13 years of cultured limbal epithelial cell therapy: a review of the outcomes

Systematic review and meta-analysis investigating autograft versus allograft cultivated limbal epithelial transplantation in limbal stem cell deficiency

PURPOSE

Currently, regenerative medicine has attracted much attention among researchers investigating new methods to treat ocular surface diseases. Based on this new concept, cultivated limbal epithelial transplantation (CLET), whether in the form of autograft or allograft, has emerged as a promising surgical procedure for treating limbal stem cell deficiency (LSCD). Given that there is no updated comparison between autograft and allograft CLETs, the present review and meta-analysis aims to compare and determine the efficacy of two different CLET techniques, autologous versus allogeneic, based on a literature review of relevant studies.

METHODS

A comprehensive search of electronic databases, including PubMed, Web of Science, Cochrane Library, Embase and Scopus, for related articles was performed in March 2018 to obtain relevant articles and to conduct a meta-analysis investigating the success rate of ocular surface regeneration and two-line improvement in best-corrected visual acuity (BCVA) using autograft versus allograft transplantations.

RESULTS

A total of 30 studies, including 1306 eyes from 1288 patients with LSCD, with a sample size ranging from 6 to 200 and follow-up period of 0.6-156 months, were reviewed. Of 1306 eyes, 982 (75.2%) underwent autograft and 324 (24.8%) received allografts from living or deceased donors. Meta-analysis revealed that there was no significant difference between autograft and allograft CLETs in terms of success rate and two-line BCVA improvement. The prospective studies showed a zero difference between the two groups; only two retrospective studies included in the analysis pulled the autografts up to 1.82 and 1.2 times more than allografts in terms of success rate and two-line BCVA improvement, respectively [pooled OR 1.82 (95% CI 0.80-4.11); pooled OR 1.2 (95% CI 0.54-2.65)]. There was no statistically significant evidence of bias in the meta-analysis in terms of success rates and two-line BCVA improvement.

CONCLUSIONS

The present analysis revealed no significant differences in success rates or visual improvement between autograft and allograft surgical techniques.

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.

Early Results of Penetrating Keratoplasty in Patients With Unilateral Chemical Injury After Simple Limbal Epithelial Transplantation

PURPOSE

To evaluate clinical outcomes of sequential PKP in eyes with unilateral chemical injury, which have previously undergone autologous simple limbal epithelial transplantation (SLET) at a tertiary eye center in North India.

METHODS

This is a single-center, retrospective, noncomparative interventional case series reviewing patients with unilateral limbal stem cell deficiency treated by SLET and sequential PKP between 2012 and 2017. The primary outcome was defined as allograft survival, defined as a completely epithelialized, clear, avascular graft. The secondary outcome was improvement in best-corrected visual acuity by 2 lines or any complications.

RESULTS

Seven eyes of 7 patients, all aged below 40 years, who underwent SLET followed by PKP for unilateral ocular surface injury were included. Most of the patients were male (71.4%), and alkali injury (42.8%) was the most common cause of limbal stem cell deficiency. The mean duration between SLET and PK was 9.5 ± 11.9 months (2-36 mo), and the mean follow-up duration after PKP was 15.1 ± 5.4 months (6-21 mo). A successful outcome after SLET was achieved in all 7 patients and clear grafts in 6 patients, with a graft survival rate of 85% at 6 months. Visual success was noted in 4 patients. Poor vision in 3 patients was due to glaucoma, amblyopia, and graft failure.

CONCLUSIONS

PKP was found to have a good outcome when the surface has been stabilized by SLET as an initial procedure in unilateral ocular chemical injury. The visual outcome was restricted mainly by other causes such as glaucoma and amblyopia.

Limbal Stem Cell Transplantation: Clinical Results, Limits, and Perspectives

Limbal stem cell deficiency (LSCD) is a clinical condition characterized by damage of cornea limbal stem cells, which results in an impairment of corneal epithelium turnover and in an invasion of the cornea by the conjunctival epithelium. In these patients, the conjunctivalization of the cornea is associated with visual impairment and cornea transplantation has poor prognosis for recurrence of the conjunctivalization. Current treatments of LSCD are aimed at replacing the damaged corneal stem cells in order to restore a healthy corneal epithelium. The autotransplantation of limbal tissue from the healthy, fellow eye is effective in unilateral LSCD but leads to depauperation of the stem cell reservoir. In the last decades, novel techniques such as cultivated limbal epithelial transplantation (CLET) have been proposed in order to reduce the damage of the healthy fellow eye. Clinical and experimental evidence showed that CLET is effective in inducing long-term regeneration of a healthy corneal epithelium in patients with LSCD with a success rate of 70%–80%. Current limitations for the treatment of LSCD are represented by the lack of a marker able to unequivocally identify limbal stem cells and the treatment of total, bilateral LSCD which requires other sources of stem cells for ocular surface reconstruction.

Different Effects of Pro-Inflammatory Factors and Hyperosmotic Stress on Corneal Epithelial Stem/Progenitor Cells and Wound Healing in Mice

Chronic inflammation and severe dry eye are two important adverse factors for the successful transplant of cultured limbal stem cells. The aim of this study was to investigate the effects of inflammation and hyperosmotic stress (a key pathological factor in dry eye) on corneal epithelial stem cells (CESCs) and corneal epithelial wound healing. We observed that the CESCs exhibited significant morphological changes when treated with interleukin‐1 beta (IL‐1β), tumor necrosis factor alpha (TNF‐α), or hyperosmotic stress. Colony‐forming efficiency or colony‐forming size was decreased with the increasing concentrations of IL‐1β, TNF‐α, or hyperosmotic stress, which was exacerbated when treated simultaneously with pro‐inflammatory factors and hyperosmotic stress. However, the colony‐forming capacity of CESCs recovered more easily from pro‐inflammatory factor treatment than from hyperosmotic stress treatment. Moreover, when compared with pro‐inflammatory factors treatment, hyperosmotic stress treatment caused a more significant increase of apoptotic and necrotic cell numbers and cell cycle arrest in the G2/M phase. Furthermore, the normal ability of corneal epithelial wound healing in the mice model was suppressed by both pro‐inflammatory factors and hyperosmotic stress treatment, and especially severely by hyperosmotic stress treatment. In addition, inflammation combined with hyperosmotic stress treatment induced more serious epithelial repair delays and apoptosis in corneal epithelium. Elevated levels of inflammatory factors were found in hyperosmotic stress‐treated cells and mice corneas, which persisted even during the recovery period. The results suggested that pro‐inflammatory factors cause transient inhibition, while hyperosmotic stress causes severe apoptosis and necrosis, persistent cell cycle arrest of CESCs, and severe corneal wound healing delay. Stem Cells Translational Medicine2019;8:46–57

Comparative study of substrate free and amniotic membrane scaffolds for cultivation of limbal epithelial sheet

Transplantation of cultivated limbal epithelial transplantation has been proven to restore the corneal surface in limbal stem cell deficiency (LSCD). Here we comparatively investigated the optimized conditions and the efficiency of limbal epithelial sheet growth in three media conditions as well as with substrate free (transwell), human amniotic membrane (HAM) sutured onto transwell inserts (HAMTW), and HAM slide scaffold (HAMS). Outcomes evaluated were outgrowth sheet size from limbal explants, expression of stem/progenitor cell markers p63α, ABCG2 and CK15, and colony formation efficiency (CFE). Additionally, limbal epithelial sheets on HAMS were transplanted into corneas of LSCD rabbit models. Limbal epithelial sheets with 5% human AB serum showed the greatest increase in ABCG2 efflux activity (JC1^low), p63α expression, and CFE compared in both conditions without HAM and with HAM, respectively. The outgrowth sheet size, cell yield, and Ki67 expression were increased in limbal epithelial sheets on HAMS compared to transwell and HAMTW. ABCG2 efflux activity, p63α and CK15 expressions, and CFE were also increased in limbal epithelial sheets on HAMS as well. In corneas of transplanted rabbit LSCD models, p63α expressions were noted in the basal layers and CK12 expressions were observed in superficial layers. Cultivation of limbal epithelial sheet on HAMS with xeno-free medium enhances the growth and stemness of limbal epithelial sheets.

Twenty years of limbal epithelial therapy: an update on managing limbal stem cell deficiency

Limbal stem cell damage after chemical injury, autoimmune disorders or iatrogenic trauma leads to corneal conjunctivalisation with new vessel formation, epithelium instability and visual loss. Limbal stem cell transplantation includes reconstructive surgical procedures to restore a corneal epithelium. The recognised options are: conjunctival limbal autograft, in which stem cells are taken from the patient's healthy eye; conjunctival limbal allograft, in which stem cells are taken from a living, related or dead donor and the keratolimbal allograft. Each of these procedures has some drawbacks; in particular, the conjunctival limbal autograft needs a relatively healthy fellow eye and needs a relatively large amount of donor tissue from the healthy eye (about one-third of the healthy limbal stem cell tissue) with potential risks to the donor eye. In the case of keratolimbal allograft transplants, the recipient needs an immunosuppressive treatment to reduce the risk of rejection with the associate possible side effects. More modern treatment options are reviewed. Cultivated oral mucosa epithelial transplantation success rate can vary between 50% and 70% at 3-4 years of follow-up. Simple limbal epithelial transplantation results show a success rate from 75.2% to 83.8% after 1 year of follow-up. Inclusion criteria for autologous cultivated limbal epithelial transplantation as approved by the National Institute of Health and Care Excellence are also shown in this paper. On the basis of these more contemporary treatment options, a stepladder approach to evaluate which procedure is most appropriate and personalised to the patient's conditions is proposed.

Amniotic Membrane Extract Eye Drop Promotes Limbal Stem Cell Proliferation and Corneal Epithelium Healing

Objective

Human amniotic membrane (HAM) is used as a supporter for limbal stem cell (LSC) expansion and corneal surgery. The aim of study is to use HAM extracts from healthy donors to enhance proliferation of LSCs in vitro and in vivo.

Materials and Methods

In this interventional experimental study, the effective and cytotoxic doses of the amniotic membrane extract eye drops (AMEED) was assessed by adding different concentrations of AMEED (0-2.0 mg/ml) to LSC cultures for 14 days. Subsequently, the expression levels of ATP-binding cassette sub-family G member 2 (ABCG2, a putative stem cell marker), cytokeratin 3 (K3, corneal maker), K12 and K19 (corneal-conjunctival cell makers) were assessed by real-time polymerase chain reaction (PCR). In the second step, the corneal epithelium of 10 rabbits was mechanically removed, and the right eye of each rabbit was treated with 1 mg/ml AMEED [every 2 hours (group 1) or every 6 hours (group 2)]. The left eyes only received an antibiotic. The corneal healing process, conjunctival infection, degree of eyelid oedema, degree of photophobia, and discharge scores were evaluated during daily assessments. Finally, corneal tissues were biopsied for pathologic evidences.

Results

In comparison to the positive control [10% foetal bovine serum (FBS)], 0.1-1 mg/ml AMEED induced LSC proliferation, upregulated ABCG2, and downregulated K3. There were no remarkable differences in the expression levels of K12 and K19 (P>0.05). Interestingly, in the rabbits treated with AMEED, the epithelium healing duration decreased from 4 days in the control group to 3 days in the two AMEED groups, with lower mean degrees of eyelid oedema, chemosis, and infection compared to the control group. No pathologic abnormalities were observed in either of the AMEED groups.

Conclusion

AMEED increases LSCs proliferation ex vivo and accelerates corneal epithelium healing in vivo without any adverse effects. It could be used as a supplement for LSC expansion in cell therapy.

The current state of stem cell therapy for ocular disease

Herein, we review the safety, efficacy, regulatory standards and ethical implications of the use of stem cells in ocular disease. A literature review was conducted, registered clinical trials reviewed, and expert opinions sought. Guidelines and codes of conduct from international societies and professional bodies were also reviewed. Collated data is presented on current progress in the field of ocular regenerative medicine, future challenges, the clinical trial process and ethical considerations in stem cell therapy. A greater understanding of the function and location of ocular stem cells has led to rapid advances in possible therapeutic applications. However, in the context of significant technical challenges and potential long-term complications, it is imperative that stem cell practices operate within formal clinical trial frameworks. While there remains broad scope for innovation, ongoing evidence-based review of potential interventions and the development of standardized protocols are necessary to ensure patient safety and best practice in ophthalmic care.

Pigmentation Is Associated with Stemness Hierarchy of Progenitor Cells Within Cultured Limbal Epithelial Cells

Ex vivo cultured human limbal epithelial stem/progenitor cells (hLESCs) are the main source for regenerative therapy of limbal stem cell deficiency (LSCD), which is worldwide one of the major causes of corneal blindness. Despite many stemness-associated markers have been identified within the limbal niche, the phenotype of the earliest hLESCs has not been hitherto identified. We sought to confirm or refute the use of tumor protein p63 (p63) and ATP binding cassette subfamily B member 5 (ABCB5) as surrogate markers for hLESCs early within the limbal differentiation hierarchy. Based on a robust fluorescence-activated cell sorting and subsequent RNA isolation protocol, a comprehensive transcriptomic profile was obtained from four subpopulations of cultured hLESCs. The subpopulations were defined by co-expression of two putative stem/progenitor markers, the p63 and ABCB5, and the corneal differentiation marker cytokeratin 3. A comparative transcriptomic analysis yielded novel data that indicated association between pigmentation and differentiation, with the p63 positive populations being the most pigmented and immature of the progenitors. In contrast, ABCB5, either alone or in co-expression patterns, identified more committed progenitor cells with less pigmentation. In conclusion, p63 is superior to ABCB5 as a marker for stemness. Stem Cells 2018;36:1411-1420.

Repairing the corneal epithelium using limbal stem cells or alternative cell-based therapies

INTRODUCTION

The corneal epithelium is maintained by limbal stem cells (LSCs) that reside in the basal epithelial layer of the tissue surrounding the cornea termed the limbus. Loss of LSCs results in limbal stem cell deficiency (LSCD) that can cause severe visual impairment. Patients with partial LSCD may respond to conservative therapies designed to rehabilitate the remaining LSCs. However, if these conservative approaches fail or, if complete loss of LSCs occurs, transplantation of LSCs or their alternatives is the only option. While a number of clinical studies utilizing diverse surgical and cell culture techniques have shown favorable results, a universal cure for LSCD is still not available. Knowledge of the potential risks and benefits of current approaches, and development of new technologies, is essential for further improvement of LSCD therapies.

AREAS COVERED

This review focuses on cell-based LSCD treatment approaches ranging from current available clinical therapies to preclinical studies of novel promising applications.

EXPERT OPINION

Improved understanding of LSC identity and development of LSC expansion methods will influence the evolution of successful LSCD therapies. Ultimately, future controlled clinical studies enabling direct comparison of the diverse employed approaches will help to identify the most effective treatment strategies.

Results of simple limbal epithelial transplantation in unilateral ocular surface burn

Purpose:

This study aimed to report the long-term outcomes of autologous Simple Limbal Epithelial Transplantation (SLET) performed for unilateral limbal stem cell deficiency (LSCD) following chemical burn at a tertiary eye center in North India.

Methods:

This was a single-center prospective interventional case series of patients who developed unilateral LSCD after suffering from ocular surface burns and who underwent SLET between October 2012 and May 2016 with a follow-up period of at least 6 months. The primary outcome measure was restoration of a completely epithelized, stable, and avascular corneal surface. The secondary outcome measure was percentage of eyes, which reported visual gain.

Results:

The study included 30 eyes of 30 patients, 18 adults and 12 children, at a median follow-up of 1.1 years (range: 6 months to 3.5 years), 21 of 30 eyes (70%; 95% confidence interval, 53.6%–86.2%) maintained successful outcome. Visual acuity gain was seen in 71.4% of successful cases. The clinical factors associated with failure were identified as acid injury, severe symblepharon at the time of presentation, and SLET combined with penetrating keratoplasty (PK).

Conclusion:

Autologous SLET is an effective limbal cell transplantation technique for the treatment of unilateral LSCD. It is especially beneficial for centers where cell cultivation laboratory is unavailable. Presence of severe symblepharon, which requires PK peroperatively, has poor outcome.

Limbal Stem Cell Deficiency-Demography and Underlying Causes

PURPOSE

To determine the demographic features of patients affected by limbal stem cell deficiency (LSCD), and to identify the underlying causes of LSCD.

DESIGN

Retrospective, multicenter case series.

SETTING

Two large tertiary care ophthalmology hospitals.

SUBJECTS

Patients with a diagnosis of LSCD presenting from January 1, 2005 to December 31, 2014.

METHODS

Records of patients with a clinical diagnosis of LSCD were reviewed. Demographic details and clinical features at presentation, as well as the underlying cause of LSCD (if identified), were noted. Descriptive statistical analysis and chart preparation were done. Main outcome measures were type of LSCD (unilateral or bilateral), age and sex of patients, extent of LSCD (clock hours of limbus involved), and underlying cause of LSCD.

RESULTS

We found 1331 patients with LSCD in the 10-year period under study. Unilateral LSCD was more common (791 patients) than bilateral LSCD (540 patients). Out of 1331 patients, 875 (65.74%) were male. The median age of patients was 24 years. Extent of LSCD could be determined in 1849 eyes, of which 1239 eyes (67.00%) had total LSCD. The underlying cause of LSCD could be identified in 1512 eyes. In cases of unilateral LSCD, ocular surface burns was the commonest identifiable cause (83.73%). The leading identifiable causes of bilateral LSCD were ocular surface burns (29.95%), allergic conjunctivitis (29.48%), Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) (23.11%), aniridia (9.43%), and mucous membrane pemphigoid (3.54%). Lime ("chuna") injury was responsible for ocular surface burns in 352 out of 567 cases in which the agent was identified (62.08%).

CONCLUSIONS

In our study, unilateral LSCD was more common than bilateral LSCD. Young male subjects were commonly affected, with a majority of eyes suffering from total LSCD. Overall, ocular surface burns are the leading cause of LSCD. Unilateral and bilateral LSCD had a markedly different distribution of causes, necessitating different approaches to management.

Simple limbal epithelial transplantation (SLET) in failed cultivated limbal epithelial transplantation (CLET) for unilateral chronic ocular burns

AIMS

Cultivated limbal epithelial transplantation (CLET) fails in around 20%-30% of cases. This study aimed to report the clinical outcomes of autologous simple limbal epithelial transplantation (SLET) in eyes with recurrent unilateral limbal stem cell deficiency (LSCD) due to failure of CLET.

METHODS

This was a prospective case series which included 30 eyes of 30 patients who underwent SLET between 2010 and 2016 after failure of one (n=24) or two (n=6) previous CLET procedures for chronic unilateral ocular burns. The primary outcome measure was success of SLET defined on the basis of relative improvement in five objective criteria: best corrected visual acuity (BCVA), and grades of symblepharon, corneal conjunctivalisation, vascularisation and opacification.

RESULTS

At a mean follow-up of 2.3 years, 24 (80%) of the 30 eyes maintained a successful outcome. Kaplan-Meier analysis showed a 5-year survival probability of 77%±8%. At 1 year postoperatively statistically significant improvement was noted in BCVA (logarithm of the minimum angle of resolution of 3 to 1) and in the median grades of corneal conjunctivalisation (2 to 0), vascularisation (2 to 0) and opacification (2 to 1) (P≤0.0026). In 62.5% of successful cases, BCVA improved to 20/200 or better. The success rate of SLET in failed CLET was better than that of repeat CLET (53.5%, P=0.011). None of the donor eyes developed any complications.

CONCLUSION

SLET is an effective alternative to CLET in eyes with recurrence of LSCD after previously failed CLET procedures. Since SLET is single-staged and less expensive, it is probably preferable to repeating CLET.

Native and synthetic scaffolds for limbal epithelial stem cell transplantation

Limbal stem cell deficiency (LSCD) is a complex blinding disease of the cornea, which cannot be treated with conventional corneal transplants. Instead, a stem cell (SC) graft is required to replenish the limbal epithelial stem cell (LESC) reservoir, which is ultimately responsible for regenerating the corneal epithelium. Current therapies utilize limbal tissue biopsies that harbor LESCs as well as tissue culture expanded cells. Typically, this tissue is placed on a scaffold that supports the formation of corneal epithelial cell sheets, which are then transferred to diseased eyes. A wide range of biological and synthetic materials have been identified as carrier substrates for LESC, some of which have been used in the clinic, including amniotic membrane, fibrin, and silicon hydrogel contact lenses, each with their own advantages and limitations. This review will provide a brief background of LSCD, focusing on bio-scaffolds that have been utilized in limbal stem cell transplantation (LSCT) and materials that are being developed as potentially novel therapeutics for patients with this disease.

STATEMENT OF SIGNIFICANCE

The outcome of patients with corneal blindness that receive stem cell grafts to restore eye health and correct vision varies considerably and may be due to the different biological and synthetic scaffolds used to deliver these cells to the ocular surface. This review will highlight the positive attributes and limitations of the myriad of carriers developed for clinical use as well as those that are being trialled in pre-clinical models. The overall focus is on developing a standardized therapy for patients, however due to the multiple causes of corneal blindness, a personal regenerative medicine approach may be the best option.

Navigating Market Authorization: The Path Holoclar Took to Become the First Stem Cell Product Approved in the European Union

Gene therapy, cell therapy, and tissue engineering have the potential to revolutionize the treatment of disease and injury. Attaining marketing authorization for such advanced therapy medicinal products (ATMPs) requires a rigorous scientific evaluation by the European Medicines Agency—authorization is only granted if the product can fulfil stringent requirements for quality, safety, and efficacy. However, many ATMPs are being provided to patients under alternative means, such as “hospital exemption” schemes. Holoclar (ex vivo expanded autologous human corneal epithelial cells containing stem cells), a novel treatment for eye burns, is one of the few ATMPs to have been granted marketing authorization and is the first containing stem cells. This review highlights the differences in standards between an authorized and unauthorized medicinal product, and specifically discusses how the manufacture of Holoclar had to be updated to achieve authorization. The result is that patients will have access to a therapy that is manufactured to high commercial standards, and is supported by robust clinical safety and efficacy data. stemcellstranslationalmedicine2018;7:146–154

Comparison of culture media indicates a role for autologous serum in enhancing phenotypic preservation of rabbit limbal stem cells in explant culture

In this study, we aimed to compare the effects of six different cell culture media and autologous serum (AS) on the phenotypic characteristics of rabbit limbal epithelial stem cells (LESC) cultivated on porous polyethylene terephthalate (PET) membranes. Limbal explants from rabbit corneas were grown on PET membrane inserts in five different media: DMEM-F12 with fetal bovine serum (FBS) (DMEM-F12-FBS), with pluripotin (DMEM-F12-pluripotin) and with autologous serum (DMEM-F12-AS), Epilife, Keratinocyte Serum Free Medium (KSFM) and Defined-Keratinocyte Serum Free Medium. The effects of different media were evaluated by total cell yield from explants, measuring the expression of proteins by immunofluorescence and gene expression by Real Time PCR. In all five media tested, most of the limbal epithelial cells (LEC) which proliferated from explants were positive for cytokeratin (CK) 14 (85-90%), indicating that all five media support the growth of LESC from explants. The expression of differentiation markers; CK 3 and 12 was highest in DMEM-F12-FBS (56%), was lower in Epilife and KSFM (26 and 19%, respectively), with the lowest values (13%) obtained in DMEM-F12-AS. Gene expression of limbal cultures on PET membrane inserts was compared to fresh limbal tissue. In DMEM-F12-FBS, DMEM-F12-pluripotin, and DMEM-F12-AS, expression of potential LESC markers CXCR4 and polycomb complex protein BMI-1 were similar to limbal tissue. DMEM-F12 with 10% AS maintained a higher percentage of potential stem cell marker genes and lower expression of genes involved in differentiation compared to Epilife or KSFM. Our study shows that rabbit LEC can be cultivated on PET inserts using DMEM-F12 with autologous serum without a requirement for amniotic membrane or feeder cells.

Limbal stem cells: identity, developmental origin, and therapeutic potential

The cornea is our window to the world and our vision is critically dependent on corneal clarity and integrity. Its epithelium represents one of the most rapidly regenerating mammalian tissues, undergoing full-turnover over the course of approximately 1-2 weeks. This robust and efficient regenerative capacity is dependent on the function of stem cells residing in the limbus, a structure marking the border between the cornea and the conjunctiva. Limbal stem cells (LSC) represent a quiescent cell population with proliferative capacity residing in the basal epithelial layer of the limbus within a cellular niche. In addition to LSC, this niche consists of various cell populations such as limbal stromal fibroblasts, melanocytes and immune cells as well as a basement membrane, all of which are essential for LSC maintenance and LSC-driven regeneration. The LSC niche's components are of diverse developmental origin, a fact that had, until recently, prevented precise identification of molecularly defined LSC. The recent success in prospective LSC isolation based on ABCB5 expression and the capacity of this LSC population for long-term corneal restoration following transplantation in preclinical in vivo models of LSC deficiency underline the considerable potential of pure LSC formulations for clinical therapy. Additional studies, including genetic lineage tracing of the developmental origin of LSC will further improve our understanding of this critical cell population and its niche, with important implications for regenerative medicine. WIREs Dev Biol 2018, 7:e303. doi: 10.1002/wdev.303 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cells and Disease Adult Stem Cells, Tissue Renewal, and Regeneration > Tissue Stem Cells and Niches Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration.

Limbal Stem Cell Deficiency and Treatment with Stem Cell Transplantation

The cornea is the outermost tissue of the eye and it must be transparent for the maintenance of good visual function. The superficial epithelium of the cornea, which is renewed continuously by corneal stem cells, plays a critical role in the permanence of this transparency. These stem cells are localized at the cornea-conjunctival transition zone, referred to as the limbus. When this zone is affected/destroyed, limbal stem cell deficiency ensues. Loss of limbal stem cell function allows colonization of the corneal surface by conjunctival epithelium. Over 6 million people worldwide are affected by corneal blindness, and limbal stem cell deficiency is one of the main causes. Fortunately, it is becoming possible to recover vision by autologous transplantation of limbal cells obtained from the contralateral eye in unilateral cases. Due to the potential risks to the donor eye, only a small amount of tissue can be obtained, in which only 1-2% of the limbal epithelial cells are actually limbal stem cells. Vigorous attempts are being made to expand limbal stem cells in culture to preserve or even enrich the stem cell population. Ex vivo expanded limbal stem cell treatment in limbal stem cell deficiency was first reported in 1997. In the 20 years since, various protocols have been developed for the cultivation of limbal epithelial cells. It is still not clear which method promotes effective stem cell viability and this remains a subject of ongoing research. The most preferred technique for limbal cell culture is the explant culture model. In this approach, a small donor eye limbal biopsy is placed as an explant onto a biocompatible substrate (preferably human amniotic membrane) for expansion. The outgrowth (cultivated limbal epithelial cells) is then surgically transferred to the recipient eye. Due to changing regulations concerning cell-based therapy, the implementation of cultivated limbal epithelial transplantation in accordance with Good Laboratory Practice using xenobiotic-free systems is becoming widely accepted both in Turkey and worldwide.

Pluripotent Stem Cells and Other Innovative Strategies for the Treatment of Ocular Surface Diseases

The cornea provides two thirds of the refractive power of the eye and protection against insults such as infection and injury. The outermost tissue of the cornea is renewed by stem cells located in the limbus. Depletion or destruction of these stem cells may lead to blinding limbal stem cell deficiency (LSCD) that concerns millions of patients around the world. Innovative strategies based on adult stem cell therapies have been developed in the recent years but they are still facing numerous unresolved issues, and the long term results can be deceiving. Today there is a clear need to improve these therapies, and/or to develop new approaches for the treatment of LSCD. Here, we review the current cell-based therapies used for the treatment of ocular diseases, and discuss the potential of pluripotent stem cells (embryonic and induced pluripotent stem cells) in corneal repair. As the secretion of paracrine factors is known to have a crucial role in maintaining stem cell homeostasis and in wound repair, we also consider the therapeutic potential of a promising novel pathway, the exosomes. Exosomes are nano-sized vesicles that have the ability to transfer RNAs and proteins to recipient cells, and several studies demonstrated their role in cell protection and wound healing. Exosomes could circumvent the hurdles of stem-cell based approaches, and they could become a strong candidate as an alternative therapy for ocular surface diseases.

Human adipose-derived stem cells support the growth of limbal stem/progenitor cells

The most efficient method to expand limbal stem cells (LSCs) in vitro for clinical transplantation is to culture single LSCs directly on growth-arrested mouse fibroblast 3T3 cells. To reduce possible xenobiotic contamination from 3T3s, primary human adipose-derived stem cells (ASCs) were examined as feeder cells to support the expansion of LSCs in vitro. To optimize the ASC-supported culture, freshly isolated limbal epithelial cells in the form of single cells (SC-ASC) or cell clusters (CC-ASC) were cultured using three different methods: LSCs seeded directly on feeder cells, a 3-dimensional (3D) culture system and a 3D culture system with fibrin (fibrin 3D). The expanded LSCs were examined at the end of a 2-week culture. The standard 3T3 culture served as control. Expansion of SC-ASC showed limited proliferation and exhibited differentiated morphology. CC-ASC generated epithelial cells with undifferentiated morphology in all culture methods, among which CC-ASC in 3D culture supported the highest cell doubling (cells doubled 9.0 times compared to cells doubled 4.9 times in control) while maintained the percentage of putative limbal stem/progenitor cells compared to the control. There were few cell-cell contacts between cultured LSCs and ASCs in 3D CC-ASC. In conclusion, ASCs support the growth of LSCs in the form of cell clusters but not in single cells. 3D CC-ASC could serve as a substitute for the standard 3T3 culture to expand LSCs.

Gamma-irradiated human amniotic membrane decellularised with sodium dodecyl sulfate is a more efficient substrate for the ex vivo expansion of limbal stem cells

The gold standard substrate for the ex vivo expansion of human limbal stem cells (LSCs) remains the human amniotic membrane (HAM) but this is not a defined substrate and is subject to biological variability and the potential to transmit disease. To better define HAM and mitigate the risk of disease transmission, we sought to determine if decellularisation and/or γ-irradiation have an adverse effect on culture growth and LSC phenotype. Ex vivo limbal explant cultures were set up on fresh HAM, HAM decellularised with 0.5M NaOH, and 0.5% (w/v) sodium dodecyl sulfate (SDS) with or without γ-irradiation. Explant growth rate was measured and LSC phenotype was characterised by histology, immunostaining and qRT-PCR (ABCG2, ΔNp63, Ki67, CK12, and CK13). Ƴ-irradiation marginally stiffened HAM, as measured by Brillouin spectromicroscopy. HAM stiffness and γ-irradiation did not significantly affect the LSC phenotype, however LSCs expanded significantly faster on Ƴ-irradiated SDS decellularised HAM (p<0.05) which was also corroborated by the highest expression of Ki67 and putative LSC marker, ABCG2. Colony forming efficiency assays showed a greater yield and proportion of holoclones in cells cultured on Ƴ-irradiated SDS decellularised HAM. Together our data indicate that SDS decellularised HAM may be a more efficacious substrate for the expansion of LSCs and the use of a γ-irradiated HAM allows the user to start the manufacturing process with a sterile substrate, potentially making it safer.

STATEMENT OF SIGNIFICANCE

Despite its disadvantages, including its biological variability and its ability to transfer disease, human amniotic membrane (HAM) remains the gold standard substrate for limbal stem cell (LSC) culture. To address these disadvantages, we used a decellularised HAM sterilised by gamma-irradiation for LSC culture. We cultured LSCs on fresh HAM, HAM decellularised with NaOH, HAM decellularised with sodium dodecyl sulfate (SDS) and HAM decellularised with SDS and sterilised with gamma-irradiation. We demonstrated that although HAM decellularised with SDS and sterilised with gamma-irradiation is significantly stiffer this does not affect LSC culture growth rate or the phenotype of cultured LSCs. We therefore recommend the use of SDS decellularised gamma-irradiated HAM in future LSC clinical trials.

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.

Laminin-511 and -521-based matrices for efficient ex vivo-expansion of human limbal epithelial progenitor cells

Optimization of culture conditions for human limbal epithelial stem/progenitor cells (LEPC) that incorporate the in vivo cell-matrix interactions are essential to enhance LEPC ex vivo-expansion and transplantation efficiency. Here, we investigate the efficacy of laminin (LN) isoforms preferentially expressed in the limbal niche as culture matrices for epithelial tissue engineering. Analyses of expression patterns of LN chains in the human limbal niche provided evidence for enrichment of LN-α2, -α3, -α5, -β1, -β2, -β3, -γ1, -γ2 and -γ3 chains in the limbal basement membrane, with LN-α5 representing a signature component specifically produced by epithelial progenitor cells. Recombinant human LN-521 and LN-511 significantly enhanced in vitro LEPC adhesion, migration and proliferation compared to other isoforms, and maintained phenotype stability. The bioactive LN-511-E8 fragment carrying only C-terminal domains showed similar efficacy as full-length LN-511. Functional blocking of α3β1 and α6β1 integrins suppressed adhesion of LEPC to LN-511/521-coated surfaces. Cultivation of LEPC on fibrin-based hydrogels incorporating LN-511-E8 resulted in firm integrin-mediated adhesion to the scaffold and well-stratified epithelial constructs, with maintenance of a progenitor cell phenotype in their (supra)basal layers. Thus, the incorporation of chemically defined LN-511-E8 into biosynthetic scaffolds represents a promising approach for xeno-free corneal epithelial tissue engineering for ocular surface reconstruction.

Cultivated limbal epithelial transplantation

PURPOSE OF REVIEW

To provide an updated literature review on the status of cultivated limbal (corneal) epithelial transplantation. Cultivated limbal stem-cell transplantation recently received regulatory approval. We provide a comprehensive overview of recent developments in the field.

RECENT FINDINGS

The current article reviews and highlights recent developments in the field of cultivated limbal stem-cell transplantation as retrieved from a literature search for the last year.

SUMMARY

The implications of clinical/research findings in terms of transplanted cell source and cultivation methods in limbal stem-cell transplantation are reviewed.

A hyaluronan hydrogel scaffold-based xeno-free culture system for ex vivo expansion of human corneal epithelial stem cells

PurposeTo develop a hyaluronan hydrogel scaffold-based xeno-free culture system for ex vivo cultivation of human corneal epithelial stem cells (CESCs).Patients and MethodsCESCs were cultivated from donor limbal explants on the HyStem-C Hydrogel bio-scaffold in 12-well plates for 3 weeks. Group A used the traditional supplemented hormonal epidermal medium (SHEM) and group B used the defined SHEM (without fetal bovine serum and toxin A, adding 20% serum replacement). The growth and morphology of the cultured cells were assessed by phase contrast microscope. The expressions of specific cell markers were assessed by immunofluorescence staining and quantitative real-time PCR (qRT-PCR).ResultsSuccessful cultures of CESCs were obtained in both groups, resulting in multilayered stratified epithelia. Comparing to group A, the cells in group B was grown slightly slower and formed less cellular layers at the end of culture. The corneal specific cytokeratin (K) 12 and differentiation markers, involucrin, and connexin 43, were mainly expressed in the superficial cellular layers in both groups. Interestingly, certain basal cells were immune-positive to proposed stem cell markers such as K19, ABCG2, and integrin β1 in both groups. There was no significant difference between the two groups with regard to the gene expression levels of all these selected corneal markers (all P>0.05).ConclusionsThe hyaluronan hydrogel scaffold-based xeno-free culture system may support the expansion of regenerative CESCs without the risk of xeno component contamination. The regenerated epithelium maintains similar characteristics of native corneal epithelium.

Allogenic cultivated limbal stem cell transplantation versus cadaveric keratolimbal allograft in ocular surface disorder: 1-year outcome

PURPOSE

To compare the outcome of allogenic ex vivo cultivated limbal stem cell transplantation (LSCT) versus cadaveric keratolimbal allograft in patients with limbal stem cell deficiency (LSCD).

METHODS

In this prospective interventional study from Army Hospital Research and Referral in New Delhi, 50 eyes of 40 patients with ocular surface disorder having LSCD underwent either cultivated LSCT (group 1: 25 eyes of 20 patients) or keratolimbal allograft transplantation (group 2: 25 eyes of 20 patients). The outcome measures were gain of two or more lines of best-corrected visual acuity (BCVA), absence of conjunctival vascularization over cornea, corneal neovascularization regression, regression of visually significant corneal opacity (iris details poorly visible), Schirmer's 1 ≥10 s, tear break-up time (TBUT) ≥10 s, and absence of fluorescein staining.

RESULTS

At 1 year of follow-up, both groups experienced significant improvement in all outcome measures, but there was no significant difference between both groups in improvement of two or more lines of BCVA (P = 0.841), absence of conjunctival vascularization over cornea (P = 0.812), corneal neovascularization (P = 0.074), visually significant corneal opacity (P = 0.075), Schirmer's 1 ≥10 s (P = 0.814), TBUT ≥10 s (P = 0.382), or absence of fluorescein stain (P = 1.00).

CONCLUSION

Both allogenic ex vivo cultivated LSCT and cadaveric keratolimbal allograft transplantation are comparable in terms of visual gain and ocular surface restoration.

Successful Consecutive Expansion of Limbal Explants Using a Biosafe Culture Medium under Feeder Layer-Free Conditions

PURPOSE

Transplantation of in vitro cultured limbal epithelial stem cells (LESCs) is a treatment widely used for LESC deficiency. However, the number of limbal tissue donors is limited, and protocols for LESC cultivation often include compounds and/or feeder layers that can induce side effects and/or increase the cost of the culture procedure. We investigated the feasibility of obtaining more than one limbal primary culture (LPC) from the same biopsy using a culture medium in which several potentially harmful compounds were replaced at the same time by biosafe supplements, allowing the LESC cultivation without feeder layers.

MATERIALS AND METHODS

We established feeder layer-free LPCs with three culture media: (1) a modified supplemental hormonal epithelial medium, containing potential harmful components (cholera toxin, dimethylsulfoxide, and fetal bovine serum [FBS]), (2) IOBA-FBS, a medium with FBS but with no other harmful supplements, and (3) IOBA-HS, similar to IOBA-FBS but with human serum instead of FBS. Additionally, the same limbal explant was consecutively cultured with IOBA-HS producing three cultures. LPCs were characterized by real-time reverse transcription polymerase chain reaction and/or immunofluorescence.

RESULTS

LPCs cultured with the three media under feeder layer-free conditions showed cuboidal cells and no significant differences in the percentage of positive cells for limbal (ABCG2, p63, and K14) and corneal (K3, K12) proteins. Except for ABCG2, the relative mRNA expression of the LESC markers was significantly higher when IOBA-FBS or IOBA-HS was used. LPC1 showed characteristics similar to LPC0, while LPC2 cell morphology became elongated and the expression of some LESC markers was diminished.

CONCLUSION

IOBA-HS enables the culturing of up to two biosafe homologous LPCs from one limbal tissue under feeder layer-free conditions. The routine use of this culture medium could improve both the biosafety and the number of available LPCs for potential clinical transplantation, as well as decrease the expense of the culture procedure.

Supra-organization and optical anisotropies of the extracellular matrix in the amniotic membrane and limbal stroma before and after explant culture

In this research we evaluated the supramolecular organizations and the optical anisotropical properties of the de-epithelialized human amniotic membrane and rabbit limbal stroma, before and after explant culture. Birefringence, monochromatic light spectral absorption and linear dichroism of the main extracellular matrix biopolymers, that is, the fibrillar collagens and proteoglycans, were investigated by polarized light microscopy combined with image analysis. Our results demonstrated that the culture procedure-induced stimuli altered the supra-organizational characteristics (in terms of collagens/proteoglycans spatial orientation and ordered-aggregational state) of the amniotic and limbal extracellular matrix, which led to changes in optical anisotropical properties.

Limbal Stem Cells from Aged Donors Are a Suitable Source for Clinical Application

Limbal stem cells (LSC) are the progenitor cells that maintain the transparency of the cornea. Limbal stem cell deficiency (LSCD) leads to corneal opacity, inflammation, scarring, and blindness. A clinical approach to treat this condition consists in LSC transplantation (LSCT) after ex vivo expansion of LSC. In unilateral LSCD, an autologous transplant is possible, but cases of bilateral LSCD require allogenic LSCT. Cadaveric donors represent the most important source of LSC allografts for treatment of bilateral LSCD when living relative donors are not available. To evaluate the suitability of aged cadaveric donors for LSCT, we compared three pools of LSC from donors of different ages (<60 years, 60–75 years, and >75 years). We evaluated graft quality in terms of percent of p63-positive (p63+) cells by immunofluorescence, colony forming efficiency, and mRNA and protein expression of p63, PAX6, Wnt7a, E-cadherin, and cytokeratin (CK) 12, CK3, and CK19. The results showed that LSC cultures from aged donors can express ≥3% of p63+ cells—considered as the minimum value for predicting favorable clinical outcomes after LSCT—suggesting that these cells could be a suitable source of LSC for transplantation. Our results also indicate the need to evaluate LSC graft quality criteria for each donor.

Effect of Cryopreserved Amniotic Membrane Orientation on the Expression of Limbal Mesenchymal and Epithelial Stem Cell Markers in Prolonged Limbal Explant Cultures

PURPOSE

To evaluate the effect of prolonged limbal explants cultured without any scaffolds or on amniotic membrane (AM) on the viability, proliferation and differentiation potential of putative phenotypically defined cultured limbal mesenchymal (LMSC) and epithelial stem cells (LESC).

METHODS

Limbal explants were cultivated on cryopreserved intact AM or plastic plates using medium supplemented with only human serum. AM was positioned with either the epithelial or stromal side up. The outgrowing cells were immunophenotyped for the co-expression of mesenchymal stem cell markers (CD73/CD90/CD105 positive and CD45 negative), proliferation and putative progenitor markers (CXCR4, CD117), epithelial markers and antigen presenting cell markers (CD80, CD83, CD86) by flow cytometry. Immunohistochemistry on limbal cultures cultivated on AM was carried out with antibodies against pan-cytokeratin, p63, Ki67.

RESULTS

Morphological and immunostaining analyses revealed two distinct stem cell population types, which could be identified over prolonged culturing time periods. Expression of LMSC markers and CXCR4 was significantly higher (p < 0.05) in cultures cultivated without AM. However, no statistically significant difference was observed in CD117 expression. The cells cultivated on AM retained an epithelial cell structure, which was further confirmed by histology examination. Histology revealed limbal epithelial growth and p63, Ki67 positive cells on both sides of AM.

CONCLUSION

Limbal cells cultivated on AM exhibited a lower expression profile of LMSC and CXCR4 markers as limbal cells cultivated on plastic culture plates. However, CD117 expression was similar. Histology confirmed limbal epithelial cell growth on both sides of AM, with no morphological differences, or positivity of cells for p63 and Ki67.

The effect of culture medium and carrier on explant culture of human limbal epithelium: A comparison of ultrastructure, keratin profile and gene expression

Patients with limbal stem cell deficiency (LSCD) often experience pain and photophobia due to recurrent epithelial defects and chronic inflammation of the cornea. Successfully restoring a healthy corneal surface in these patients by transplantation of ex vivo expanded human limbal epithelial cells (LECs) may alleviate these symptoms and significantly improve their quality of life. The clinical outcome of transplantation is known to be influenced by the quality of transplanted cells. Presently, several different protocols for cultivation and transplantation of LECs are in use. However, no consensus on an optimal protocol exists. The aim of this study was to examine the effect of culture medium and carrier on the morphology, staining of selected keratins and global gene expression in ex vivo cultured LECs. Limbal biopsies from cadaveric donors were cultured for three weeks on human amniotic membrane (HAM) or on tissue culture coated plastic (PL) in either a complex medium (COM), containing recombinant growth factors, hormones, cholera toxin and fetal bovine serum, or in medium supplemented only with human serum (HS). The expanded LECs were examined by light microscopy (LM), transmission electron microscopy (TEM), immunohistochemistry (IHC) for keratins K3, K7, K8, K12, K13, K14, K15 and K19, as well as microarray and qRT-PCR analysis. The cultured LECs exhibited similar morphology and keratin staining on LM, TEM and IHC examination, regardless of the culture condition. The epithelium was multilayered, with cuboidal basal cells and flattened superficial cells. Cells were attached to each other by desmosomes. Adhesion complexes were observed between basal cells and the underlying carrier in LECs cultured on HAM, but not in LECs cultured on PL. GeneChip Human Gene 2.0 ST microarray (Affymetrix) analysis revealed that 18,653 transcripts were ≥2 fold up or downregulated (p ≤ 0.05). Cells cultured in the same medium (COM or HS) showed more similarities in gene expression than cells cultured on the same carrier (HAM or PL). When each condition was compared to HAM/COM, no statistical difference was found in the transcription level of the selected genes associated with keratin expression, stemness, proliferation, differentiation, apoptosis, corneal wound healing or autophagy. In conclusion, the results indicate that ex vivo cultures of LECs on HAM and PL, using culture media supplemented with COM or HS, yield tissues with similar morphology and keratin staining. The gene expression appears to be more similar in cells cultured in the same medium (COM or HS) compared to cells cultured on the same carrier (HAM or PL).

Contact Lenses: A Delivery Device for Stem Cells to Treat Corneal Blindness

: Worldwide, 45 million people are blind. Corneal blindness is a major cause of visual loss, estimated to affect 10 million. For the most difficult to treat patients, including those with a disease called limbal stem cell deficiency, a donor corneal graft is not a viable option; thus, patients are treated with specialized stem cell grafts, which fail in a significant proportion (30 to 50%) of subjects. This unacceptable failure rate means there is a pressing need to develop minimally invasive, long-lasting, cost-effective therapies to improve patient quality of life and lessen the economic burden. Restoring vision in patients with severe corneal disease is the main focus of our research program; however, to achieve our goals and deliver the best quality stem cell therapy, we must first understand the basic biology of these cells, including their residence, the factors that support their long-term existence, markers to identify and isolate them, and carriers that facilitate expansion, delivery, and protection during engraftment. We recently achieved some of these goals through the discovery of stem cell markers and the development of a novel and innovative contact lens-based cell transfer technique that has been successfully trialed on patients with corneal blindness. Although several popular methodologies are currently available to nurture and transfer stem cells to the patients' ocular surface, contact lenses provide many advantages that will be discussed in this review article. The job for clinician-researchers will be to map precisely how these cells contribute to restoring ocular health and whether improvements in the quality of cells and the cell delivery system can be developed to reduce disease burden.

From discovery to approval of an advanced therapy medicinal product-containing stem cells, in the EU

In 1997, the human corneal epithelium was reconstructed in vitro and transplanted on patients. Later, it became a routine treatment, before regulations considered advanced therapy medicinal products and drugs on the same lines. Manufacturing, before and after good manufacturing practice setting, was established in different facilities and the clinical application in several hospitals. Advanced therapy medicinal products, including stem cells, are unique products with different challenges than other drugs: some uncertainties, in addition to benefit, cannot be avoided. This review will focus on all recent developments in the stem cell-based corneal therapy.

Human limbal mesenchymal stem cells express ABCB5 and can grow on amniotic membrane

Aim: To isolate and characterize limbal mesenchymal stem cells (LMSCs) from human corneoscleral rings. Materials & methods: Cells were isolated from corneoscleral rings and cultured in a mesenchymal stem cell (MSC)-selective media and examined for differentiation, phenotyping and characterization. Results: LMSCs were capable of trilineage differentiation, adhered to tissue culture plastic, expressed HLA class I and cell surface antigens associated with human MSC while having no/low expression of HLA class II and negative hematopoietic lineage markers. They were capable for CXCL12-mediated cellular migration. LMSCs adhered, proliferated on amniotic membrane and expressed the common putative limbal stem cell markers. Conclusion: Limbal-derived MSC exhibited plasticity, could maintain limbal markers expression and demonstrated viable growth on amniotic membrane.