The OV-TL 12/30 clone of anti-cytokeratin 7 antibody as a new marker of corneal conjunctivalization in patients with limbal stem cell deficiency

Diagnostic Algorithm for Surgical Management of Limbal Stem Cell Deficiency

BACKGROUND

Limbal stem cell deficiency (LCSD) presents several challenges. Currently, there is no clearly defined systematic approach to LSCD diagnosis that may guide surgical tactics.

METHODS

The medical records of 34 patients with LSCD were analyzed. Diagnostic modalities included standard (visometry, tonometry, visual field testing, slit-lamp biomicroscopy with corneal fluorescein staining, Schirmer test 1, ultrasonography) and advanced ophthalmic examination methods such as anterior segment optical coherence tomography, in vivo confocal microscopy, impression cytology, and enzyme-linked immunoassay.

RESULTS

Standard ophthalmological examination was sufficient to establish the diagnosis of LSCD in 20 (58.8%) cases, whereas advanced evaluation was needed in 14 (41.2%) cases. Depending on the results, patients with unilateral LSCD were scheduled to undergo glueless simple limbal epithelial transplantation (G-SLET) or simultaneous G-SLET and lamellar keratoplasty. Patients with bilateral LSCD with normal or increased corneal thickness were enrolled in the paralimbal oral mucosa epithelium transplantation (pLOMET) clinical trial.

CONCLUSIONS

Based on the diagnostic and surgical data analyzed, the key points in LSCD diagnosis were identified, helping to guide the surgeon in selecting the appropriate surgical procedure. Finally, we proposed a novel step-by-step diagnostic algorithm and original surgical guidelines for the treatment of patients with LSCD.

Immunocytochemical characterization of ex vivo cultured conjunctival explants; marker validation for the identification of squamous epithelial cells and goblet cells

Tissue-engineered products are at the cutting edge of innovation considering their potential to functionally and structurally repair various tissue defects when the body's own regenerative capacity is exhausted. At the ocular surface, the wound healing response to extensive conjunctival damage results in tissue repair with structural alterations or permanent scar formation rather than regeneration of the physiological conjunctiva. Conjunctival tissue engineering therefore represents a promising therapeutic option to reconstruct the ocular surface in severe cicatrizing pathologies. During the rapid race to be a pioneer, it seems that one of the fundamental steps of tissue engineering has been neglected; a proper cellular characterization of the tissue-engineered equivalents, both morphologically and functionally. Currently, no consensus has been reached on an identification strategy and/or markers for the characterization of cultured squamous epithelial and goblet cells. This study therefore evaluated the accuracy of promising markers to identify differentiated conjunctival-derived cells in human primary explant cultures through immunocytochemistry, including keratins (i.e., K7, K13, and K19) and mucins (i.e., MUC1, MUC5AC, and PAS-positivity). Comparison of the in vivo and in vitro cellular profiles revealed that the widely used goblet cell marker K7 does not function adequately in an in vitro setting. The other investigated markers offer a powerful tool to distinguish cultured squamous epithelial cells (i.e., MUC1 and K13), goblet cells (i.e., MUC5AC and PAS-staining), and conjunctival-derived cells in general (i.e., K19). In conclusion, this study emphasizes the power alongside potential pitfalls of conjunctival markers to assess the clinical safety and efficacy of conjunctival tissue-engineered products.

Characterization and functional performance of a commercial human conjunctival epithelial cell line

The conjunctiva is a complex tissue that covers the eye beginning at the corneal limbus and extending over the inner surfaces of the eyelids. Due to its important functions in maintaining the health of the ocular surface, adequate in vitro models of conjunctival structure and function are essential to understand its roll in different pathologies. Because there is scarcity of human conjunctival tissue that can be used in research, cell lines are often the only option for initial studies. An immortalized human conjunctival epithelial cell (IM-HConEpiC) line is now commercially available; however, it is not very well characterized. In this study, we have developed a new protocol to culture these cells without the use of collagen-coated culture surfaces, but with a defined cell culture medium. We characterized IM-HConEpiCs cultured under these conditions and corroborated that the cells maintained a conjunctival epithelial phenotype, including acidic and neutral mucins, junctional proteins E-cadherin and zonula occludens 1, and expression of CK8 and CK19, among others. In addition, we analyzed the response to oxidative stress and inflammatory stimuli and found that IM-HConEpiCs respond as expected for conjunctival epithelial tissue. For instance, cells exposed to oxidative stress increased the production of reactive oxygen species, and that increase was blocked in the presence of an antioxidant agent. In addition, after stimulation with TNF-α, IM-HConEpiCs significantly increased the production of IL-1β, IL-6, IL-8, and IP-10. Therefore, with this study we conclude that IM-HConEpiCs can be a useful tool in functional studies to determine the response of the conjunctiva to pathological conditions and/or to test new therapeutic strategies.

Wnt/β-catenin signaling stimulates the self-renewal of conjunctival stem cells and promotes corneal conjunctivalization

Limbal stem cell deficiency causes conjunctivalization characterized by the covering of the corneal surface with conjunctival epithelium. However, the driving force for the encroachment of these conjunctival cells is unclear. Conjunctival stem cells are bipotent stem cells that can proliferate and differentiate into conjunctival epithelial cells and goblet cells to maintain regeneration of the conjunctival epithelium. Here, we show a robust proliferative response of conjunctival stem cells and upregulation of Wnt2b and Wnt3a gene expression in the conjunctivae of mice with induced limbal stem cell deficiency. Topical application of the Wnt/β-catenin signaling activator CHIR resulted in increased proliferation of ΔNp63α-positive stem cells in the basal layers of the bulbar and forniceal conjunctivae and enhanced invasion of conjunctival epithelial and goblet cells into the corneal surface. We also found that in cultures of stem cells isolated from the human conjunctiva, Wnt/β-catenin pathway activation improved the expansion of the ΔNp63α/ABCG2 double-positive cell population by promoting the proliferation and preventing the differentiation of these cells. These expanded stem cells formed a stratified epithelium containing goblet cells under airlift culture conditions. Our data reveal that Wnt/β-catenin signaling contributes to the pathological process of limbal stem cell deficiency by promoting the self-renewal of conjunctival stem cells and suggest that these cells are a driving force in corneal conjunctivalization.

A major signaling pathway that regulates stem cell function acts as a key mediator of conjunctival invasion into the cornea following eye injuries. Using human tissue and mouse models, a team from South Korea led by Chang Rae Rho of Daejeon St. Mary’s Hospital and Jungmook Lyu of Konyang University, Daejon, showed how insults to the eye can spur the proliferation of stem cells found in the conjunctiva, the thin membrane covering the white part of the eyeball. This cell growth and self-renewal is driven by increased activity of the Wnt/β-catenin signaling pathway, leading to conjunctivalization of the cornea, the transparent outer layer of the eye, resulting in corneal opacity and loss of vision. Therapies that manipulate this signaling pathway could help improve vision for people with certain corneal diseases.

Interleukin-13 increases the stemness of limbal epithelial stem cells cultures

This study aimed to determine the effect of interleukin-13 (IL13) on the stemness, differentiation, proliferation, clonogenicity, and morphology of cultured limbal epithelial cells (LECs). Human limbal explants were used to culture LECs up to the second passage (P0-P2) with or without IL13 (IL13+ and IL13-, respectively). Cells were analyzed by qPCR (for the expression of ΔNp63α, BMI-1, keratin (K) 3, K7, K12, K14, K17, mucin 4, and MKI67) and immunofluorescence staining for p63α. The clonogenic ability was determined by colony-forming assay (CFA), and their metabolic activity was measured by WST-1 assay. The results of the CFA showed a significantly increased clonogenic ability in P1 and P2 cultures when LECs were cultured with IL13. In addition, the expression of putative stem cell markers (ΔNp63α, K14, and K17) was significantly higher in all IL13+ cultures compared to IL13-. Similarly, immunofluorescence analysis showed a significantly higher percentage of p63α positive cells in P2 cultures with IL13 than without it. LECs cultures without IL13 lost their cuboidal morphology with a high nucleocytoplasmic ratio after P1. The use of IL13 also led to significantly higher proliferation in P2, which can be reflected by a higher ability to reach confluence in P2 cultures. On the other hand, IL13 had no effect on corneal epithelial cell differentiation (K3 and K12 expression), and the expression of the conjunctival marker K7 significantly increased in all IL13+ cultures compared to the respective cell culture without IL13. This study showed that IL13 enhanced the stemness of LECs by increasing the clonogenicity and the expression of putative stem cell markers of LECs while maintaining their stem cell morphology. We established IL13 as a culture supplement for LESCs, which increases their stemness potential in culture, even after the second passage, and may lead to the greater success of LESCs transplantation in patients with LSCD.

Efficacy and outcome of simple limbal epithelial transplantation for limbal stem cell deficiency verified by epithelial phenotypes integrated with clinical evaluation

PURPOSE

To evaluate the efficacy and outcome of simple limbal epithelial transplantation (SLET) for limbal stem cell deficiency (LSCD) using epithelial phenotype detection integrated with clinical manifestation.

METHODS

This prospective multicenter study included patients with LSCD who underwent autologous SLET (autoSLET) and living-related allogenic SLET (Lr-alloSLET). All patients were assessed by slit-lamp biomicroscopy, in vivo confocal microscopy (IVCM), and impression cytology with immunofluorescence staining (ICIF) before and after surgery. The criteria for success were the presence of a clinically non-conjunctivalized cornea and corneal epithelium detected by IVCM or ICIF. Otherwise, the case would be considered a failure. Visual improvement and risk factors for SLET failure were analyzed.

RESULTS

A total of 28 eyes of 26 patients (11 autoSLET and 17 Lr-alloSLET) were included. The median age was 53 years (range, 35-63), and the follow-up time was 29.5 months (range, 17.5-39.8). The overall survival rate was 89.3% at 2 years and 75.6% at 3 years with no difference between autoSLET and Lr-alloSLET (p = 0.24). Seven eyes subsequently underwent penetrating keratoplasty. Immunohistochemistry analysis showed that all corneal buttons had corneal epithelium and limbal stem cell markers. Visual improvement was achieved in both SLET groups (p < 0.001). Failed SLET developed between 5 and 32 months postoperatively. However, absolute risk factors for SLET failure were unidentified.

CONCLUSION

The efficacy of autoSLET and Lr-alloSLET for LSCD was excellent. Limbal explants can regenerate and restore the corneal surface while maintaining the characteristics of limbal stem cells as shown by epithelial phenotype detection and immunohistochemistry integrated with clinical evaluation.

Phenotypic Characterization of Corneal Epithelium in Long-Term Follow-Up of Patients Post-Autologous Cultivated Oral Mucosal Epithelial Transplantation

PURPOSE

To analyze the phenotype of the corneal epithelium in patients with long-term follow-up who underwent autologous cultivated oral mucosal epithelial transplantation (COMET) using in vivo confocal microscopy (IVCM) and impression cytology with immunofluorescence staining (ICIF).

METHODS

Thirteen eyes from patients with severe limbal stem cell deficiency, who underwent COMET at least 48 months before, were recruited in this noncomparative cohort study. After eye examination, IVCM and ICIF were performed. Clinical manifestations of the cornea were evaluated and compared with epithelial findings detected by IVCM and ICIF [cytokeratin (CK) 3, CK7, and CK12]. Two corneal buttons derived from patients receiving the corneal transplantation post-COMET were sent for immunohistochemistry (CK3, CK6, CK7, CK12, paired box gene 6, p63, zonula occludens-1, and integrin β -1).

RESULTS

The mean age of patients was 51.2 ± 20.6 years, and the mean follow-up time since COMET was 78.7 ± 16.3 months. Six of 13 eyes showed clinically successful COMET. In these eyes, IVCM demonstrated predominant cornea-like epithelium and ICIF reported positivity for CK3 and CK12, confirming the presence of oral mucosal and corneal epithelium. Meanwhile, 7 eyes showed total conjunctivalization, corresponding with substantial conjunctival epithelium detected by IVCM and positivity for conjunctival (CK7) and oral mucosal epithelial (CK3) markers detected by ICIF. The immunohistochemistry of corneal buttons stained positive for oral mucosal, corneal epithelial, and stem cell markers (CK3, CK12, and p63).

CONCLUSIONS

In long-term follow-up of COMET, epithelium of successful patients demonstrated cornea-like phenotype, whereas failed cases revealed mainly conjunctival phenotype. However, there were evidences that oral mucosal epithelial cells remained across the cornea in both successful and failed COMET as detected by IVCM and ICIF.

Recent Advances in Stem Cell Therapy for Limbal Stem Cell Deficiency: A Narrative Review

Destruction of the limbus and depletion of limbal stem cells (LSCs), the adult progenitors of the corneal epithelium, leads to limbal stem cell deficiency (LSCD). LSCD is a rare, progressive ocular surface disorder which results in conjunctivalisation and neovascularisation of the corneal surface. Many strategies have been used in the treatment of LSCD, the common goal of which is to regenerate a self-renewing, transparent, and uniform epithelium on the corneal surface. The development of these techniques has frequently resulted from collaboration between stem cell translational scientists and ophthalmologists. Direct transplantation of autologous or allogeneic limbal tissue from a healthy donor eye is regarded by many as the technique of choice. Expansion of harvested LSCs in vitro allows smaller biopsies to be taken from the donor eye and is considered safer and more acceptable to patients. This technique may be utilised in unilateral cases (autologous) or bilateral cases (living related donor). Recently developed, simple limbal epithelial transplant (SLET) can be performed with equally small biopsies but does not require in vitro cell culture facilities. In the case of bilateral LSCD, where autologous limbal tissue is not available, autologous oral mucosa epithelium can be expanded in vitro and transplanted to the diseased eye. Data on long-term outcomes (over 5 years of follow-up) for many of these procedures is needed, and it remains unclear how they produce a self-renewing epithelium without recreating the vital stem cell niche. Bioengineering techniques offer the ability to re-create the physical characteristics of the stem cell niche, while induced pluripotent stem cells offer an unlimited supply of autologous LSCs. In vivo confocal microscopy and anterior segment OCT will complement impression cytology in the diagnosis, staging, and follow-up of LSCD. In this review we analyse recent advances in the pathology, diagnosis, and treatment of LSCD.

Corneal Epithelial Thickness Measured Using Anterior Segment Optical Coherence Tomography as a Diagnostic Parameter for Limbal Stem Cell Deficiency

OBJECTIVE

Using anterior segment optical coherence tomography (AS-OCT), we investigated the epithelial thickness (ET) of the central cornea and limbal regions in patients with limbal stem cell deficiency (LSCD) as a diagnostic and staging parameter.

DESIGN

Prospective, cross-sectional study.

METHODS

The central corneal epithelium thickness (CET) and maximum limbal epithelium thickness (mLET) were measured in the superior, inferior, nasal, and temporal limbus on AS-OCT images of the normal and eyes with LSCD. CET was obtained by 1-point (OCT-CET1) and 3-point measurement (OCT-CET3). The values of OCT-CET1 and OCT-CET3 were compared to the CET obtained with in vivo confocal microscopy (IVCM-CET).

RESULTS

Sixty-eight eyes of 50 patients with LSCD and 52 eyes of 34 normal subjects were included. The mean (±standard deviation) OCT-CET3 was 55.0 ± 3.0 μm (range, 50.6-62.0 μm) in the control group and 41.6 ± 10.8 μm (range, 0-56.3 μm) in the LSCD group (P < .001). OCT-CET3 had a better correlation with IVCM-CET (r = 0.91) than did OCT-CET1 (r = 0.87, P = .001). The degree of reduction in OCT-CET3 increased in more advanced clinical stages of LSCD (all P < .001). The OCT-CET3 cutoff value that suggests LSCD was 46.6 μm. Compared with the control group, the LSCD group had decreases in mLET in all 4 limbal regions (all P < .001). The sensitivity and specificity of OCT-CET3 is the highest among all mLET in detecting LSCD.

CONCLUSIONS

Both CET and mLET were thinner in patients with LSCD than in normal subjects. OCT-CET3 appears to be a reliable parameter to confirm LSCD when there is clinical suspicion.

Ex vivo cultivated oral mucosal epithelial cell transplantation for limbal stem cell deficiency: a review

Destruction or dysfunction of limbal epithelial stem cells (LESCs) leads to unilateral or bilateral limbal stem cell deficiency (LSCD). Fifteen years have passed since the first transplantation of ex vivo cultivated oral mucosal epithelial cells (COMET) in humans in 2004, which represents the first use of a cultured non-limbal autologous cell type to treat bilateral LSCD. This review summarizes clinical outcomes from COMET studies published from 2004 to 2019 and reviews results with emphasis on the culture methods by which grafted cell sheets were prepared.

Insulin-like growth factor binding protein-7: A marker of conjunctivalization in an animal model of limbal stem cell deficiency

PURPOSE

Limbal stem cell deficiency (LSCD) is characterized by the loss of limbal epithelial stem cells, resulting in a pathological process termed 'conjunctivalization' which compromises corneal transparency, leading to blindness. Current diagnosis for LSCD is limited because reliable conjunctiva-specific biomarkers are lacking. This study sought to address this shortcoming through the serendipitous discovery of insulin-like growth factor binding protein (IGFBP)-7.

METHODS

IGFBP-7 expression was determined in normal (n=83) and conjunctivalized (n=52) mouse corneas with experimentally-induced LSCD, and in cadaveric normal human corneas (n=7) and human pterygia (n=15); a disease characterized by the invasion of a conjunctivalized, fibrovascular pannus. Clinical assessments including slit-lamp microscopy, fluorescein staining and impression cytology, and biochemical, molecular and immunological assays were also conducted.

RESULTS

Mass spectrometry of conditioned media from mouse limbal explant-derived cells revealed the presence of IGFBP-7. This factor was expressed in normal limbal and conjunctival epithelium and conjunctivalized corneas from mice with LSCD, and in human pterygium epithelium but not in normal mouse or human corneal epithelium. Four weeks after inducing LSCD, IGFBP-7 staining was increased by 2.9-fold in mouse corneas compared to steady-state, and by 1.6-fold in impression cytology specimens derived from the same mice. Notably, IGFBP-7 was detected approximately 2-weeks earlier than Muc5AC.

CONCLUSIONS

This study provides novel insights into the specificity of IGFBP-7 for the mammalian conjunctival epithelium in health and disease. A point-of-care test for IGFBP-7 could be developed to assist clinicians in early diagnosis, and in monitoring disease progression, severity and therapeutic outcomes in patients with LSCD.

Global Consensus on Definition, Classification, Diagnosis, and Staging of Limbal Stem Cell Deficiency

PURPOSE

Despite extensive knowledge gained over the last 3 decades regarding limbal stem cell deficiency (LSCD), the disease is not clearly defined, and there is lack of agreement on the diagnostic criteria, staging, and classification system among treating physicians and research scientists working on this field. There is therefore an unmet need to obtain global consensus on the definition, classification, diagnosis, and staging of LSCD.

METHODS

A Limbal Stem Cell Working Group was first established by The Cornea Society in 2012. The Working Group was divided into subcommittees. Four face-to-face meetings, frequent email discussions, and teleconferences were conducted since then to obtain agreement on a strategic plan and methodology from all participants after a comprehensive literature search, and final agreement was reached on the definition, classification, diagnosis, and staging of LSCD. A writing group was formed to draft the current manuscript, which has been extensively revised to reflect the consensus of the Working Group.

RESULTS

A consensus was reached on the definition, classification, diagnosis, and staging of LSCD. The clinical presentation and diagnostic criteria of LSCD were clarified, and a staging system of LSCD based on clinical presentation was established.

CONCLUSIONS

This global consensus provides a comprehensive framework for the definition, classification, diagnosis, and staging of LSCD. The newly established criteria will aid in the correct diagnosis and formulation of an appropriate treatment for different stages of LSCD, which will facilitate a better understanding of the condition and help with clinical management, research, and clinical trials in this area.

Interleukin-13 maintains the stemness of conjunctival epithelial cell cultures prepared from human limbal explants

To use human limbal explants as an alternative source for generating conjunctival epithelium and to determine the effect of interleukin-13 (IL-13) on goblet cell number, mucin expression, and stemness. Human limbal explants prepared from 17 corneoscleral rims were cultured with or without IL-13 (IL-13+ and IL-13-, respectively) and followed up to passage 2 (primary culture [P0]-P2). Cells were characterized by alcian blue/periodic acid-Schiff (AB/PAS) staining (goblet cells); immunofluorescent staining for p63α (progenitor cells), Ki-67 (proliferation), MUC5AC (mucin, goblet cells), and keratin 7 (K7, conjunctival epithelial and goblet cells); and by quantitative real-time polymerase chain reaction for expression of the p63α (TP63), MUC5AC, MUC4 (conjunctival mucins), K3, K12 (corneal epithelial cells), and K7 genes. Clonogenic ability was determined by colony-forming efficiency (CFE) assay. Using limbal explants, we generated epithelium with conjunctival phenotype and high viability in P0, P1, and P2 cultures under IL-13+ and IL-13- conditions, i.e., epithelium with strong K7 positivity, high K7 and MUC4 expression and the presence of goblet cells (AB/PAS and MUC5AC positivity; MUC5AC expression). p63α positivity was similar in IL-13+ and IL-13- cultures and was decreased in P2 cultures; however, there was increased TP63 expression in the presence of IL-13 (especially in the P1 cultures). Similarly, IL-13 increased proliferative activity in P1 cultures and significantly promoted P0 and P1 culture CFE. IL-13 did not increase goblet cell number in the P0-P2 cultures, nor did it influence MUC5AC and MUC4 expression. By harvesting unattached cells on day 1 of P1 we obtained goblet cell rich subpopulation showing AB/PAS, MUC5AC, and K7 positivity, but with no growth potential. In conclusion, limbal explants were successfully used to develop conjunctival epithelium with the presence of putative stem and goblet cells and with the ability to preserve the stemness of P0 and P1 cultures under IL-13 influence.

Corneal keratin aggresome (CKAGG) formation and clearance by proteasome activation

Purpose

To understand the mechanism of corneal keratin expression and clearance in corneal epithelium with Limbal Stem Cell Deficiency (LSCD). The hypothesis is that LSCD-induced proteasome dysfunction is a contributing factor to keratin aggregation, causing corneal keratin aggresome (CKAGG) formation.

Method

LSCD was surgically induced in rabbit corneas. LSCD corneal epithelial cells (D-CEC) were collected to investigate keratin K4 and K13 expression and CKAGG formation. Oral mucosal epithelial cells (OMECS) were isolated and cultured to study K4 and K13 expression. Cultured cells were treated with proteasome inhibitor to induce CKAGG formation.

Results

K4 and K13 were strongly expressed in D-CEC, with additional higher molecular weight bands of K4 and K13, suggesting CKAGG formation. Double staining of K4/K13 and ubiquitin showed co-localization of these keratins with ubiquitin in D-CEC. Proteasome inhibition also showed K4/K13 modification and accumulation in cultured OMECS, similar to D-CEC. Proteasome activation was then performed in cultured OMEC. There was no accumulation of keratins, and levels of unmodified keratins were found significantly reduced.

Conclusion

Results showed an abnormal expression of K4 and K13 after LSCD-induced proteasome dysfunction, which coalesce to form CKAGG in Corneal Epithelial Cells (CEC). We propose that CKAGG formation may be one of the causative factors of morphological alterations in the injured corneal epithelium, and that CKAGG could potentially be cleared by enhancing proteasome activity.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Immunocytochemical Diagnosis of Limbal Stem Cell Deficiency: Comparative Analysis of Current Corneal and Conjunctival Biomarkers

PURPOSE

To evaluate and compare corneal and conjunctival biomarkers for immunocytochemical diagnosis of limbal stem cell deficiency (LSCD).

METHODS

In accordance with the current literature, we selected K12 as the corneal biomarker and K7/K13/K19/MUC5AC as the conjunctival ones. The specificity and accuracy for each biomarker were assessed and compared on 10 healthy subjects and tissues of deceased donors. Twelve eyes of 9 patients clinically suspected of LSCD were enrolled. Epithelial cells (ECs) from the central cornea were collected using impression cytology (IC) and assessed for each biomarker. The presence of conjunctival cells in the central cornea was diagnostic proof of LSCD, whereas the detection of corneal residual cells would quantify the degree of LSCD.

RESULTS

K12 and K7/K13/MUC5AC are, respectively, highly specific of corneal and conjunctival differentiation, whereas K19 is not. Normal corneal ECs are not desquamative enough to be suitable for IC. Among 12 eyes with suspected LSCD, 84% (10 of 12) of IC samples were suitable for analysis. K3/K7/K19 immunostaining was positive in 100%, MUC5AC in 40%, and K12 was never observed.

CONCLUSIONS

Clinical examination can lead to misdiagnosis of LSCD. Immunocytochemical detection of K7/K13 on corneal ECs collected by IC is reproducible, noninvasive, and highly effective in this indication, but without any quantification of the degree of the disease. This time-consuming technique requires skilled technicians and laboratory facilities, reserving it for planned limbal reconstruction.

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.

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.

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.

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.

Biopsy harvesting site and distance from the explant affect conjunctival epithelial phenotype ex vivo

The purpose of the study was to investigate if the number of goblet cells expanded ex vivo from a conjunctival explant is affected by the biopsy harvesting site on the conjunctiva and the distance from the explant. Conjunctival explants from six regions: superior and inferior bulbus, fornix, and tarsus of male Sprague-Dawley rats were grown in RPMI 1640 with 10% fetal bovine serum on coverslips for eight days. Histochemical and immunofluorescent staining of goblet (CK-7/UEA-1/MUC5AC), stratified squamous, non-goblet (CK-4), proliferating (PCNA) and progenitor (ABCG2) cells were analyzed by epifluorescence and laser confocal microscopy. Outgrowth was measured with NIH ImageJ. For statistical analysis the Mann-Whitney test and Spearman's rank-order correlation test were used. Cultures from superior and inferior fornix contained the most goblet cells as indicated by the presence of CK-7+, UEA-1+ and MUC5AC+ cells. Superior and inferior forniceal cultures displayed 60.8% ± 9.2% and 64.7% ± 6.7% CK-7+ cells, respectively, compared to the superior tarsal (26.6% ± 8.4%; P < 0.05), superior bulbar (31.0% ± 4.0%; P < 0.05), inferior bulbar (38.5% ± 9.3%; P < 0.05) and inferior tarsal cultures (27.7% ± 8.3%; P < 0.05). While 28.4% ± 6.3% of CK-7+ goblet cells co-labeled with PCNA, only 7.4% ± 1.6% of UEA-1+ goblet cells did (P < 0.01). CK-7+ goblet cells were located at a lower concentration close to the explant (39.8% ± 3.1%) compared to near the leading edge (58.2% ± 4.5%; P < 0.05). Both markers for goblet cell secretory product (UEA-1 and MUC5AC), however, displayed the opposite pattern with a higher percentage of positive cells close to the explant than near the leading edge (P < 0.05). The percentage of CK-4+ cells was higher near the explant compared to near the leading edge (P < 0.01). The percentage of CK-7+ goblet cells in the cultures did not correlate with the outgrowth size (r(s) = -0.086; P = 0.435). The percentage of UEA-1+ goblet cells correlated negatively with outgrowth size (r(s) = -0.347; P < 0.01), whereas the percentage of CK-4+ cells correlated positively with the outgrowth size (r(s) = 0.473; P < 0.05). We conclude that forniceal explants yield the highest number of goblet cells ex vivo and thereby seem to be optimal for goblet cell transplantation. We also suggest that CK-7+/UEA-1- cells represent highly proliferative immature goblet cells. These cells could be important during conjunctival migration as they are mostly located close to the leading edge and their density does not decrease with increasing outgrowth size.