Derivation of Corneal Keratocyte-Like Cells from Human Induced Pluripotent Stem Cells

Generation of Retinal Ganglion Cells from Reprogrammed Keratocytes of Non-Glaucoma and Glaucoma Donors

Human induced pluripotent stem cell (hiPSC)-based disease modeling can be successfully recapitulated to mimic disease characteristics across various human pathologies. Glaucoma, a progressive optic neuropathy, primarily affects the retinal ganglion cells (RGCs). While multiple groups have successfully generated RGCs from non-diseased hiPSCs, producing RGCs from glaucomatous human samples holds significant promise for understanding disease pathology by revealing patient-specific disease signatures. Given that keratocytes originate from the neural crest and previous reports suggest that ocular fibroblasts from glaucomatous donors carry pathogenic signatures, it is highly plausible that these signatures imprinted within the keratocytes will also be present in the derived RGCs. Thus, we aimed to generate RGCs from both glaucomatous and non-glaucomatous donor keratocytes and validate disease-specific signatures in 3D retinal organoids and in isolated RGCs. Our protocol describes the generation of iPSCs from keratocytes of both glaucomatous and non-glaucomatous donors, followed by their differentiation into retinal organoids. Subsequent isolation and culturing of RGCs were performed. Disease signatures in the RGCs were validated in both 3D retinal organoids (ROs) and 2D RGC cultures, and glaucomatous RGCs in 3D and 2D cultures demonstrated increased cleaved CASP3 and significant RGC loss, indicating disease imprints in the hiPSC-derived RGCs. This model offers a venue and high throughput platform for studying glaucomatous disease pathology and holds significant potential for drug discovery using RGCs derived from human donors. © 2025 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Culturing of keratocytes from human cadaveric donors Basic Protocol 2: Reprogramming donor keratocytes into iPSCs Basic Protocol 3: Evaluation of chromosomal loss during reprogramming in iPSCs by karyotyping Basic Protocol 4: Generation of 3D ROs Basic Protocol 5: Dissociation and culturing of RGCs from 3D ROs Support Protocol 1: Immunostaining for phenotypic characterization of cells Support Protocol 2: Sectioning of 3D ROs and immunostaining Support Protocol 3: Western blotting for cleaved CASP3 and THY1.

Trehalose extricates impaired mitochondrial and autophagy dysregulation in patient iPSC-derived macular corneal dystrophy disease model

BACKGROUND

Patient-derived induced pluripotent stem cell (iPSCs) represents a powerful tool for elucidating the underlying disease mechanisms. Macular corneal dystrophy (MCD) is an intractable and progressive bilateral corneal disease affecting the corneal stroma due to mutation/s in carbohydrate sulfotransferase 6 (CHST6) gene. The underlying molecular mechanisms leading to MCD are unclear due to a lack of human contextual model and limited access to affected corneal stromal keratocytes (CSKs) from MCD patients. This has restricted the current treatment option for MCD to restorative corneal transplantation thereby lending itself to the use of iPSCs.

METHODS

induced pluripotent stem cells (iPSCs) were generated from two MCD patients and a healthy participant by senai virus based reprogramming of the peripheral mononuclear blood cells (PBMCs). The iPSCs were characterized based on the expression of pluripotent markers and formation of embryoid bodies possessing tri-lineage potential. Directed differentiation of the iPSCs to corneal stromal keratocytes (CSKs) was done via intermediate induction of neural crest cells. The iCSKs were characterized by immunocytochemistry and qPCR. Proteostat staining of the iCSKs was done to validate the disease phenotype invitro. Expression of autophagy markers in the iCSKs and JC staining were visualized by immunochemistry and live-cell imaging in trehalose treated iCSKs.

RESULTS

We show that the MCD iPSC-derived CSKs (MCDiCSKs) exhibits impaired autophagy assessed by the profiles of autophagy-associated proteins (LAMP1, LC3II/I, p62 and Beclin-1) and mitochondrial membrane potential. Significantly higher protein aggregates in MCDiCSKs was seen compared with the control, which could be rescued upon autophagy modulation. Hence, we treated MCD-iCSKs with trehalose (autophagy inducer) and showed that it protects MCD-iCSKs from mitochondrial dysfunction and maintains autophagic degradation.

CONCLUSION

Our study highlights the possible pathological mechanisms involved in MCD. We found trehalose ameliorate the impaired mitochondrial and autophagy dysregulation in patient iPSC-derived macular corneal dystrophy disease model, which could be a potential alternative for MCD management.

Embryoid body-based differentiation of human-induced pluripotent stem cells into cells with a corneal stromal keratocyte phenotype

OBJECTIVE

The transparency of the cornea is determined by the extracellular matrix, which is secreted by corneal stromal keratocytes (CSKs). Human-induced pluripotent stem cell (hiPSC)-derived keratocytes (hiPSC-CSKs) can be used in cell-based therapy for treating corneal blindness. Our goal was to develop an effective small molecule-based technique for differentiating hiPSCs into keratocytes.

METHODS AND ANALYSIS

hiPSCs were cultured in chemically defined medium, and embryoid bodies (EBs) were generated; these EBs were induced into CSKs using keratocyte-differentiated medium. The expression of keratocyte-specific markers was assessed using quantitative RT-PCR, immunostaining and Western blotting.

RESULTS

We found that the expression of genes encoding keratocyte markers, including aldehyde dehydrogenase 1 family member A1 (ALDH1A1), lumican and keratocan, was upregulated. Immunostaining showed positive staining for ALDH1A1 and keratocan in the hiPSC-CSK samples. Similarly, western blot analysis indicated that ALDH1A1 and keratocan expression levels were significantly greater in the hiPSC-CSKs than in the control cells. In addition, hiPSC-CSKs were not transformed into fibroblasts or myofibroblasts.

CONCLUSION

We established an innovative and effective method to generate CSKs via the EB-based differentiation of hiPSCs, which might be employed for cell-based therapy of corneal stromal opacities.

Focus on seed cells: stem cells in 3D bioprinting of corneal grafts

Corneal opacity is one of the leading causes of severe vision impairment. Corneal transplantation is the dominant therapy for irreversible corneal blindness. However, there is a worldwide shortage of donor grafts and consequently an urgent demand for alternatives. Three-dimensional (3D) bioprinting is an innovative additive manufacturing technology for high-resolution distribution of bioink to construct human tissues. The technology has shown great promise in the field of bone, cartilage and skin tissue construction. 3D bioprinting allows precise structural construction and functional cell printing, which makes it possible to print personalized full-thickness or lamellar corneal layers. Seed cells play an important role in producing corneal biological functions. And stem cells are potential seed cells for corneal tissue construction. In this review, the basic anatomy and physiology of the natural human cornea and the grafts for keratoplasties are introduced. Then, the applications of 3D bioprinting techniques and bioinks for corneal tissue construction and their interaction with seed cells are reviewed, and both the application and promising future of stem cells in corneal tissue engineering is discussed. Finally, the development trends requirements and challenges of using stem cells as seed cells in corneal graft construction are summarized, and future development directions are suggested.

Current Advances in Corneal Stromal Stem Cell Biology and Therapeutic Applications

Corneal stromal stem cells (CSSCs) are of particular interest in regenerative ophthalmology, offering a new therapeutic target for corneal injuries and diseases. This review provides a comprehensive examination of CSSCs, exploring their anatomy, functions, and role in maintaining corneal integrity. Molecular markers, wound healing mechanisms, and potential therapeutic applications are discussed. Global corneal blindness, especially in more resource-limited regions, underscores the need for innovative solutions. Challenges posed by corneal defects, emphasizing the urgent need for advanced therapeutic interventions, are discussed. The review places a spotlight on exosome therapy as a potential therapy. CSSC-derived exosomes exhibit significant potential for modulating inflammation, promoting tissue repair, and addressing corneal transparency. Additionally, the rejuvenation potential of CSSCs through epigenetic reprogramming adds to the evolving regenerative landscape. The imperative for clinical trials and human studies to seamlessly integrate these strategies into practice is emphasized. This points towards a future where CSSC-based therapies, particularly leveraging exosomes, play a central role in diversifying ophthalmic regenerative medicine.

Corneal stromal regeneration-keratoconus cell therapy: a review

BACKGROUND

Keratoconus is a corneal ectatic disease caused by stromal thinning leading to astigmatism and progressive loss of vision. Loss of the keratocytes and excessive degradation of collagen fibres by matrix metalloproteinases are the molecular signatures of the disease. Despite several limitations, corneal collagen cross-linking and keratoplasty are the most widely used treatment options for keratoconus. In the pursuit of alternative treatment modalities, clinician scientists have explored cell therapy paradigms for treating the condition.

METHODS

Articles pertaining to keratoconus cell therapy with relevant key words were used to search in PubMed, Researchgate, and Google Scholar. The articles were selected based on their relevance, reliability, publication year, published journal, and accessibility.

RESULTS

Various cellular abnormalities have been reported in keratoconus. Diverse cell types such as mesenchymal stromal cells, dental pulp cells, bone marrow stem cells, haematopoietic stem cells, adipose-derived stem cells apart from embryonic and induced pluripotent stem cells can be used for keratoconus cell therapy. The results obtained show that there is a potential for these cells from various sources as a viable treatment option.

CONCLUSION

There is a need for consensus with respect to the source of cells, mode of delivery, stage of disease, and duration of follow-up, to establish a standard operating protocol. This would eventually widen the cell therapy options for corneal ectatic diseases beyond keratoconus.

Intracorneal Implantation of 3D Bioprinted Scaffolds Containing Mesenchymal Stromal Cells Using Femtosecond-Laser-Assisted Intrastromal Keratoplasty

Injury of the cornea is a complex biological process. Regeneration of the corneal stroma can be facilitated by the presence of mesenchymal stromal cells (MSCs) and application of tissue equivalents. A new tissue-engineering strategy for corneal stroma regeneration is presented using cellularized 3D bioprinted hydrogel constructs implanted into organ cultured porcine corneas using femtosecond laser-assisted intrastromal keratoplasty. The ex vivo cultured, MSC-loaded 3D bioprinted structures remain intact, support cell survival, and contain de novo synthesized extracellular matrix components and migrating cells throughout the observation period. At day 14 postimplantation, the cellularized tissue equivalents contain few or no cells, as demonstrated by optical coherence tomography imaging and immunofluorescent staining. This study successfully combines a laboratory-based method with modern, patient-care practice to produce a cell-laden tissue equivalent for corneal implantation. Optimal bioink composition and cellularization of tissue equivalents are essential in fine-tuning a method to promote the current technique as a future treatment modality.

From bench to clinic: Emerging therapies for corneal scarring

Corneal diseases are one of the leading causes of moderate-to-severe visual impairment and blindness worldwide, after glaucoma, cataract, and retinal disease in overall importance. Given its tendency to affect people at a younger age than other blinding conditions such as cataract and glaucoma, corneal scarring poses a huge burden both on the individuals and society. Furthermore, corneal scarring and fibrosis disproportionately affects people in poorer and remote areas, making it a significant ophthalmic public health problem. Traditional medical strategies, such as topical corticosteroids, are not effective in preventing fibrosis or scars. Corneal transplantation, the only effective sight-restoring treatment for corneal scars, is curbed by challenges including a severe shortage of tissue, graft rejection, secondary conditions, cultural barriers, the lack of well-trained surgeons, operating rooms, and well-equipped infrastructures. Thanks to tremendous research efforts, emerging therapeutic options including gene therapy, protein therapy, cell therapy and novel molecules are in development to prevent the progression of corneal scarring and compliment the surgical options currently available for treating established corneal scars in clinics. In this article, we summarise the most relevant preclinical and clinical studies on emerging therapies for corneal scarring in recent years, showing how these approaches may prevent scarring in its early development.

Induced Pluripotent Stem Cell-Derived Corneal Cells: Current Status and Application

Deficiency and dysfunction of corneal cells leads to the blindness observed in corneal diseases such as limbal stem cell deficiency (LSCD) and bullous keratopathy. Regenerative cell therapies and engineered corneal tissue are promising treatments for these diseases [1]. However, these treatments are not yet clinically feasible due to inadequate cell sources. The discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka has provided a multitude of opportunities in research because iPSCs can be generated from somatic cells, thus providing an autologous and unlimited source for corneal cells. Compared to other stem cell sources such as mesenchymal and embryonic, iPSCs have advantages in differentiation potential and ethical concerns, respectively. Efforts have been made to use iPSCs to model corneal disorders and diseases, drug testing [2], and regenerative medicine [1]. Autologous treatments based on iPSCs can be exorbitantly expensive and time-consuming, but development of stem cell banks with human leukocyte antigen (HLA)- homozygous cell lines can provide cost- and time-efficient allogeneic alternatives. In this review, we discuss the early development of the cornea because protocols differentiating iPSCs toward corneal lineages rely heavily upon recapitulating this development. Differentiation of iPSCs toward corneal cell phenotypes have been analyzed with an emphasis on feeder-free, xeno-free, and well-defined protocols, which have clinical relevance. The application, challenges, and potential of iPSCs in corneal research are also discussed with a focus on hurdles that prevent clinical translation.

Advances in Regulatory Strategies of Differentiating Stem Cells towards Keratocytes

Corneal injury is a commonly encountered clinical problem which led to vision loss and impairment that affects millions of people worldwide. Currently, the available treatment in clinical practice is corneal transplantation, which is limited by the accessibility of donors. Corneal tissue engineering appears to be a promising alternative for corneal repair. However, current experimental strategies of corneal tissue engineering are insufficient due to inadequate differentiation of stem cell into keratocytes and thus cannot be applied in clinical practice. In this review, we aim to clarify the role and effectiveness of both biochemical factors, physical regulation, and the combination of both to induce stem cells to differentiate into keratocytes. We will also propose novel perspectives of differentiation strategy that may help to improve the efficiency of corneal tissue engineering.

Artificial Cornea: Past, Current, and Future Directions

Corneal diseases are a leading cause of blindness with an estimated 10 million patients diagnosed with bilateral corneal blindness worldwide. Corneal transplantation is highly successful in low-risk patients with corneal blindness but often fails those with high-risk indications such as recurrent or chronic inflammatory disorders, history of glaucoma and herpetic infections, and those with neovascularisation of the host bed. Moreover, the need for donor corneas greatly exceeds the supply, especially in disadvantaged countries. Therefore, artificial and bio-mimetic corneas have been investigated for patients with indications that result in keratoplasty failure. Two long-lasting keratoprostheses with different indications, the Boston type-1 keratoprostheses and osteo-odonto-keratoprostheses have been adapted to minimise complications that have arisen over time. However, both utilise either autologous tissue or an allograft cornea to increase biointegration. To step away from the need for donor material, synthetic keratoprostheses with soft skirts have been introduced to increase biointegration between the device and native tissue. The AlphaCor™, a synthetic polymer (PHEMA) hydrogel, addressed certain complications of the previous versions of keratoprostheses but resulted in stromal melting and optic deposition. Efforts are being made towards creating synthetic keratoprostheses that emulate native corneas by the inclusion of biomolecules that support enhanced biointegration of the implant while reducing stromal melting and optic deposition. The field continues to shift towards more advanced bioengineering approaches to form replacement corneas. Certain biomolecules such as collagen are being investigated to create corneal substitutes, which can be used as the basis for bio-inks in 3D corneal bioprinting. Alternatively, decellularised corneas from mammalian sources have shown potential in replicating both the corneal composition and fibril architecture. This review will discuss the limitations of keratoplasty, milestones in the history of artificial corneal development, advancements in current artificial corneas, and future possibilities in this field.

Corneal supply and the use of technology to reduce its demand: A review

Recovery and access to end-of-life corneal tissue for corneal transplantation, training and research is globally maldistributed. The reasons for the maldistribution are complex and multifaceted, and not well defined or understood. Currently there are few solutions available to effectively address these issues. This review provides an overview of the system, key issues impacting recovery and allocation and emphasises how end-user ophthalmologists and researchers, with support from administrators and the wider sector, can assist in increasing access long-term through sustaining eye banks nationally and globally. We posit that prevention measures and improved surgical techniques, together with the development of novel therapies will play a significant role in reducing demand and enhance the equitable allocation of corneas.

Stem cell therapy in ocular pathologies in the past 20 years

Stem cell therapies are successfully used in various fields of medicine. This new approach of research is also expanding in ophthalmology. Huge investments, resources and important clinical trials have been performed in stem cell research and in potential therapies. In recent years, great strides have been made in genetic research, which permitted and enhanced the differentiation of stem cells. Moreover, the possibility of exploiting stem cells from other districts (such as adipose, dental pulp, bone marrow stem cells, etc.) for the treatment of ophthalmic diseases, renders this topic fascinating. Furthermore, great strides have been made in biomedical engineering, which have proposed new materials and three-dimensional structures useful for cell therapy of the eye. The encouraging results obtained on clinical trials conducted on animals have given a significant boost in the creation of study protocols also in humans. Results are limited to date, but clinical trials continue to evolve. Our attention is centered on the literature reported over the past 20 years, considering animal (the most represented in literature) and human clinical trials, which are limiting. The aim of our review is to present a brief overview of the main types of treatments based on stem cells in the field of ophthalmic pathologies.

Effect of porcine corneal stromal extract on keratocytes from SMILE-derived lenticules

Propagating large amounts of human corneal stromal cells (hCSCs) in vitro while maintaining the physiological quality of their phenotypes is necessary for their application in cell therapy. Here, a novel medium to propagate hCSCs obtained from small incision lenticule extraction (SMILE)-derived lenticules was investigated and the feasibility of intrastromal injection of these hCSCs was assessed. Primary hCSCs were cultured in porcine corneal stroma extract (pCSE) with RIFA medium including ROCK inhibitor Y27632, insulin-transferrin-selenium, fibroblast growth factor 2, L-ascorbate 2-phosphate and 0.5% FBS (RIFA medium + pCSE). Protein profiling of the pCSE was identified using nanoscale liquid chromatography coupled to tandem mass spectrometry (nano LC-MS/MS). After subculturing in RIFA medium + pCSE or 10% FBS normal medium (NM), hCSCs at P4 were transplanted into mouse corneal stroma. Compared with NM, ALDH3A1, keratocan and lumican were significantly more expressed in the RIFA medium + pCSE. ALDH3A1 was also more expressed in the RIFA medium + pCSE than in the RIFA medium. Fibronectin and α-SMA were less expressed in the RIFA medium + pCSE than in the NM. Using Metascape analysis, the pCSE with its anti-fibrosis, pro-proliferation and anti-apoptosis activities, was beneficial for hCSC cultivation. The intrastromally implanted hCSCs in the RIFA medium + pCSE had positive CD34 expression but negative CD45 expression 35 days after injection. We provide a valuable new medium that is advantageous for the proliferation of hCSCs with the properties of physiological keratocytes. Intrastromal injection of hCSCs in RIFA medium + pCSE has the potential for clinical cell therapy.

Corneal Stroma Regeneration: New Approach for the Treatment of Cornea Disease

Corneal grafting is one of the most common forms of human tissue transplantation. The corneal stroma is responsible for many characteristics of the cornea. For these reasons, an important volume of research has been made to replicate the corneal stroma in the laboratory to find an alternative to classical corneal transplantation techniques.There is an increasing interest today in cell therapy of the corneal stroma using induced pluripotent stem cells or mesenchymal stem cells since these cells have shown to be capable of producing new collagen within the host stroma and even to improve its transparency.The first clinical experiment on corneal stroma regeneration in advanced keratoconus cases has been reported and included. Fourteen patients were randomized and enrolled into 3 experimental groups: (1) patients underwent implantation of autologous adipose-derived adult stem cells alone, (2) patients received decellularized donor corneal stroma laminas, and (3) patients received implantation of recellularized donor laminas with adipose-derived adult stem cells. Clinical improvement was detected with all cases in their visual, pachymetric, and topographic parameters of the operated corneas.Other recent studies have used allogenic SMILE implantation lenticule corneal inlays, showing also an improvement in different visual, topographic, and keratometric parameters.In the present report, we try to summarize the available preclinical and clinical evidence about the emerging topic of corneal stroma regeneration.

Corneal stroma regeneration: Preclinical studies

Corneal grafting is one of the most common and successful forms of human tissue transplantation in the world, but the need for corneal grafting is growing and availability of human corneal donor tissue to fulfill this increasing demand is not assured worldwide. The stroma is responsible for many features of the cornea, including its strength, refractive power and transparency, so enormous efforts have been put into replicating the corneal stroma in the laboratory to find an alternative to classical corneal transplantation. Unfortunately this has not been yet accomplished due to the extreme difficulty in mimicking the highly complex ultrastructure of the corneal stroma, and none of the obtained substitutes that have been assayed has been able to replicate this complexity yet. In general, they can neither match the mechanical properties nor recreate the local nanoscale organization and thus the transparency and optical properties of a normal cornea. In this context, there is an increasing interest in cellular therapy of the corneal stroma using Induced Pluripotent Stem Cells (iPSCs) or mesenchymal stem cells (MSCs) from either ocular or extraocular sources, as they have proven to be capable of producing new collagen within the host stroma, modulate preexisting scars and enhance transparency by corneal stroma remodeling. Despite some early clinical data is already available, in the current article we will summary the available preclinical evidence about the topic corneal stroma regeneration. Both, in vitro and in vivo experiments in the animal model will be shown.

Sphere-forming corneal cells repopulate dystrophic keratoconic stroma: Implications for potential therapy

BACKGROUND

Keratoconus is a degenerative corneal disease characterised by aberrant cell behaviour and loss of matrix that can result in vision loss. Cells extracted from peripheral corneas can form stem cell-enriched spheres, which have shown the potential to repopulate the normal peripheral corneal stroma in vitro upon sphere implantation but have not been previously studied in keratoconic tissue.

AIM

To investigate the therapeutic potential of stem cell-enriched spheres formed from extracted peripheral human corneal cells when introduced to keratoconic tissue.

METHODS

Stem cell-enriched spheres were formed from extracts of normal cadaveric human peripheral corneal cells. These spheres were implanted into incisions created in full thickness and onto the surface of 10 µm thin sections of keratoconic and normal stromal tissues in vitro. Tissue sections were used to maximise use of limited keratoconic tissue available for research. Living cells were stained with Calcein-AM and visualised with stereo and fluorescence microscopy to assess survival and behaviours between the time of implantation day 0 and 14 d (D14) from implantation. Sphere cells in implanted tissues were characterised for stem cell and differentiation markers using immunohistochemistry and droplet digital PCR to assess the potential implications of these characteristics in the use of spheres in keratoconus treatment.

RESULTS

Spheres were successfully implanted into full-thickness central corneal tissue and onto the surface of 10 µm thin en face tissue sections. No observable differences were seen in sphere migration, proliferation or differentiation in keratoconic tissue compared to normal between day 0 and D14. Spheres stained positively with Calcein-AM up to D14. Cell migration increased from day 0 to D14, occurring radially in three dimensions from the sphere and in alignment with tissue edges. Cell proliferation marker, EdU, was detected at day 10. Implanted spheres stained positively for putative stem cell markers ∆Np63α and ABCB5, while ABCG2, ABCB5, ∆Np63 and p63α were detectable by droplet digital PCR up to D14. Double immunolabelling revealed absence of ABCB5 staining in migrated cells but positive staining of alpha smooth muscle actin (myofibroblast marker) in some migrated cells. Droplet digital PCR showed similar expression patterns of differentiation markers but a reduction in stem cell markers between normal and keratoconic tissue with an increase in stromal cell markers and a reduction in epithelial cell markers, indicating an appropriate response to repopulating diseased tissue.

CONCLUSION

Cells from implanted stem cell-enriched spheres can repopulate a keratoconic corneal stromal surface in a directed manner and exhibit migratory stromal cell phenotypes.

Decellularization and recellularization of cornea: Progress towards a donor alternative

The global shortage of donor corneas for transplantation has led to corneal bioengineering being investigated as a method to generate transplantable tissues. Decellularized corneas are among the most promising materials for engineering corneal tissue since they replicate the complex structure and composition of real corneas. Decellularization is a process that aims to remove cells from organs or tissues resulting in a cell-free scaffold consisting of the tissues extracellular matrix. Here different decellularization techniques are described, including physical, chemical and biological methods. Analytical techniques to confirm decellularization efficiency are also discussed. Different cell sources for the recellularization of the three layers of the cornea, recellularization methods used in the literature and techniques used to assess the outcome of the implantation of such scaffolds are examined. Studies involving the application of decellularized corneas in animal models and human clinical studies are discussed. Finally, challenges for this technology are explored involving scalability, automatization and regulatory affairs.

Cellular therapy of the corneal stroma: a new type of corneal surgery for keratoconus and corneal dystrophies

Cellular therapy of the corneal stroma, with either ocular or extraocular stem cells, has been gaining a lot of interest over the last decade. Multiple publications from different research groups are showing its potential benefits in relation to its capacity to improve or alleviate corneal scars, improve corneal transparency in metabolic diseases by enhancing the catabolism of the accumulated molecules, generate new organized collagen within the host stroma, and its immunosuppressive and immunomodulatory properties. Autologous extraocular stem cells do not require a healthy contralateral eye and they do not involve any ophthalmic procedures for their isolation. Mesenchymal stem cells have been the most widely assayed and have the best potential to differentiate into functional adult keratocytes in vivo and in vitro. While embryonic stem cells have been partially abandoned due to ethical implications, the discovery of the induced pluripotent stem cells (iPSC) has opened a new and very promising field for future research as they are pluripotent cells with the capacity to theoretically differentiate into any cell type, with the special advantage that they are obtained from adult differentiated cells. Cellular delivery into the corneal stroma has been experimentally assayed in vivo in multiple ways: systemic versus local injections with or without a carrier. Encouraging preliminary human clinical data is already available although still very limited, and further research is necessary in order to consolidate the clinical applications of this novel therapeutic line.

Corneal cell therapy: with iPSCs, it is no more a far-sight

Human-induced pluripotent stem cells (hiPSCs) provide a personalized approach to study conditions and diseases including those of the eye that lack appropriate animal models to facilitate the development of novel therapeutics. Corneal disease is one of the most common causes of blindness. Hence, significant efforts are made to develop novel therapeutic approaches including stem cell-derived strategies to replace the diseased or damaged corneal tissues, thus restoring the vision. The use of adult limbal stem cells in the management of corneal conditions has been clinically successful. However, its limited availability and phenotypic plasticity necessitate the need for alternative stem cell sources to manage corneal conditions. Mesenchymal and embryonic stem cell-based approaches are being explored; nevertheless, their limited differentiation potential and ethical concerns have posed a significant hurdle in its clinical use. hiPSCs have emerged to fill these technical and ethical gaps to render clinical utility. In this review, we discuss and summarize protocols that have been devised so far to direct differentiation of human pluripotent stem cells (hPSCs) to different corneal cell phenotypes. With the summarization, our review intends to facilitate an understanding which would allow developing efficient and robust protocols to obtain specific corneal cell phenotype from hPSCs for corneal disease modeling and for the clinics to treat corneal diseases and injury.

Cellular Therapy With Human Autologous Adipose-Derived Adult Stem Cells for Advanced Keratoconus

PURPOSE

The aim of this phase 1 study was to preliminarily evaluate the safety and efficacy of autologous adipose-derived adult stem cell (ADASC) implantation within the corneal stroma of patients with advanced keratoconus.

METHODS

Five consecutive patients were selected. Autologous ADASCs were obtained by elective liposuction. ADASCs (3 × 10) contained in 1 mL saline were injected into the corneal stroma through a femtosecond-assisted 9.5-mm diameter lamellar pocket under topical anesthesia. Patients were reviewed at 1 day, 1 week, 1, 3, and 6 months postoperatively. Visual function, manifest refraction, slit-lamp biomicroscopy, intraocular pressure, endothelial cell density, corneal topography, corneal optical coherence tomography, and corneal confocal biomicroscopy were recorded.

RESULTS

No intraoperative or postoperative complications were recorded, with full corneal transparency recovery within 24 hours. Four patients completed the full follow-up. All patients improved their visual function (mean: 1 line of unaided and spectacle-corrected distance vision and 2 lines of rigid contact lens distance vision). Manifest refraction and topographic keratometry remained stable. Corneal optical coherence tomography showed a mean improvement of 16.5 μm in the central corneal thickness, and new collagen production was observed as patchy hyperreflective areas at the level of the stromal pocket. Confocal biomicroscopy confirmed the survival of the implanted stem cells at the surgical plane. Intraocular pressure and endothelial cell density remained stable.

CONCLUSIONS

Cellular therapy of the human corneal stroma in vivo with autologous ADASCs appears to be safe. Stem cells survive in vivo with intrastromal new collagen production. Future studies with larger samples are required to confirm these preliminary results.

Concise Review: Stem Cells for Corneal Wound Healing

Corneal wound healing is a complex process that occurs in response to various injuries and commonly used refractive surgery. It is a significant clinical problem, which may lead to serious complications due to either incomplete (epithelial) or excessive (stromal) healing. Epithelial stem cells clearly play a role in this process, whereas the contribution of stromal and endothelial progenitors is less well studied. The available evidence on stem cell participation in corneal wound healing is reviewed, together with the data on the use of corneal and non-corneal stem cells to facilitate this process in diseased or postsurgical conditions. Important aspects of corneal stem cell generation from alternative cell sources, including pluripotent stem cells, for possible transplantation upon corneal injuries or in disease conditions are also presented. Stem Cells 2017;35:2105-2114.

Wound-Healing Studies in Cornea and Skin: Parallels, Differences and Opportunities

The cornea and the skin are both organs that provide the outer barrier of the body. Both tissues have developed intrinsic mechanisms that protect the organism from a wide range of external threats, but at the same time also enable rapid restoration of tissue integrity and organ-specific function. The easy accessibility makes the skin an attractive model system to study tissue damage and repair. Findings from skin research have contributed to unravelling novel fundamental principles in regenerative biology and the repair of other epithelial-mesenchymal tissues, such as the cornea. Following barrier disruption, the influx of inflammatory cells, myofibroblast differentiation, extracellular matrix synthesis and scar formation present parallel repair mechanisms in cornea and skin wound healing. Yet, capillary sprouting, while pivotal in proper skin wound healing, is a process that is rather associated with pathological repair of the cornea. Understanding the parallels and differences of the cellular and molecular networks that coordinate the wound healing response in skin and cornea are likely of mutual importance for both organs with regard to the development of regenerative therapies and understanding of the disease pathologies that affect epithelial-mesenchymal interactions. Here, we review the principal events in corneal wound healing and the mechanisms to restore corneal transparency and barrier function. We also refer to skin repair mechanisms and their potential implications for regenerative processes in the cornea.

[Corneal cell therapy-an overview]

In recent years, the cultivation and expansion of primary corneal cells has made significant progress. The transplantation of cultured limbal epithelial cells represents a successful and established treatment of the ocular surface. Cultivated corneal endothelial cells are undergoing a clinical trial in Japan. Stromal keratocytes can now be expanded in vitro. A wide range of stem cell sources is being tested in vitro and animal models for their possible application in corneal cell therapy. This article gives an overview of recent advancements and prevailing limitations for the use of different cell sources in the therapy of corneal disease.