated cell. Thus, these cells can be stimulated or inhibited by light, quasi functionally remote controlled. In this way artificial photoreceptors are induced from the remaining cells, which has already been successfully employed in animal experiments. This type of treatment is already being tested on patients and leads to an improvement in vision, but so far only data from one patient are available. The use of optogenetics additionally requires special eyeglasses to adapt the light impulses in adequate strength and wavelength for the respective optogenes. Another exciting approach is cell replacement therapy of retinal pigment epithelium (RPE) and photoreceptor cells to exchange degenerated cell material. This appears to be very successful for RPE cells in clinical trials. Obtaining human photoreceptors from stem cells is technically possible, but very laborious. The integration of the transplanted photoreceptors into the host retinal tissue also needs further optimization for broader clinical applications; however, both cell replacement and optogenetics approaches are promising, so that the translation from basic research into clinical application will be successful.

Gene-independent therapeutic interventions to maintain and restore light sensitivity in degenerating photoreceptors

Neurodegenerative retinal diseases are a prime cause of blindness in industrialized countries. In many cases, there are no therapeutic treatments, although they are essential to improve patients' quality of life. A set of disease-causing genes, which primarily affect photoreceptors, has already been identified and is of major interest for developing gene therapies. Nevertheless, depending on the nature and the state of the disease, gene-independent strategies are needed. Various strategies to halt disease progression or maintain function of the retina are under research. These therapeutic interventions include neuroprotection, direct reprogramming of affected photoreceptors, the application of non-coding RNAs, the generation of artificial photoreceptors by optogenetics and cell replacement strategies. During recent years, major breakthroughs have been made such as the first optogenetic application to a blind patient whose visual function partially recovered by targeting retinal ganglion cells. Also, RPE cell transplantation therapies are under clinical investigation and show great promise to improve visual function in blind patients. These cells are generated from human stem cells. Similar therapies for replacing photoreceptors are extensively tested in pre-clinical models. This marks just the start of promising new cures taking advantage of developments in the areas of genetic engineering, optogenetics, and stem-cell research. In this review, we present the recent therapeutic advances of gene-independent approaches that are currently under clinical evaluation. Our main focus is on photoreceptors as these sensory cells are highly vulnerable to degenerative diseases, and are crucial for light detection.

Stem cell-derived retinal pigment epithelium transplantation in age-related macular degeneration: recent advances and challenges

PURPOSE OF REVIEW

Age-related macular degeneration (AMD) is one of the leading causes of irreversible vision loss in the world with more than 80% of the prevalence accounted for by the nonneovascular (NNAMD) or 'dry' form of the disease. NNAMD does not have any definitive treatment once vision loss has ensued and presents a major unmet medical need. This review will highlight stem cell-based therapies that are a promising form of treatment for advanced NNAMD.

RECENT FINDINGS

In the past decade, clinical trials utilizing both induced pluripotent stem cell-derived RPE and human embryonic stem cell-derived RPE have been aggressively pursued as potential treatments of RPE loss and prevention of overlying neurosensory atrophy. While promising preliminary results demonstrating safety and potential efficacy have been published, new challenges have also been identified. These include selecting the most appropriate cell-based therapy, identifying and managing potential immune response as well as characterizing anatomic and functional efficacy. In this review, we will discuss some of these challenges in light of the available data from several early phase clinical trials and discuss the strategies that are being considered to further advance the field.

SUMMARY

Cell-based therapies demonstrate promising potential to treat advanced stages of NNAMD. Several early phase clinical trials using both induced pluripotent stem cells (iPSC) and human embryonic stem cell derived (hESC) have demonstrated safety and preliminary signs of efficacy and highlighted remaining challenges which appear surmountable. These challenges include development of selection criteria for use of cell suspensions versus RPE sheets, especially in light of immunological properties of RPE that are intrinsic to the status of RPE differentiation in each of these cell formulations.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

Subretinal Therapy: Technological Solutions to Surgical and Immunological Challenges

Recent advances in ocular gene and cellular therapy rely on precisely controlled subretinal delivery. Due to its inherent limitations, manual delivery can lead to iatrogenic damage to the retina, the retinal pigment epithelium, favor reflux into the vitreous cavity. In addition, it suffers from lack of standardization, variability in delivery and the need to maintain proficiency. With or without surgical damage, an eye challenged with an exogenous viral vector or transplanted cells will illicit an immune response. Understanding how such a response manifests itself and to what extent immune privilege protects the eye from a reaction can help in anticipating short- and long-term consequences. Avoidance of spillover from areas of immune privilege to areas which either lack or have less protection should be part of any mitigation strategy. In that regard, robotic technology can provide reproducible, standardized delivery which is not dependent on speed of injection. The advantages of microprecision medical robotic technology for precise targeted deliveries are discussed.

Cell maturation influences the ability of hESC-RPE to tolerate cellular stress

Background

Transplantation of human pluripotent stem cell-derived retinal pigment epithelium (RPE) is an urgently needed treatment for the cure of degenerative diseases of the retina. The transplanted cells must tolerate cellular stress caused by various sources such as retinal inflammation and regain their functions rapidly after the transplantation. We have previously shown the maturation level of the cultured human embryonic stem cell-derived RPE (hESC-RPE) cells to influence for example their calcium (Ca²⁺) signaling properties. Yet, no comparison of the ability of hESC-RPE at different maturity levels to tolerate cellular stress has been reported.

Methods

Here, we analyzed the ability of the hESC-RPE populations with early (3 weeks) and late (12 weeks) maturation status to tolerate cellular stress caused by chemical cell stressors protease inhibitor (MG132) or hydrogen peroxide (H₂O₂). After the treatments, the functionality of the RPE cells was studied by transepithelial resistance, immunostainings of key RPE proteins, phagocytosis, mitochondrial membrane potential, Ca²⁺ signaling, and cytokine secretion.

Results

The hESC-RPE population with late maturation status consistently showed improved tolerance to cellular stress in comparison to the population with early maturity. After the treatments, the early maturation status of hESC-RPE monolayer showed impaired barrier properties. The hESC-RPE with early maturity status also exhibited reduced phagocytic and Ca²⁺ signaling properties, especially after MG132 treatment.

Conclusions

Our results suggest that due to better tolerance to cellular stress, the late maturation status of hESC-RPE population is superior compared to monolayers with early maturation status in the transplantation therapy settings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02712-7.

Detection of Mycoplasma Contamination in Transplanted Retinal Cells by Rapid and Sensitive Polymerase Chain Reaction Test

Contamination of cells/tissues by infectious pathogens (e.g., fungi, viruses, or bacteria, including mycoplasma) is a major problem in cell-based transplantation. In this study, we tested a polymerase chain reaction (PCR) method to provide rapid, simple, and sensitive detection of mycoplasma contamination in laboratory cultures for clinical use. This mycoplasma PCR system covers the Mycoplasma species (spp.) listed for testing in the 17th revision of the Japanese Pharmacopoeia, and we designed it for use in transplantable retinal cells. Here, we analyzed mycoplasma contamination in induced pluripotent stem cell (iPS cell)-derived transplantable retinal pigment epithelium (RPE) cells. In the spike tests to RPE cells with nine species of class Mollicutes bacteria, including seven Mycoplasma spp. and one of each Acholeplasma spp. and Ureaplasma spp., contamination at the concentration of 100 and 10 CFU/mL were detected with 100% probability in all cases, while 1 CFU/mL had a detection rate of 0–75%. DNA prepared from bacteria species other than class Mollicutes species was not detectable, indicating the specificity of this PCR. While iPS cells and iPS-RPE cells established in our laboratory were all negative by this PCR, some of the commercially available cell lines were positive. Cells for transplantation should never have infection, as once pathogens are implanted into the eyes, they can cause severe intraocular inflammation. Thus, it is imperative to monitor for infections in the transplants, although generally, mycoplasma infection is difficult to detect.

Retina stem cells, hopes and obstacles

Retinal degeneration is a major contributor to visual dysfunction worldwide. Although it comprises several eye diseases, loss of retinal pigment epithelial (RPE) and photoreceptor cells are the major contributors to their pathogenesis. Early therapies included diverse treatments, such as provision of anti-vascular endothelial growth factor and many survival and trophic factors that, in some cases, slow down the progression of the degeneration, but do not effectively prevent it. The finding of stem cells (SC) in the eye has led to the proposal of cell replacement strategies for retina degeneration. Therapies using different types of SC, such as retinal progenitor cells (RPCs), embryonic SC, pluripotent SCs (PSCs), induced PSCs (iPSCs), and mesenchymal stromal cells, capable of self-renewal and of differentiating into multiple cell types, have gained ample support. Numerous preclinical studies have assessed transplantation of SC in animal models, with encouraging results. The aim of this work is to revise the different preclinical and clinical approaches, analyzing the SC type used, their efficacy, safety, cell attachment and integration, absence of tumor formation and immunorejection, in order to establish which were the most relevant and successful. In addition, we examine the questions and concerns still open in the field. The data demonstrate the existence of two main approaches, aimed at replacing either RPE cells or photoreceptors. Emerging evidence suggests that RPCs and iPSC are the best candidates, presenting no ethical concerns and a low risk of immunorejection. Clinical trials have already supported the safety and efficacy of SC treatments. Serious concerns are pending, such as the risk of tumor formation, lack of attachment or integration of transplanted cells into host retinas, immunorejection, cell death, and also ethical. However, the amazing progress in the field in the last few years makes it possible to envisage safe and effective treatments to restore vision loss in a near future.

Immunologic Rejection of Transplanted Retinal Pigmented Epithelium: Mechanisms and Strategies for Prevention

Replacement of dysfunctional retinal pigmented epithelium (RPE) with grafts derived from stem cells has the potential to improve vision for patients with retinal disorders. In fact, the potential is such that a great number of groups are attempting to realize this therapy through individual strategies with a variety of stem cell products, hosts, immunomodulatory regimen, and techniques to assess the success of their design. Comparing the findings of different investigators is complicated by a number of factors. The immune response varies greatly between xenogeneic and allogeneic transplantation. A unique immunologic environment is created in the subretinal space, the target of RPE grafts. Both functional assessment and imaging techniques used to evaluate transplants are susceptible to erroneous conclusions. Lastly, the pharmacologic regimens used in RPE transplant trials are as numerous and variable as the trials themselves, making it difficult to determine useful results. This review will discuss the causes of these complicating factors, digest the strategies and results from clinical and preclinical studies, and suggest places for improvement in the design of future transplants and investigations.

A ROCK Inhibitor Promotes Graft Survival during Transplantation of iPS-Cell-Derived Retinal Cells

Currently, retinal pigment epithelium (RPE) transplantation includes sheet and single-cell transplantation, the latter of which includes cell death and may be highly immunogenic, and there are some issues to be improved in single-cell transplantation. Y-27632 is an inhibitor of Rho-associated protein kinase (ROCK), the downstream kinase of Rho. We herein investigated the effect of Y-27632 in vitro on retinal pigment epithelium derived from induced pluripotent stem cells (iPS-RPE cells), and also its effects in vivo on the transplantation of iPS-RPE cell suspensions. As a result, the addition of Y-27632 in vitro showed suppression of apoptosis, promotion of cell adhesion, and higher proliferation and pigmentation of iPS-RPE cells. Y-27632 also increased the viability of the transplant without showing obvious retinal toxicity in human iPS-RPE transplantation into monkey subretinal space in vivo. Therefore, it is possible that ROCK inhibitors can improve the engraftment of iPS-RPE cell suspensions after transplantation.