The culture and transplantation of human limbal stem cells

In Vivo Confocal Microscopy in Limbal Stem Cell Deficiency After Mesenchymal Stem Cell Transplantation: A Sub-analysis from a Phase I-II Clinical Trial

INTRODUCTION

The aim of this work is to evaluate the effect of mesenchymal stem cell transplantation (MSCT) and cultivated limbal epithelial transplantation (CLET) therapies on the limbus of patients suffering from limbal stem cell deficiency (LSCD).

METHODS

A sub-analysis of a phase I-II randomized, controlled, and double-masked clinical trial was performed to assess the changes in the anatomical structures of the limbus. In vivo confocal microscopy (IVCM) analysis was carried out in LSCD eyes before and 12 months after allogeneic MSCT or CLET. Epithelial phenotype of the central cornea, as well as the presence of transition zones and palisades of Vogt in the limbus, were assessed using Wilcoxon test.

RESULTS

Twenty-three LSCD (14 MSCT and nine CLET) eyes were included. The epithelial phenotype of the central cornea improved significantly (p < 0.001) from 15 (eight MSCT, seven CLET) and eight (six MSCT, two CLET) LSCD eyes showing conjunctival and mixed phenotypes, respectively, to eight (five MSCT, three CLET), five (two MSCT, three CLET), and ten (seven MSCT, three CLET) eyes showing conjunctival, mixed, and corneal phenotypes, respectively. Transition areas and palisades of Vogt were observed in at least one quadrant in nine (five MSCT, four CLET) and 16 (nine MSCT, seven CLET), and in four (two MSCT, two CLET) and six (three MSCT, three CLET) LSCD eyes before and after surgery, respectively. Changes in the transition zones and palisades were solely significant (p = 0.046) for the nasal and inferior quadrants, respectively.

CONCLUSIONS

MSCT and CLET improved the central corneal epithelial phenotype despite only minor changes in the anatomical structures of the limbus, as detected by IVCM technology.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT01562002.

Corneal Superficial Plaque Formation After Recombinant Human Nerve Growth Factor Use in a Patient With Neurotrophic Keratopathy and Limbal Stem Cell Deficiency From Mucous Membrane Pemphigoid

PURPOSE

The aim of this study was to report a rare observation of corneal superficial plaque formation after topical recombinant human nerve growth factor (rhNGF) treatment for a nonhealing epithelial defect in a patient with advanced mucous membrane pemphigoid, limbal stem cell deficiency, and neurotrophic keratopathy.

METHODS

This study was a case report.

RESULTS

A 72-year-old man with a complex course of mucous membrane pemphigoid, leading to cicatrizing keratoconjunctivits, limbal stem cell deficiency, and neurotrophic keratopathy presented with a recurrent persistent epithelial defect in the right eye. After a long course of unsuccessful epithelial healing, despite various treatment modalities, he was administered topical rhNGF (cenegermin 0.002%; Oxervate, Dompé US Inc., Boston, MA) which successfully resolved the epithelial defect. However, on day 22 posttreatment, an unusual white, thick, adherent corneal superficial plaque formed. rhNGF was stopped and the plaque was carefully removed. Subsequently, there was no recurrence, and the patient's epithelial healing remained stable.

CONCLUSIONS

Although the successful resolution of the persistent epithelial defect with rhNGF administration was notable, the development of the unusual epithelial overgrowth emphasizes the importance of vigilant monitoring and evaluation when using rhNGF in complex ocular conditions. Making informed decisions on the timing of discontinuing rhNGF can lead to desirable effects of the drug while mitigating additional side effects when managing such challenging cases.

Hyaluronan supports the limbal stem cell phenotype during ex vivo culture

BACKGROUND

Hyaluronan (HA) has previously been identified as an integral component of the limbal stem cell niche in vivo. In this study, we investigated whether a similar HA matrix is also expressed in vitro providing a niche supporting limbal epithelial stem cells (LESCs) during ex vivo expansion. We also investigated whether providing exogenous HA in vitro is beneficial to LESCs during ex vivo expansion.

METHOD

Human LESCs (hLESCs) were isolated from donor corneas and a mouse corneal epithelial progenitor cell line (TKE2) was obtained. The HA matrix was identified surrounding LESCs in vitro using immunocytochemistry, flow cytometry and red blood exclusion assay. Thereafter, LESCs were maintained on HA coated dishes or in the presence of HA supplemented in the media, and viability, proliferation, cell size, colony formation capabilities and expression of putative stem cell markers were compared with cells maintained on commonly used coated dishes.

RESULTS

hLESCs and TKE2 cells express an HA-rich matrix in vitro, and this matrix is essential for maintaining LESCs. Further supplying exogenous HA, as a substrate and supplemented to the media, increases LESC proliferation, colony formation capabilities and the expression levels of putative limbal stem cell markers.

CONCLUSION

Our data show that both exogenous and endogenous HA help to maintain the LESC phenotype. Exogenous HA provides improved culture conditions for LESC during ex vivo expansion. Thus, HA forms a favorable microenvironment for LESCs during ex vivo expansion and, therefore, could be considered as an easy and cost-effective substrate and/or supplement for culturing LESCs in the clinic.

Characterization of the secretory profile and exosomes of limbal stem cells in the canine species

Limbal stem cells (LSCs) are a quiescent cell population responsible for the renewal of the corneal epithelium. Their deficiency is responsible for the conjunctivization of the cornea that is seen in different ocular pathologies, both in humans and in the canine species. The canine species represents an interesting preclinical animal model in ocular surface pathologies. However, the role of LSCs in physiological and pathological conditions in canine species is not well understood. Our objective was to characterize for the first time the soluble factors and the proteomic profile of the secretome and exosomes of canine LSCs (cLSCs). In addition, given the important role that fibroblasts play in the repair of the ocular surface, we evaluated the influence of the secretome and exosomes of cLSCs on their proliferation in vitro. Our results demonstrated a secretory profile of cLSCs with high concentrations of MCP-1, IL-8, VEGF-A, and IL-10, as well as significant production of exosomes. Regarding the proteomic profile, 646 total proteins in the secretome and 356 in exosomes were involved in different biological processes. Functionally, the cLSC secretome showed an inhibitory effect on the proliferation of fibroblasts in vitro, which the exosomes did not. These results open the door to new studies on the possible use of the cLSC secretome or some of its components to treat certain pathologies of the ocular surface in canine species.

Response of human oral mucosal epithelial cells to different storage temperatures: A structural and transcriptional study

PURPOSE

Seeking to improve the access to regenerative medicine, this study investigated the structural and transcriptional effects of storage temperature on human oral mucosal epithelial cells (OMECs).

METHODS

Cells were stored at four different temperatures (4°C, 12°C, 24°C and 37°C) for two weeks. Then, the morphology, cell viability and differential gene expression were examined using light and scanning electron microscopy, trypan blue exclusion test and TaqMan gene expression array cards, respectively.

RESULTS

Cells stored at 4°C had the most similar morphology to non-stored controls with the highest viability rate (58%), whereas the 37°C group was most dissimilar with no living cells. The genes involved in stress-induced growth arrest (GADD45B) and cell proliferation inhibition (TGFB2) were upregulated at 12°C and 24°C. Upregulation was also observed in multifunctional genes responsible for morphology, growth, adhesion and motility such as EFEMP1 (12°C) and EPHA4 (4°C-24°C). Among genes used as differentiation markers, PPARA and TP53 (along with its associated gene CDKN1A) were downregulated in all temperature conditions, whereas KRT1 and KRT10 were either unchanged (4°C) or downregulated (24°C and 12°C; and 24°C, respectively), except for upregulation at 12°C for KRT1.

CONCLUSIONS

Cells stored at 12°C and 24°C were stressed, although the expression levels of some adhesion-, growth- and apoptosis-related genes were favourable. Collectively, this study suggests that 4°C is the optimal storage temperature for maintenance of structure, viability and function of OMECs after two weeks.

Anti-VEGF Treatment in Corneal Diseases

BACKGROUND

Corneal neovascularization (CN) is a clue feature of different ocular pathological conditions and can lead to corneal edema and opacification with subsequent vision loss. Vascular endothelial growth factor (VEGF), which plays a key role in new vessels formation, proliferation and migration, was found to be up-regulated in these conditions. Nowadays, it is possible to downregulate the angiogenic process by using anti-VEGF agents administered by different routes.

OBJECTIVE

To evaluate the efficacy, safety and possible future directions of anti-VEGF agents used for the treatment of CNV owing to different aetiologies.

METHODS

A computerized search of articles dealing with the topic of anti-VEGF therapy in CN was conducted in PubMed, Scopus and Medline electronic databases. The following key phrases were used: anti-VEGF agents, corneal neovascularization, bevacizumab, ranibizumab, vascular endothelial growth factor, angiogenesis.

RESULTS

The use of anti-VEGF therapy in the treatment of CN reduced pathological vessel density without causing significant side effects. Various administration routes such as topical, subconjunctival and intrastromal ones are available, and the choice depends on patient and disease characteristics. Much more effectiveness is achieved in case of early administration before mature and wellestablished vessels take place. A combined approach between various drugs including anti-VEGF agents should be adopted in those cases at higher risk of neovascularization recurrence such as chronic long-standing diseases where ischemic and inflammatory stimuli are not definitively reversed.

CONCLUSION

The efficacy and safety of anti-VEGF agents support their adoption into the daily clinical practice for the management of CN.

KIT ligand produced by limbal niche cells under control of SOX10 maintains limbal epithelial stem cell survival by activating the KIT/AKT signalling pathway

Homeostasis and function of limbal epithelial stem cells (LESCs) rely on the limbal niche, which, if dysfunctional, leads to limbal epithelial stem cell deficiency (LSCD) and impaired vision. Hence, recovery of niche function is a principal therapeutic goal in LSCD, but the molecular mechanisms of limbal niche homeostasis are still largely unknown. Here, we report that the neural crest transcription factor SOX10, which is expressed in neural crest‐derived limbal niche cells (LNCs), is required for LNCs to promote survival of LESCs both in vivo and in vitro. In fact, using mice with a Sox10 mutation and in vitro coculture experiments, we show that SOX10 in LNCs stimulates the production of KIT ligand (KITL), which in turn activates in LESCs the KIT‐AKT signalling pathway that protects the cells against activated CASPASE 3‐associated cell death. These results suggest that SOX10 and the KITL/KIT‐AKT pathway play key roles in limbal niche homeostasis and LESC survival. These findings provide molecular insights into limbal niche function and may point to rational approaches for therapeutic interventions in LSCD.

Optisol-GS Storage of Cultured Human Limbal Epithelial Cells at Ambient Temperature Is Superior to Hypothermic Storage

PURPOSE

To investigate the feasibility of using Optisol-GS as a convenient, xenogeneic-free alternative for storage of cultured human limbal epithelial cells (HLECS) for use in treatment of limbal stem cell deficiency (LSCD). In the present study, we compared storage of cultured HLEC using the conventional hypothermic Optisol-GS storage method at 4°C versus storage at 23°C (room temperature).

MATERIALS AND METHODS

HLECs were cultured for three weeks on amniotic membrane (AM), transferred to polypropylene containers and stored in Optisol-GS for 4 days at 23°C and 4°C. A calcein-acetoxymethyl ester/ethidium homodimer-1 assay was used to assess viability. Morphology and phenotype were analyzed by light microscopy and immunohistochemistry, respectively.

RESULTS

Expression of stem cell and proliferation markers p63, ∆Np63α, ABCG2, K19, K3, Cx43, Ki67, and PCNA was maintained at pre-storage control levels during storage at 23°C. ABCG2 and PCNA expression were both significantly altered during storage at 4°C. HLEC cell sheet viability also significantly declined following storage at 4°C. HLEC sheets stored at 4°C demonstrated extensive detachment of basal cells from the AM in sharp contrast to storage at 23°C, where attachment to the AM was maintained throughout the storage period.

CONCLUSIONS

The present study demonstrates the feasibility of short-term storage of cultured HLECs in Optisol-GS, which offers a convenient standardized xenogeneic-free storage method. Storage temperature highly affected the results. Maintenance of cell viability, morphology and undifferentiated proliferative phenotype of cultured HLEC sheets favored storage at 23°C.

Stem cell function is conserved during short-term storage of cultured epidermal cell sheets at 12°C

Transplantation of cultured epidermal cell sheets (CES) can be life-saving for patients with large area burns. CES have also been successfully used to regenerate eye and urethral epithelia in animal models. Short-term storage aims to extend the transplantation window, offers flexibility in timing surgery and allows testing of CES quality, phenotype and sterility. This study investigated extended CES storage and explored the effect of additional re-incubation recovery time following storage. The proliferative quality of stored confluent versus pre-confluent CES was also investigated using functional testing. CES were stored at 12°C and results compared to non-stored control CES. Investigation of timepoints during 15 days storage revealed that viability began to deteriorate by day 11 and was associated with increased lactate in the storage medium. The percentage of apoptotic cells also significantly increased by day 11. Flow cytometry analysis of integrin β1 expression and cell size indicated best retention of stem cells at 7 days of storage. Functional testing of pre-confluent and confluent cells following 7 days storage showed that pre-confluent cells responded well to 1-day re-incubation after storage; they became highly prolific, increasing in number by ~67%. Conversely, proliferation in stored confluent cells declined by ~50% with 1-day re-incubation. Pre-confluent stored CES also had far superior stem cell colony forming efficiency (CFE) performance compared to the confluent group. Re-incubation improved CFE in both groups, but the pre-confluent group again out-performed the confluent group with significantly more colonies. In conclusion, a maximum storage period of 7 days is recommended. Use of pre-confluent cells and one day recovery incubation greatly improves viability, colony-forming ability and proliferation of cells stored for 7 days at 12°C. Thus, these recommendations should be considered under culture and storage of high-quality CES for clinical use.

Influence of polydimethylsiloxane substrate stiffness on corneal epithelial cells

Many cell types are known to modulate their behaviour in response to changes in material stiffness; however, little is known about how stiffness affects corneal epithelial cells. This study aims to investigate the response of a corneal epithelial cell line to polydimethylsiloxane (PDMS) substrates with a range of Young's moduli from 10 to 1500 kPa. Cellular morphology, proliferation, differentiation and mechanobiology were examined. Cells grown on PDMS adopted the typical cobblestone morphology exhibited by the corneal epithelium. Proliferative markers pERK and Ki67 were higher in cells cultured on stiffer substrates compared with those on softer substrates. Material stiffness was also found to influence the cell phenotype with cells on stiffer substrates having higher cytokeratin 3 gene expression, a mature epithelial marker, while cells on softer substrates expressed more cytokeratin 14, a basal epithelial marker. Cells grown on softer substrates also displayed higher levels of focal adhesions and intermediate filaments compared with cells on stiff substrates. This research will aid in designing novel biomaterials for the culture and transplantation of corneal epithelial cells.

Allogeneic Ex Vivo Expanded Corneal Epithelial Stem Cell Transplantation: A Randomized Controlled Clinical Trial

Limbal stem cell deficiency (LSCD) is a disease resulting from the loss or dysfunction of epithelial stem cells, which seriously impairs sight. Autologous limbal stem cell transplantation is effective in unilateral or partial bilateral disease but not applicable in total bilateral disease. An allogeneic source of transplantable cells for use in total bilateral disease can be obtained from culture of donated cadaveric corneal tissue. We performed a controlled multicenter study to examine the feasibility, safety, and efficacy of allogeneic corneal epithelial stem cells in the treatment of bilateral LSCD. Patients were randomized to receive corneal epithelial stem cells cultured on amniotic membrane (AM): investigational medicinal product (IMP) or control AM only. Patients received systemic immunosuppression. Primary endpoints were safety and visual acuity, secondary endpoint was change in composite ocular surface score (OSS). Sixteen patients were treated and 13 patients completed all assessments. Safety was demonstrated and 9/13 patients had improved visual acuity scores at the end of the trial, with no significant differences between IMP and control groups. Patients in the IMP arm demonstrated significant, sustained improvement in OSS, whereas those in the control arm did not. Serum cytokine levels were measured during and after the period of immune suppression and we identified strongly elevated levels of CXCL8 in the serum of patients with aniridia, which persisted throughout the trial. This first randomized control trial of allogeneic corneal epithelial stem cells in severe bilateral LSCD demonstrates the feasibility and safety of this approach. Stem Cells Translational Medicine 2019;8:323-331.

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.

Effect of Transportation on Cultured Limbal Epithelial Sheets for Worldwide Treatment of Limbal Stem Cell Deficiency

Limbal stem cell deficiency can be treated with transplantation of cultured human limbal epithelial cells (LEC). It can be advantageous to produce LEC in centralized labs and thereafter ship them to eye clinics. The present study used transport simulations of LEC to determine if vigorous shaking during transport altered the viability, morphology and phenotype during a 4 day-long storage of LEC with a previously described serum-free storage method. Inserts with LEC cultured on amniotic membranes were sutured to caps inside air-tight containers with generous amounts of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)-buffered minimal essential medium (MEM). The containers were distributed among the following testing conditions: 6 hours with full containers, 36 hours with full containers, 36 hours with container three quarters full of medium, and 36 hours with container full of medium containing a shear-protecting agent (Pluronic-F68). Compared to stored, but non-transported controls, no statistically significant changes in viability and immunohistochemical staining were observed. The epithelial sheets remained intact. However, an air-liquid interface in the containers reduced the number of desmosomes and hemi-desmosomes compared to the controls. In conclusion, cultured LEC sheets appear to endure vigorous shaking for at least 36 hours if the container is full.

Improvement of Storage Medium for Cultured Human Retinal Pigment Epithelial Cells Using Factorial Design

Storage of human retinal pigment epithelium (hRPE) can contribute to the advancement of cell-based RPE replacement therapies. The present study aimed to improve the quality of stored hRPE cultures by identifying storage medium additives that, alone or in combination, contribute to enhancing cell viability while preserving morphology and phenotype. hRPE cells were cultured in the presence of the silk protein sericin until pigmentation. Cells were then stored for 10 days in storage medium plus sericin and either one of 46 different additives. Individual effects of each additive on cell viability were assessed using epifluorescence microscopy. Factorial design identified promising additive combinations by extrapolating their individual effects. Supplementing the storage medium with sericin combined with adenosine, L-ascorbic acid and allopurinol resulted in the highest cell viability (98.6 ± 0.5%) after storage for three days, as measured by epifluorescence microscopy. Flow cytometry validated the findings. Proteomics identified 61 upregulated and 65 downregulated proteins in this storage group compared to the unstored control. Transmission electron microscopy demonstrated the presence of melanosomes after storage in the optimized medium. We conclude that the combination of adenosine, L-ascorbic acid, allopurinol and sericin in minimal essential medium preserves RPE pigmentation while maintaining cell viability during storage.

Limbal and Conjunctival Epithelial Cell Cultivation on Contact Lenses-Different Affixing Techniques and the Effect of Feeder Cells

OBJECTIVES

Corneal blindness due to limbal stem-cell deficiency can be treated by transplantation of cultivated limbal epithelial stem cells (LESCs). We examined LESC cultivation on a contact lens (CL) carrier. Our goal was to optimize explant affixation and assess the possible benefit of 3T3 feeder cells.

METHODS

Human cadaver limbal and conjunctival explants were allowed to attach to CLs under the airflow of the laminar box (dried group) or affixed on CLs using suturing (sutured group) or tissue adhesives (glued group), then cultivated with or without 3T3 feeder cells. Outgrowth efficiency was statistically analyzed. CEBPδ, p63, CK3/12, and CK13 were detected by immunofluorescence in expanded cells.

RESULTS

Suturing and gluing provided excellent sample attachment, whereas drying was less effective. Cell expansion was better in sutured than in dried or glued samples. Presence of 3T3 feeder resulted in significantly better cell growth (P=0.048), most importantly in dried samples (P=0.008). Stepwise regression analysis indicated that cell expansion was dependent on the affixing method (P<0.001) and the presence of feeder layer (P=0.003). Expanded cells maintained their CK expression profiles and expressed putative stem-cell markers p63 and CEBPδ. The 3T3 feeder did not influence the expression of putative LESC markers or growth rate.

CONCLUSIONS

Suturing is an effective way to fasten explants to CLs. 3T3 fibroblasts are not necessary in this system, although they may enhance cell outgrowth when samples are exposed to stress. However, once cells begin to expand, neither expression of putative stem-cell markers nor growth rate is influenced by feeder cells.

Limbal Stem Cell Transplantation and Complications

Corneal epithelial stem cells are adult somatic stem cells located at the limbus and represent the ultimate source of transparent corneal epithelium. When these limbal stem cells become dysfunctional or deficient, limbal stem cell deficiency (LSCD) develops. LSCD is a major cause of corneal scarring and is particularly prevalent in chemical and thermal burns of the ocular surface. LSCD leads to conjunctivalization of the corneal surface, neovascularization, recurrent or persistent epithelial defects, ocular surface inflammation, and scarring that, in turn, lead to decreased vision, pain, and impaired quality of life. Several techniques have been reported for limbal stem cell transplantation (LSCT). We introduce the surgical techniques, examine the success rate, and discuss the postoperative complications of conjunctival limbal autograft (CLAU), cultivated limbal stem cell transplantation (CLET), simple limbal epithelial transplantation (SLET), and limbal allograft, including keratolimbal allografts (KLAL) and living-related conjunctival allograft (LR-CLAL).

Optimization of Storage Temperature for Retention of Undifferentiated Cell Character of Cultured Human Epidermal Cell Sheets

Cultured epidermal cell sheets (CES) containing undifferentiated cells are useful for treating skin burns and have potential for regenerative treatment of other types of epithelial injuries. The undifferentiated phenotype is therefore important for success in both applications. This study aimed to optimize a method for one-week storage of CES for their widespread distribution and use in regenerative medicine. The effect of storage temperatures 4 °C, 8 °C, 12 °C, 16 °C, and 24 °C on CES was evaluated. Analyses included assessment of viability, mitochondrial reactive oxygen species (ROS), membrane damage, mitochondrial DNA (mtDNA) integrity, morphology, phenotype and cytokine secretion into storage buffer. Lowest cell viability was seen at 4 °C. Compared to non-stored cells, ABCG2 expression increased between temperatures 8–16 °C. At 24 °C, reduced ABCG2 expression coincided with increased mitochondrial ROS, as well as increased differentiation, cell death and mtDNA damage. P63, C/EBPδ, CK10 and involucrin fluorescence combined with morphology observations supported retention of undifferentiated cell phenotype at 12 °C, transition to differentiation at 16 °C, and increased differentiation at 24 °C. Several cytokines relevant to healing were upregulated during storage. Importantly, cells stored at 12 °C showed similar viability and undifferentiated phenotype as the non-stored control suggesting that this temperature may be ideal for storage of CES.

Simultaneous Keratolimbal Autograft and Penetrating Autokeratoplasty: A Single-Stage Procedure to Restore Monocular Vision of a Blind Patient With Limbal Stem Cell Deficiency

PURPOSE

To describe the technique of simultaneous keratolimbal autograft and penetrating autokeratoplasty to restore monocular vision of a blind patient with limbal stem cell deficiency (LSCD).

METHODS

A patient with acquired monocular vision due to loss of the left eye owing to LSCD postblast injury presented with acute loss of vision in the right eye due to central retinal artery occlusion. Simultaneous keratolimbal autograft and penetrating autokeratoplasty were performed in attempt to restore his vision in the left eye.

RESULTS

Postoperatively, the anterior chamber was well formed along with mild graft edema on day 1. Topo-guided suture removal was started at 4 months. The graft maintained clear transparency at 1-year follow-up, and the best-corrected visual acuity improved from hand movement to 20/50.

CONCLUSIONS

Keratolimbal autograft and penetrating autokeratoplasty, as a one-stage procedure, proved to be effective in restoring monocular vision in a patient with LSCD.

A Simple Mechanical Procedure to Create Limbal Stem Cell Deficiency in Mouse

Limbal stem cell deficiency (LSCD) is a state of malfunction or loss of limbal epithelial stem cells, after which the corneal epithelium is replaced with conjunctiva. Patients suffer from recurrent corneal defects, pain, inflammation, and loss of vision. Previously, a murine model of LSCD was described and compared to two other models. The goal was to produce a consistent mouse model of LSCD that both mimics the phenotype in humans and lasts long enough to make it possible to study the disease pathophysiology and to evaluate new treatments. Here, the technique is described in more detail. A motorized tool with a rotating burr has been designed to remove the rust rings from the corneal surface or to smooth the pterygium bed in patients. It is a suitable device to create the desired LSCD model. It is a readily available, easy-to-use tool with a fine tip that makes it appropriate for working on small eyes, as in mice. Its application prevents unnecessary trauma to the eye and it does not result in unwanted injuries, as often is the case with chemical injury models. As opposed to a blunt scraper, it removes the epithelium with the basement membrane. In this protocol, the limbal area was abraded two times, and then the whole corneal epithelium was shaved from limbus to limbus. To avoid stroma injury, care was taken not to brush the corneal surface once the epithelium was already removed.

Storage Temperature Alters the Expression of Differentiation-Related Genes in Cultured Oral Keratinocytes

Purpose

Storage of cultured human oral keratinocytes (HOK) allows for transportation of cultured transplants to eye clinics worldwide. In a previous study, one-week storage of cultured HOK was found to be superior with regard to viability and morphology at 12°C compared to 4°C and 37°C. To understand more of how storage temperature affects cell phenotype, gene expression of HOK before and after storage at 4°C, 12°C, and 37°C was assessed.

Materials and Methods

Cultured HOK were stored in HEPES- and sodium bicarbonate-buffered Minimum Essential Medium at 4°C, 12°C, and 37°C for one week. Total RNA was isolated and the gene expression profile was determined using DNA microarrays and analyzed with Partek Genomics Suite software and Ingenuity Pathway Analysis. Differentially expressed genes (fold change > 1.5 and P < 0.05) were identified by one-way ANOVA. Key genes were validated using qPCR.

Results

Gene expression of cultures stored at 4°C and 12°C clustered close to the unstored control cultures. Cultures stored at 37°C displayed substantial change in gene expression compared to the other groups. In comparison with 12°C, 2,981 genes were differentially expressed at 37°C. In contrast, only 67 genes were differentially expressed between the unstored control and the cells stored at 12°C. The 12°C and 37°C culture groups differed most significantly with regard to the expression of differentiation markers. The Hedgehog signaling pathway was significantly downregulated at 37°C compared to 12°C.

Conclusion

HOK cultures stored at 37°C showed considerably larger changes in gene expression compared to unstored cells than cultured HOK stored at 4°C and 12°C. The changes observed at 37°C consisted of differentiation of the cells towards a squamous epithelium-specific phenotype. Storing cultured ocular surface transplants at 37°C is therefore not recommended. This is particularly interesting as 37°C is the standard incubation temperature used for cell culture.

Concise review: transplantation of cultured oral mucosal epithelial cells for treating limbal stem cell deficiency-current status and future perspectives

A number of diseases and external factors can deplete limbal stem cells, causing pain and visual loss. Ten years have passed since the first transplantation of cultured oral mucosal epithelial cells in humans, representing the first autologous cell-based therapy for severe bilateral limbal stem cell deficiency. Its steady increase in popularity since then can be attributed to the accumulating evidence of its efficacy in reverting limbal stem cell deficiency. In this review, the focus is on clinical, and to a lesser degree laboratory, features of cultured oral mucosal epithelial transplants over the past 10 years. Comparisons with other available technologies are made. Avenues for research to stimulate further improvements in clinical results and allow worldwide distribution of limbal stem cell therapy based on oral mucosal cells are discussed. These include storage and transportation of cultured oral mucosal epithelial sheets and in vivo culture of oral mucosal epithelial cells.

Transcriptome Analysis of Cultured Limbal Epithelial Cells on an Intact Amniotic Membrane following Hypothermic Storage in Optisol-GS

The aim of the present study was to investigate the molecular mechanisms underlying activation of cell death pathways using genome-wide transcriptional analysis in human limbal epithelial cell (HLEC) cultures following conventional hypothermic storage in Optisol-GS. Three-week HLEC cultures were stored in Optisol-GS for 2, 4, and 7 days at 4 °C. Partek Genomics Suite software v.6.15.0422, (Partec Inc., St. Louis, MO, USA) was used to identify genes that showed significantly different (P < 0.05) levels of expression following hypothermic storage compared to non-stored cell sheets. There were few changes in gene expression after 2 days of storage, but several genes were differently regulated following 4 and 7 days of storage. The histone-coding genes HIST1H3A and HIST4H4 were among the most upregulated genes following 4 and 7 days of hypothermic storage. Bioinformatic analysis suggested that these two genes are involved in a functional network highly associated with cell death, necrosis, and transcription of RNA. HDAC1, encoding histone deacetylase 1, was the most downregulated gene after 7 days of storage. Together with other downregulated genes, it is suggested that HDAC1 is involved in a regulating network significantly associated with cellular function and maintenance, differentiation of cells, and DNA repair. Our data suggest that the upregulated expression of histone-coding genes together with downregulated genes affecting cell differentiation and DNA repair may be responsible for increased cell death following hypothermic storage of cultured HLEC. In summary, our results demonstrated that a higher number of genes changed with increasing storage time. Moreover, in general, larger differences in absolute gene expression values were observed with increasing storage time. Further understanding of these molecular mechanisms is important for optimization of storage technology for limbal epithelial sheets.

Concise Review: Comparison of Culture Membranes Used for Tissue Engineered Conjunctival Epithelial Equivalents

The conjunctival epithelium plays an important role in ensuring the optical clarity of the cornea by providing lubrication to maintain a smooth, refractive surface, by producing mucins critical for tear film stability and by protecting against mechanical stress and infectious agents. A large number of disorders can lead to scarring of the conjunctiva through chronic conjunctival inflammation. For controlling complications of conjunctival scarring, surgery can be considered. Surgical treatment of symblepharon includes removal of the scar tissue to reestablish the deep fornix. The surgical defect is then covered by the application of a tissue substitute. One obvious limiting factor when using autografts is the size of the defect to be covered, as the amount of healthy conjunctiva is scarce. These limitations have led scientists to develop tissue engineered conjunctival equivalents. A tissue engineered conjunctival epithelial equivalent needs to be easily manipulated surgically, not cause an inflammatory reaction and be biocompatible. This review summarizes the various substrates and membranes that have been used to culture conjunctival epithelial cells during the last three decades. Future avenues for developing tissue engineered conjunctiva are discussed.

Human pluripotent stem cell-derived limbal epithelial stem cells on bioengineered matrices for corneal reconstruction

Corneal epithelium is renewed by limbal epithelial stem cells (LESCs), a type of tissue-specific stem cells located in the limbal palisades of Vogt at the corneo-scleral junction. Acute trauma or inflammatory disorders of the ocular surface can destroy these stem cells, leading to limbal stem cell deficiency (LSCD) - a painful and vision-threatening condition. Treating these disorders is often challenging and complex, especially in bilateral cases with extensive damage. Human pluripotent stem cells (hPSCs) provide new opportunities for corneal reconstruction using cell-based therapy. Here, we investigated the use of hPSC-derived LESC-like cells on bioengineered collagen matrices in serum-free conditions, aiming for clinical applications to reconstruct the corneal epithelium and partially replace the damaged stroma. Differentiation of hPSCs towards LESC-like cells was directed using small-molecule induction followed by maturation in corneal epithelium culture medium. After four to five weeks of culture, differentiated cells were seeded onto bioengineered matrices fabricated as transparent membranes of uniform thickness, using medical-grade porcine collagen type I and a hybrid cross-linking technology. The bioengineered matrices were fully transparent, with high water content and swelling capacity, and parallel lamellar microstructure. Cell proliferation of hPSC-LESCs was significantly higher on bioengineered matrices than on collagen-coated control wells after two weeks of culture, and LESC markers p63 and cytokeratin 15, along with proliferation marker Ki67 were expressed even after 30 days in culture. Overall, hPSC-LESCs retained their capacity to self-renew and proliferate, but were also able to terminally differentiate upon stimulation, as suggested by protein expression of cytokeratins 3 and 12. We propose the use of bioengineered collagen matrices as carriers for the clinically-relevant hPSC-derived LESC-like cells, as a novel tissue engineering approach for corneal reconstruction.

Comparative proteomics reveals human pluripotent stem cell-derived limbal epithelial stem cells are similar to native ocular surface epithelial cells

Limbal epithelial stem cells (LESCs) are tissue-specific stem cells responsible for renewing the corneal epithelium. Acute trauma or chronic disease affecting LESCs may disrupt corneal epithelial renewal, causing vision threatening and painful ocular surface disorders, collectively referred to as LESC deficiency (LESCD). These disorders cannot be treated with traditional corneal transplantation and therefore alternative cell sources for successful cell-based therapy are needed. LESCs derived from human pluripotent stem cells (hPSCs) are a prospective source for ocular surface reconstruction, yet critical evaluation of these cells is crucial before considering clinical applications. In order to quantitatively evaluate hPSC-derived LESCs, we compared protein expression in native human corneal cells to that in hPSC-derived LESCs using isobaric tag for relative and absolute quantitation (iTRAQ) technology. We identified 860 unique proteins present in all samples, including proteins involved in cell cycling, proliferation, differentiation and apoptosis, various LESC niche components, and limbal and corneal epithelial markers. Protein expression profiles were nearly identical in LESCs derived from two different hPSC lines, indicating that the differentiation protocol is reproducible, yielding homogeneous cell populations. Their protein expression profile suggests that hPSC-derived LESCs are similar to the human ocular surface epithelial cells, and possess LESC-like characteristics.

Effect of Storage Temperature on the Phenotype of Cultured Epidermal Cells Stored in Xenobiotic-Free Medium

PURPOSE

Cultured epidermal cell sheets (CECS) are used in the treatment of large area burns to the body and have potential to treat limbal stem cell deficiency (LSCD) as shown in animal studies. Despite widespread use, storage options for CECS are limited. Short-term storage allows flexibility in scheduling surgery, quality control and improved transportation to clinics worldwide. Recent evidence points to the phenotype of cultured epithelial cells as a critical predictor of post-operative success following transplantation of CECS in burns and in transplantation of cultured epithelial cells in patients with LSCD. This study, therefore assessed the effect of a range of temperatures, spanning 4-37 °C, on the phenotype of CECS stored over a 2-week period in a xenobiotic-free system.

MATERIALS AND METHODS

Progenitor cell (p63, ΔNp63α and ABCG2) and differentiation (C/EBPδ and CK10) associated marker expression was assessed using immunocytochemistry. Immunohistochemistry staining of normal skin for the markers p63, ABCG2 and C/EBPδ was also carried out. Assessment of progenitor cell side population (SP) was performed using JC1 dye by flow cytometry.

RESULTS

P63 expression remained relatively constant throughout the temperature range but was significantly lower compared to control between 20 and 28 °C (p < 0.05). High C/EBPδ together with low p63 suggested more differentiation beginning at 20 °C and above. Lower CK10 and C/EBPδ expression most similar to control was seen at 12 °C. The percentage of ABCG2 positive cells was most similar to control between 8 and 24 °C. Between 4 and 24 °C, the SP fluctuated, but was not significantly different compared to control. Results were supported by staining patterns indicating differentiation status associated with markers in normal skin sections.

CONCLUSIONS

Lower storage temperatures, and in particular 12 °C, merit further investigation as optimal storage temperature for maintenance of undifferentiated phenotype in CECS.

Pre-Clinical Cell-Based Therapy for Limbal Stem Cell Deficiency

The cornea is essential for normal vision by maintaining transparency for light transmission. Limbal stem cells, which reside in the corneal periphery, contribute to the homeostasis of the corneal epithelium. Any damage or disease affecting the function of these cells may result in limbal stem cell deficiency (LSCD). The condition may result in both severe pain and blindness. Transplantation of ex vivo cultured cells onto the cornea is most often an effective therapeutic strategy for LSCD. The use of ex vivo cultured limbal epithelial cells (LEC), oral mucosal epithelial cells, and conjunctival epithelial cells to treat LSCD has been explored in humans. The present review focuses on the current state of knowledge of the many other cell-based therapies of LSCD that have so far exclusively been explored in animal models as there is currently no consensus on the best cell type for treating LSCD. Major findings of all these studies with special emphasis on substrates for culture and transplantation are systematically presented and discussed. Among the many potential cell types that still have not been used clinically, we conclude that two easily accessible autologous sources, epidermal stem cells and hair follicle-derived stem cells, are particularly strong candidates for future clinical trials.

Effect of Storage Temperature on Structure and Function of Cultured Human Oral Keratinocytes

Purpose/Aims

To assess the effect of storage temperature on the viability, phenotype, metabolism, and morphology of cultured human oral keratinocytes (HOK).

Materials and Methods

Cultured HOK cells were stored in HEPES- and sodium bicarbonate-buffered Minimum Essential Medium (MEM) at nine temperatures in approximately 4°C increments from 4°C to 37°C for seven days. Cells were characterized for viability by calcein fluorescence, phenotype retention by immunocytochemistry, metabolic parameters (pH, glucose, lactate, and O₂) within the storage medium by blood gas analysis, and morphology by scanning electron microscopy and light microscopy.

Results

Relative to the cultured, but non-stored control cells, a high percentage of viable cells were retained only in the 12°C and 16°C storage groups (85%±13% and 68%±10%, respectively). Expression of ABCG2, Bmi1, C/EBPδ, PCNA, cytokeratin 18, and caspase-3 were preserved after storage in the 5 groups between 4°C and 20°C, compared to the non-stored control. Glucose, pH and pO₂ in the storage medium declined, whereas lactate increased with increasing storage temperature. Morphology was best preserved following storage of the three groups between 12°C, 16°C, and 20°C.

Conclusion

We conclude that storage temperatures of 12°C and 16°C were optimal for maintenance of cell viability, phenotype, and morphology of cultured HOK. The storage method described in the present study may be applicable for other cell types and tissues; thus its significance may extend beyond HOK and the field of ophthalmology.

Potential Role of Induced Pluripotent Stem Cells (IPSCs) for Cell-Based Therapy of the Ocular Surface

The integrity and normal function of the corneal epithelium are crucial for maintaining the cornea’s transparency and vision. The existence of a cell population with progenitor characteristics in the limbus maintains a dynamic of constant epithelial repair and renewal. Currently, cell-based therapies for bio replacement—cultured limbal epithelial transplantation (CLET) and cultured oral mucosal epithelial transplantation (COMET)—present very encouraging clinical results for treating limbal stem cell deficiency (LSCD) and restoring vision. Another emerging therapeutic approach consists of obtaining and implementing human progenitor cells of different origins in association with tissue engineering methods. The development of cell-based therapies using stem cells, such as human adult mesenchymal or induced pluripotent stem cells (IPSCs), represent a significant breakthrough in the treatment of certain eye diseases, offering a more rational, less invasive, and better physiological treatment option in regenerative medicine for the ocular surface. This review will focus on the main concepts of cell-based therapies for the ocular surface and the future use of IPSCs to treat LSCD.

Effect of storage temperature on cultured epidermal cell sheets stored in xenobiotic-free medium

Cultured epidermal cell sheets (CECS) are used in regenerative medicine in patients with burns, and have potential to treat limbal stem cell deficiency (LSCD), as demonstrated in animal models. Despite widespread use, short-term storage options for CECS are limited. Advantages of storage include: flexibility in scheduling surgery, reserve sheets for repeat operations, more opportunity for quality control, and improved transportation to allow wider distribution. Studies on storage of CECS have thus far focused on cryopreservation, whereas refrigeration is a convenient method commonly used for whole skin graft storage in burns clinics. It has been shown that preservation of viable cells using these methods is variable. This study evaluated the effect of different temperatures spanning 4°C to 37°C, on the cell viability, morphology, proliferation and metabolic status of CECS stored over a two week period in a xenobiotic–free system. Compared to non-stored control, best cell viability was obtained at 24°C (95.2±9.9%); reduced cell viability, at approximately 60%, was demonstrated at several of the temperatures (12°C, 28°C, 32°C and 37°C). Metabolic activity was significantly higher between 24°C and 37°C, where glucose, lactate, lactate/glucose ratios, and oxygen tension indicated increased activation of the glycolytic pathway under aerobic conditions. Preservation of morphology as shown by phase contrast and scanning electron micrographs was best at 12°C and 16°C. PCNA immunocytochemistry indicated that only 12°C and 20°C allowed maintenance of proliferative function at a similar level to non-stored control. In conclusion, results indicate that 12°C and 24°C merit further investigation as the prospective optimum temperature for short-term storage of cultured epidermal cell sheets.

The impact of storage temperature on the morphology, viability, cell number and metabolism of cultured human conjunctival epithelium

PURPOSE

To evaluate the effect of storage temperature on the morphology, viability, cell number and metabolism of cultured human conjunctival epithelial cells (HCjEs).

MATERIALS AND METHODS

Three-day cultured HCjEs were stored at nine different temperatures between 4 °C and 37 °C for four and seven days. Phenotype was assessed by immunofluorescence microscopy, morphology by scanning electron microscopy, viability and cell number by a microplate fluorometer and glucose metabolism by a blood gas analyzer.

RESULTS

Cultured cells not subjected to storage expressed the conjunctival cytokeratins 7 and 19 and the proliferation marker proliferating cell nuclear antigen. Cell morphology was best maintained following four-day storage between 12 °C and 28 °C and following 12 °C storage after seven days. Assessed by propidium iodide uptake, the percentage of viable cells after four-day storage was maintained only between 12 °C and 28 °C, whereas it had decreased in all other groups (p < 0.05; n = 4). After seven days this percentage was maintained in the 12 °C group, but it had decreased in all other groups, compared to the control (p < 0.05; n = 4). The total number of cells remaining in the cultures after four-day storage, compared to the control, had declined in all groups (p < 0.05; n = 4), except 12 °C and 20 °C groups. Following seven days this number had decreased in all groups (p < 0.01; n = 4), except 12 °C storage. Four-day storage at 12 °C demonstrated superior preservation of the number of calcein-stained viable cells (p < 0.05) and the least accumulation of ethidium homodimer 1-stained dead cells (p < 0.001), compared to storage at 4 °C and 24 °C (n = 6). The total metabolism of glucose to lactate after four-day storage was higher in the 24 °C group compared to 4 °C and 12 °C groups, as well as the control (p < 0.001; n = 3).

CONCLUSIONS

Storage at 12 °C appears optimal for preserving the morphology, viability and total cell number in stored HCjE cultures. The superior cell preservation at 12 °C may be related to temperature-associated effects on cell metabolism.

Antioxidants Improve the Viability of Stored Adult Retinal Pigment Epithelial-19 Cultures

Introduction

There is increasing evidence that retinal pigment epithelium (RPE) can be used to treat age-related macular degeneration, one of the leading causes of blindness worldwide. However, the best way to store RPE to enable worldwide distribution is unknown. We investigated the effects of supplementing our previously published storage method with seven additives, attempting to improve the number of viable adult retinal pigment epithelial (ARPE)-19 cells after storage.

Materials and methods

ARPE-19 cells were cultured on multiwell plates before being stored for 1 week at 16 °C. Unsupplemented Minimal Essential Medium (MEM) (control) and a total of seven individual additives (DADLE ([d-Ala², d-Leu⁵]-encephalin), capsazepine, docosahexaenoic acid (DHA), resveratrol, quercetin, simvastatin and sulforaphane) at three to four concentrations in MEM were tested. The individual effect of each additive on cell viability was analyzed with a microplate fluorometer. Cell phenotype was investigated by both microplate fluorometer and epifluorescence microscopy, and morphology by scanning electron microscopy.

Results

Supplementation of the storage medium with DADLE, capsazepine, DHA or resveratrol significantly increased the number of viable cells by 86.1% ± 41.9%, 67.9% ± 24.7%, 36.5% ± 10.3% and 21.1% ± 6.4%, respectively, compared to cells stored in unsupplemented MEM. DHA and resveratrol significantly reduced caspase-3 expression, while expression of RPE65 was maintained across groups.

Conclusion

The number of viable ARPE-19 cells can be increased by the addition of DADLE, capsazepine, DHA or resveratrol to the storage medium without perturbing apoptosis or differentiation.

Electronic supplementary material

The online version of this article (doi:10.1007/s40123-014-0024-9) contains supplementary material, which is available to authorized users.

Optimization of Storage Temperature for Cultured ARPE-19 Cells

Purpose. The establishment of future retinal pigment epithelium (RPE) replacement therapy is partly dependent on the availability of tissue-engineered RPE cells, which may be enhanced by the development of suitable storage methods for RPE. This study investigates the effect of different storage temperatures on the viability, morphology, and phenotype of cultured RPE. Methods. ARPE-19 cells were cultured under standard conditions and stored in HEPES-buffered MEM at nine temperatures (4°C, 8°C, 12°C, 16°C, 20°C, 24°C, 28°C, 32°C, and 37°C) for seven days. Viability and phenotype were assessed by a microplate fluorometer and epifluorescence microscopy, while morphology was analyzed by scanning electron microscopy. Results. The percentage of viable cells preserved after storage was highest in the 16°C group (48.7% ± 9.8%; P < 0.01 compared to 4°C, 8°C, and 24°C–37°C; P < 0.05 compared to 12°C). Ultrastructure was best preserved at 12°C, 16°C, and 20°C. Expression of actin, ZO-1, PCNA, caspase-3, and RPE65 was maintained after storage at 16°C compared to control cells that were not stored. Conclusion. Out of nine temperatures tested between 4°C and 37°C, storage at 12°C, 16°C, and 20°C was optimal for maintenance of RPE cell viability, morphology, and phenotype. The preservation of RPE cells is critically dependent on storage temperature.

Stem cell-based therapy for corneal epithelial reconstruction: present and future

Limbal stem cell deficiency is a painful and potentially blinding disease. Cultured limbal epithelial transplantation (CLET) is frequently performed for corneal surface reconstruction with variable clinical success. This work summarizes recent developments and trends that have the potential to increase safety and efficacy of CLET in the future. Apart from gradual transition to xenobiotic-free culture systems, novel biofunctional scaffolds presenting components of stem cell microenvironments aim at promoting long-term maintenance of stem cells in vitro and after transplantation. Hair follicles and other tissues may serve as autologous sources of adult stem cells in bilateral ocular surface disease. However, despite all progress made in the fields of tissue engineering and cell therapy, it is unlikely that CLET will yield fully satisfactory clinical results until the factors that govern limbal stem cell maintenance and differentiation are identified.

Stem Cells and Ocular Tissue Regeneration

PURPOSE

Millions worldwide have visual impairments caused by dysfunctional eye components, including cornea, lens, retina, and optic nerve, or the visual cortex in the brain. Insufficient cornea donation and inherent artificial lens problems demand alternative treatment strategies for cornea diseases and cataracts, whereas retinal degenerative diseases, including glaucoma, macular degeneration, and retinitis pigmentosa, still lack effective treatments. Stem cells have been investigated for their potential in various eye-specific pathologies to replace lost retinal ganglion cells and photoreceptors in retinal degenerative diseases and toward engineering transplantable patient-specific cornea or lens.

DESIGN

Many stem cell types, including putative resident eye stem cells, mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells, have been investigated for their potential to generate specific cell types in the eye in culture and after transplantation and to engineer eye tissues in combination with structural scaffolds.

METHOD

Cultured stem cells and in vitro differentiated eye-specific cells are transplanted into different locations of the eye to test their ability to produce functional cells for supporting eye functions. In addition, stem cells have been directly tested in vitro for their capacity to engineer eye-specific tissues.

RESULTS

Different stem cell types have been shown to have distinct capacities to produce eye-specific cells or even the entire retina.

CONCLUSIONS

Stem cells offer great hope for treating various eye pathologies. Despite recent progress, many challenges must still be overcome before the era of stem cell-based therapy in the eye truly arrives.

Limbal epithelial cell therapy: past, present, and future

The cornea, the clear window at the front of the eye, transmits light to the retina to enable vision. The corneal surface is renewed by stem cells located at the peripheral limbal region. These cells can be destroyed by a number of factors, including chemical burns, infections, and autoimmune diseases, which result in limbal stem cell deficiency (LSCD), a condition that can lead to blindness. Established therapy for LSCD based on ex vivo expanded limbal epithelial cells is currently at a stage of refinement. Therapy for LSCD is also rapidly evolving to include alternative cell types and clinical approaches as treatment modalities. In the present perspectives chapter, strategies to treat LSCD are discussed and advances in this important field of regenerative medicine are highlighted.

Progenitor cells for ocular surface regenerative therapy

The integrity and normal function of the corneal epithelium are essential for maintaining the cornea's transparency and vision. The existence of a cell population with progenitor characteristics in the limbus maintains a dynamic of constant epithelial repair and renewal. Currently, cell-based therapies for bio-replacement, such as cultured limbal epithelial transplantation and cultured oral mucosal epithelial transplantation, present very encouraging clinical results for treating limbal stem cell deficiencies. Another emerging therapeutic strategy consists of obtaining and implementing human progenitor cells of different origins using tissue engineering methods. The development of cell-based therapies using stem cells, such as human adult mesenchymal stromal cells, represents a significant breakthrough in the treatment of certain eye diseases and also offers a more rational, less invasive and more physiological approach to ocular surface regeneration.

Bone marrow cells and CD117-positive haematopoietic stem cells promote corneal wound healing

PURPOSE

The present study was conducted to evaluate the therapeutic effects of topically applied bone marrow (BM) cells and CD117-positive haematopoietic stem (CD117(+)) cells on alkali-induced corneal ulcers.

METHODS

Bone marrow cells and CD117(+) cells were isolated from syngenic mice and labelled with an intracellular cell tracer. Defined corneal wounds were produced in 89 eyes of syngenic mice and allowed to partially heal in vivo for 6 hr. The alkali-burned eyes were enucleated 6 hr postinjury and randomly divided into three groups. Control group (33 eyes) was incubated with medium only. The treatment groups received either BM cells (30 eyes) or CD117(+) cells (26 eyes) suspended in medium. Re-epithelialization process of corneal defects was qualitatively and quantitatively assessed and statistically analysed. The corneas were examined by histological and immunohistochemical methods.

RESULTS

We found that the re-epithelialization of corneal wounds in both treatment groups was significantly accelerated as compared to the control group. During the follow-up period (85 hr), the corneal transparency was comparable in all groups. Morphological investigations of corneas from control and treatment group showed no evident differences in the phenotype of the regenerated epithelium. Additionally, corneas in the treatment groups were devoid of donor-derived BM cells and CD117(+) cells, respectively.

CONCLUSIONS

This study provides evidence that topical application of BM cells or CD117(+) cells can be used to reconstruct corneal surfaces. Because neither BM cells nor CD117(+) cells were integrated into the corneal epithelium, we suggest that soluble factors could be responsible for the positive effect of BM cells and CD117(+) cells on corneal wound healing.

Limbal stem cell deficiency in patients with inherited stem cell disorder of dyskeratosis congenita

The aim of this study is to present the limbal stem cell deficiency (LSCD) cases with features resembling dyskeratosis congenita (DC), a heritable disease of stem cells principally caused by telomerase deficiency. The clinical, laboratory and molecular findings of four cases are presented. A complete systemic examination was performed in a standardized manner for each patient. Laboratory measurements included investigations of the tests used for screening DC. All eight known disease-causing genes in DC (DKC1, TERC, TERT, NOP10, NHP2, TINF2, C16orf57, and TCAB1) were screened for mutations. The family members of the cases were also assessed, when possible. In all four patients, multisystem involvement was present, along with the disorder affecting corneal LSCs. The affected tissues were mainly the skin and its adnexa, the oral cavity and the hematopoietic system, which are rapidly renewing tissues, consistent with the presence of a stem cell disorder. Similarly affected cases were seen in different generations in families, suggesting an underlying inherited disorder. No mutation was detected in any of the known disease-causing genes in these patients. Based on the presented cases and with the contribution of the review of previously reported DC cases available, we suggest that DC is one of the inherited causes of LSCD and that those cases presenting with LSCD might represent a subgroup of DC caused by mutations in an as yet undefined gene.

Concise review: limbal stem cell deficiency, dysfunction, and distress

The cornea is the clear tissue at the front of the eye that transmits light to the retina at the back of the eye. The cornea is covered by an epithelium and surrounded by a narrow band of tissue known as the limbus. The limbus has two important roles in maintaining a healthy corneal epithelium. First, stem cells for the corneal epithelium reside at the limbus and not in the cornea. Second, the limbus acts as a barrier separating the clear avascular corneal epithelium from the surrounding vascular conjunctival tissue. A failure of these limbal functions can result in the painful and blinding disease of limbal stem cell deficiency. In this disease, the corneal epithelium cannot be maintained by the stem cells, and the corneal surface becomes replaced by hazy conjunctival tissue. There are many causes of limbal stem cell deficiency, such as burns to the eye, inflammatory diseases, and hereditary diseases. Current understanding of the pathophysiology of the disease is discussed here. In particular, understanding whether the limbal stem cells are lost or become dysfunctional or indeed whether the limbal microenvironment is disturbed is important when developing appropriate management strategies for the disease.

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

The cornea is the clear tissue at the front of the eye which enables the transmission of light to the retina for normal vision. The surface of the cornea is composed of an epithelium which is renewed by stem cells located at the periphery of the cornea, a region known as the limbus. These limbal stem cells can become deficient as a result of various diseases of the eye's surface, resulting in the blinding disease of limbal stem cell deficiency. The treatment of this disease is often difficult and complex. In 1997, it was proposed that a small amount of limbal tissue containing limbal stem cells could be culture expanded and then transplanted. Since then various case reports and case series have been reported showing promising results. Here, we review the outcomes of this procedure over the past 13 years with the aim of highlighting the best culture and surgical techniques to date.