Ex vivo expansion and transplantation of limbal epithelial stem cells

Regulatory requirements in the good manufacturing practice production of an epithelial cell graft for ocular surface reconstruction

In the past decade, stem cell therapy has been increasingly employed for the treatment of various diseases. Subsequently, there has been a great interest in the manufacture of stem cells under good manufacturing practice, which is required by law for their use in humans. The cells for sight Stem Cell Therapy Research Unit, based at UCL Institute of Ophthalmology, delivers somatic cell-based and tissue-engineered therapies to patients suffering from blinding eye diseases at Moorfields Eye Hospital (London, UK). The following article is based on our experience in the conception, design, construction, validation and manufacturing within a good manufacturing practice manufacturing facility based in the UK. As such the regulations can be extrapolated to the 28 members stated within the EU. However, the principles may have a broad relevance outside the EU.

Culture of Oral Mucosal Epithelial Cells for the Purpose of Treating Limbal Stem Cell Deficiency

The cornea is critical for normal vision as it allows allowing light transmission to the retina. The corneal epithelium is renewed by limbal epithelial cells (LEC), which are located in the periphery of the cornea, the limbus. Damage or disease involving LEC may lead to various clinical presentations of limbal stem cell deficiency (LSCD). Both severe pain and blindness may result. Transplantation of cultured autologous oral mucosal epithelial cell sheet (CAOMECS) represents the first use of a cultured non-limbal autologous cell type to treat this disease. Among non-limbal cell types, CAOMECS and conjunctival epithelial cells are the only laboratory cultured cell sources that have been explored in humans. Thus far, the expression of p63 is the only predictor of clinical outcome following transplantation to correct LSCD. The optimal culture method and substrate for CAOMECS is not established. The present review focuses on cell culture methods, with particular emphasis on substrates. Most culture protocols for CAOMECS used amniotic membrane as a substrate and included the xenogeneic components fetal bovine serum and murine 3T3 fibroblasts. However, it has been demonstrated that tissue-engineered epithelial cell sheet grafts can be successfully fabricated using temperature-responsive culture surfaces and autologous serum. In the studies using different substrates for culture of CAOMECS, the quantitative expression of p63 was generally poorly reported; thus, more research is warranted with quantification of phenotypic data. Further research is required to develop a culture system for CAOMECS that mimics the natural environment of oral/limbal/corneal epithelial cells without the need for undefined foreign materials such as serum and feeder cells.

Human Platelet Lysate as a Replacement for Fetal Bovine Serum in Limbal Stem Cell Therapy

PURPOSE

To evaluate the use of human platelet lysate (HPL) as an alternative supplement for limbal explant culture.

METHODS

Culture media were prepared using either 10% pooled HPL (PHPL), single donor HPL, or fetal bovine serum (FBS). Limbal tissues, obtained from the Minnesota Lions Eye Bank, were cultured in each medium on plastic plates or on denuded amniotic membrane (AM). Immunofluorescence staining was performed for ABCG2, tumor protein p63α, and cytokeratin 3 (K3). Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to evaluate the expression of ABCG2 and p63. Limbal explants grown in each medium were labeled with bromodeoxyuridine (BrdU) to assess the proliferative capacity in each medium. Concentration of growth factors including epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), and platelet derived growth factor (PDGF) in HPL and PHPL was compared to that in human serum (HS).

RESULTS

Immunofluorescence staining on AM showed prominent expression of ABCG2, p63α but sparse expression of K3 in HPL and PHPL supplemented medium. Real time-PCR showed 1.7 fold higher expression of ABCG2 in PHPL supplemented medium (p = 0.03), and similar expression of p63 in HPL and PHPL supplemented medium compared to FBS medium. The proliferation assay showed that LSCs retained their proliferative potential in HPL supplemented medium. Higher concentration of growth factors were found in HPL, compared to HS.

CONCLUSIONS

Human platelet lysate has higher concentration of grown factors and is effective in maintaining growth and stem cell phenotype of corneal limbal explant cultures.

Limbal Stem Cell Deficiency: Current Treatment Options and Emerging Therapies

Severe ocular surface disease can result in limbal stem cell deficiency (LSCD), a condition leading to decreased visual acuity, photophobia, and ocular pain. To restore the ocular surface in advanced stem cell deficient corneas, an autologous or allogenic limbal stem cell transplantation is performed. In recent years, the risk of secondary LSCD due to removal of large limbal grafts has been significantly reduced by the optimization of cultivated limbal epithelial transplantation (CLET). Despite the great successes of CLET, there still is room for improvement as overall success rate is 70% and visual acuity often remains suboptimal after successful transplantation. Simple limbal epithelial transplantation reports higher success rates but has not been performed in as many patients yet. This review focuses on limbal epithelial stem cells and the pathophysiology of LSCD. State-of-the-art therapeutic management of LSCD is described, and new and evolving techniques in ocular surface regeneration are being discussed, in particular, advantages and disadvantages of alternative cell scaffolds and cell sources for cell based ocular surface reconstruction.

Stem Cell Therapy for Corneal Epithelium Regeneration following Good Manufacturing and Clinical Procedures

Objective. To evaluate outcomes of cultivated limbal epithelial transplantation (CLET) for management of ocular surface failure due to limbal stem cell deficiency (LSCD). Design. Prospective, noncomparative, interventional case series and extensive comparison with recent similar studies. Participants. Twenty eyes with LSCD underwent CLET (11 autologous; 9 allogeneic) and were followed up for 3 years. Etiologies were divided into 3 prognostic categories: Group 1, chemical injuries (7 eyes); Group 2, immune-based inflammation (4 eyes); and Group 3, noninflammatory diseases (9 eyes). Intervention. Autologous and allogeneic limbal epithelial cells were cultivated on amniotic membranes and transplanted. Evaluations were based on clinical parameters, survival analysis, and in vivo confocal microscopy (IVCM). European Union Tissues/Cells Directive and good manufacturing procedures were followed. Main Outcome Measures. Improved clinical parameters, absence of epithelial defects, and improved central corneal epithelial phenotype. Results. Success rate was 80% at 1-2 years and 75% at 3 years. Autografts and allografts had similar survival. Success rate was significantly lower in prognostic Group 1 (42.9%) than in Groups 2-3 (100% each). All clinical parameters improved substantially. By IVCM, 80% of cases improved in epithelial status. Conclusions. CLET improved corneal epithelium quality, with subsequent improvement in symptoms, quality of life, and vision. These results confirm that CLET is a valid therapy for ocular surface failure.

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.

Corneal stem cells and tissue engineering: Current advances and future perspectives

Major advances are currently being made in regenerative medicine for cornea. Stem cell-based therapies represent a novel strategy that may substitute conventional corneal transplantation, albeit there are many challenges ahead given the singularities of each cellular layer of the cornea. This review recapitulates the current data on corneal epithelial stem cells, corneal stromal stem cells and corneal endothelial cell progenitors. Corneal limbal autografts containing epithelial stem cells have been transplanted in humans for more than 20 years with great successful rates, and researchers now focus on ex vivo cultures and other cell lineages to transplant to the ocular surface. A small population of cells in the corneal endothelium was recently reported to have self-renewal capacity, although they do not proliferate in vivo. Two main obstacles have hindered endothelial cell transplantation to date: culture protocols and cell delivery methods to the posterior cornea in vivo. Human corneal stromal stem cells have been identified shortly after the recognition of precursors of endothelial cells. Stromal stem cells may have the potential to provide a direct cell-based therapeutic approach when injected to corneal scars. Furthermore, they exhibit the ability to deposit organized connective tissue in vitro and may be useful in corneal stroma engineering in the future. Recent advances and future perspectives in the field are discussed.

Ex vivo human corneal epithelial cell expansion from a xeno-feeder-free system

PURPOSE

The purpose of this study was to establish a simple, xeno-feeder-free method for cultivating human corneal epithelial cells.

METHODS

Limbal tissue explants from a cadaver were cultured in Iscove's modified Dulbecco's medium and low-calcium Panserin 801 medium in a 1:1 ratio. The outgrowing cells were characterized by flow cytometry, immunohistochemistry and real-time PCR (rtPCR). Limbal epithelial cells were expanded in a xeno-feeder-free, low-calcium medium and airlifted for 2 weeks each.

RESULTS

Migration of fibroblast-like stromal cells initially occurred from the limbal explants, and then epithelial cells migrated and grew on the stromal cells as an autofeeder layer. After airlifting, the cultured epithelium consisted of two to three layers. The cultured cells expressed stem cell-associated markers (ABCG2 and ΔNp63), differentiation markers (CK3 and CK12) and extracellular matrix-associated markers (lumican and decorin). rtPCR showed increased expression of markers for epithelial progenitor cells compared to fresh limbal tissue. Side population cells comprised 0.43 ± 0.04% of the cells (n = 5) in the primary culture. Flow cytometry showed that 49.12, 40.44 and 44.55% of the cells from the explants expressed E-cadherin, ΔNp63 and ABCG2, respectively.

CONCLUSION

This explant culture system using stromal cells as an autofeeder layer was useful in expanding human corneal epithelial cells. This system may offer clinical insight for the expansion of limbal progenitor cells for the reconstruction of the ocular surface.

Transforming ocular surface stem cell research into successful clinical practice

It has only been a quarter of a century since the discovery of adult stem cells at the human corneo-scleral limbus. These limbal stem cells are responsible for generating a constant and unending supply of corneal epithelial cells throughout life, thus maintaining a stable and uniformly refractive corneal surface. Establishing this hitherto unknown association between ocular surface disease and limbal dysfunction helped usher in therapeutic approaches that successfully addressed blinding conditions such as ocular burns, which were previously considered incurable. Subsequent advances in ocular surface biology through basic science research have translated into innovations that have made the surgical technique of limbal stem cell transplantation simpler and more predictable. This review recapitulates the basic biology of the limbus and the rationale and principles of limbal stem cell transplantation in ocular surface disease. An evidence-based algorithm is presented, which is tailored to clinical considerations such as laterality of affliction, severity of limbal damage and concurrent need for other procedures. Additionally, novel findings in the form of factors influencing the survival and function of limbal stem cells after transplantation and the possibility of substituting limbal cells with epithelial stem cells of other lineages is also discussed. Finally this review focuses on the future directions in which both basic science and clinical research in this field is headed.

Response of human limbal epithelial cells to wounding on 3D RAFT tissue equivalents: effect of airlifting and human limbal fibroblasts

Limbal epithelial stem cell deficiency can cause blindness but may be treated by human limbal epithelial cell (hLE) transplantation, normally on human amniotic membrane. Clinical outcomes using amnion can be unreliable and so we have developed an alternative tissue equivalent (TE), RAFT (Real Architecture for 3D Tissue), which supports hLE expansion, and stratification when airlifted. Human limbal fibroblasts (hLF) may be incorporated into RAFT TEs, where they support overlying hLE and improve phenotype. However, the impact of neither airlifting nor hLF on hLE function has been investigated. hLE on RAFT TEs (±hLF and airlifting) were wounded using heptanol and re-epithelialisation (fluorescein diacetate staining), and percentage putative stem cell marker p63α and proliferative marker Ki67 expression (wholemount immunohistochemistry), measured. Airlifted, hLF- RAFT TEs were unable to close the wound and p63α expression was 7 ± 0.2% after wounding. Conversely, non-airlifted, hLF- RAFT TEs closed the wound within 9 days and p63α expression was higher at 22 ± 5% (p < 0.01). hLE on both hLF- and hLF+ RAFT TEs (non-airlifted) closed the wound and p63α expression was 26 ± 8% and 36 ± 3% respectively (ns). Ki67 expression by hLE increased from 1.3 ± 0.5% before wounding to 7.89 ± 2.53% post-wounding for hLF- RAFT TEs (p < 0.01), and 0.8 ± 0.08% to 17.68 ± 10.88% for hLF+ RAFT TEs (p < 0.05), suggesting that re-epithelialisation was a result of proliferation. These data suggest that neither airlifting nor hLF are necessarily required to maintain a functional epithelium on RAFT TEs, thus simplifying and shortening the production process. This is important when working towards clinical application of regenerative medicine products.

Inhibition of blood vessel formation by a chondrocyte-derived extracellular matrix

In this study, the chondrocyte-derived extracellular matrix (CECM) was evaluated for its activity to inhibit vessel invasion in vitro and in vivo. Human umbilical vein endothelial cells (HUVECs) and rabbit chondrocytes were plated on a bio-membrane made of CECM or human amniotic membrane (HAM). The adhesion, proliferation, and tube formation activity of HUVECs and chondrocytes were examined. The CECM and HAM powders were then mixed individually in Matrigel and injected subcutaneously into nude mice to examine vessel invasion in vivo after 1 week. Finally, a rabbit model of corneal neovascularization (NV) was induced by 3-point sutures in the upper cornea, and CECM and HAM membranes were implanted onto the corneal surface at day 5 after suture injury. The rabbits were sacrificed at 7 days after transplantation and the histopathological analysis was performed. The adhesion and proliferation of HUVECs were more efficient on the HAM than on the CECM membrane. However, chondrocytes on each membrane showed an opposite result being more efficient on the CECM membrane. The vessel invasion in vivo also occurred more deeply and intensively in Matrigel containing HAM than in the one containing CECM. In the rabbit NV model, CECM efficiently inhibited the neovessels formation and histological remodeling in the injured cornea. In summary, our findings suggest that CECM, an integral cartilage ECM composite, shows an inhibitory effect on vessel invasion both in vitro and in vivo, and could be a useful tool in a variety of biological and therapeutic applications including the prevention of neovascularization after cornea injury.

Results of a phase I/II clinical trial: standardized, non-xenogenic, cultivated limbal stem cell transplantation

BACKGROUND

To determine if a standardized, non-xenogenic, reduced manipulation cultivation and surgical transplantation of limbal stem cell grafts is a safe and effective treatment option for patients with total and partial limbal stem cell deficiency.

METHODS

In vitro cellular outgrowth and phenotype of the limbal epithelial cell and composite grafts were validated using a new protocol. Patients received either autologous (n = 15) or allogenic (n = 3) explants cultured using a standardized protocol free from xenogenic products. The resulting grafts were transplanted using a reduced manipulation surgical technique.

RESULTS

The majority of cells (>50%) displayed a progenitor phenotype typified by positive immunofluorescence for ∆Np63, CK14 and ABCG2 and low immunofluorescence for CK3/12 and desmoglein 3 proteins. The surgical protocol was designed to minimize manipulation and the graft itself was secured without sutures. The transplant recipients were followed for a mean of 24 months. Twelve of the 18 transplant recipients were graded as anatomically successful (67%), based on the defined success parameters. There was a significant reduction in corneal neovascularization, which was accompanied by an improvement in pain though not photophobia or central corneal opacity post transplant. The transplantation protocol showed no measureable effect on visual acuity.

CONCLUSION

We conclude that this standardized culture system and surgical approach is safe and effective in reducing corneal neovascularization. The technique is free from animal contaminants and maintains a large proportion of progenitor cells. Although this technique did not improve visual function, restoring a functional epithelial cell layer and reducing corneal neovascularization provides an improved platform for a penetrating keratoplasty to ultimately improve visual function.

Challenges in the development of a reference standard and potency assay for the clinical production of RAFT tissue equivalents for the cornea

Aim: To develop a reference standard and potency assay for Real Architecture For 3D Tissues (RAFT) tissue equivalents intended for use in limbal epithelial stem cell (LESC) therapy for the cornea. Methods: RAFT, a cell-seeded plastic compressed collagen construct with LESCs cultured on the surface, was manufactured with the goal of achieving GMP compliance. RAFTs were tested for reproducibility of manufacture (reference standard) and subsequently wounded and monitored for re-epithelialization (potency assay). Results: RAFT tissue equivalents produced with cells from different biological donors were capable of supporting multilayered epithelium in culture. The potency assay demonstrated re-epithelialization following wounding, indicating the potential efficacy of RAFT constructs. Conclusion: We have presented our attempts at creating a reference standard and potency assay for the clinical manufacture of RAFT for the treatment of LESC deficiency. However, it remains challenging for adult stem cell therapies (including LESC therapy) to fully meet regulatory requirements when dealing with a limited source of autologous cells with inherent biological variation between donors.

Optimal isolation and xeno-free culture conditions for limbal stem cell function

PURPOSE

To preserve limbal stem cell (LSC) function in vitro with xenobiotic-free culture conditions.

METHODS

Limbal epithelial cells were isolated from 139 donors using 15 variations of three dissociation solutions. All culture conditions were compared to the baseline condition of murine 3T3-J3 feeders with xenobiotic (Xeno) keratinocyte growth medium at 20% O2. Five Xeno and Xeno-free media with increasing concentrations of calcium and epidermal growth factor (EGF) were evaluated at 5%, 14%, and 20% O2. Human MRC-5, dermal (fetal, neonatal, or adult), and limbal stromal fibroblasts were compared. Statistical analysis was performed on the number of maximum serial weekly passages, percentage of aborted colonies, colony-forming efficiency (CFE), p63α(bright) cells, and RT-PCR ratio of p63α/K12. Immunocytochemistry and RT-PCR for p63α, ABCG2, Bmi1, C/EBPδ , K12, and MUC1 were performed to evaluate phenotype.

RESULTS

Dispase/TrypLE was the isolation method that consistently showed the best yield, viability, and CFE. On 3T3-J2 feeders, Xeno-free medium with calcium 0.1 mM and EGF 10 ng/mL at 20% O2 supported more passages with equivalent percentage of aborted colonies, p63α(bright) cells, and p63α/K12 RT-PCR ratio compared to baseline Xeno-media. With this Xeno-free medium, MRC-5 feeders showed the best performance, followed by fetal, neonatal, adult HDF, and limbal fibroblasts. MRC-5 feeders supported serial passages with sustained high expression of progenitor cell markers at levels as robust as the baseline condition without significant difference between 20% and 5% O2.

CONCLUSIONS

The LSC function can be maintained in vitro under appropriate Xeno-free conditions.

Three-year outcomes of cultured limbal epithelial allografts in aniridia and Stevens-Johnson syndrome evaluated using the Clinical Outcome Assessment in Surgical Trials assessment tool

Limbal stem cell deficiency (LSCD) is an eye disorder in which the stem cells responsible for forming the surface skin of the cornea are destroyed by disease. This results in pain, loss of vision, and a cosmetically unpleasant appearance. Many new treatments, including stem cell therapies, are emerging for the treatment of this condition, but assessment of these new technologies is severely hampered by the lack of biomarkers for this disease or validated tools for assessing its severity. The aims of this study were to design and test the reliability of a tool for grading LSCD, to define a set of core outcome measures for use in evaluating treatments for this condition, and to demonstrate their utility. This was achieved by using our defined outcome set (which included the Clinical Outcome Assessment in Surgical Trials of Limbal stem cell deficiency [COASTL] tool) to evaluate the 3-year outcomes for allogeneic ex vivo cultivated limbal epithelial transplantation (allo-CLET) in patients who had bilateral total LSCD secondary to aniridia or Stevens-Johnson syndrome. The results demonstrate that our new grading tool for LSCD, the COASTL tool, is reliable and repeatable, and that improvements in the biomarkers used in this tool correlate positively with improvements in visual acuity. The COASTL tool showed that following allo-CLET there was a decrease in LSCD severity and an increase in visual acuity up to 12 months post-treatment, but thereafter LSCD severity and visual acuity progressively deteriorated.

Review of alternative carrier materials for ocular surface reconstruction

Severe ocular surface disorders can result in deficiency of limbal stem cells that is potentially associated with chronic inflammation, impaired vision and even blindness. Advanced stem cells deficiency requires reconstruction of the OS with autologous or allogeneic limbal stem cells. To address such deficiency, a limbal tissue biopsy is taken and limbal cells are expanded on a carrier, which then can be used for OS reconstruction. Human amniotic membrane - currently the most common carrier for transplantation of limbal epithelial stem cells - has the downsides of carrying the risk of disease transmission, limited transparency, variable and unstable quality and low mechanical strength. This article reviews the advantages and disadvantages of the established carrier materials for limbal stem cell transplantation, as well as discussing emerging alternatives, including carriers based on collagen, fibrin, siloxane hydrogel contact lenses, poly(ε-caprolactone), gelatin-chitosan, silk fibroin, human anterior lens capsule, keratin, poly(lactide-co-glycolide), polymethacrylate, hydroxyethylmethacrylate and poly(ethylene glycol) for their potential use in the treatment of limbal stem cell deficiency.

Epithelial wound healing on keratin film, amniotic membrane and polystyrene in vitro

PURPOSE

Corneal epithelial wound healing is a major issue in ocular surface (OS) reconstruction. Aim of this study was to evaluate parameters of epithelial wound healing in vitro on transparent keratin films (KFs) derived from human hair in comparison with amniotic membrane (AM) and polystyrene.

MATERIALS AND METHODS

The human corneal epithelial cell line (HCE-T) was expanded on KF, AM and commercially available 24-well polystyrene cell culture plates in vitro to compare cell proliferation, migration and attachment by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, scratch-wound healing and adhesion assay. Cells cultured on KF and AM at an air-liquid interface for 14 d were stained with hematoxylin and eosin for histology.

RESULTS

The highest proliferation of HCE-T cells was observed on polystyrene at all time points (p < 0.05). At a seeding density of 5 × 10(3) cells/well, no difference in proliferation was found between AM and KF after 24 h and 72 h (p = 0.582 and p = 0.066), while higher proliferation was observed on AM compared to KF after 48 h (p = 0.005). At a seeding density of 1 × 10(4) cells/well, no difference was found between AM and KF after 24 h (p = 0.252), while higher proliferation was observed on AM compared to KF after 48 h and 72 h (p = 0.001 and p = 0.003). The significantly fastest cell migration was observed on polystyrene at all time points (p < 0.01). Cell migration was significantly higher on KF compared to AM at 48 h (p < 0.05). After 30 min, there were significantly more cells attached to AM compared to polystyrene and KF (p = 0.032 and p = 0.001). No significant difference in cell attachment was observed between KF and polystyrene (p = 0.147). Histology demonstrated that HCE-T cells cultured on KF and AM at an air-liquid interface for 14 d form a multilayered epithelium similar to normal human corneal epithelium.

CONCLUSION

Transparent KFs derived from human hair support proliferation, migration, adhesion and differentiation of HCE-T cells in vitro. Therefore, it could be a promising alternative to AM for OS reconstruction.

Chitosan-gelatin biopolymers as carrier substrata for limbal epithelial stem cells

The aim of this work was to evaluate semi-synthetic biopolymers based on chitosan (CH) and gelatin (G) as potential in vitro carrier substrata for human limbal epithelial cells (hLECs). To that end, human corneal epithelial cells (HCE) were cultured onto different CH-G membranes. None of the polymers were cytotoxic and cell proliferation was higher when CH was functionalized with G. Expression levels of corneal epithelial markers (K3, K12, E-caherin, desmoplakin, and zonula occludens (ZO)-1) were better maintained in HCE cells grown on CH-G 20:80 membranes than other proportions. Consequently, CH-G 20:80 was chosen for the subsequent expansion of hLECs. Cells derived from limbal explants were successfully expanded on CH-G 20:80 membranes using a culture medium lacking components of non-human animal origin. The expression levels found for corneal (K3 and K12) and limbal epithelial stem cells (K15) specific markers were similar to or higher than those found in limbal cells grown onto the control substratum. Our results demonstrate that CH-G 20:80 membranes are suitable for the expansion and maintenance of stem cells derived from the limbal niche. These results strongly support the use of polymers as alternative substrata for the transplantation of cultivated limbal cells onto the ocular surface.

A simple alkaline method for decellularizing human amniotic membrane for cell culture

Human amniotic membrane is a standard substratum used to culture limbal epithelial stem cells for transplantation to patients with limbal stem cell deficiency. Various methods were developed to decellularize amniotic membrane, because denuded membrane is poorly immunogenic and better supports repopulation by dissociated limbal epithelial cells. Amniotic membrane denuding usually involves treatment with EDTA and/or proteolytic enzymes; in many cases additional mechanical scraping is required. Although ensuring limbal cell proliferation, these methods are not standardized, require relatively long treatment times and can result in membrane damage. We propose to use 0.5 M NaOH to reliably remove amniotic cells from the membrane. This method was used before to lyse cells for DNA isolation and radioactivity counting. Gently rubbing a cotton swab soaked in NaOH over the epithelial side of amniotic membrane leads to nearly complete and easy removal of adherent cells in less than a minute. The denuded membrane is subsequently washed in a neutral buffer. Cell removal was more thorough and uniform than with EDTA, or EDTA plus mechanical scraping with an electric toothbrush, or n-heptanol plus EDTA treatment. NaOH-denuded amniotic membrane did not show any perforations compared with mechanical or thermolysin denuding, and showed excellent preservation of immunoreactivity for major basement membrane components including laminin α2, γ1-γ3 chains, α1/α2 and α6 type IV collagen chains, fibronectin, nidogen-2, and perlecan. Sodium hydroxide treatment was efficient with fresh or cryopreserved (10% dimethyl sulfoxide or 50% glycerol) amniotic membrane. The latter method is a common way of membrane storage for subsequent grafting in the European Union. NaOH-denuded amniotic membrane supported growth of human limbal epithelial cells, immortalized corneal epithelial cells, and induced pluripotent stem cells. This simple, fast and reliable method can be used to standardize decellularized amniotic membrane preparations for expansion of limbal stem cells in vitro before transplantation to patients.

Concise review: immunological properties of ocular surface and importance of limbal stem cells for transplantation

Cornea transplantation has been considered to be different from other solid organ transplantation because of the assumed immune-privileged state of the anterior chamber of the eye. Three major lines of thought regarding the molecular mechanisms of immune privilege in the eye are as follows: (a) anatomical, cellular, and molecular barriers in the eye; (b) anterior chamber-associated immune deviation; and (c) immunosuppressive microenvironment in the eye. However, cornea transplants suffer allograft rejection when breached by vascularization. In recent developments, cellular corneal transplantation from cultivated limbal epithelial cells has shown impressive advances as a future therapy. The limbal stem cell niche contains stem cells that promote proliferation and migration and have immunosuppressive mechanisms to protect them from immunological reactions. Limbal stem cells are also noted to display an enhanced expression of genes for the antiapoptotic proteins, a property that is imperative for the survival of transplanted tissues. Further investigation of the molecular mechanisms regulating the immune regulation of limbal stem cells is relevant in the clinical setting to promote the survival of whole corneal and limbal stem cell transplantation.

Ex-vivo ocular surface stem cell therapies: current techniques, applications, hurdles and future directions

Engineered tissue derived from ocular surface stem cells (SCs) are a cutting edge biotechnology for repair and restoration of severely damaged eyes as a result of ocular surface dysfunction because of SC failure. Ex-vivo SC expansion techniques have advanced significantly since the first patients were treated in the late 1990s. The techniques and clinical reports reviewed here highlight the evolution and successes of these techniques, while also revealing gaps in our understanding of ocular surface and SC biology that drives further research and development in this field. Although hurdles still remain before stem-cell-based therapies are more widely available for patients with devastating ocular surface disease, recent discoveries in the field of mesenchymal SCs and the potential of induced pluripotent SCs heralds a promising future for clinicians and our patients.

In vitro simulation of corneal epithelium microenvironment induces a corneal epithelial-like cell phenotype from human adipose tissue mesenchymal stem cells

PURPOSE

Transplantation of autologous corneal stem cells in not possible in cases of bilateral limbal stem cell deficiency (LSCD). To restore the ocular surface in these patients, an autologous extraocular source of stem cells is desirable to avoid dependence on deceased donor tissue and host immunosuppression of allogenic transplants. While bone marrow-derived mesenchymal stem cells (MSCs) can acquire certain characteristics of corneal epithelial cells, subcutaneous adipose tissue (AT) is more readily available and accessible. The aim of this study was to determine if extraocular human AT-derived MSCs (hAT-MSCs) can acquire in vitro some features of corneal epithelial-like cells.

METHODS

hAT-MSCs were isolated from human lipoaspirates and expanded up to 3-4 passages. We studied the immunophenotype of MSCs and demonstrated its multipotent capacity to differentiate toward osteoblasts, adipocytes and chondrocytes. To test the capacity of differentiation of hAT-MSCs toward corneal epithelial-like cells, hAT-MSCs were cultured on substrata of plastic or collagen IV. We used basal culture medium (BM), BM conditioned with human corneal epithelial cells (HCEcBM) and BM conditioned with limbal fibroblasts (LFcBM).

RESULTS

The hAT-MSCs incubated for 15 days with HCEcBM acquired more polygonal and complex morphology as evaluated by phase-contrast microscopy and flow cytometry. Additionally, the expression of transforming growth factor-β receptor CD105 and corneal epithelial marker CK12 got increased as evaluated by flow cytometry, real-time reverse-transcription polymerase chain reaction, western blot and immunostaining. These changes were absent in hAT-MSCs incubated with unconditioned BM or with LFcBM.

CONCLUSIONS

Corneal epithelial-like cells can be induced from extraocular hAT-MSCs by subjecting them to an in vitro microenvironment containing conditioning signals derived from differentiated human corneal epithelial cells. Our results suggest that hAT-MSCs could provide a novel source of stem cells that hold the potential to restore sight lost in patients suffering from bilateral ocular surface failure due to LSCD.

Phenotypic evaluation of severely damaged ocular surface after reconstruction by cultured limbal epithelial cell transplantation

OBJECTIVE

To report the clinical outcome of autologous cultured limbal epithelial cell transplantation (CLECT) followed by deep anterior lamellar keratoplasty (DALK) in paediatric eyes and to correlate the clinical outcome with the phenotype of rejuvenated corneal epithelium.

METHODS

Four patients with total limbal stem cell deficiency (LSCD) underwent autologous CLECT. Cultivated cell sheets were transplanted onto the damaged ocular surface followed by DALK surgery. Excised corneal buttons were subjected to histopathological analysis. Data recorded included age, sex, laterality, nature of injury, follow-up period, severity of stem cell deficiency, visual acuity, Schirmer's test and impression cytology.

RESULTS

At a mean follow-up period of 19.5 ± 7.4 (range 9-26) months after CLECT, all 4 eyes showed epithelialized and clinically stabilized ocular surface. Manual DALK was performed in all 4 eyes, with a mean follow-up of 9.75 ± 4.5 (range 5-15) months. All eyes exhibited smooth and clear corneal epithelium with improved visual acuity. Excised corneal buttons demonstrated organized corneal epithelial morphology and showed expression of cornea-specific CK3/12 marker.

CONCLUSION

Restoration of severely damaged ocular surface following chemical injury by using 2-stage meticulous approaches offers a new modality for the treatment of severe LSCD. Transplantation of cultivated autologous limbal epithelial cell sheet followed by DALK surgery can efficiently restore the corneal phenotype with improved vision.

Human corneal epithelial subpopulations: oxygen dependent ex vivo expansion and transcriptional profiling

Corneal epithelium is being regenerated throughout life by limbal epithelial stem cells (LESCs) believed to be located in histologically defined stem cell niches in corneal limbus. Defective or dysfunctional LESCs result in limbal stem cell deficiency (LSCD) causing pain and decreased visual acuity. Since the first successful treatment of LSCD by transplantation of ex vivo expanded LESCs in 1997, many attempts have been carried out to optimize culture conditions to improve the outcome of surgery. To date, progress in this field of bioengineering is substantially hindered by both the lack of specific biomarkers of LESCs and the lack of a precise molecular characterization of in situ epithelial subpopulations. The aim of this dissertation was to optimize culture systems with regard to the environmental oxygen concentration for selective ex vivo expansion of LESCs and to analyse in situ subpopulations in human corneal epithelium using a combination of laser capture microdissection and RNA sequencing for global transcriptomic profiling. We compared dissociation cultures, using either expansion on γ-irradiated NIH/3T3 feeder cells in serum-rich medium or expansion directly on plastic in serum-free EpiLife medium, using a range of physiologically relevant oxygen concentrations (2%, 5%, 10%, 15% and 20%). Using immunocytochemistry and advanced fluorescence microscopy, cells were characterized regarding growth, cell cycle distribution, colony-forming efficiency (CFE), phenotypes and cytomorphometry. Limbal epithelial cells expanded in 2% O2 exhibited slow growth, low fraction of cells in S/G2 , high CFE, high expression of stem cell markers ABCG2 and p63α, and low fraction of differentiation marker CK3 resembling a LESC phenotype. The effect of hypoxia to maintain LESCs in culture was not dependent on the system used for propagation (Bath et al. 2013a). Laser capture microdissection was used to isolate cellular subpopulations in situ from the spatially defined differentiation pathway in human corneal epithelium according to an optimized protocol for maintenance of expression profiles. Isolated total RNA from basal limbal crypts (BLCs), superficial limbal crypts (SLCs), paracentral/central cornea and limbal stroma was amplified and converted to fragmented cDNA libraries for use in deep paired-end next-generation sequencing. Global transcriptional profiling was carried out using bioinformatics. The location of primitive cells in BLCs, migratory and activated cells in SLCs and differentiated cells in paracentral/central cornea was evident from mapping of significantly upregulated genes in each compartment to the gene ontology (GO). Interestingly, many GO terms in BLCs were also involved in neurogenic processes, whereas many GO terms in SLCs were related to vasculature. Mapping upregulated genes in BLCs to pathway annotations in Kyoto Encyclopedia of Genes and Genomes described many active pathways as signalling and cancer-associated pathways. We supply extensive information on possible novel biomarkers, reveal insight into both active pathways and novel regulators of LESCs such as Lrig1 and SOX9 and provide an immense amount of data for future exploration (Bath et al. 2013b). Selective ex vivo expansion of LESCs in hypoxia and the comprehensive molecular characterization of corneal epithelial subpopulations in situ are expected to be beneficial for the future treatment of LSCD by cultured limbal epithelial transplantation.

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.

Limbal side population cells: a future treatment for limbal stem cell deficiency

Corneal blindness carries a morbidity that affects quality of life and is often associated with an increased economic burden. In this review, we focus on the severe and painful condition of limbal stem cell deficiency, an important cause of corneal blindness. Conventional corneal transplantation usually results in graft failure and is contraindicated in this condition. Ex vivo-expanded limbal epithelial transplantation has been used as a cellular-based therapy to regenerate and reconstruct the ocular surface as a mode of treatment. Enrichment methods for stem cells are a strategy to improve the outcome of limbal stem cell transplantation. Here we discuss the side population assay as a functional assay to enrich for stem cells as an important source of limbal stem cells. The challenges in ex vivo-expanded limbal stem cell transplantation are wide and varied and will be addressed in this review with regard to improving the clinical outcomes of cultivated limbal stem cell transplantation.

Combined microfabrication and electrospinning to produce 3-D architectures for corneal repair

Corneal stem cell niches are located within the limbus of the eye and are believed to play an important role in corneal regeneration. These niches are often lost in corneal disease or trauma. Our work explores the design of artificial limbal stem cell niches by the fabrication of biodegradable electrospun rings containing bespoke microfeatures. In creating artificial niches, we seek to provide a physically protective environment for limbal cells to act as a cell reservoir for tissue regeneration purposes. This study describes the first step in this challenge to produce structures which structurally approximate to the limbal niches. This was achieved using a combination of electrospinning and microfabrication. Initial microfabricated structures were developed using microstereolithography via a layer-by-layer photocuring approach based on the patterning of photocurable polymers, in this case polyethylene glycol diacrylate. This was then used as a template on which to electrospin a biodegradable membrane of poly(lactic-co-glycolic acid) 50:50, which incorporates the features of the underlying microfabricated structures. The study describes preliminary evaluation of these constructs using rabbit limbal epithelial and stromal cells.

In vivo confocal microscopy in diagnosis of limbal stem cell deficiency

PURPOSE

To correlate in vivo confocal microscopy and impression cytology features of the corneal surface epithelia in patients with clinical features of partial or total limbal stem cell deficiency and to examine the limbal morphology.

DESIGN

Prospective case-control observational study.

METHODS

Twenty eyes of 17 consecutive patients (mean age 53.9 ± 9.2 years) presenting with clinical suspect of limbal stem cell deficiency and 10 eyes of 10 healthy control subjects were enrolled. In vivo confocal microscopy and impression cytology (PAS, cytokeratin 12, and cytokeratin 19) staining were performed in the central cornea. The inter-examination agreement was determined. Confocal microscopy scans were obtained in all patients to assess microscopic structure of the corneoscleral limbus, in all quadrants.

RESULTS

Confocal microscopy and impression cytology agreement in testing the diagnostic hypotheses was high (κ = 0.85). The 2 methods were concordant in 18 out of 20 examined eyes (90%), revealing the presence of just corneal epithelium in 7 cases, just conjunctival epithelium (total limbal stem cell deficiency) in 5 cases, and mixed epithelium in 6 cases (partial limbal stem cell deficiency). Confocal imaging of the limbus revealed normal palisades of Vogt structure and epithelial transition in the healthy eyes while demonstrating a variable degree of alterations, including loss of the limbal palisades and of the normal epithelial mosaic, cystic epithelial changes, and subepithelial fibrosis, in the eyes affected by partial or total limbal stem cell deficiency.

CONCLUSIONS

Confocal microscopy was useful for the noninvasive in vivo diagnosis of limbal stem cell deficiency, with a high degree of concordance with impression cytology, and to detect limbal alterations associated with partial or total conjunctivalization of the cornea.

The culture of limbal epithelial cells

The transplantation of cultured limbal epithelial cells (LEC) has since its first application in 1997 emerged as a promising technique for treating limbal stem cell deficiency. The culture methods hitherto used vary with respect to preparation of the harvested tissue, choice of culture medium, culture time, culture substrates, and supplementary techniques. In this chapter, we describe a procedure for establishing human LEC cultures using a feeder-free explant culture technique with human amniotic membrane (AM) as the culture substrate.

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.

Limbal epithelial stem cell identification using immunoblotting analysis

The unambiguous identification of limbal epithelial stem cells is currently a major challenge in corneal stem cell biology. Specific molecular markers which characterize these cells are lacking. At present, the best strategy for identification of limbal epithelial stem cells is to investigate a variety of putative markers for these cells in a differentiated (cytokeratin (CK) 3: CK3, integrin α6), undifferentiated (CK14), and naive state (∆Np63α, ATP-binding cassette subfamily G member 2 (ABCG2), integrin α9, Notch-1), alongside functional assays which indicate their stemness. The focus of this chapter is to highlight advances in the Western blotting technique for quantitative assessment of corneal epithelial cell markers, and the use of this technique for investigation of a range of different protein markers which identify limbal epithelial stem cells.

Characterization of the phenotype and functionality of corneal epithelial cells derived from mouse embryonic stem cells

AIMS

To investigate the optimum conditions for the differentiation of a mouse embryonic stem cell line towards corneal epithelial cell fate.

MATERIALS & METHODS

The effect of conditioned media from both metabolically active (to produce lineage A) and growth-arrested limbal fibroblasts (lineage G) were compared with basal media (lineage N) in terms of morphology and marker expression, assessed by immunocytochemistry and reverse transcription PCR. Cultures were transplanted into a porcine ex vivo model to investigate their ability for wound healing and cornea repair.

RESULTS

Lineage N exhibited cobblestone morphology and expressed CK12 and p63α, while OCT4 and SSEA1 were downregulated. Post-transplantation, these cells were able to multilayer and heal after wounding while maintaining marker expression.

CONCLUSION

Lineages with corneal epithelial-like characteristics, which are derived from embryonic stem cells, have potential for use in the study of corneal wound healing and therapy.

In vitro reconstruction and characterization of tissue-engineered human corneal epithelium with seeder cells from an untransfected human corneal epithelial cell line

AIM

To demonstrate the morphology and structure of in vitro reconstructed tissue-engineered human corneal epithelium (TE-HCEP) with seeder cells from an untransfected HCEP cell line.

METHODS

The TE-HCEPs were reconstructed in vitro with seeder cells from an untransfected HCEP cell line, and scaffold carriers of denuded amniotic membrane (dAM) in air-liquid interface culture for 3, 5, 7 and 9 days, respectively. The specimens were examined with hematoxylin-eosin (HE) staining of paraffin-section, immunocytochemical staining, scanning and transmission electron microscopy.

RESULTS

During in vitro reconstruction of TE-HCEP, HCEP cells formed a 3-4, 6-7 and 8-10 layers of an HCEP-like structure on dAMs in air-liquid interface culture for 3, 5 and 7 days, respectively. But the cells deceased to 5-6 layers and the structure of straified epithelium became loose at day 9. And the cells maintained positive expression of marker proteins (keratin 3 and keratin 12), cell-junction proteins (zonula occludens-1, E-cadherin, connexin 43 and integrin β1) and membrane transport protein of Na(+)-K(+) ATPase. The HCEP cells in TE-HCEP were rich in microvilli on apical surface and established numerous cell-cell and cell-dAM junctions at day 5.

CONCLUSION

The morphology and structure of the reconstructed TE-HCEP were similar to those of HCEP in vivo. The HCEP cells in the reconstructed TE-HCEP maintained the properties of HCEP cells, including abilities of forming intercellular and cell-extracellular matrix junctions and abilities of performing membrane transportation. The untransfected HCEP cells and dAMs could promisingly be used in reconstruction HCEP equivalent for clinical corneal epithelium transplantation.

Ex vivo expanded autologous limbal epithelial cells on amniotic membrane using a culture medium with human serum as single supplement

In patients with limbal stem cell deficiency (LSCD), transplantation of ex vivo expanded human limbal epithelial cells (HLECs) can restore the structural and functional integrity of the corneal surface. However, the protocol for cultivation and transplantation of HLECs differ significantly, and in most protocols growth additives such as cholera toxins, exogenous growth factors, hormones and fetal calf serum are used. In the present article, we compare for the first time human limbal epithelial cells (HLECs) cultivated on human amniotic membrane (HAM) in a complex medium (COM) including fetal bovine serum to a medium with human serum as single growth supplement (HSM), and report on our first examinations of HLECs expanded in autologous HSM and used for transplant procedures in patients with LSCD. Expanded HLECs were examined by genome-wide microarray, RT-PCR, Western blotting, and for cell viability, morphology, expression of immunohistochemical markers and colony forming efficiency. Cultivation of HLECs in HSM produced a multilayered epithelium where cells with markers associated with LESCs were detected in the basal layers. There were few transcriptional differences and comparable cell viability between cells cultivated in HSM and COM. The p63 gene associated with LESCs were expressed 3.5 fold more in HSM compared to COM, and Western blotting confirmed a stronger p63α band in HSM cultures. The cornea-specific keratin CK12 was equally found in both culture conditions, while there were significantly more CK3 positive cells in HSM. Cells in epithelial sheets on HAM remaining after transplant surgery of patients with LSCD expressed central epithelial characteristics, and dissociated cells cultured at low density on growth-arrested fibroblasts produced clones containing 21 ± 12% cells positive for p63α (n = 3). In conclusion, a culture medium without growth additives derived from animals or from animal cell cultures and with human serum as single growth supplement may serve as an equivalent replacement for the commonly used complex medium for ex vivo expansion of HLECs on HAM.

Recent Advances and Future Challenges in Ocular Surface Reconstruction: On the Road to Translational Medicine

Severe ocular surface diseases are some of the most challenging entities currently facing ophthalmologists. The purpose of this review was to describe the recent advances, current developments, and future challenges related to ocular surface reconstruction from both the basic science and clinical aspects. To date, many candidate corneal epithelial stem-cell markers for tissue-engineered culture transplants have been proposed worldwide. Several groups have reported the long-term clinical results of cultivated epithelial transplantation for treating severe ocular surface disease. In an attempt to further develop the surgical procedures of ocular surface reconstruction, several groups recently reported using cells obtained from novel sources, surrounding cell substrates, and safer culture processes. As a result of the basic research and breakthroughs in the field of corneal regenerative medicine, great progress has been made in the basic understanding and development of new therapeutic tools.

Culture of corneal limbal epithelial stem cells: experience from benchtop to bedside in a tertiary care hospital in India

PURPOSE

To standardize the technique of ex vivo culture of limbal epithelial stem cells (LESCs) using locally available adapted methods and evaluate the outcome of transplantation in patients with limbal stem cell deficiency.

METHODS

Limbal tissue specimens were isolated from cadaveric corneoscleral rims, living related donors, or contralateral eye of the patients. Harvested tissue was cultured on denuded human amniotic membrane (dHAM) using various techniques to stabilize dHAM. The optimization of in vitro culture conditions was achieved by modifications in culture media (culture media 1 and 2). The LESCs were cultured in both types of media for 2 weeks, and growth patterns were observed. Expanded cells were further characterized by immunocytochemistry (K3/12, K19, and ABCG2) and reverse transcriptase polymerase chain reaction (K12, Cx43, Pax6, ABCG2, p63, and K19). The cultivated epithelium was transplanted in 50 patients with total and partial limbal stem cell deficiencies.

RESULTS

Stabilization of dHAM was successfully achieved using coverslips. The outgrowth was observed within 1-3 days of culture using both types of culture media (P = 0.20), but cultures in culture medium 1 reached confluency faster than cultures in culture medium 2 (P = 0.0004). Histopathological analysis showed multilayer formation and immunostaining, and reverse transcriptase polymerase chain reaction data confirmed the expression of both stem cell markers (K19, p63, and ABCG2) and differentiation markers (K3, K12, and Cx43). Patients who had undergone limbal stem cell transplantation showed a stable ocular surface with improved visual acuity over a long-term follow-up period.

CONCLUSIONS

LESCs were successfully cultured using locally available adapted methods, and their clinical benefits verified by transplantation.

Matrix revolution: molecular mechanism for inflammatory corneal neovascularization and restoration of corneal avascularity by epithelial stem cell transplantation

Corneal neovascularization (CNV) associated with severe limbal stem cell (LSC) deficiency remains a challenging ocular surface disease in that corneal inflammation may persist and progress, and the condition will not improve without LSC transplantation. A prominent feature after successful LSC transplantation is the suppression of corneal inflammation and CNV, which is generally attributed to the endogenous anti-angiogenic/anti-inflammatory factors secreted by corneal epithelial cells. In addition, corneal epithelial basement membrane (EBM) plays a unique role in the regulation of angiogenesis; several potent anti-angiogenic factors are derived from the matrix component of EBM, such as endostatin (from collagen XVIII) and restin (from collagen XV). Also, angio-inhibitory thrombospondin and tissue inhibitor of metalloproteinase-3 are deposited in EBM. Moreover, the heparan sulphate proteoglycan in EBM can bind and sequester VEGF and FGF-2 from activation. Recently, cultivated corneal epithelial transplantation (CCET) and cultivated oral mucosal epithelial transplantation (COMET) have emerged as promising techniques for the treatment of LSC deficiency. When human limbo-corneal epithelial (HLE) cells are cultivated on cryopreserved amniotic membrane, production of endostatin, restin, and IL-1ra is enhanced. This highlights the significance of delicate epithelial-matrix interactions in the generation of anti-angiogenic/anti-inflammatory factors by HLE cells, and this may, in part, explain the rapid restoration of corneal avascularity following CCET. In addition, whether epithelial stem cells can persist after transplantation is the key for CCET and COMET. Emerging evidence of long-term survival of cultivated epithelial cells after transplantation suggest that epithelial stem cells can be isolated and cultivated in vitro, and can re-establish the epithelial phenotype in vivo. Taken together, the merits of enhanced anti-angiogenic activity and the preservation of corneal epithelial stem cells encourage further application of this tissue engineering technique for ocular surface reconstruction.

Limbal stem cell deficiency and ocular phenotype in ectrodactyly-ectodermal dysplasia-clefting syndrome caused by p63 mutations

OBJECTIVE

To describe the ocular phenotype in patients with ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome (MIM#604292) and to determine the pathogenic basis of visual morbidity.

DESIGN

Retrospective case series.

PARTICIPANTS

Nineteen families (23 patients) affected by EEC syndrome from the United Kingdom, Ireland, and Italy.

METHODS

General medical examination to fulfill the diagnostic criteria for EEC syndrome and determine the phenotypic severity. Mutational analysis of p63 was performed by polymerase chain reaction-based bidirectional Sanger sequencing. All patients with EEC syndrome underwent a complete ophthalmic examination and ocular surface assessment. Limbal stem cell deficiency (LSCD) was diagnosed clinically on the basis of corneal conjunctivalization and anatomy of the limbal palisades of Vogt. Impression cytology using immunofluorescent antibodies was performed in 1 individual. Histologic and immunohistochemical analyses were performed on a corneal button and corneal pannus from 2 EEC patients.

MAIN OUTCOME MEASURES

The EEC syndrome phenotypic severity (EEC score), best-corrected Snellen visual acuity (decimal fraction), slit-lamp biomicroscopy, tear function index, tear breakup time, LSCD, p63 DNA sequence variants, impression cytology, and corneal histopathology.

RESULTS

Eleven heterozygous missense mutations in the DNA binding domain of p63 were identified in all patients with EEC syndrome. All patients had ocular involvement and the commonest was an anomaly of the meibomian glands and lacrimal drainage system defects. The major cause of visual morbidity was progressive LSCD, which was detected in 61% (14/23). Limbal stem cell deficiency was related to advancing age and caused a progressive keratopathy, resulting in a dense vascularized corneal pannus, and eventually leading to visual impairment. Histologic analysis and impression cytology confirmed LSCD.

CONCLUSIONS

Heterozygous p63 mutations cause the EEC syndrome and result in visual impairment owing to progressive LSCD. There was no relationship of limbal stem cell failure with the severity of EEC syndrome, as classified by the EEC score, or the underlying molecular defect in p63.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Long-term effectiveness of autologous cultured limbal stem cell grafts in patients with limbal stem cell deficiency due to chemical burns

BACKGROUND

Chemical burns cause depletion of limbal stem cells and eventually lead to corneal opacity and visual loss. We investigated the long-term effectiveness of autologous cultured limbal stem cell grafts in patients with limbal stem cell deficiency.

DESIGN

Prospective, non-comparative interventional case series.

PARTICIPANTS

Sixteen eyes from 16 patients with severe, unilateral limbal stem cell deficiency caused by chemical burns.

METHODS

Autologous ex vivo cultured limbal stem cells were grafted onto the recipient eye after superficial keratectomy.

MAIN OUTCOME MEASURES

Clinical parameters of limbal stem cell deficiency (stability/transparency of the corneal epithelium, superficial corneal vascularization and pain/photophobia), visual acuity, cytokeratin expression on impression cytology specimens and histology on excised corneal buttons.

RESULTS

At 12 months post-surgery, evaluation of the 16 patients showed that 10 (62.6%) experienced complete restoration of a stable and clear epithelium and 3 (18.7%) had partially successful outcomes (re-appearance of conjunctiva in some sectors of the cornea and instable corneal surface). Graft failure (no change in corneal surface conditions) was seen in three (18.7%) patients. Penetrating keratoplasty was performed in seven patients, with visual acuity improving up to 0.8 (best result). For two patients, regeneration of the corneal epithelium was confirmed by molecular marker (p63, cytokeratin 3, 12 and 19, mucin 1) analysis. Follow-up times ranged from 12 to 50 months.

CONCLUSIONS

Grafts of autologous limbal stem cells cultured onto fibrin glue discs can successfully regenerate the corneal epithelium in patients with limbal stem cell deficiency, allowing to perform successful cornea transplantation and restore vision.

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.