c-Kit+ cells isolated from human fetal retinas represent a new population of retinal progenitor cells

Human fetal tissue is critical for biomedical research

Human fetal tissue and cells derived from fetal tissue are crucial for biomedical research. Fetal tissues and cells are used to study both normal development and developmental disorders. They are broadly applied in vaccine development and production. Further, research using cells from fetal tissue is instrumental for studying many infectious diseases, including a broad range of viruses. These widespread applications underscore the value of fetal tissue research and reflect an important point: cells derived from fetal tissues have capabilities that cells from other sources do not. In many cases, increased functionality of cells derived from fetal tissues arises from increased proliferative capacity, ability to survive in culture, and developmental potential that is attenuated in adult tissues. This review highlights important, representative applications of fetal tissue for science and medicine.

Single-cell transcriptome analysis of xenotransplanted human retinal organoids defines two migratory cell populations of nonretinal origin

Human retinal organoid transplantation could potentially be a treatment for degenerative retinal diseases. How the recipient retina regulates the survival, maturation, and proliferation of transplanted organoid cells is unknown. We transplanted human retinal organoid-derived cells into photoreceptor-deficient mice and conducted histology and single-cell RNA sequencing alongside time-matched cultured retinal organoids. Unexpectedly, we observed human cells that migrated into all recipient retinal layers and traveled long distances. Using an unbiased approach, we identified these cells as astrocytes and brain/spinal cord-like neural precursors that were absent or rare in stage-matched cultured organoids. In contrast, retinal progenitor-derived rods and cones remained in the subretinal space, maturing more rapidly than those in the cultured controls. These data suggest that recipient microenvironment promotes the maturation of transplanted photoreceptors while inducing or facilitating the survival of migratory cell populations that are not normally derived from retinal progenitors. These findings have important implications for potential cell-based treatments of retinal diseases.

Stimulation of C-Kit+ Retinal Progenitor Cells by Stem Cell Factor Confers Protection Against Retinal Degeneration

C-kit/CD117, expressed in a series of tissue-specific progenitor cells, plays an important role in tissue regeneration and tissue homeostasis. We previously demonstrated that organoid-derived c-kit⁺ retinal progenitor cells can facilitate the restoration of degenerated retina. Meanwhile, we have identified a population of endogenous c-kit⁺ cells in retinas of adult mouse. However, the exact role of these cells in retinal degeneration remains unclear. Here, we demonstrated that stimulation of endogenous c-kit⁺ cells by stem cell factor (SCF) conferred protection against retinal degeneration. Retinal degeneration was induced by intravitreal injection of N-methyl-D-aspartate (NMDA). NMDA challenge increased the total number of c-kit⁺ cells in the retinal ganglion cell layer (GCL), while deregulated the protein level of SCF, which was mainly expressed in Müller cells. Both flash electroretinogram (fERG) and light/dark transition tests showed that intravitreal injection of SCF effectively improved the visual function of NMDA-treated mice. Mechanistically, SCF administration not only prevented the loss of retinal ganglion cells (RGCs), but also maintained the function of RGCs as quantified by fERG. Further, we performed transcriptome sequencing analysis of the retinal cells isolated from SCF-treated mice and the parallel control. Gene Ontology analysis showed that SCF-induced transcriptome changes were closely correlated with eye development-related pathways. Crystallins and several protective factors such as Pitx3 were significantly upregulated by SCF treatment. Our results revealed the role of SCF stimulated c-kit⁺ cells in the protection of RGCs in NMDA-treated mice, via inhibiting the loss of RGCs. Administration of SCF can act as a potent strategy for treating retinal degeneration-related diseases.

miR-381-3p Cooperated With Hes1 to Regulate the Proliferation and Differentiation of Retinal Progenitor Cells

Retinal progenitor cells (RPCs) transplantation has become a promising therapy for retinal degeneration, which is a major kind of ocular diseases causing blindness. Since RPCs have limited proliferation and differentiation abilities toward retinal neurons, it is urgent to resolve these problems. MicroRNAs have been reported to have vital effects on stem cell fate. In our study, the data showed that overexpression of miR-381-3p repressed Hes1 expression, which promoted RPCs differentiation, especially toward neuronal cells, and inhibited RPCs proliferation. Knockdown of endogenous miR-381-3p increased Hes1 expression to inhibit RPCs differentiation and promote proliferation. In addition, a luciferase assay demonstrated that miR-381-3p directly targeted the Hes1 3’ untranslated region (UTR). Taken together, our study demonstrated that miR-381-3p regulated RPCs proliferation and differentiation by targeting Hes1, which provides an experimental basis of RPCs transplantation therapy for retinal degeneration.

A look into retinal organoids: methods, analytical techniques, and applications

Inherited retinal diseases (IRDs) cause progressive loss of light-sensitive photoreceptors in the eye and can lead to blindness. Gene-based therapies for IRDs have shown remarkable progress in the past decade, but the vast majority of forms remain untreatable. In the era of personalised medicine, induced pluripotent stem cells (iPSCs) emerge as a valuable system for cell replacement and to model IRD because they retain the specific patient genome and can differentiate into any adult cell type. Three-dimensional (3D) iPSCs-derived retina-like tissue called retinal organoid contains all major retina-specific cell types: amacrine, bipolar, horizontal, retinal ganglion cells, Müller glia, as well as rod and cone photoreceptors. Here, we describe the main applications of retinal organoids and provide a comprehensive overview of the state-of-art analysis methods that apply to this model system. Finally, we will discuss the outlook for improvements that would bring the cellular model a step closer to become an established system in research and treatment development of IRDs.

Retinal Organoid Technology: Where Are We Now?

It is difficult to regenerate mammalian retinal cells once the adult retina is damaged, and current clinical approaches to retinal damages are very limited. The introduction of the retinal organoid technique empowers researchers to study the molecular mechanisms controlling retinal development, explore the pathogenesis of retinal diseases, develop novel treatment options, and pursue cell/tissue transplantation under a certain genetic background. Here, we revisit the historical background of retinal organoid technology, categorize current methods of organoid induction, and outline the obstacles and potential solutions to next-generation retinal organoids. Meanwhile, we recapitulate recent research progress in cell/tissue transplantation to treat retinal diseases, and discuss the pros and cons of transplanting single-cell suspension versus retinal organoid sheet for cell therapies.

Synaptic repair and vision restoration in advanced degenerating eyes by transplantation of retinal progenitor cells

Stem cell transplantation shows enormous potential for treatment of incurable retinal degeneration (RD). To determine if and how grafts connect with the neural circuits of the advanced degenerative retina (ADR) and improve vision, we perform calcium imaging of GCaMP5-positive grafts in retinal slices. The organoid-derived C-Kit⁺/SSEA1^- (C-Kit⁺) retinal progenitor cells (RPCs) become synaptically organized and build spontaneously active synaptic networks in three major layers of ADR. Light stimulation of the host photoreceptors elicits distinct neuronal responses throughout the graft RPCs. The graft RPCs and their differentiated offspring cells in inner nuclear layer synchronize their activities with the host cells and exhibit presynaptic calcium flux patterns that resemble intact retinal neurons. Once graft-to-host network is established, progressive vision loss is stabilized while control eyes continually lose vision. Therefore, transplantation of organoid-derived C-Kit⁺ RPCs can form functional synaptic networks within ADR and it holds promising avenue for advanced RD treatment.

Retinal Stem Cell 'Retirement Plans': Growth, Regulation and Species Adaptations in the Retinal Ciliary Marginal Zone

The vertebrate retina develops from a specified group of precursor cells that adopt distinct identities and generate lineages of either the neural retina, retinal pigmented epithelium, or ciliary body. In some species, including teleost fish and amphibians, proliferative cells with stem-cell-like properties capable of continuously supplying new retinal cells post-embryonically have been characterized and extensively studied. This region, termed the ciliary or circumferential marginal zone (CMZ), possibly represents a conserved retinal stem cell niche. In this review, we highlight the research characterizing similar CMZ-like regions, or stem-like cells located at the peripheral margin, across multiple different species. We discuss the proliferative parameters, multipotency and growth mechanisms of these cells to understand how they behave in vivo and how different molecular factors and signalling networks converge at the CMZ niche to regulate their activity. The evidence suggests that the mature retina may have a conserved propensity for homeostatic growth and plasticity and that dysfunction in the regulation of CMZ activity may partially account for dystrophic eye growth diseases such as myopia and hyperopia. A better understanding of the properties of CMZ cells will enable important insight into how an endogenous generative tissue compartment can adapt to altered retinal physiology and potentially even restore vision loss caused by retinal degenerative conditions.

Longitudinal single-cell RNA-seq of hESCs-derived retinal organoids

Human retina development involves multiple well-studied signaling pathways that promote the genesis of a wide arrange of different cell types in a complex architectural structure. Human embryonic stem cells (hESCs)-derived retinal organoids could recapitulate the human retinal development. We performed single-cell RNA-seq of retinal organoids from 5 time points (D36, D66, D96, D126, D186) and identified 9 distinct populations of cells. In addition, we analyzed the molecular characteristics of each main population and followed them from genesis to maturity by pseudotime analysis and characterized the cell-cell interactions between different cell types. Interestingly, we identified insulin receptor (INSR) as a specifically expressed receptor involved in the genesis of photoreceptors, and pleiothropin (PTN)-protein tyrosine phosphatase receptor type Z1 (PTPRZ1) as a mediator of a previously unknown interaction between Müller and retinal progenitor cells. Taken together, these findings provide a rich transcriptome-based lineage map for studying human retinal development and modeling developmental disorders in retinal organoids.

SCF/SCFR signaling plays an important role in the early morphogenesis and neurogenesis of human embryonic neural retina

The stem cell factor receptor (SCFR) has been demonstrated to be expressed in the neural retina of mice, rat and human for decades. Previous reports indicated that the SCFR correlates with glia differentiation of late retinal progenitor cells (RPCs), retinal vasculogenesis and homeostasis of the blood-retinal barrier. However, the role of SCF/SCFR signaling in the growth and development of the neural retina (NR), especially in the early embryonic stage, remains poorly understood. Here, we show that SCF/SCFR signaling orchestrates invagination of the human embryonic stem cell (hESC)-derived NR via regulation of cell cycle progression, cytoskeleton dynamic and apical constriction of RPCs in the ciliary marginal zone (CMZ). Furthermore, activation of SCF/SCFR signaling promotes neurogenesis in the central-most NR via acceleration of the migration of immature ganglion cells and repressing apoptosis. Our study reveals an unreported role for SCF/SCFR signaling in controlling ciliary marginal cellular behaviors during early morphogenesis and neurogenesis of the human embryonic NR, providing a new potential therapeutic target for human congenital eye diseases such as anophthalmia, microphthalmia and congenital high myopia.

Organoid-derived C-Kit+/SSEA4- human retinal progenitor cells promote a protective retinal microenvironment during transplantation in rodents

Stem cell therapy may replace lost photoreceptors and preserve residual photoreceptors during retinal degeneration (RD). Unfortunately, the degenerative microenvironment compromises the fate of grafted cells, demanding supplementary strategies for microenvironment regulation. Donor cells with both proper regeneration capability and intrinsic ability to improve microenvironment are highly desired. Here, we use cell surface markers (C-Kit⁺/SSEA4⁻) to effectively eliminate tumorigenic embryonic cells and enrich retinal progenitor cells (RPCs) from human embryonic stem cell (hESC)-derived retinal organoids, which, following subretinal transplantation into RD models of rats and mice, significantly improve vision and preserve the retinal structure. We characterize the pattern of integration and materials transfer following transplantation, which likely contribute to the rescued photoreceptors. Moreover, C-Kit⁺/SSEA4⁻ cells suppress microglial activation, gliosis and the production of inflammatory mediators, thereby providing a healthier host microenvironment for the grafted cells and delaying RD. Therefore, C-Kit⁺/SSEA4⁻ cells from hESC-derived retinal organoids are a promising therapeutic cell source.

Stem cell transplantation to treat retinal degeneration could be limited by the degenerative microenvironment. Here, the authors show that C-Kit⁺/SSEA4^– progenitor cells enriched from human embryonic stem cell derived retinal organoids protect retinal structure, suppress microglial activation, gliosis and inflammation.

Enhanced proliferation and differentiation of retinal progenitor cells through a self-healing injectable hydrogel

Fabrication of self-healing injectable CS-Odex hydrogels via a dynamic Schiff-base linkage for RPC delivery.

Mussel-inspired injectable hydrogel and its counterpart for actuating proliferation and neuronal differentiation of retinal progenitor cells

Biomaterials-mediated retinal progenitor cell (RPC)-based transplantation therapy has shown substantial potential for retinal degeneration (RD), but it is limited by the poor RPC survival, proliferation and differentiation. Herein, the gelatin-hyaluronic acid (Gel-HA)-based hydrogels formed via moderate Michael-type addition reaction with or without the introduction of mussel-inspired polydopamine (PDA), i.e. Gel-HA-PDA and its counterpart Gel-HA hydrogels are developed, and their effects on the biological behaviour of RPCs, including adhesion, survival, proliferation, differentiation, delivery and migration are investigated. The hybrid hydrogels can adopt the intricate structure of the retina with suitable mechanical strength, degradation rate and biological activity to support cellular adhesion, survival and delivery. Meanwhile, Gel-HA hydrogel can remarkably promote RPC proliferation with much larger cell clusters, while Gel-HA-PDA hydrogel significantly enhances RPC adhesion and migration, and directs RPCs to preferentially differentiate toward retinal neurons such as photoreceptors (the most crucial cell-type for RD treatment), which is mainly induced by the activation of integrin α5β1-phosphatidylinositol-3-kinase (PI3K) pathway. This study demonstrates that Gel-HA hydrogel possesses great potential for RPC proliferation, while mussel-inspired PDA-modified Gel-HA hydrogel with superior biocompatibility can significantly promote RPC neuronal differentiation, providing new insights for developing biomedical materials applied for RPC-based transplantation therapy.

Features specific to retinal pigment epithelium cells derived from three-dimensional human embryonic stem cell cultures - a new donor for cell therapy

Retinal pigment epithelium (RPE) transplantation is a particularly promising treatment of retinal degenerative diseases affecting RPE-photoreceptor complex. Embryonic stem cells (ESCs) provide an abundant donor source for RPE transplantation. Herein, we studied the time-course characteristics of RPE cells derived from three-dimensional human ESCs cultures (3D-RPE). We showed that 3D-RPE cells possessed morphology, ultrastructure, gene expression profile, and functions of authentic RPE. As differentiation proceeded, 3D-RPE cells could mature gradually with decreasing proliferation but increasing functions. Besides, 3D-RPE cells could form polarized monolayer with functional tight junction and gap junction. When grafted into the subretinal space of Royal College of Surgeons rats, 3D-RPE cells were safe and efficient to rescue retinal degeneration. This study showed that 3D-RPE cells were a new donor for cell therapy of retinal degenerative diseases.

Next generation organoids for biomedical research and applications

Organoids are in vitro cultures of miniature fetal or adult organ-like structures. Their potentials for use in tissue and organ replacement, disease modeling, toxicology studies, and drug discovery are tremendous. Currently, major challenges facing human organoid technology include (i) improving the range of cellular heterogeneity for a particular organoid system, (ii) mimicking the native micro- and matrix-environment encountered by cells within organoids, and (iii) developing robust protocols for the in vitro maturation of organoids that remain mostly fetal-like in cultures. To tackle these challenges, we advocate the principle of reverse engineering that replicates the inner workings of in vivo systems with the goal of achieving functionality and maturation of the resulting organoid structures with the input of minimal intrinsic (cellular) and environmental (matrix and niche) constituents. Here, we present an overview of organoid technology development in several systems that employ cell materials derived from fetal and adult tissues and pluripotent stem cell cultures. We focus on key studies that exploit the self-organizing property of embryonic progenitors and the role of designer matrices and cell-free scaffolds in assisting organoid formation. We further explore the relationship between adult stem cells, niche factors, and other current developments that aim to enhance robust organoid maturation. From these works, we propose a standardized pipeline for the development of future protocols that would help generate more physiologically relevant human organoids for various biomedical applications.

Using CRISPR-Cas9 to Generate Gene-Corrected Autologous iPSCs for the Treatment of Inherited Retinal Degeneration

Patient-derived induced pluripotent stem cells (iPSCs) hold great promise for autologous cell replacement. However, for many inherited diseases, treatment will likely require genetic repair pre-transplantation. Genome editing technologies are useful for this application. The purpose of this study was to develop CRISPR-Cas9-mediated genome editing strategies to target and correct the three most common types of disease-causing variants in patient-derived iPSCs: (1) exonic, (2) deep intronic, and (3) dominant gain of function. We developed a homology-directed repair strategy targeting a homozygous Alu insertion in exon 9 of male germ cell-associated kinase (MAK) and demonstrated restoration of the retinal transcript and protein in patient cells. We generated a CRISPR-Cas9-mediated non-homologous end joining (NHEJ) approach to excise a major contributor to Leber congenital amaurosis, the IVS26 cryptic-splice mutation in CEP290, and demonstrated correction of the transcript and protein in patient iPSCs. Lastly, we designed allele-specific CRISPR guides that selectively target the mutant Pro23His rhodopsin (RHO) allele, which, following delivery to both patient iPSCs in vitro and pig retina in vivo, created a frameshift and premature stop that would prevent transcription of the disease-causing variant. The strategies developed in this study will prove useful for correcting a wide range of genetic variants in genes that cause inherited retinal degeneration.

Evidence for a retinal progenitor cell in the postnatal and adult mouse

Progress in cell therapy for retinal disorders has been challenging. Recognized retinal progenitors are a heterogeneous population of cells that lack surface markers for the isolation of live cells for clinical implementation. In the present application, our objective was to use the stem cell factor receptor c-Kit (CD117), a surface marker, to isolate and evaluate a distinct progenitor cell population from retinas of postnatal and adult mice. Here we report that, by combining traditional methods with fate mapping, we have identified a c-Kit-positive (c-Kit⁺) retinal progenitor cell (RPC) that is self-renewing and clonogenic in vitro, and capable of generating many cell types in vitro and in vivo. Based on cell lineage tracing, significant subpopulations of photoreceptors in the outer nuclear layer and bipolar, horizontal, amacrine and Müller cells in the inner nuclear layer are the progeny of c-Kit⁺ cells in vivo. The RPC progeny contributes to retinal neurons and glial cells, which are responsible for the conversion of light into visual signals. The ability to isolate and expand in vitro live c-Kit⁺ RPCs makes them a future therapeutic option for retinal diseases.

Treatment Paradigms for Retinal and Macular Diseases Using 3-D Retina Cultures Derived From Human Reporter Pluripotent Stem Cell Lines

We discuss the use of pluripotent stem cell lines carrying fluorescent reporters driven by retinal promoters to derive three-dimensional (3-D) retina in culture and how this system can be exploited for elucidating human retinal biology, creating disease models in a dish, and designing targeted drug screens for retinal and macular degeneration. Furthermore, we realize that stem cell investigations are labor-intensive and require extensive resources. To expedite scientific discovery by sharing of resources and to avoid duplication of efforts, we propose the formation of a Retinal Stem Cell Consortium. In the field of vision, such collaborative approaches have been enormously successful in elucidating genetic susceptibility associated with age-related macular degeneration.

Progress of stem/progenitor cell-based therapy for retinal degeneration

Retinal degeneration (RD), such as age-related macular degeneration (AMD) and retinitis pigmentosa, is one of the leading causes of blindness. Presently, no satisfactory therapeutic options are available for these diseases principally because the retina and retinal pigmented epithelium (RPE) do not regenerate, although wet AMD can be prevented from further progression by anti-vascular endothelial growth factor therapy. Nevertheless, stem/progenitor cell approaches exhibit enormous potential for RD treatment using strategies mainly aimed at the rescue and replacement of photoreceptors and RPE. The sources of stem/progenitor cells are classified into two broad categories in this review, which are (1) ocular-derived progenitor cells, such as retinal progenitor cells, and (2) non-ocular-derived stem cells, including embryonic stem cells, induced pluripotent stem cells, and mesenchymal stromal cells. Here, we discuss in detail the progress in the study of four predominant stem/progenitor cell types used in animal models of RD. A short overview of clinical trials involving the stem/progenitor cells is also presented. Currently, stem/progenitor cell therapies for RD still have some drawbacks such as inhibited proliferation and/or differentiation in vitro (with the exception of the RPE) and limited long-term survival and function of grafts in vivo. Despite these challenges, stem/progenitor cells represent the most promising strategy for RD treatment in the near future.

Adult human retinal Müller glia display distinct peripheral and macular expression of CD117 and CD44 stem cell-associated proteins

Experimental evidence suggests human Müller glia exhibit neural progenitor properties in vitro. CD117 and CD44 are known to be expressed by stem cells, the survival of which appears to depend critically on interactions with hyaluronan-rich extracellular matrix (ECM). Here, we characterise Müller glia expression of CD117 and CD44 in normal adult human retina and describe how it correlates with hyaluronan distribution in ocular ECM. By using chromogen-based immunohistochemistry, CD117 expression was found in entire Müller glia cytoplasm spanning from inner to outer limiting membrane in both peripheral retina (PR) and macular retina (MR), mirroring expression of the established Müller glia marker vimentin. Unlike vimentin, CD117 was also strongly expressed by Müller glia nuclei. Relative to total inner nuclear layer (INL) nuclei, more CD117+ Müller glia nuclei were seen in PR than MR. By contrast, CD44 expression was found predominantly in Müller glia apical processes of PR; no expression was found in MR. Astral blue staining demonstrated the presence of hyaluronan in cortical vitreous and the interphotoreceptor matrix (IPM) in both MR and PR. Our findings demonstrate that: (i) both CD117 and CD44 are expressed by human adult Müller glia; (ii) CD117 is a robust nuclear and cytoplasmic immunohistochemical marker of Müller glia; and (iii) that while CD117 is expressed by the entire Müller glia in both PR and MR, CD44 is only expressed by Müller glia apices in PR. Since the apices of Müller glia are in direct contact with the hyaluronan-rich IPM, the Müller glia-IPM interface in PR is likely a favourable region for supporting progenitor or stem cell-like signalling. These observations provide novel insights into potential stem-cell favouring microenvironments in mature human retina.

Experimental Study of the Biological Properties of Human Embryonic Stem Cell-Derived Retinal Progenitor Cells

Retinal degenerative diseases are among the leading causes of blindness worldwide, and cell replacement is considered as a promising therapeutic. However, the resources of seed cells are scarce. To further explore this type of therapy, we adopted a culture system that could harvest a substantial quantity of retinal progenitor cells (RPCs) from human embryonic stem cells (hESCs) within a relatively short period of time. Furthermore, we transplanted these RPCs into the subretinal spaces of Royal College of Surgeons (RCS) rats. We quantified the thickness of the treated rats' outer nuclear layers (ONLs) and explored the visual function via electroretinography (ERG). It was found that the differentiated cells expressed RPC markers and photoreceptor progenitor markers. The transplanted RPCs survived for at least 12 weeks, resulting in beneficial effects on the morphology of the host retina, and led to a significant improvement in the visual function of the treated animals. These therapeutic effects suggest that the hESCs-derived RPCs could delay degeneration of the retina and partially restore visual function.

Grafted c-kit+/SSEA1- eye-wall progenitor cells delay retinal degeneration in mice by regulating neural plasticity and forming new graft-to-host synapses

Background

Despite diverse pathogenesis, the common pathological change observed in age-related macular degeneration and in most hereditary retinal degeneration (RD) diseases is photoreceptor loss. Photoreceptor replacement by cell transplantation may be a feasible treatment for RD. The major obstacles to clinical translation of stem cell-based cell therapy in RD remain the difficulty of obtaining sufficient quantities of appropriate and safe donor cells and the poor integration of grafted stem cell-derived photoreceptors into the remaining retinal circuitry.

Methods

Eye-wall c-kit⁺/stage-specific embryonic antigen 1 (SSEA1)⁻ cells were isolated via fluorescence-activated cell sorting, and their self-renewal and differentiation potential were detected by immunochemistry and flow cytometry in vitro. After labeling with quantum nanocrystal dots and transplantation into the subretinal space of rd1 RD mice, differentiation and synapse formation by daughter cells of the eye-wall c-kit⁺/SSEA1⁻ cells were evaluated by immunochemistry and western blotting. Morphological changes of the inner retina of rd1 mice after cell transplantation were demonstrated by immunochemistry. Retinal function of rd1 mice that received cell grafts was tested via flash electroretinograms and the light/dark transition test.

Results

Eye-wall c-kit⁺/SSEA1⁻ cells were self-renewing and clonogenic, and they retained their proliferative potential through more than 20 passages. Additionally, eye-wall c-kit⁺/SSEA1⁻ cells were capable of differentiating into multiple retinal cell types including photoreceptors, bipolar cells, horizontal cells, amacrine cells, Müller cells, and retinal pigment epithelium cells and of transdifferentiating into smooth muscle cells and endothelial cells in vitro. The levels of synaptophysin and postsynaptic density-95 in the retinas of eye-wall c-kit⁺/SSEA1⁻ cell-transplanted rd1 mice were significantly increased at 4 weeks post transplantation. The c-kit⁺/SSEA1⁻ cells were capable of differentiating into functional photoreceptors that formed new synaptic connections with recipient retinas in rd1 mice. Transplantation also partially corrected the abnormalities of inner retina of rd1 mice. At 4 and 8 weeks post transplantation, the rd1 mice that received c-kit⁺/SSEA1⁻ cells showed significant increases in a-wave and b-wave amplitude and the percentage of time spent in the dark area.

Conclusions

Grafted c-kit⁺/SSEA1⁻ cells restored the retinal function of rd1 mice via regulating neural plasticity and forming new graft-to-host synapses.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0451-8) contains supplementary material, which is available to authorized users.

Intermittent high oxygen influences the formation of neural retinal tissue from human embryonic stem cells

The vertebrate retina is a highly multilayered nervous tissue with a large diversity of cellular components. With the development of stem cell technologies, human retinas can be generated in three-dimensional (3-D) culture in vitro. However, understanding the factors modulating key productive processes and the way that they influence development are far from clear. Oxygen, as the most essential element participating in metabolism, is a critical factor regulating organic development. In this study, using 3-D culture of human stem cells, we examined the effect of intermittent high oxygen treatment (40% O₂) on the formation and cellular behavior of neural retinas (NR) in the embryonic body (EB). The volume of EB and number of proliferating cells increased significantly under 40% O₂ on day 38, 50, and 62. Additionally, the ratio of PAX6+ cells within NR was significantly increased. The neural rosettes could only develop with correct apical-basal polarity under 40% O₂. In addition, the generation, migration and maturation of retinal ganglion cells were enhanced under 40% O₂. All of these results illustrated that 40% O₂ strengthened the formation of NR in EB with characteristics similar to the in vivo state, suggesting that the hyperoxic state facilitated the retinal development in vitro.

Efficacy and Safety of Human Retinal Progenitor Cells

PURPOSE

We assessed the long-term efficacy and safety of human retinal progenitor cells (hRPC) using established rodent models.

METHODS

Efficacy of hRPC was tested initially in Royal College of Surgeons (RCS) dystrophic rats immunosuppressed with cyclosporine/dexamethasone. Due to adverse effects of dexamethasone, this drug was omitted from a subsequent dose-ranging study, where different hRPC doses were tested for their ability to preserve visual function (measured by optokinetic head tracking) and retinal structure in RCS rats at 3 to 6 months after grafting. Safety of hRPC was assessed by subretinal transplantation into wild type (WT) rats and NIH-III nude mice, with analysis at 3 to 6 and 9 months after grafting, respectively.

RESULTS

The optimal dose of hRPC for preserving visual function/retinal structure in dystrophic rats was 50,000 to 100,000 cells. Human retinal progenitor cells integrated/survived in dystrophic and WT rat retina up to 6 months after grafting and expressed nestin, vimentin, GFAP, and βIII tubulin. Vision and retinal structure remained normal in WT rats injected with hRPC and there was no evidence of tumors. A comparison between dexamethasone-treated and untreated dystrophic rats at 3 months after grafting revealed an unexpected reduction in the baseline visual acuity of dexamethasone-treated animals.

CONCLUSIONS

Human retinal progenitor cells appear safe and efficacious in the preclinical models used here.

TRANSLATIONAL RELEVANCE

Human retinal progenitor cells could be deployed during early stages of retinal degeneration or in regions of intact retina, without adverse effects on visual function. The ability of dexamethasone to reduce baseline visual acuity in RCS dystrophic rats has important implications for the interpretation of preclinical and clinical cell transplant studies.

Human RPE Stem Cell-Derived RPE Preserves Photoreceptors in the Royal College of Surgeons Rat: Method for Quantifying the Area of Photoreceptor Sparing

PURPOSE

Numerous preclinical studies have shown that transplantation of stem cell-derived retinal pigment epithelial cell (RPE) preserves photoreceptor cell anatomy in the dystrophic Royal College of Surgeons (RCS) rat. How rescue is spatially distributed over the eye, relative to the transplantation site, is less clear. To understand spatial variations in transplant efficacy, we have developed a method to measure the spatial distribution of rescued photoreceptor cells.

METHODS

Human RPE Stem Cell-derived RPE (RPESC-RPE) cells were subretinally injected into RCS rat eyes. After tissue recovery and orientating the globe, a series of retinal sections were cut through the injected area. Sections were stained with DAPI (4',6-diamidino-2-phenylindole) and a number of photoreceptor nuclei were counted across the nasal-temporal and superior-inferior axes. These data were used to construct 2D maps of the area of photoreceptor cell saving.

RESULTS

Photoreceptor cell preservation was detected in the injected temporal hemisphere and occupied areas greater than 4 mm(2) centered near the injection sites. Rescue was directed toward the central retina and superior and inferior poles, with maximal number of rescued photoreceptor cells proximal to the injection sites.

CONCLUSIONS

RPESC-RPE transplantation preserves RCS photoreceptor cells. The photoreceptor cell contour maps readily convey the extent of rescue across the eye. The consistent alignment and quantification of results using this method allow the application of other downstream statistical analyses and comparisons to better understand transplantation therapy in the eye.

Immunological Properties of Corneal Epithelial-Like Cells Derived from Human Embryonic Stem Cells

Transplantation of ex vivo expanded corneal limbal stem cells (LSCs) has been the main treatment for limbal stem cell deficiency, although the shortage of donor corneal tissues remains a major concern for its wide application. Due to the development of tissue engineering, embryonic stem cells (ESCs)-derived corneal epithelial-like cells (ESC-CECs) become a new direction for this issue. However, the immunogenicity of ESC-CECs is a critical matter to be solved. In the present study, we explored the immunological properties of ESC-CECs, which were differentiated from ESCs. The results showed that ESC-CECs had a similar character and function with LSCs both in vitro and in vivo. In ESC-CECs, a large number of genes related with immune response were down-regulated. The expressions of MHC-I, MHC-II, and co-stimulatory molecules were low, but the expression of HLA-G was high. The ESC-CECs were less responsible for T cell proliferation and NK cell lysis in vitro, and there was less immune cell infiltration after transplantation in vivo compared with LSCs. Moreover, the immunological properties were not affected by interferon-γ. All these results indicated a low immunogenicity of ESC-CECs, and they can be promising in clinical use.