Human embryonic stem cell-derived retinal pigment epithelium transplants as a potential treatment for wet age-related macular degeneration

Advances in the study of tissue-engineered retinal pigment epithelial cell sheets

Regarded as the most promising treatment modality for retinal degenerative diseases, retinal pigment epithelium cell replacement therapy holds significant potential. Common retinal degenerative diseases, including Age-related Macular Degeneration, are frequently characterized by damage to the unit comprising photoreceptors, retinal pigment epithelium, and Bruch's membrane. The selection of appropriate tissue engineering materials, in conjunction with retinal pigment epithelial cells, for graft preparation, can offer an effective treatment for retinal degenerative diseases. This article presents an overview of the research conducted on retinal pigment epithelial cell tissue engineering, outlining the challenges and future prospects.

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.

Towards Stem/Progenitor Cell-Based Therapies for Retinal Degeneration

Retinal degeneration (RD) is a leading cause of blindness worldwide and includes conditions such as retinitis pigmentosa (RP), age-related macular degeneration (AMD), and Stargardt's disease (STGD). These diseases result in the permanent loss of vision due to the progressive and irreversible degeneration of retinal cells, including photoreceptors (PR) and the retinal pigment epithelium (RPE). The adult human retina has limited abilities to regenerate and repair itself, making it challenging to achieve complete self-replenishment and functional repair of retinal cells. Currently, there is no effective clinical treatment for RD. Stem cell therapy, which involves transplanting exogenous stem cells such as retinal progenitor cells (RPCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs), or activating endogenous stem cells like Müller Glia (MG) cells, holds great promise for regenerating and repairing retinal cells in the treatment of RD. Several preclinical and clinical studies have shown the potential of stem cell-based therapies for RD. However, the clinical translation of these therapies for the reconstruction of substantial vision still faces significant challenges. This review provides a comprehensive overview of stem/progenitor cell-based therapy strategies for RD, summarizes recent advances in preclinical studies and clinical trials, and highlights the major challenges in using stem/progenitor cell-based therapies for RD.

Immunosuppression in stem cell clinical trials of neural and retinal cell types: A systematic review

BACKGROUND

Pharmacologic immunosuppression regimes are commonly employed in stem cell clinical trials to mitigate host immune rejection and promote survival and viability of transplanted cells. Immunosuppression and cell survival has been extensively studied in retinal and spinal tissues. The applicability of stem cell therapy is rapidly expanding to other sensory organs such as the ear and hearing. As regenerative therapy is directed to new areas, a greater understanding of immunosuppression strategies and their efficacy is required to facilitate translation to organ-specific biologic microenvironments.

OBJECTIVE

This systematic review appraises the current literature regarding immunosuppression strategies employed in stem cell trials of retinal and neural cells.

METHODS

This systematic review was performed in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Inclusion criteria included studies presenting data on neural or retinal cells as part of an in-human clinical trial that detailed the immunosuppression regime used. Exclusion criteria included non-English language studies, animal studies, review articles, case reports, editorials, and letters. The databases Medline, Embase, Scopus, Web of Science, and the Cochrane Library were searched from inception to February 2024. Risk of bias was evaluated using the ROBINS-I tool.

RESULTS

Eighteen articles fit the inclusion criteria. Nine articles concerned retinal cells, 5 concerned spinal cord injury, and 4 concerned amyotrophic lateral sclerosis. A multi-drug and short-term immunosuppression regime were commonly employed in the identified studies. Detected immune responses in treated patients were rare. Common immunosuppression paradigms included tacrolimus, mycophenolate mofetil and tapering doses of steroids. Local immunosuppression with steroids was employed in some studies concerning retinal diseases.

DISCUSSION

A short-term course of systemic immunosuppression seemed efficacious for most included studies, with some showing grafted cells viable months to years after immunosuppression had stopped. Longer-term follow-up is required to see if this remains the case. Side effects related to immunosuppression were uncommon.

Regenerative treatment of ophthalmic diseases with stem cells: Principles, progress, and challenges

Background

Degenerate eye disorders, such as glaucoma, cataracts and age-related macular degeneration (AMD), are prevalent causes of blindness and visual impairment worldwide. Other eye disorders, including limbal stem cell deficiency (LSCD), dry eye diseases (DED), and retinitis pigmentosa (RP), result in symptoms such as ocular discomfort and impaired visual function, significantly impacting quality of life. Traditional therapies are limited, primarily focus on delaying disease progression, while emerging stem cell therapy directly targets ocular tissues, aiming to restore ocular function by reconstructing ocular tissue.

Main text

The utilization of stem cells for the treatment of diverse degenerative ocular diseases is becoming increasingly significant, owing to the regenerative and malleable properties of stem cells and their functional cells. Currently, stem cell therapy for ophthalmopathy involves various cell types, such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and retinal progenitor cells (RPCs). In the current article, we will review the current progress regarding the utilization of stem cells for the regeneration of ocular tissue covering key eye tissues from the cornea to the retina. These therapies aim to address the loss of functional cells, restore damaged ocular tissue and or in a paracrine-mediated manner. We also provide an overview of the ocular disorders that stem cell therapy is targeting, as well as the difficulties and opportunities in this field.

Conclusions

Stem cells can not only promote tissue regeneration but also release exosomes to mitigate inflammation and provide neuroprotection, making stem cell therapy emerge as a promising approach for treating a wide range of eye disorders through multiple mechanisms.

Cell therapy for retinal disease

PURPOSE OF REVIEW

This review presents an update on completed stem cell therapy trials aimed at retinal diseases.

RECENT FINDINGS

In recent years, several clinical trials have been conducted examining the safety and role of cell therapy in diseases, including age-related macular degeneration, Stargardt's macular dystrophy, and retinitis pigmentosa. Studies have utilized a variety of cell lines, modes of delivery, and immunosuppressive regimens. The prevalence of fraudulent cell therapy clinics poses threats to patients.

SUMMARY

Clinical trials have begun to characterize the safety of cell therapy in retinal disease. While studies have described the potential benefits of cell therapy, larger studies powered to evaluate this efficacy are required to continue progressing toward preventing retinal disease. Nonapproved cell therapy clinics require regulation and patient education to avoid patient complications.

Standardisation is the key to the sustained, rapid and healthy development of stem cell-based therapy

BACKGROUND

Stem cell-based therapy (SCT) is an important component of regenerative therapy that brings hope to many patients. After decades of development, SCT has made significant progress in the research of various diseases, and the market size has also expanded significantly. The transition of SCT from small-scale, customized experiments to routine clinical practice requires the assistance of standards. Many countries and international organizations around the world have developed corresponding SCT standards, which have effectively promoted the further development of the SCT industry.

METHODS

We conducted a comprehensive literature review to introduce the clinical application progress of SCT and focus on the development status of SCT standardization.

RESULTS

We first briefly introduced the types and characteristics of stem cells, and summarized the current clinical application and market development of SCT. Subsequently, we focused on the development status of SCT-related standards as of now from three levels: the International Organization for Standardization (ISO), important international organizations, and national organizations. Finally, we provided perspectives and conclusions on the significance and challenges of SCT standardization.

CONCLUSIONS

Standardization plays an important role in the sustained, rapid and healthy development of SCT.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

Cell therapy for retinal degenerative disorders: a systematic review and three-level meta-analysis

BACKGROUND

Retinal degenerative disorders (RDDs) cause vision loss by damaging retinal neurons and photoreceptors, affecting individuals of all ages. Cell-based therapy has emerged as an effective approach for the treatment of RDDs with promising results. This meta-analysis aims to comprehensively evaluate the efficacy of cell therapy in treating age-related macular degeneration (AMD), retinitis pigmentosa (RP), and Stargardt macular degeneration (SMD) as the most prevalent RDDs.

METHODS

PubMed, Scopus, Web of Science, and Embase were searched using keywords related to various retinal diseases and cell therapy treatments until November 25th, 2023. The studies' quality was evaluated using the Joanna Briggs Institute's (JBI) checklist for quasi-experimental studies. Visual acuity measured as LogMAR score was used as our main outcome. A three-level random-effect meta-analysis was used to explore the visual acuity in patients who received cell-based therapy. Heterogeneity among the included studies was evaluated using subgroup and sensitivity analyses. Moreover, meta-regression for the type of cells, year of publication, and mean age of participants were performed.

RESULTS

Overall, 8345 studies were retrieved by the search, and 39 met the eligibility criteria, out of which 18 studies with a total of 224 eyes were included in the meta-analysis. There were 12 studies conducted on AMD, 7 on SMD, and 2 on RP. Cell therapy for AMD showed significant improvement in LogMAR (p < 0.05). Also, cell therapy decreased the LogMAR score in SMD and RP (p < 0.01 and p < 0.0001, respectively). Across all conditions, no substantial publication bias was detected (p < 0.05).

CONCLUSION

The findings of the study highlight that the application of cell therapy can enhance the visual acuity in AMD, SMD, and RP.

Identifying Hmga2 preserving visual function by promoting a shift of Müller glia cell fate in mice with acute retinal injury

BACKGROUND

Unlike in lower vertebrates, Müller glia (MG) in adult mammalian retinas lack the ability to reprogram into neurons after retinal injury or degeneration and exhibit reactive gliosis instead. Whether a transition in MG cell fate from gliosis to reprogramming would help preserve photoreceptors is still under exploration.

METHODS

A mouse model of retinitis pigmentosa (RP) was established using MG cell lineage tracing mice by intraperitoneal injection of sodium iodate (SI). The critical time point for the fate determination of MG gliosis was determined through immunohistochemical staining methods. Then, bulk-RNA and single-cell RNA seq techniques were used to elucidate the changes in RNA transcription of the retina and MG at that time point, and new genes that may determine the fate transition of MG were screened. Finally, the selected gene was specifically overexpressed in MG cells through adeno-associated viruses (AAV) in the mouse RP model. Bulk-RNA seq technique, immunohistochemical staining methods, and visual function testing were used to elucidate and validate the mechanism of new genes function on MG cell fate transition and retinal function.

RESULTS

Here, we found the critical time point for MG gliosis fate determination was 3 days post SI injection. Hmga2 was screened out as a candidate regulator for the cell fate transition of MG. After retinal injury caused by SI, the Hmga2 protein is temporarily and lowly expressed in MG cells. Overexpression of Hmga2 in MG down-regulated glial cell related genes and up-regulated photoreceptor related genes. Besides, overexpressing Hmga2 exclusively to MG reduced MG gliosis, made MG obtain cone's marker, and retained visual function in mice with acute retinal injury.

CONCLUSION

Our results suggested the unique reprogramming properties of Hmga2 in regulating the fate transition of MG and neuroprotective effects on the retina with acute injury. This work uncovers the reprogramming ability of epigenetic factors in MG.

Beyond Vision: An Overview of Regenerative Medicine and Its Current Applications in Ophthalmological Care

Regenerative medicine (RM) has emerged as a promising and revolutionary solution to address a range of unmet needs in healthcare, including ophthalmology. Moreover, RM takes advantage of the body's innate ability to repair and replace pathologically affected tissues. On the other hand, despite its immense promise, RM faces challenges such as ethical concerns, host-related immune responses, and the need for additional scientific validation, among others. The primary aim of this review is to present a high-level overview of current strategies in the domain of RM (cell therapy, exosomes, scaffolds, in vivo reprogramming, organoids, and interspecies chimerism), centering around the field of ophthalmology. A search conducted on clinicaltrials.gov unveiled a total of at least 209 interventional trials related to RM within the ophthalmological field. Among these trials, there were numerous early-phase studies, including phase I, I/II, II, II/III, and III trials. Many of these studies demonstrate potential in addressing previously challenging and degenerative eye conditions, spanning from posterior segment pathologies like Age-related Macular Degeneration and Retinitis Pigmentosa to anterior structure diseases such as Dry Eye Disease and Limbal Stem Cell Deficiency. Notably, these therapeutic approaches offer tailored solutions specific to the underlying causes of each pathology, thus allowing for the hopeful possibility of bringing forth a treatment for ocular diseases that previously seemed incurable and significantly enhancing patients' quality of life. As advancements in research and technology continue to unfold, future objectives should focus on ensuring the safety and prolonged viability of transplanted cells, devising efficient delivery techniques, etc.

Gains of 20q11.21 in human pluripotent stem cells: Insights from cancer research

The genetic abnormalities observed in hPSC cultures worldwide have been suggested to pose an important hurdle in their safe use in regenerative medicine due to the possibility of oncogenic transformation by mutant cells in the patient posttransplantation. One of the best-characterized genetic lesions in hPSCs is the gain of 20q11.21, found in 20% of hPSC lines worldwide, and strikingly, also amplified in 20% of human cancers. In this review, we have curated the existing knowledge on the incidence of this mutation in hPSCs and cancer, explored the significance of chromosome 20q11.21 amplification in cancer progression, and reviewed the oncogenic role of the genes in the smallest common region of gain, to shed light on the significance of this mutation in hPSC-based cell therapy. Lastly, we discuss the state-of-the-art strategies devised to detect aneuploidies in hPSC cultures, avoid genetic changes in vitro cultures of hPSCs, and strategies to eliminate genetically abnormal cells from culture.

Generating Retinas through Guided Pluripotent Stem Cell Differentiation and Direct Somatic Cell Reprogramming

Retinal degeneration diseases affect millions of people worldwide but are among the most difficult eye diseases to cure. Studying the mechanisms and developing new therapies for these blinding diseases requires researchers to have access to many retinal cells. In recent years there has been substantial advances in the field of biotechnology in generating retinal cells and even tissues in vitro, either through programmed sequential stem cell differentiation or direct somatic cell lineage reprogramming. The resemblance of these in vitro-generated retinal cells to native cells has been increasingly utilized by researchers. With the help of these in vitro retinal models, we now have a better understanding of human retinas and retinal diseases. Furthermore, these in vitro-generated retinal cells can be used as donor cells which solves a major hurdle in the development of cell replacement therapy for retinal degeneration diseases, while providing a promising option for patients suffering from these diseases. In this review, we summarize the development of pluripotent stem cell-to-retinal cell differentiation methods, the recent advances in generating retinal cells through direct somatic cell reprogramming, and the translational applications of retinal cells generated in vitro. Finally, we discuss the limitations of the current protocols and possible future directions for improvement.

Extracellular vesicles from organoid-derived human retinal progenitor cells prevent lipid overload-induced retinal pigment epithelium injury by regulating fatty acid metabolism

Retinal degeneration (RD), a group of diseases leading to irreversible vision loss, is characterised by retinal pigment epithelium (RPE) or retinal neuron damage and loss. With fewer risks of immune rejection and tumorigenesis, stem cell-secreted extracellular vesicles (EVs) offer a new cell-free therapeutic paradigm for RD, which remains to be investigated. Human retinal organoid-derived retinal progenitor cells (hERO-RPCs) are an easily accessible and advanced cell source for RD treatment. However, hERO-RPCs-derived EVs require further characterisation. Here, we compared the characteristics of EVs from hERO-RPCs (hRPC-EVs) with those of human embryonic stem cell (hESC)-derived EVs (hESC-EVs) as controls. Based on in-depth proteomic analysis, we revealed remarkable differences between hRPC-EVs and hESC-EVs. A comparison between EVs and their respective cells of origin demonstrated that the protein loading of hRPC-EVs was more selective than that of hESC-EVs. In particular, hESC-EVs were enriched with proteins related to angiogenesis and cell cycle, whereas hRPC-EVs were enriched with proteins associated with immune modulation and retinal development. More importantly, compared with that of hESC-EVs, hRPC-EVs exhibited a lower correlation with cell proliferation and a unique capacity to regulate lipid metabolism. It was further confirmed that hRPC-EVs potentially eliminated lipid deposits, inhibited lipotoxicity and oxidative stress, and enhanced phagocytosis and survival of oleic acid-treated ARPE-19 cells. Mechanistically, hRPC-EVs are integrated into the mitochondrial network of oleic acid-treated ARPE-19 cells, and increased the level of mitochondrial fatty acid β-oxidation-related proteins. Thus, organoid-derived hRPC-EVs represent a promising source of cell-free therapy for RD, especially for blinding diseases related to abnormal lipid metabolism in RPE cells.

Ex vivo cultivated retinal pigment epithelial cell transplantation for the treatment of rabbit corneal endothelial dysfunction

OBJECTIVE

Stem cell therapy is a promising strategy for the treatment of corneal endothelial dysfunction, and the need to find functional alternative seed cells of corneal endothelial cells (CECs) is urgent. Here, we determined the feasibility of using the retinal pigment epithelium (RPE) as an equivalent substitute for the treatment of corneal endothelial dysfunction.

METHODS

RPE cells and CECs in situ were obtained from healthy New Zealand male rabbits, and the similarities and differences between them were analyzed by electron microscopy, immunofluorescent staining, and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Rabbit primary RPE cells and CECs were isolated and cultivated ex vivo, and Na+/K+-ATPase activity and cellular permeability were detected at passage 2. The injection of cultivated rabbit primary RPE cells, CECs and human embryonic stem cell (hESC)-derived RPE cells was performed on rabbits with corneal endothelial dysfunction. Then, the therapeutic effects were evaluated by corneal transparency, central corneal thickness, enzyme linked immunosorbent assay (ELISA), qRT-PCR and immunofluorescent staining.

RESULTS

The rabbit RPE cells were similar in form to CECs in situ and ex vivo, showing a larger regular hexagonal shape and a lower cell density, with numerous tightly formed cell junctions and hemidesmosomes. Moreover, RPE cells presented a stronger barrier and ionic pumping capacity than CECs. When intracamerally injected into the rabbits, the transplanted primary RPE cells could dissolve corneal edema and decrease corneal thickness, with effects similar to those of CECs. In addition, the transplantation of hESC-derived RPE cells exhibited a similar therapeutic effect and restored corneal transparency and thickness within seven days. qRT-PCR results showed that the expressions of CEC markers, like CD200 and S100A4, increased, and the RPE markers OTX2, BEST1 and MITF significantly decreased in the transplanted RPE cells. Furthermore, we have demonstrated that rabbits transplanted with hESC-derived RPE cells maintained normal corneal thickness and exhibited slight pigmentation in the central cornea one month after surgery. Immunostaining results showed that the HuNu-positive transplanted cells survived and expressed ZO1, ATP1A1 and MITF.

CONCLUSION

RPE cells and CECs showed high structural and functional similarities in barrier and pump characteristics. Intracameral injection of primary RPE cells and hESC-derived RPE cells can effectively restore rabbit corneal clarity and thickness and maintain normal corneal function. This study is the first to report the effectiveness of RPE cells for corneal endothelial dysfunction, suggesting the feasibility of hESC-derived RPE cells as an equivalent substitute for CECs.

hPSC-derived RPE transplantation for the treatment of macular degeneration

Macular degeneration (MD) is a group of diseases characterized by irreversible and progressive vision loss. Patients with MD suffer from severely impaired central vision, especially elderly people. Currently, only one type of MD, wet age-related macular degeneration (AMD), can be treated with anti-vascular endothelium growth factor (VEGF) drugs. Other types of MD remain difficult to treat. With the advent of human pluripotent stem cells (hPSCs) and their differentiation into retinal pigmented epithelium (RPE), it is promising to treat patients with MD by transplantation of hPSC-derived RPE into the subretinal space. In this review, the current progress in hPSC-derived RPE transplantation for the treatment of patients with MD is described from bench to bedside, including hPSC differentiation into RPE and the characterization and usage of hPSC-derived RPE for transplantation into patients with MD.

Stem Cell Therapy, the Market, the Opportunities and the Threat

Stem cell therapy is going to become the most widely used type of therapy in regenerative medicine. The stem cell therapy market has grown at an exponential rate in recent years. The purpose of the present paper is to review the stem cell market and the factors affecting it. The methods used included a literature review across reputable databases, and identifying articles and trusted financial reports related to the stem cell therapy market. Results show that the stem cell market growth rate is increasing, so that, the global stem cell market size was valued at US$297 million in 2022 and is anticipated to grow at a compound annual growth rate of 16.8% from 2022 to 2027, driven by factors such as clinical trials with promising results, increasing funding for stem cell research, growing number of technologies and facilities for cell therapy, and rising demand for regenerative medicine. However, the market also faces some challenges such as ethical concerns, regulatory hurdles, and the high cost of stem cell therapies and products. To enhance the development of the market further, policymakers and regulatory bodies must simplify the complicated process of obtaining regulatory approvals for clinical use. However, there are growing concerns about the increasing number of unapproved treatments using stem cells.

Acellularized Uvea Hydrogel as Novel Injectable Platform for Cell-Based Delivering Treatment of Retinal Degeneration and Optimizing Retinal Organoids Inducible System

Replenishing the retina with retinal pigment epithelial (RPE) cells derived from pluripotent stem cells (PSCs) has great promise for treating retinal degenerative diseases, but it is limited by poor cell survival and integration in vivo. Herein, porcine acellular sclera and uvea extracellular matrix (ECM) and their counterpart hydrogels are developed, and their effects on the biological behavior of human induced pluripotent stem cell (hiPSC)-derived RPE cells (hiPSC-RPE) and embryoid body (hiPSC-EB) differentiation are investigated. Both acellular ECM hydrogels have excellent biocompatibility and suitable biodegradability without evoking an obvious immune response. Most importantly, the decellularized uvea hydrogel-delivered cells' injection remarkably promotes the hiPSC-RPE cells' survival and integration in the subretinal space, rescues the photoreceptor cells' death and retinal gliosis, and restores vision in rats with retinal degeneration for a long duration. In addition, medium supplementation with decellularized uvea peptides promotes hiPSC-EBs onset morphogenesis and neural/retinal differentiation, forming layered retinal organoids. This study demonstrates that ECM hydrogel-delivered hiPSC-RPE cells' injection may be a useful approach for treating retinal degeneration disease, combined with an optimized retinal seeding cells' induction program, which has potential for clinical application.

Hydrogels to Support Transplantation of Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells

PURPOSE

Retinal pigment epithelial (RPE) cells are highly specialized neural cells with several functions essential for vision. Progressive deterioration of RPE cells in elderly individuals can result in visual impairment and, ultimately, blinding disease. While human embryonic stem cell-derived RPE cell (hESC-RPE) growth conditions are generally harsher than those of cell lines, the subretinal transplantation of hESC-RPE is being clinically explored as a strategy to recover the damaged retina and improve vision. The cell-adhesion ability of the support is required for RPE transplantation, where pre-polarized cells can maintain specific functions on the scaffold. This work examined four typical biodegradable hydrogels as supports for hESC-RPE growth.

METHODS

Four biodegradable hydrogels were examined: gelatin methacryloyl (GelMA), hyaluronic acid methacryloyl (HAMA), alginate, and fibrin hydrogels. ARPE-19 and hESC-RPE cells were seeded onto the hydrogels separately, and the ability of these supports to facilitate adherence, proliferation, and homogeneous distribution of differentiated hESC-RPE cells was investigated. Furthermore, the hydrogel's subretinal bio-compatibility was assessed in vivo.

RESULTS

We showed that ARPE-19 and hESC-RPE cells adhered and proliferated only on the fibrin support. The monolayer formed when cells reached confluency, demonstrating the polygonal semblance, and revealing actin filaments that moved along the cytoplasm. The expression of tight junction proteins at cell interfaces on the 14th day of seeding demonstrated the barrier function of epithelial cells on polymeric surfaces and the interaction between cells. Moreover, the expression of proteins crucial for retinal functions and matrix production was positively affected by fibrin, with an increment of PEDF. Our in vivo investigation with fibrin hydrogels revealed high short-term subretinal biocompatibility.

CONCLUSIONS

The research of stem cell-based cell therapy for retinal degenerative diseases is more complicated than that of cell lines. Our results showed that fibrin is a suitable scaffold for hESC-RPE transplantation, which could be a new grafting material for tissue engineering RPE cells.

Induced retinal pigment epithelial cells with anti-epithelial-to-mesenchymal transition ability delay retinal degeneration

The hostile microenvironment of the retina in patients with age-related macular degeneration (AMD) may trigger epithelial-to-mesenchymal transition (EMT) of grafted retinal pigment epithelial (RPE) cells, thus attenuating the therapeutic outcome. Here, we transformed human dedifferentiated induced pluripotent stem cell-derived RPE (iPSC-RPE) cells into induced RPE (iRPE) cells using a cocktail of four transcription factors (TFs)—CRX, MITF-A, NR2E1, and C-MYC. These critical TFs maintained the epithelial property of iRPE cells by regulating the expression of bmp7, forkhead box f2, lin7a, and pard6b, and conferred resistance to TGF-β-induced EMT in iRPE cells by targeting ppm1a. The iRPE cells with Tet-on system-regulated c-myc expression exhibited EMT resistance and better therapeutic function compared with iPSC-RPE cells in rat AMD model. Our study demonstrates that endowing RPE cells with anti-EMT property avoids the risk of EMT after cells are grafted into the subretinal space, and it may provide a suitable candidate for AMD treatment.

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CRX, MITF-A, NR2E1, and C-MYC transform De-iPSC-RPE cells into iRPE cells

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iRPE cells have resistance to TGF-β-induced EMT

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BMP7, FOXF2, LIN7A, PARD6B, and PPM1A mediate the functions of TFs in iRPE cells

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iRPE cells have better retinal protective function than iPSC-RPE cells

Applying stem cell therapy in intractable diseases: a narrative review of decades of progress and challenges

Background and Objective

Stem cell therapy (SCT) is one of the vastly researched branches of regenerative medicine as a therapeutic tool to treat incurable diseases. With the use of human stem cells such as embryonic stem cells (ESCs), adult stem cells (ASCs) and induced pluripotent stem cells (iPSCs), stem cell therapy aims to regenerate or repair damaged tissues and congenital defects. As stem cells are able to undergo infinite self-renewal, differentiate into various types of cells and secrete protective paracrine factors, many researchers have investigated the potential of SCT in regenerative medicine. Therefore, this review aims to provide a comprehensive review on the recent application of SCT in various intractable diseases, namely, haematological diseases, neurological diseases, diabetes mellitus, retinal degenerative disorders and COVID-19 infections along with the challenges faced in the clinical translation of SCT.

Methods

An extensive search was conducted on Google scholar, PubMed and Clinicaltrials.gov using related keywords. Latest articles on stem cell therapy application in selected diseases along with their challenges in clinical applications were selected.

Key content and findings

In vitro and in vivo studies involving SCT are shown to be safe and efficacious in treating various diseases covered in this review. There are also a number of small-scale clinical trials that validated the positive therapeutic outcomes of SCT. Nevertheless, the effectiveness of SCT are highly variable as some SCT works best in patients with early-stage diseases while in other diseases, SCT is more likely to work in patients in late stages of illnesses. Among the challenges identified in SCT translation are uncertainty in the underlying stem cell mechanism, ethical issues, genetic instability and immune rejection.

Conclusions

SCT will be a revolutionary treatment in the future that will provide hope to patients with intractable diseases. Therefore, studies ought to be done to ascertain the long-term effects of SCT while addressing the challenges faced in validating SCT for clinical use. Moreover, as there are many studies investigating the safety and efficacy of SCT, future studies should look into elucidating the regenerative and reparative capabilities of stem cells which largely remains unknown.

Direct conversion of human umbilical cord mesenchymal stem cells into retinal pigment epithelial cells for treatment of retinal degeneration

Age-related macular degeneration (AMD) is a major vision-threatening disease. Although mesenchymal stem cells (MSCs) exhibit beneficial neural protective effects, their limited differentiation capacity in vivo attenuates their therapeutic function. Therefore, the differentiation of MSCs into retinal pigment epithelial (RPE) cells in vitro and their subsequent transplantation into the subretinal space is expected to improve the outcome of cell therapy. Here, we transdifferentiated human umbilical cord MSCs (hUCMSCs) into induced RPE (iRPE) cells using a cocktail of five transcription factors (TFs): CRX, NR2E1, C-MYC, LHX2, and SIX6. iRPE cells exhibited RPE specific properties, including phagocytic ability, epithelial polarity, and gene expression profile. In addition, high expression of PTPN13 in iRPE cells endows them with an epithelial-to-mesenchymal transition (EMT)-resistant capacity through dephosphorylating syntenin1, and subsequently promoting the internalization and degradation of transforming growth factor-β receptors. After grafting into the subretinal space of the sodium iodate-induced rat AMD model, iRPE cells demonstrated a better therapeutic function than hUCMSCs. These results suggest that hUCMSC-derived iRPE cells may be promising candidates to reverse AMD pathophysiology.

Stem cell-based therapy for human diseases

Recent advancements in stem cell technology open a new door for patients suffering from diseases and disorders that have yet to be treated. Stem cell-based therapy, including human pluripotent stem cells (hPSCs) and multipotent mesenchymal stem cells (MSCs), has recently emerged as a key player in regenerative medicine. hPSCs are defined as self-renewable cell types conferring the ability to differentiate into various cellular phenotypes of the human body, including three germ layers. MSCs are multipotent progenitor cells possessing self-renewal ability (limited in vitro) and differentiation potential into mesenchymal lineages, according to the International Society for Cell and Gene Therapy (ISCT). This review provides an update on recent clinical applications using either hPSCs or MSCs derived from bone marrow (BM), adipose tissue (AT), or the umbilical cord (UC) for the treatment of human diseases, including neurological disorders, pulmonary dysfunctions, metabolic/endocrine-related diseases, reproductive disorders, skin burns, and cardiovascular conditions. Moreover, we discuss our own clinical trial experiences on targeted therapies using MSCs in a clinical setting, and we propose and discuss the MSC tissue origin concept and how MSC origin may contribute to the role of MSCs in downstream applications, with the ultimate objective of facilitating translational research in regenerative medicine into clinical applications. The mechanisms discussed here support the proposed hypothesis that BM-MSCs are potentially good candidates for brain and spinal cord injury treatment, AT-MSCs are potentially good candidates for reproductive disorder treatment and skin regeneration, and UC-MSCs are potentially good candidates for pulmonary disease and acute respiratory distress syndrome treatment.

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.

Clinical applications of pluripotent stem cells and their derivatives: current status and future perspectives

Pluripotent stem cells (PSCs) can differentiate into specific cell types and thus hold great promise in regenerative medicine to treat certain diseases. Hence, several studies have been performed harnessing their salutary properties in regenerative medicine. Despite several challenges associated with the clinical applications of PSCs, worldwide efforts are harnessing their potential in the regeneration of damaged tissues. Several clinical trials have been performed using PSCs or their derivatives. However, the delay in publishing the data obtained in the trials has led to a lack of awareness about their outcomes, resulting in apprehension about cellular therapies. Here, the authors review the published papers containing data from recent clinical trials done with PSCs. PSC-derived extracellular vesicles hold great potential in regenerative therapy. Since published papers containing the data obtained in clinical trials on PSC-derived extracellular vesicles are not available yet, the authors have reviewed some of the pre-clinical work done with them.

Biobanking of human pluripotent stem cells in China

In recent years, significant progress has been made internationally in the development of human pluripotent stem cell (hPSC)‐derived products for serious and widespread disorders. Biobanking of the cellular starting materials is a crucial component in the delivery of safe and regulatory compliant cell therapies. In China, key players in these developments have been the recently launched National Stem Cell Resource Center (NSCRC) and its partner organizations in Guangzhou and Shanghai who together, have more than 600 hPSC lines formally recorded in the Chinese Ministry of Science and Technology's stem cell registry. In addition, 47 of these hPSCs have also been registered with the hPSCreg project which means they are independently certified for use in European Commission funded research projects. The NSCRC are currently using their own cell lines to manufacture eight different cell types qualified for clinical use, that are being used in nine clinical studies for different indications. The Institute of Zoology at the Chinese Academy of Sciences (IOZ‐CAS) has worked with NSCRC to establish Chinese and international standards in stem cell research. IOZ‐CAS was also a founding partner in the International Stem Cell Banking Initiative which brings together key stem cell banks to agree minimum standards for the provision of pluripotent stem cells for research and clinical use. Here, we describe recent developments in China in the establishment of hPSCs for use in the manufacture of cell therapies and the significant national and international coordination which has now been established to promote the translation of Chinese hPSC‐based products into clinical use according to national and international standards.

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

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

Stem Cell-based Treatment Strategies for Degenerative Diseases of the Retina

BACKGROUND

The main cause of progressive vision impairment in retinal degenerative diseases is the dysfunction of photoreceptors and the underlying retinal pigment epithelial cells. The inadequate regenerative capacity of the neural retina and lack of established therapeutic options demand the development of clinical-grade protocols to halt the degenerative process in the eye or replace the damaged cells by using stem cell-derived products. Recently, stem cell-based regenerative therapies have been at the forefront of clinical investigations for retinal dystrophies.

OBJECTIVE

This article will review different stem cell-based therapies currently employed for retinal degenerative diseases, recent clinical trials, and major challenges in the translation of these therapies from bench to bedside.

METHODOLOGY

A systematic literature review was conducted to identify potentially relevant articles published in MEDLINE/PubMed, Embase, ClinicalTrials.gov, Drugs@FDA, European Medicines Agency, and World Health Organization International Clinical Trials Registry Platform.

RESULTS

Transplantation of healthy cells to replace damaged cells in the outer retina is a clinically relevant concept because the inner retina that communicates with the visual areas of the brain remains functional even after the photoreceptors are completely lost. Various methods have been established for the differentiation of pluripotent stem cells into different retinal cell types that can be used for therapies. Factors released from transplanted somatic stem cells showed trophic support and photoreceptor rescue during the early stages of the disease. Several preclinical and phase I/II clinical studies using terminally differentiated photoreceptor/retinal pigment epithelial cells derived from pluripotent stem cells have shown proof of concept for visual restoration in Age-related Macular Degeneration (AMD), Stargardt disease, and Retinitis Pigmentosa (RP).

CONCLUSION

Cell replacement therapy has great potential for vision restoration. The results obtained from the initial clinical trials are encouraging and indicate its therapeutic benefits. The current status of the therapies suggests that there is a long way to go before these results can be applied to routine clinical practice. Input from the ongoing multicentre clinical trials will give a more refined idea for the future design of clinical-grade protocols to transplant GMP level HLA matched cells.

OUP accepted manuscript

Human pluripotent stem cell (hPSC)-derived retinal pigment epithelium (RPE) is extensively used in RPE research, disease modeling, and transplantation therapies. For successful outcomes, a thorough evaluation of their physiological authenticity is a necessity. Essential determinants of this are the different ion channels of the RPE, yet studies evaluating this machinery in hPSC-RPE are scarce. We examined the functionality and localization of potassium (K⁺) channels in the human embryonic stem cell (hESC)-derived RPE. We observed a heterogeneous pattern of voltage-gated K⁺ (K_V) and inwardly rectifying K⁺ (Kir) channels. Delayed rectifier currents were recorded from most of the cells, and immunostainings showed the presence of K_V1.3 channel. Sustained M-currents were also present in the hESC-RPE, and based on immunostaining, these currents were carried by KCNQ1-KCNQ5 channel types. Some cells expressed transient A-type currents characteristic of native human fetal RPE (hfRPE) and cultured primary RPE and carried by K_V1.4 and K_V4.2 channels. Of the highly important Kir channels, we found that Kir7.1 is present both at the apical and basolateral membranes of the hESC- and fresh native mouse RPE. Kir currents, however, were recorded only from 14% of the hESC-RPE cells with relatively low amplitudes. Compared to previous studies, our data suggest that in the hESC-RPE, the characteristics of the delayed rectifier and M-currents resemble native adult RPE, while A-type and Kir currents resemble native hfRPE or cultured primary RPE. Overall, the channelome of the RPE is a sensitive indicator of maturity and functionality affecting its therapeutic utility.

Cell-based therapies for retinal diseases: a review of clinical trials and direct to consumer "cell therapy" clinics

Background

The retinal pigment epithelium (RPE) is implicated in the pathophysiology of many retinal degenerative diseases. This cell layer is also an ideal target for cell-based therapies. Several early phase clinical trials evaluating cell therapy approaches for diseases involving the RPE, such as age-related macular degeneration and Stargardt's macular dystrophy have been published. However, there have also been numerous reports of complications from unproven “cell therapy” treatments marketed by “cell therapy” clinics. This review aims to outline the particular approaches in the different published clinical trials for cell-based therapies for retinal diseases. Additionally, the controversies surrounding experimental treatments offered outside of legitimate studies are presented.

Main body

Cell-based therapies can be applied to disorders that involve the RPE via a variety of techniques. A defining characteristic of any cell therapy treatment is the cell source used: human embryonic stem cells, induced pluripotent stem cells, and human umbilical tissue-derived cells have all been studied in published trials. In addition to the cell source, various trials have evaluated particular immunosuppression regiments, surgical approaches, and outcome measures. Data from early phase studies investigating cell-based therapies in non-neovascular age-related macular degeneration (70 patients, five trials), neovascular age-related macular degeneration (12 patients, four trials), and Stargardt’s macular dystrophy (23 patients, three trials) have demonstrated safety related to the cell therapies, though evidence of significant efficacy has not been reported. This is in contrast to the multiple reports of serious complications and permanent vision loss in patients treated at “cell therapy” clinics. These interventions are marketed directly to patients, funded by the patient, lack Food and Drug Administration approval, and lack significant oversight.

Conclusion

Currently, there are no proven effective cell-based treatments for retinal diseases, although several trials have investigated potential therapies. These studies reported favorable safety profiles with multiple surgical approaches, with cells derived from multiple sources, and with utilized different immunosuppressive regiments. However, data demonstrating the efficacy and long-term safety are still pending. Nevertheless, “cell therapy” clinics continue to conduct direct-to consumer marketing for non-FDA-approved treatments with potentially blinding complications.

Pluripotent stem cell therapy for retinal diseases

Pluripotent stem cells (PSCs), which include human embryonic stem cells (hESCs) and induced pluripotent stem cell (iPSC), have been used to study development of disease processes, and as potential therapies in multiple organ systems. In recent years, there has been increasing interest in the use of PSC-based transplantation to treat disorders of the retina in which retinal cells have been functionally damaged or lost through degeneration. The retina, which consists of neuronal tissue, provides an excellent system to test the therapeutic utility of PSC-based transplantation due to its accessibility and the availability of high-resolution imaging technology to evaluate effects. Preclinical trials in animal models of retinal diseases have shown improvement in visual outcomes following subretinal transplantation of PSC-derived photoreceptors or retinal pigment epithelium (RPE) cells. This review focuses on preclinical studies and clinical trials exploring the use of PSCs for retinal diseases. To date, several phase I/II clinical trials in patients with age-related macular degeneration (AMD) and Stargardt disease (STGD1) have demonstrated the safety and feasibility of PSC-derived RPE transplantation. Additional phase I/II clinical trials using PSC-derived RPE or photoreceptor cells for the treatment of AMD, STGD1, and also retinitis pigmentosa (RP) are currently in the pipeline. As this field continues to evolve, additional technologies may enhance PSC-derived cell transplantation through gene-editing of autologous cells, transplantation of more complex cellular structures such as organoids, and monitoring of transplanted cells through novel imaging technologies.

Development-related mitochondrial properties of retinal pigment epithelium cells derived from hEROs

AIM

To explore the temporal mitochondrial characteristics of retinal pigment epithelium (RPE) cells obtained from human embryonic stem cells (hESC)-derived retinal organoids (hEROs-RPE), to verify the optimal period for using hEROs-RPE as donor cells from the aspect of mitochondria and to optimize RPE cell-based therapeutic strategies for age-related macular degeneration (AMD).

METHODS

RPE cells were obtained from hEROs and from spontaneous differentiation (SD-RPE). The mitochondrial characteristics were analyzed every 20d from day 60 to 160. Mitochondrial quantity was measured by MitoTracker Green staining. Transmission electron microscopy (TEM) was adopted to assess the morphological features of the mitochondria, including their distribution, length, and cristae. Mitochondrial membrane potentials (MMPs) were determined by JC-1 staining and evaluated by flow cytometry, reactive oxygen species (ROS) levels were evaluated by flow cytometry, and adenosine triphosphate (ATP) levels were measured by a luminometer. Differences between two groups were analyzed by the independent-samples t-test, and comparisons among multiple groups were made using one-way ANOVA or Kruskal-Wallis H test when equal variance was not assumed.

RESULTS

hEROs-RPE and SD-RPE cells from day 60 to 160 were successfully differentiated from hESCs and expressed RPE markers (Pax6, MITF, Bestrophin-1, RPE65, Cralbp). RPE features, including a cobblestone-like morphology with tight junctions (ZO-1), pigments and microvilli, were also observed in both hEROs-RPE and SD-RPE cells. The mitochondrial quantities of hEROs-RPE and SD-RPE cells both peaked at day 80. However, the cristae of hEROs-RPE mitochondria were less mature and abundant than those of SD-RPE mitochondria at day 80, with hEROs-RPE mitochondria becoming mature at day 100. Both hEROs-RPE and SD-RPE cells showed low ROS levels from day 100 to 140 and maintained a normal MMP during this period. However, hEROs-RPE mitochondria maintained a longer time to produce high levels of ATP (from day 120 to 140) than SD-RPE cells (only day 120).

CONCLUSION

hEROs-RPE mitochondria develop more slowly and maintain a longer time to supply high-level energy than SD-RPE mitochondria. From the mitochondrial perspective, hEROs-RPE cells from day 100 to 140 are an optimal cell source for treating AMD.

A phase I clinical trial of human embryonic stem cell-derived retinal pigment epithelial cells for early-stage Stargardt macular degeneration: 5-years' follow-up

Objectives

To evaluate the long‐term biosafety and efficacy of transplantation of human embryonic stem cells‐derived retinal pigment epithelial (hESC‐RPE) cells in early‐stage of Stargardt macular degeneration (STGD1).

Materials and methods

Seven patients participated in this prospective clinical study, where they underwent a single subretinal transplantation of 1 × 10⁵ hESC‐RPE cells in one eye, whereas the fellow eye served as control. These patients were reassessed for a 60‐month follow‐up through systemic and ophthalmic examinations.

Results

None of the patients experienced adverse reactions systemically or locally, except for two who had transiently high intraocular pressure post‐operation. Functional assessments demonstrated that all of the seven operated eyes had transiently increased or stable visual function 1‐4 months after transplantation. At the last follow‐up visit, two of the seven eyes showed visual function loss than the baseline; however, one of them showed a stable visual acuity when compared with the change of fellow eye. Obvious small high reflective foci in the RPE layer were displayed after the transplantation, and maintained until the last visit. Interestingly, three categories of patients who were classified based on autofluorescence, exhibited distinctive patterns of morphological and functional change.

Conclusions

Subretinal transplantation of hESC‐RPE in early‐stage STGD1 is safe and tolerated in the long term. Further investigation is needed for choosing proper subjects according to the multi‐model image and function assessments.

Submacular integration of hESC-RPE monolayer xenografts in a surgical non-human primate model

Background

Human pluripotent stem cells (hPSCs) provide a promising cell source for retinal cell replacement therapy but often lack standardized cell production and live-cell shipment logistics as well as rigorous analyses of surgical procedures for cell transplantation in the delicate macula area. We have previously established a xeno- and feeder cell-free production system for hPSC differentiated retinal pigment epithelial (RPE) cells, and herein, a novel immunosuppressed non-human primate (NHP) model with a disrupted ocular immune privilege is presented for transplanting human embryonic stem cell (hESC)-derived RPE on a scaffold, and the safety and submacular graft integration are assessed. Furthermore, the feasibility of intercontinental shipment of live hESC-RPE is examined.

Methods

Cynomolgus monkeys were systemically immunosuppressed and implanted with a hESC-RPE monolayer on a permeable polyester-terephthalate (PET) scaffold. Microscope-integrated intraoperative optical coherence tomography (miOCT)-guided surgery, postoperative follow-up incorporated scanning laser ophthalmoscopy, spectral domain (SD-) OCT, and full-field electroretinography (ERG) were used as outcome measures. In addition, histology was performed after a 28-day follow-up.

Results

Intercontinental cell shipment, which took >30 h from the manufacturing to the transplantation site, did not alter the hESC-RPE quality. The submacular hESC-RPE xenotransplantation was performed in 11 macaques. The miOCT typically revealed foveal disruption. ERG showed amplitude and peak time preservation in cases with favorable surgical outcomes. Histology confirmed photoreceptor preservation above the grafts and in vivo phagocytosis by hESC-RPE, albeit evidence of cytoplasmic redistribution of opsin in photoreceptors and glia hypertrophy. The immunosuppression protocol efficiently suppressed retinal T cell infiltration and microglia activation.

Conclusion

These results suggest both structural and functional submacular integrations of hESC-RPE xenografts. It is anticipated that surgical technique refinement will further improve the engraftment of macular cell therapeutics with significant translational relevance to improve future clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02395-6.

Recent trends in stem cell-based therapies and applications of artificial intelligence in regenerative medicine

Stem cells are undifferentiated cells that can self-renew and differentiate into diverse types of mature and functional cells while maintaining their original identity. This profound potential of stem cells has been thoroughly investigated for its significance in regenerative medicine and has laid the foundation for cell-based therapies. Regenerative medicine is rapidly progressing in healthcare with the prospect of repair and restoration of specific organs or tissue injuries or chronic disease conditions where the body’s regenerative process is not sufficient to heal. In this review, the recent advances in stem cell-based therapies in regenerative medicine are discussed, emphasizing mesenchymal stem cell-based therapies as these cells have been extensively studied for clinical use. Recent applications of artificial intelligence algorithms in stem cell-based therapies, their limitation, and future prospects are highlighted.

Cell Replacement Therapy for Retinal and Optic Nerve Diseases: Cell Sources, Clinical Trials and Challenges

The aim of this review was to provide an update on the potential of cell therapies to restore or replace damaged and/or lost cells in retinal degenerative and optic nerve diseases, describing the available cell sources and the challenges involved in such treatments when these techniques are applied in real clinical practice. Sources include human fetal retinal stem cells, allogenic cadaveric human cells, adult hippocampal neural stem cells, human CNS stem cells, ciliary pigmented epithelial cells, limbal stem cells, retinal progenitor cells (RPCs), human pluripotent stem cells (PSCs) (including both human embryonic stem cells (ESCs) and human induced pluripotent stem cells (iPSCs)) and mesenchymal stem cells (MSCs). Of these, RPCs, PSCs and MSCs have already entered early-stage clinical trials since they can all differentiate into RPE, photoreceptors or ganglion cells, and have demonstrated safety, while showing some indicators of efficacy. Stem/progenitor cell therapies for retinal diseases still have some drawbacks, such as the inhibition of proliferation and/or differentiation in vitro (with the exception of RPE) and the limited long-term survival and functioning of grafts in vivo. Some other issues remain to be solved concerning the clinical translation of cell-based therapy, including (1) the ability to enrich for specific retinal subtypes; (2) cell survival; (3) cell delivery, which may need to incorporate a scaffold to induce correct cell polarization, which increases the size of the retinotomy in surgery and, therefore, the chance of severe complications; (4) the need to induce a localized retinal detachment to perform the subretinal placement of the transplanted cell; (5) the evaluation of the risk of tumor formation caused by the undifferentiated stem cells and prolific progenitor cells. Despite these challenges, stem/progenitor cells represent the most promising strategy for retinal and optic nerve disease treatment in the near future, and therapeutics assisted by gene techniques, neuroprotective compounds and artificial devices can be applied to fulfil clinical needs.

Emerging biological therapies for the treatment of age-related macular degeneration

INTRODUCTION

Age-related macular degeneration (AMD) is the leading cause of blindness in individuals over age 50 in developed countries. Current therapy for nonexudative AMD (neAMD) is aimed at modifying risk factors and vitamin supplementation to slow progression, while intravitreal anti-vascular endothelial factor (VEGF) injections are the mainstay for treatment of choroidal neovascularization in exudative AMD (eAMD).

AREAS COVERED

Over the past decade, promising therapies have emerged that aim to improve the current standard of care for both diseases. Clinical trials for neAMD are investigating targets in the complement cascade, vitamin A metabolism, metformin, and tetracycline, whereas clinical trials for eAMD are aiming to decrease treatment burden through novel port delivery systems, increasing drug half-life, and targeting new sites of the VEGF cascade. Stem cell and gene therapy are also being evaluated for treatment of neAMD and eAMD.

EXPERT OPINION

With an aging population, the need for effective, long term, low burden treatment options for AMD will be in increasingly high demand. Current investigations aim to address the shortcomings of current treatment options with breakthrough treatment approaches. Therapeutics in the pipeline hold promise for improving the treatment of AMD, and are on track for widespread use within the next decade.

MgFe-LDH Nanoparticles: A Promising Leukemia Inhibitory Factor Replacement for Self-Renewal and Pluripotency Maintenance in Cultured Mouse Embryonic Stem Cells

Leukemia inhibitory factor (LIF), an indispensable bioactive protein that sustains self-renewal and pluripotency in stem cells, is vital for mouse embryonic stem cell (mESC) culture. Extensive research is conducted on reliable alternatives for LIF as its clinical application in stable culture and large-scale expansion of ESCs is limited by its instability and high cost. However, few studies have sought to replace LIF with nanoparticles to provide a xeno-free culture condition. MgAl-LDH (layered double hydroxide) nanoparticles can partially replace LIF in maintaining pluripotency of mESCs; however, the requirement and tolerance for aluminum ions in mice are far lesser than those of iron ions. Hence, MgFe-LDH nanoparticles are selected for this study. MgFe-LDH is superior to MgAl-LDH in maintaining self-renewal and pluripotency of mESCs, in the absence of LIF and mouse embryonic fibroblast. Furthermore, combined transcriptomic and proteomic analysis confirms that MgFe-LDH can activate the LIF receptor (LIFR)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B(AKT), LIFR/JAK/janus kinase (JAK)/signal transducer and activator of transcription 3(STAT3), and phospho-signal transducer and activator of transcription 3(p-STAT3)/ten-eleven translocation (TET) signaling pathways, while the extra Fe2+ provided by MgFe-LDH would also enhance TET1/2 abundance thus affecting the TET1/2 regulated pluripotency related marker expression and TET1/2 meditated DNA demethylation. These results suggest that MgFe-LDH nanoparticles can thus be used as an affordable and efficient replacement for LIF in mESC cultivation.

Large-scale generation of megakaryocytes from human embryonic stem cells using transgene-free and stepwise defined suspension culture conditions

OBJECTIVES

Ex vivo engineered production of megakaryocytes (MKs) and platelets (PLTs) from human pluripotent stem cells is an alternative approach to solve shortage of donor-donated PLTs in clinics and to provide induced PLTs for transfusion. However, low production yields are observed and the generation of clinically applicable MKs and PLTs from human pluripotent stem cells without genetic modifications still needs to be improved.

MATERIALS AND METHODS

We defined an optimal, stepwise and completely xeno-free culture protocol for the generation of MKs from human embryonic stem cells (hESCs). To generate MKs from hESCs on a large scale, we improved the monolayer induction manner to define three-dimensional (3D) and sphere-like differentiation systems for MKs by using a special polystyrene CellSTACK culture chamber.

RESULTS

The 3D manufacturing system could efficiently generate large numbers of MKs from hESCs within 16-18 days of continuous culturing. Each CellSTACK culture chamber could collect on an average 3.4 × 108 CD41+ MKs after a three-stage orderly induction process. MKs obtained from hESCs via 3D induction showed significant secretion of IL-8, thrombospondin-1 and MMP9. The induced cells derived from hESCs in our culture system were shown to have the characteristics of MKs as well as the function to form proPLTs and release PLTs. Furthermore, we generated clinically applicable MKs from clinical-grade hESC lines and confirmed the biosafety of these cells.

CONCLUSIONS

We developed a simple, stepwise, 3D and completely xeno-free/feeder-free/transgene-free induction system for the generation of MKs from hESCs. hESC-derived MKs were shown to have typical MK characteristics and PLT formation ability. This study further enhances the clinical applications of MKs or PLTs derived from pluripotent stem cells.

Human Stem Cell-Derived Retinal Pigment Epithelial Cells as a Model for Drug Screening and Pre-Clinical Assays Compared to ARPE-19 Cell Line

Background and Objectives

Eye diseases have a high socioeconomic impact on society and may be one of the fields in which most stem cell-related scientific accomplishments have been achieved recently. In this context, human Pluripotent Stem Cell (hPSC) technology arises as an important tool to produce and study human Embryonic Stem cell derived-Retinal Pigmented Epithelial Cells (hES-RPE) for several applications, such as cell therapy, disease modeling, and drug screening. The use of this technology in pre-clinical phases attends to the overall population desire for animal-free product development. Here, we aimed to compare hES-RPE cells with ARPE-19, one of the most commonly used retinal pigmented epithelial immortalized cell lines.

Methods and Results

Functional, cellular and molecular data obtained suggest that hES-RPE cells more closely resembles native RPEs compared to ARPE-19. Furthermore, hES-RPE revealed an interesting robustness when cultured on human Bruch’s membrane explants and after exposure to Cyclosporine (CSA), Sirolimus (SRL), Tacrolimus (TAC), Leflunomide (LEF) and Teriflunomide (TER). On these conditions, hES-RPE cells were able to survive at higher drug concentrations, while ARPE-19 cell line was more susceptible to cell death.

Conclusions

Therefore, hES-RPEs seem to have the ability to incur a broader range of RPE functions than ARPE-19 and should be more thoroughly explored for drug screening.

Stem-cell-based therapies for retinal degenerative diseases: Current challenges in the establishment of new treatment strategies

Various advances have been made in the treatment of retinal diseases, including new treatment strategies and innovations in surgical devices. However, the treatment of degenerative retinal diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), continues to pose a significant challenge. In this review, we focus on the use of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to treat retinal diseases by harnessing the ability of stem cells to differentiate into different body tissues. The retina is a tissue specialized for light sensing, and its degradation leads to vision loss. As part of the central nervous system, the retina has very low regenerative capability, and therefore, treatment options are limited once it degenerates. Nevertheless, innovations in methods to induce the generation of retinal cells and tissues from ESCs/iPSCs enable the development of novel approaches for these irreversible diseases. Here we review some historical background and current clinical trials involving the use of stem-cell-derived retinal pigment epithelial cells for AMD treatment and stem cell-derived retinal cells/tissues for RP therapy. Finally, we discuss our future vision of regenerative treatment for retinal diseases with a partial focus on our studies and introduce other interesting approaches for restoring vision.

Age-Related Macular Degeneration: What Do We Know So Far?

Ageing is a natural process that everyone experiences and nobody is an exception. With ageing, our body experiences physiological changes. In this article, the focus is made on the physiological changes of our eyes related to ageing and age-related macular degeneration (AMD), which is the most common cause of incurable visual impairment in developed countries. With ageing populations increasing in many countries, more and more patients will have AMD in a foreseeable future. In Eastern Europe, blindness due to AMD, currently, is approximately 20% and there has been an increasing trend depicted in the future. Generally, AMD can be divided into early stages and two forms in an advanced (late) stage. Advanced AMD form includes neovascular AMD (wet) and geographic atrophy (late dry), both of these are associated with substantial, progressive visual impairment. The pathogenesis of AMD is complex and, by far, not completely understood. Multiple factors have been studied, for example: environmental factor, genetic factor (complement factor H), lifestyle. It has been proved that they are linked to higher the risk of developing of AMD, however, the actual pathogenesis is not yet formulated. AMD progression can also be a culprit to certain biochemical events and molecular changes linked to inflammation and pathological angiogenesis. In nowadays, we do have diagnostic methods for both early and late forms of AMD as well as ways to prevent progression of early AMD and wet AMD. However, until now, there is still no treatment for dry AMD. This article is a brief review of AMD and may hopefully lead to some future directions in early diagnostic methods and treating dry AMD.

Neural induction: Historical views and application to pluripotent stem cells

Embryonic stem (ES) cells are a useful experimental material to recapitulate the differentiation steps of early embryos, which are usually invisible and inaccessible from outside of the body, especially in mammals. ES cells have greatly facilitated the analyses of gene expression profiles and cell characteristics. In addition, understanding the mechanisms during neural differentiation is important for clinical purposes, such as developing new therapeutic methods or regenerative medicine. As neurons have very limited regenerative ability, neurodegenerative diseases are usually intractable, and patients suffer from the disease throughout their lifetimes. The functional cells generated from ES cells in vitro could replace degenerative areas by transplantation. In this review, we will first demonstrate the historical views and widely accepted concepts regarding the molecular mechanisms of neural induction and positional information to produce the specific types of neurons in model animals. Next, we will describe how these concepts have recently been applied to the research in the establishment of the methodology of neural differentiation from mammalian ES cells. Finally, we will focus on examples of the applications of differentiation systems to clinical purposes. Overall, the discussion will focus on how historical developmental studies are applied to state-of-the-art stem cell research.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part II: Cell and Tissue Engineering Therapies

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 y.o. people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting on intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, different treatment options have to be considered. Cell therapy is a very promising alternative to drug-based approaches for AMD treatment. Cells delivered to the affected tissue as a suspension have shown poor retention and low survival rate. A solution to these inconveniences has been the encapsulation of these cells on biomaterials, which contrive to their protection, gives them support, and favor their retention of the desired area. We offer a two-papers critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In this second part we review the preclinical and clinical cell-replacement approaches aiming at the development of efficient AMD-therapies, the employed cell types, as well as the cell-encapsulation and cell-implant systems. We discuss their advantages and disadvantages and how they could improve the survival and integration of the implanted cells.

Oxidative stress and mitochondrial transfer: A new dimension towards ocular diseases

Ocular cells like, retinal pigment epithelium (RPE) is a highly specialized pigmented monolayer of post-mitotic cells, which is located in the posterior segment of the eye between neuro sensory retina and vascular choroid. It functions as a selective barrier and nourishes retinal visual cells. As a result of high-level oxygen consumption of retinal cells, RPE cells are vulnerable to chronic oxidative stress and an increased level of reactive oxygen species (ROS) generated from mitochondria. These oxidative stress and ROS generation in retinal cells lead to RPE degeneration. Various sources including mtDNA damage could be an important factor of oxidative stress in RPE. Gene therapy and mitochondrial transfer studies are emerging fields in ocular disease research. For retinal degenerative diseases stem cell-based transplantation methods are developed from basic research to preclinical and clinical trials. Translational research contributions of gene and cell therapy would be a new strategy to prevent, treat and cure various ocular diseases. This review focuses on the effect of oxidative stress in ocular cell degeneration and recent translational researches on retinal degenerative diseases to cure blindness.

Improving cell survival and engraftment in vivo via layer-by-layer nanocoating of hESC-derived RPE cells

BACKGROUND

Human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cell transplants have served as a cell therapy for treating retinal degenerative diseases. However, how to optimize the survival and engraftment of hESC-RPE cells is a great challenge.

METHODS

Here, we report hESC-RPE cells that are embedded with polyelectrolytes gelatin and alginate by layer-by-layer (LbL) self-assembly technique, based on the opposite charge of alternate layers. Cells were assessed for cell survival, immunogenicity, and function in vitro and in vivo.

RESULTS

This strategy obviously decreased the immunogenicity of hESC-RPE cells without affecting its activity. LbL-RPE cell transplants into the subretinal space of Royal College of Surgeons (RCS) rats optimized cell engraftment and decreased immunogenicity compared to untreated RPE cell transplants (immunosuppression was not used during the 21-week study). Visual-functional assay with electroretinogram recordings (ERGs) also showed higher B wave amplitudes in RCS rats with LbL-RPE cell transplants.

CONCLUSIONS

We demonstrate that transplanted LbL-RPE cells have better viability and grafting efficiency, optimized immunogenicity, and visual function. Therefore, LbL engineering is a promising method to increase the efficacy of hESC-RPE cell transplantation.

Establishment of a Rapid Lesion-Controllable Retinal Degeneration Monkey Model for Preclinical Stem Cell Therapy

Background: Retinal degenerative disorders (RDs) are the main cause of blindness without curable treatment. Our previous studies have demonstrated that human-induced pluripotent stem cells can differentiate into retinal organoids with all subtypes of retina, which provides huge promise for treating these diseases. Before these methods can be realized, RD animal models are required to evaluate the safety and efficacy of stem cell therapy and to develop the surgical tools and procedures for cell transplantation in patients. This study involved the development of a monkey model of RD with controllable lesion sites, which can be rapidly prepared for the study of preclinical stem cell therapy among other applications. Methods: Sodium nitroprusside (SNP) in three doses was delivered into the monkey eye by subretinal injection (SI), and normal saline was applied as control. Structural and functional changes of the retinas were evaluated via multimodal imaging techniques and multifocal electroretinography (mfERG) before and after the treatment. Histological examination was performed to identify the target layer of the affected retina. The health status of monkeys was monitored during the experiment. Results: Well-defined lesions with various degrees of retinal degeneration were induced at the posterior pole of retina as early as 7 days after SNP SI. The damage of SNP was dose dependent. In general, 0.05 mM SNP caused mild structural changes in the retina; 0.1 mM SNP led to the loss of outer retinal layers, including the outer plexiform layer (OPL), outer nuclear layer (ONL), and retinal pigment epithelium (RPE); while 0.2 mM SNP impacted the entire layer of the retina and choroid. MfERG showed reduced amplitude in the damaged region. The structural and functional damages were not recovered at 7-month follow-up. Conclusion: A rapidly induced lesion site-controllable retinal degeneration monkey model was established by the subretinal administration of SNP, of which the optimal dose is 0.1 mM. This monkey model mimics the histological changes of advanced RDs and provides a valuable platform for preclinical assessment of stem cell therapy for RDs.

Capacity of Retinal Ganglion Cells Derived from Human Induced Pluripotent Stem Cells to Suppress T-Cells

Retinal ganglion cells (RGCs) are impaired in patients such as those with glaucoma and optic neuritis, resulting in permanent vision loss. To restore visual function, development of RGC transplantation therapy is now underway. Induced pluripotent stem cells (iPSCs) are an important source of RGCs for human allogeneic transplantation. We therefore analyzed the immunological characteristics of iPSC-derived RGCs (iPSC-RGCs) to evaluate the possibility of rejection after RGC transplantation. We first assessed the expression of human leukocyte antigen (HLA) molecules on iPSC-RGCs using immunostaining, and then evaluated the effects of iPSC-RGCs to activate lymphocytes using the mixed lymphocyte reaction (MLR) and iPSC-RGC co-cultures. We observed low expression of HLA class I and no expression of HLA class II molecules on iPSC-RGCs. We also found that iPSC-RGCs strongly suppressed various inflammatory immune cells including activated T-cells in the MLR assay and that transforming growth factor-β2 produced by iPSC-RGCs played a critical role in suppression of inflammatory cells in vitro. Our data suggest that iPSC-RGCs have low immunogenicity, and immunosuppressive capacity on lymphocytes. Our study will contribute to predicting immune attacks after RGC transplantation.