Amniotic membrane transplantation or conjunctival limbal autograft for limbal stem cell deficiency induced by 5-fluorouracil in glaucoma surgeries

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Case report: Medical treatment for limbal epithelial stem cell deficiency in patients treated for glaucoma

Limbal epithelial stem cell deficiency (LSCD) is an abnormal corneal epithelial lesion with several causes. The patient was diagnosed using fluorescein staining. Bullous keratopathy, multiple surgeries, and drug-related damage can cause LSCD in glaucoma patients. We evaluated the medical treatment course for LSCD in patients with glaucoma. We retrospectively reviewed the electronic medical records of patients diagnosed with LSCD and investigated their background, course of treatment, and classification stages of LSCD before and after treatment. The global consensus classification system (stages IA-C, IIA-B, and III) proposed by Deng et al. (Cornea 2020) was used. Seven patients (two males) and eight eyes were studied. The median age of the patients was 82 years, and the mean duration of glaucoma treatment was 8 years. The patients had open-angle glaucoma (four eyes), exfoliation glaucoma (one eye), neovascular glaucoma (one eye), normal tension glaucoma (one eye), and uveitic glaucoma (one eye). Stage classifications at diagnosis were stage IA in four eyes and stages IC, IIA, IIB, and III in one eye each. All treatments were carried out with dry eye drops, steroid eye drops, and antibiotics. The mean duration of treatment was 1.4 years. The classifications at the time of the final visit were normal corneal epithelium (three eyes), stage IA (two eyes), IIA (one eye), and III (two eyes). Three eyes (37%) improved by more than one stage and one eye deteriorated by more than one stage. LSCD is long-lasting and difficult to treat in a short period; thus, it requires careful medical attention.

The Multifold Etiologies of Limbal Stem Cell Deficiency: A Comprehensive Review on the Etiologies and Additional Treatment Options for Limbal Stem Cell Deficiency

Given the various ocular manifestations of limbal stem cell insufficiency, an awareness of the genetic, acquired, and immunological causes and associated additional treatments of limbal stem cell deficiency (LSCD) is essential for providers. We performed a comprehensive review of the literature on the various etiologies and specific therapies for LSCD. The resources utilized in this review included Medline (PubMed), Embase, and Google Scholar. All English-language articles and case reports published from November 1986 through to October 2022 were reviewed in this study. There were collectively 99 articles on these topics. No other exclusion criteria were applied. Depending on the etiology, ocular manifestations of limbal stem cell deficiency range from dry eye syndrome and redness to more severe outcomes, including corneal ulceration, ocular surface failure, and vision loss. Identifying the source of damage for LSCD is critical in the treatment process, given that therapy may extend beyond the scope of the standard protocol, including artificial tears, refractive surgery, and allogeneic stem cell transplants. This comprehensive review of the literature demonstrates the various genetic, acquired, and immunological causes of LSCD and the spectrum of supplemental therapies available.

Limbal stem cell diseases

The function of limbal stem/progenitor cells (LSCs) is critical to maintain corneal epithelial homeostasis. Many external insults and intrinsic defects can be deleterious to LSCs and their niche microenvironment, resulting in limbal stem cell dysfunction or deficiency (LSCD). Ocular comorbidities, frequent in eyes with LSCD, can exacerbate the dysfunction of residual LSCs, and limit the survival of transplanted LSCs. Clinical presentation and disease evolution vary among different etiologies of LSCD. New ocular imaging modalities and molecular markers are now available to standardize the diagnosis criteria and stage the severity of the disease. Medical therapies may be sufficient to reverse the disease if residual LSCs are present. A stepwise approach should be followed to optimize the ocular surface, eliminate the causative factors and treat comorbid conditions, before considering surgical interventions. Furthermore, surgical options are selected depending on the severity and laterality of the disease. The standardized diagnostic criteria to stage the disease is necessary to objectively evaluate and compare the efficacy of the emerging customized therapies.

Timolol induces necroptosis, apoptosis and senescence concentration-dependently in rabbit Limbal stem cells in vitro

Limbal stem cells (LSCs) are crucial for corneal transparency and vision. Any damages to LSCs might lead to limbal stem cell deficiency resulting in corneal opacification and even blindness. Here, we investigated the cytotoxicity of timolol and its underlying mechanisms in rabbit LSCs (rLSCs) in vitro. High concentrations of 0.5% and 0.25% timolol induced necroptosis in rLSCs to upregulate receptor interacting protein kinase (RIPK)1, RIPK3, mixed lineage kinase domain-like (MLKL) and phosphorylated MLKL along with downregulation of caspase-8 and caspase-2 within 4 h. While, median concentrations of 0.125% to 0.0625% timolol induced apoptosis in the rLSCs within 28 h. The apoptotic mechanism in the median-concentration timolol-treated rLSCs is probably via extrinsic apoptosis pathway by activating caspase-2, caspase-8 and caspase-3 and intrinsic apoptosis pathway triggered by excessive generation of ROS and subsequent DNA damage to upregulate Bax and Bad, downregulate Bcl-2 and Bcl-xL, subsequently disrupt mitochondrial membrane potential, cytosolically translocate cytochrome c and apoptosis-inducing factor, and activate caspase-9. In addition, low concentration of 0.03125% timolol induced senescence in the rLSCs by elevating ROS level and increasing number of senescence associated β-galactosidase positive cells at 28 h. Our findings reveal that timolol induces necroptosis, apoptosis and senescence concentration-dependently in rLSCs in vitro.

Limbal Stem Cell Deficiency After Glaucoma Surgery

PURPOSE

To characterize the clinical presentation of limbal stem cell deficiency (LSCD) associated with glaucoma surgeries.

METHODS

This is a retrospective cross-sectional study of patients with LSCD and glaucoma who presented to the Stein Eye Institute at the University of California, Los Angeles, between 2009 and 2018. Patients who underwent trabeculectomy and/or aqueous shunt surgery were included. The severity of LSCD was staged using global consensus guidelines and a clinical scoring system, and basal epithelial cell density was measured by in vivo confocal microscopy. Anatomic locations of glaucoma and non-glaucoma surgeries, locations of LSCD, and severity of LSCD were compared.

RESULTS

Fifty-one eyes of 41 patients with LSCD associated with glaucoma surgery were included in this study. LSCD in these patients uniquely featured sectoral replacement of corneal epithelium by conjunctival epithelium, without corneal neovascularization or pannus. The sites of glaucoma surgery strongly correlated with the locations of LSCD (P = 0.002). There was a trend toward increased severity of LSCD in eyes with 2 or more glaucoma surgeries as compared to eyes with 1 glaucoma surgery, although the difference did not reach statistical significance (P = 0.3). Use of topical glaucoma medications correlated with LSCD severity, while the impact of antimetabolites did not reach statistical significance. The location of glaucoma drainage surgery is correlated with the location of LSCD.

CONCLUSIONS

LSCD associated with glaucoma surgery has clinical features distinct from LSCD resulting from other etiologies. Further study is required to delineate the full impact of glaucoma surgery on limbal stem cell function and survival.

Understanding cornea epithelial stem cells and stem cell deficiency: Lessons learned using vertebrate model systems

Animal models have contributed greatly to our understanding of human diseases. Here, we focus on cornea epithelial stem cell (CESC) deficiency (commonly called limbal stem cell deficiency, LSCD). Corneal development, homeostasis and wound healing are supported by specific stem cells, that include the CESCs. Damage to or loss of these cells results in blindness and other debilitating ocular conditions. Here we describe the contributions from several vertebrate models toward understanding CESCs and LSCD treatments. These include both mammalian models, as well as two aquatic models, Zebrafish and the amphibian, Xenopus. Pioneering developments have been made using stem cell transplants to restore normal vision in patients with LSCD, but questions still remain about the basic biology of CESCs, including their precise cell lineages and behavior in the cornea. We describe various cell lineage tracing studies to follow their patterns of division, and the fates of their progeny during development, homeostasis, and wound healing. In addition, we present some preliminary results using the Xenopus model system. Ultimately, a more thorough understanding of these cornea cells will advance our knowledge of stem cell biology and lead to better cornea disease therapeutics.

Limbal stem cell deficiency secondary to systemic paclitaxel (Taxol) for breast cancer: a case report

BACKGROUND

Paclitaxel (PTX) is an antineoplastic drug widely used in treatments for ovarian, breast, and small-cell lung cancer. Although ocular effects associated with PTX have been previously described, very few studies have specifically reported systemic PTX as a contributing factor for limbal stem cell deficiency (LSCD), which is characterized by the loss of stem cell and barrier function of the limbus leading to progressive pain and reduction in visual acuity. Described here is a unique case where a patient was diagnosed with LSCD secondary to PTX use for the treatment of breast cancer, at doses of PTX far lower than what is reported in current literature.

CASE PRESENTATION

A 73-year-old woman with a previous diagnosis of breast cancer with liver metastasis presented with a complaint of increasing pain in the left eye more than the right, along with decreasing visual acuity in both eyes following 3 months of PTX therapy for recurrent liver metastases. Upon examination, best-corrected visual acuity was 20/100 in the right eye and counting fingers on the left. Peripheral neovascularization, stromal scarring, and features of limbal stem cell deficiency (LSCD) were noted on the right cornea. A central neurotrophic ulcer with thinning to 50% and 360 degrees of conjunctivalization were noted on the left. After the discontinuation PTX with doxorubicin as the substitute, there was no further progression of her LSCD, and stabilization of her ocular surface was achieved.

CONCLUSION

Although chemotherapy induced LSCD is a relatively rare adverse event, it is essential for clinicians starting new chemotherapy agents to consider the potential ocular toxicities that may result in their use. Ophthalmology review is recommended for patients after starting PTX therapy to assess for signs of LSCD, particularly in patients where drug toxicity can be aggravated due to impaired hepatic function.

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.

Conditional reprogrammed human limbal epithelial cells represent a novel in vitro cell model for drug responses

In this study, we established human limbal epithelial cells (LECs) from normal limbal tissues by using Conditional Reprogramming (CR) technology (refer to CR-LEC cells in this study). We have successfully established CR-LEC cell strains from three human donors (3 out of 3), and normal rabbits (2 out of 2) and pig (1 out of 1) as well. CR-LEC cells sustained a continuous and stable proliferation status with a normal karyotype, normal response to DNA damage, well-defined structured spheres in matrigel 3D culture. Responses of CR-LEC cells to IFN α2b, Ganciclovir and 5-Fluorouracil were different, suggesting that these drugs had different toxicities to these cells as expected. More important, there was no significant difference of responses to drugs between early and late passages of CR-LEC cells (p>0.05), indicating CR-LEC cells can serve a stable normal human cell model for toxicity assessment. Toxicity tests with monolayer cultures of CR-LEC cells were measured by staining the F-actin and Dsg-1 expression. Toxicity of three drugs at LD50 concentration resulted in a gradually increased destruction of monolayer, which is, in accordance with the irritation grade of three drugs on human cornea epithelium. Therefore, CR-LEC cells provide a novel and reliable in vitro physiological cell model for corneal toxicity assessment.

Concomitant Simple Limbal Epithelial Transplantation After Surgical Excision of Ocular Surface Squamous Neoplasia

PURPOSE

To compare the surgical outcomes of ocular surface squamous neoplasia (OSSN) following wide excisional biopsy with and without primary simple limbal epithelial transplantation (p-SLET).

DESIGN

Nonrandomized clinical study with historical controls.

METHODS

setting: Single-institutional study.

PATIENTS

Eight patients who underwent wide excisional biopsy of OSSN without p-SLET (historical controls) and 7 patients with p-SLET (cases).

INTERVENTION

Wide excisional biopsy, p-SLET.

MAIN OUTCOME MEASURES

Limbal stem cell deficiency (LSCD).

RESULTS

The tumor features of cases vs historical controls, including mean number of limbal clock hours affected by OSSN (6 vs 4; P = .12), mean tumor basal dimension (13 mm vs 8 mm; P = .11), and mean number of clock hours of corneoscleral limbal dissection owing to wide tumor excision (8 vs 7; P = .12), were comparable. The occurrence of partial LSCD in historical controls vs cases was 75% vs 0% (P = .007) at a mean follow-up period of 12 months in both groups. Of these 6 historical controls that developed LSCD, pannus was noted in 1 (13%) and pseudopterygium extending onto the cornea in 5 (63%) patients. The mean number of clock hours of LSCD was 3 (median, 2; range, 2-6) in these historical controls. The mean time interval between surgical excision of OSSN and onset of LSCD was 8 weeks (median, 6 weeks; range, 6-12 weeks).

CONCLUSION

Corneoscleral limbal dissection of ≥6 clock hours during wide excision of OSSN can cause LSCD. Concomitant p-SLET after surgical excision of OSSN prevents LSCD in cases requiring extensive corneoscleral limbal dissection.

5-Fluorouracil-Induced Apoptosis Changes in Cultured Corneal Epithelial Cells

PURPOSE

Repeated subconjunctival injections with 5-fluorouracil (5-FU) after trabeculectomy are used in glaucoma patients for the inhibition of overproliferation in wound site. Thus, a certain amount of the drug may penetrate into epithelial layer, where it causes toxicity to corneal epithelial cells. The aim of this study was to evaluate the toxic effects of 5-FU and mechanisms of drug-induced apoptosis in cultured corneal epithelial cells.

METHODS

Cellular damage and the caspase pathway were estimated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The apoptotic characteristics were detected by flow cytometry, a TUNEL test, and western blotting in cultured corneal epithelial cells.

RESULTS

The results indicated that 5-FU was toxic to corneal epithelial cells in a time- and dose-dependent manner. Pretreatment with a general caspase inhibitor (Z-VAD-FMK), a caspase-8 inhibitor (Z-IETD-FMK), and a caspase-9 inhibitor (Z-LEHD-FMK) reversed 5-FU-induced cellular damage. Following exposure to 5-FU, a flow cytometric assay with MitoLight dye demonstrated the significant loss of mitochondrial membrane potential. A positive TUNEL test revealed that cellular DNA apoptosis occurred following exposure to 0.5, 1, and 5 mg/mL 5-FU for 15 h. Positive annexin V-FITC and negative propidium iodide (PI) staining indicated that the cell membrane exhibited apoptosis upon exposure to 1 and 5 mg/mL 5-FU for 15 h. The western blot assay demonstrated upregulation of the p21 protein but downregulation of the Bcl-2 proteins induced by 5-FU.

CONCLUSION

These data reveal that 5-FU-induced cellular apoptosis in corneal epithelial cells may be mediated through caspase-8, caspase-9, and mitochondria-regulated pathways, as well as by upregulation of p21 and downregulation of Bcl-2-dependent signal transduction pathways.

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 use of an IL-1 receptor antagonist peptide to control inflammation in the treatment of corneal limbal epithelial stem cell deficiency

Corneal limbal stem cell deficiency (LSCD) may be treated using ex vivo limbal epithelial stem cells (LESCs) derived from cadaveric donor tissue. However, continuing challenges exist around tissue availability, inflammation, and transplant rejection. Lipopolysaccharide (LPS) or recombinant human IL-1β stimulated primary human keratocyte and LESC models were used to investigate the anti-inflammatory properties of a short chain, IL-1 receptor antagonist peptide for use in LESC sheet growth to control inflammation. The peptide was characterized using mass spectroscopy and high performance liquid chromatography. Peptide cytotoxicity, patterns of cell cytokine expression in response to LPS or IL-1β stimulation, and peptide suppression of this response were investigated by MTS/LDH assays, ELISA, and q-PCR. Cell differences in LPS stimulated toll-like receptor 4 expression were investigated using immunocytochemistry. A significant reduction in rIL-1β stimulated inflammatory cytokine production occurred following LESC and keratocyte incubation with anti-inflammatory peptide and in LPS stimulated IL-6 and IL-8 production following keratocyte incubation with peptide (1 mg/mL) (P < 0.05). LESCs produced no cytokine response to LPS stimulation and showed no TLR4 expression. The peptide supported LESC growth when adhered to a silicone hydrogel contact lens indicating potential use in improved LESC grafting through suppression of inflammation.

Stem cell-based therapy for treating limbal stem cells deficiency: A review of different strategies

The self renewal capability of limbal epithelial stem (LEST) cells is fundamental to the maintenance and healing of corneal epithelium. Limbal stem cell deficiency (LSCD), due to dysfunction or loss of LEST cells, therefore presents as persistent epithelial defects, corneal vascularization, conjunctivalization etc. Stem cell-based therapy, in its simplest form - limbal autograft, has been used successfully for more than a decade. For bilateral LSCD, similar approaches with limbal allografts have been unsuccessful largely due to strong immune rejection. Therefore, as an alternate strategy for treating bilateral LSCD, ex vivo expansion of the remaining LEST cells or autologous stem cells sourced from other potential sites is being explored. Different culture systems (with and without xenobiotic supplements) using substrates like amniotic membrane or fibrin gels have been used successfully for ex vivo LEST cell maintenance and reproduction by imitating the stem cell niche. This paper is organized into sections reviewing the LEST cells, LSCD and various stem cell-based approaches for treating LSCD and discussing future direction and challenges.

Adverse effects of the oral anticancer drug s-1: lacrimal passage impairment and specific features of corneal epitheliopathy

We report the incidence of lacrimal passage impairment and specific features of corneal epitheliopathy as adverse effects of the oral anticancer drug S-1, and examine the relationship between the two pathologies. We conducted a retrospective chart review of 84 patients prescribed the anticancer drug S-1. The incidence of lacrimal passage impairment and corneal epitheliopathy was 8% and 6%, respectively. Three patients experienced both pathologies, demonstrating a moderate probability of both occurring in the same patient (kappa coefficient = 0.46). The findings show that lacrimal passage impairment and specific features of corneal epitheliopathy are likely to occur in the same individual as adverse effects of S-1.

Presentation, diagnosis and management of limbal stem cell deficiency

The human corneal surface epithelium is continuously repopulated by the limbal stem cells (LSCs). Limbal Stem Cell Deficiency (LSCD) can lead to corneal opacity and vascularization, with consequent visual impairment or blindness. Many acquired and congenital diseases can lead to LCSD by direct injury to the LSCs, destruction of LSC niche, or both. Based on the severity of the disease, LSCD can present with various symptoms and signs. Although LSCD can be detected clinically, laboratory tests are necessary to confirm the diagnosis and monitor the disease progression. This article concisely reviews the clinical presentation, techniques for diagnosis and management of LSCD.

Preparation, indications and results of human amniotic membrane transplantation for ocular surface disorders

In comparison with other biologic tissues used as reconstructive grafts, the amniotic membrane has the advantage that it is thinner and better tolerated by the patient. Amniotic membrane, when appropriately preserved, can be used as a substrate replacement, such that host cells can migrate into the membrane to form new and healthy tissue. The amniotic membrane is the deeper layer of the fetal membrane; it is avascular, multilayered tissue with antiangiogenic, antiscarring and anti-inflammatory properties. Since it does not express antigens of histocompatibility, the membrane is never rejected by the receiving tissues. In addition, the beneficial effects of reducing inflammation and neovascularization persist for a long time, if properly cryopreserved.

Fetal membranes as a source of stem cells

In recent years, a constant growth of knowledge and clinical applications of stem cells have been observed. Mesenchymal stromal cells, also described as mesenchymal stem cells (MSCs) represent a particular cell type for research and therapy because of their ability to differentiate into mesodermal lineage cells. The most investigated source of MSCs is bone marrow (BM). Yet, collection of BM is an invasive procedure associated with significant discomfort to the patient. The procedure results in a relatively low number of these cells, which can decrease with donor's age. Therefore, it seems to be very important to find other sources of mesenchymal stem cells nowadays. A human placenta, which is routinely discarded postpartum, in spite of its natural aging process, is still a rich source of stem cells capable to proliferate and in vitro differentiate in many directions. Besides homing and differentiation in the area of injury, MSCs there elicit strong paracrine effects stimulating the processes of repair. In this review, we focus on the biology, characteristics and potential clinical applications of cells derived from human fetal membranes: amnion and chorion.

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.

Current Concepts in Ocular Surface Reconstruction

Diseases that affect the limbal stem cells are multifactorial and present with different stages of severity. The most important features to be considered in evaluating these patients include the degree of limbal stem cell loss, the extent of conjunctival disease, and the presence and etiology of ocular surface inflammation. Other important factors are tear film and eyelid abnormalities, keratinization of the ocular surface, laterality of the disease process, health and age of the patient. Careful consideration of all of these factors help tremendously in tailoring the most suitable method of treatment for each patient. The management of severe ocular surface disease has benefited from numerous advances in recent years. At one time, available techniques for visual rehabilitation consisted of superficial keratectomy, use of artificial tears, tarsorraphy as well as lamellar and penetrating keratoplasty. A lamellar or penetrating keratoplasty procedure resulted in a stable surface only for as long as the donor epithelium was present and once the epithelium sloughed off, the ocular surface failed due to conjunctivalization. The last few decades enjoyed the development and, especially, progress of new ocular surface reconstruction techniques such as amniotic membrane transplantation, limbal stem cell transplant procedures, transplantation of cultivated oral mucosal or limbal stem cell sheets. This review will briefly focus on the indications and methodology of each procedure and the currently available clinical data on the results of these procedures.

Limbal stem cell deficiency arising from systemic chemotherapy with hydroxycarbamide

PURPOSE

The purpose of this study was to report a case of limbal stem cell deficiency (LSCD) after systemic chemotherapy with hydroxycarbamide.

METHODS

Clinical manifestations and pathology are detailed.

RESULTS

We describe the case of a woman with sickle cell disease, who developed bilateral LSCD after treatment with hydroxycarbamide. Histologic examination confirmed the diagnosis of LSCD, revealing goblet cells, inflammatory cells, deposits of new collagen components, and neovascularization in the peripheral cornea. Matrix metalloproteinase-3, fibronectin, and collagen III were also detected in the lesions.

CONCLUSIONS

The systemic use of the antineoplastic drug, hydroxycarbamide, may cause severe LSCD. We recommend that a medication history, including that of cytotoxic drugs, be considered in evaluating LSCD.

Ocular surface tumors

Tumors of the conjunctiva and cornea comprise a large and varied spectrum of conditions. These tumors are grouped into two major categories of congenital and acquired lesions. The acquired lesions are further subdivided based on origin of the mass into surface epithelial, mucoepidermoid, melanocytic, vascular, fibrous, neural, histiocytic, myxoid, myogenic, lipomatous, lymphoid, leukemic, metastatic and secondary tumors. Ocular surface tumors include a variety of neoplasms originating from squamous epithelium, melanocytic tumors and lymphocytic resident cells of the conjunctival stroma. In this review, we highlight clinical features of these lesions, important diagnostic and investigative tools and standard care of management.

Human fetal membranes: a source of stem cells for tissue regeneration and repair?

The ability of stem cells to differentiate into multiple cell lineages has ushered in exciting possibilities for stem cell based therapies that would be used to regenerate and repair damaged tissues and organs. Stem cells isolated from the embryo, fetus, adult and also the umbilical cord and placenta are being widely tested. Recent studies show that human fetal membranes also harbour cells with stem cell like properties. The amnion and chorion contain stromal cells that display characteristics and differentiation potential similar to that of adult, bone marrow derived mesenchymal stem cells. Amniotic epithelial cells share some of the features of pluripotent embryonic stem cells and multipotent mesenchymal stem cells and differentiate into multiple cell lineages in vitro. Amniotic epithelial cells also produce numerous substances that could augment tissue regeneration and repair. This review will focus on the stem cell like properties of stromal and epithelial cells derived from human fetal membranes and their potential use in stem cell based therapies.

Transplantation of ex vivo cultured limbal epithelial stem cells: a review of techniques and clinical results

Ex vivo cultured limbal epithelial stem cells have been used successfully to treat corneal limbal stem cell deficiency. We identified 17 reports of the application of this novel cell-based therapy in humans. In addition we identified four reports of the use of culture oral mucosal epithelial cells to treat limbal stem cell deficiency. We examined these reports to discern the success rate, complication rate, visual outcome, whether there is an optimal technique and which patients are the most likely to benefit. We also discuss the different culture methods employed and the regulations governing cell banks that are providing this service. We found that the techniques used to cultivate and transplant cells varied, but that no individual method was clearly superior. The reported success rate is similar across all studies for both allografts and autografts. The clinical indications for this treatment are not clearly defined as indicated by the variety of disorders treated. Follow-up is limited and the long-term success rate is yet to be established. Nonetheless, we conclude that there is sufficient evidence to support the continued use and refinement of this procedure as a treatment for corneal stem cell deficiency.

Graft failure: II. Ocular surface complications

Risk factors for corneal transplantation failure include both immunologic factors, such as graft rejection, corneal neovascularization, and peripheral anterior synechiae, as well as non-immunologic factors, such as ocular surface disorders (OSD) and glaucoma. This review highlights the necessity of having healthy ocular surface epithelia, tears, and eyelids. It presents different types of OSD, their underlying pathology, and their impact on native cornea and corneal grafts. In addition, a range of proposed donor and surgical factors influencing surface integrity following corneal transplant are addressed. Current medical and surgical research, both pre- and post-operative that promise to further improve the outcome of corneal grafts in the context of OSD are discussed.

Congenital Corneal Anesthesia

Congenital corneal anesthesia is a rare clinical entity that poses a diagnostic dilemma, particularly in the pediatric age group. The sensory deficit may be confined to the cornea, or extend to other divisions of the trigeminal nerve. The sensory deficit may occur as an isolated abnormality, as part of a complex neurological syndrome, or it may occur in association with multiple somatic abnormalities and congenital insensitivity to pain. This condition usually presents between the ages of 8 to 12 months. Poor vision, photophobia, conjunctival injection, and corneal ulceration in the absence of pain and distress in a child should alert the clinician to the possibility of anesthetic cornea. In the early stages of presentation, punctuate keratopathy is the main feature, which may progress to non-healing persistent corneal epithelial defects. This stage may progress to acute corneal lysis and perforation. In most patients, conservative approaches such as copious lubrication, prevention of self-harm and cautious use of bandage contact lenses are effective in preventing progressive corneal damage. Tarsorrhapy is effective in promoting epithelial healing and permanent lateral tarsorraphy may prevent further development of epithelial defects. Amniotic membrane graft may be considered in order to improve epithelial healing. Corneal grafts carry a poor prognosis. Accurate initial diagnosis, evaluation, and proper management are paramount to prevent visual loss due to long-term complications of corneal anesthesia. This review of the literature outlines the problems and approaches in diagnosis, evaluation, and management of this rare condition.

[Corneal epithelial diseases related to limbal stem cell deficiency]

Treatment of corneal epithelial diseases induced by limbal stem cell deficiency is an important challenge in ocular surface reconstruction. Since the 1990s, corneal stem cells have been localized in the limbus. This new concept completely changed the way we consider ocular surface reconstruction, with new diseases now found to be isolated in the ocular surface. Limbus insufficiency syndromes are specific depending on their origin (congenital or acquired), their expression (unilateral or bilateral, partial or total), their progression (acute or chronic), and the mechanism involved (burn, infection, chronic inflammation, etc.). Some of these diseases are local diseases and others are systemic diseases. Clinically, limbus insufficiency is a switch of the normal corneal epithelial phenotype (expression of a specific keratin, avascularity, and transparency of the corneal matrix) in an opaque and fibrovascularized cornea. In terms of cellular biology, a phenotype is a terminal expression of a cell differentiation process. This process is the outcome of the interaction between the genome of a cell or a group of cells with their microenvironment. In limbus insufficiency, epithelial cells and corneal matrix are destroyed, and it is the destruction of these two components that leads to limbus insufficiency syndrome.

Subconjunctival placement of human amniotic membrane during high risk glaucoma filtration surgery

BACKGROUND AND OBJECTIVE

To determine whether subconjunctival placement of amniotic membrane improves filtration results in patients with glaucoma at high risk for surgical failure.

PATIENTS AND METHODS

Retrospective review of 17 eyes of 15 patients who had amniotic membrane applied during glaucoma surgery with or without mitomycin C or 5-fluorouracil.

RESULTS

Mean intraocular pressure decreased from 27.0 +/- 9.1 mm Hg preoperatively to 18.1 +/- 11.0 mm Hg postoperatively with a mean follow-up of 179 days. Complications included self-limited conjunctival wound dehiscence (n = 5), uveitis recurrence (n = 2), and cataract progression (n = 1).

CONCLUSIONS

The results suggest that subconjunctival placement of amniotic membrane may improve filtration outcome in high risk eyes. It will be of interest to determine whether the anti-inflammatory, anti-angiogenic, and antifibrotic properties of amniotic membrane placed subconjunctivally and under the scleral flap will improve filtration surgery outcome by a prospective, randomized study.

Amniotic Membrane Transplantation for Ocular Surface Reconstruction

The amniotic membrane, composed of 3 layers, the epithelium, basement membrane, and the stroma, was first used along with the chorion as a biologic membrane to promote healing of skin burns in 1910. In ophthalmology, it was used in 1940 in the management of conjunctival defects. Its revival in the 1990s was due to its ability to reduce ocular surface inflammation and scarring, promote rapid epithelialization due to the presence of growth factors, and antimicrobial properties. This has resulted in its application in several ocular disorders. A review of the literature shows that amniotic membrane is definitely beneficial in some but not all pathology. The future of amniotic membrane transplantation is very exciting, especially in the field of limbal stem cell research. However, further work is needed to elucidate whether it functions merely as a biologic contact lens or whether it has additional benefits.

In search of markers for the stem cells of the corneal epithelium

The anterior one-fifth of the human eye is called the cornea. It consists of several specialized cell types that work together to give the cornea its unique optical properties. As a result of its smooth surface and clarity, light entering the cornea focuses on the neural retina allowing images to come into focus in the optical centres of the brain. When the cornea is not smooth or clear, vision is impaired. The surface of the cornea consists of a stratified squamous epithelium that must be continuously renewed. The cells that make up this outer covering come from an adult stem cell population located at the corneal periphery at a site called the corneal limbus. While engaging in the search for surface markers for corneal epithelial stem cells, vision scientists have obtained a better understanding of the healthy ocular surface. In this review, we summarize the current state of knowledge of the ocular surface and its adult stem cells, and analyse data as they now exist regarding putative corneal epithelial stem cell markers.

Keratolimbal allograft in corneal reconstruction

The replenishment of corneal epithelial SC is a crucial step for reconstructing the ocular surface in patients suffering from devastating ocular surface diseases manifesting with total LSCD. KLAL is one of such procedures and has a long track record and a long follow-up for patients with bilateral total LSCD. This review summarizes the literature experiences and outline new strategies that are important to enhance the success of this procedure. Further research is needed to fully understand the biological processes involved in allogeneic tissue transplantation for preserving epithelial SC adhesion, migration, and survival.

Amniotic Membrane Transplantation in the Management of Severe Ocular Surface Disease: Indications and Outcomes

Since 1995, with the availability of cryopreserved amniotic membrane (AM), the use of AM as a patch or graft for ocular surface reconstruction has become recognized as an important alternative for treatment of persistent epithelial defects and sterile ulceration that are refractory to conventional therapy. A major problem with evaluating the efficacy of AM transplantation is the lack of controlled clinical studies. Moreover, for some diseases there is no accepted "standard" therapy, and the incidence of the disease is too low to allow proper randomization. In this review, we have attempted to assess the indications and outcomes of AM transplantation based on 661 cases reported in the peer-reviewed literature. Successful outcome was defined as the healing of an epithelial defect (corneal or conjunctival) over a specified time period and the lack of induced motility disturbance.

Corneal epithelial stem cells at the limbus: looking at some old problems from a new angle

Corneal epithelium is traditionally thought to be a self-sufficient, self-renewing tissue implying that its stem cells are located in its basal cell layer. Recent studies indicate however that corneal epithelial stem cells reside in the basal layer of peripheral cornea in the limbal zone, and that corneal and conjunctival epithelia represent distinct cell lineages. These ideas are supported by the unique limbal/corneal expression pattern of the K3 keratin marker for corneal-type differentiation; the restriction of the slow-cycling (label-retaining) cells in the limbus; the distinct keratin expression patterns of corneal and conjunctival epithelial cells even when they are provided with identical in vivo and in vitro growth environments; and the limbal cells' superior ability as compared with central corneal epithelial cells in undergoing in vitro proliferation and in reconstituting in vivo an intact corneal epithelium. The realization that corneal epithelial stem cells reside in the limbal zone provides explanations for several paradoxical properties of corneal epithelium including its 'mature-looking' basal cells, the preponderance of tumor formation in the limbal zone, and the centripetal cellular migration. The limbal stem cell concept has led to a better understanding of the strategies of corneal epithelial repair, to a new classification of various anterior surface epithelial diseases, to the use of limbal stem cells for the reconstruction of corneal epithelium damaged or lost as a consequence of trauma or disease ('limbal stem cell transplantation'), and to the rejection of the traditional notion of 'conjunctival transdifferentiation'. The fact that corneal epithelial stem cells reside outside of the cornea proper suggests that studying corneal epithelium per se without taking into account its limbal zone will yield partial pictures. Future studies need to address the signals that constitute the limbal stem cell niche, the mechanism by which amniotic membrane facilitates limbal stem cell transplantation and ex vivo expansion, and the lineage flexibility of limbal stem cells.

The amniotic membrane in ophthalmology

The amniotic membrane is the innermost of the three layers forming the fetal membranes. It was first used in 1910 in skin transplantation. Thereafter it has been used in surgical procedures related to the genito-urinary tract, skin, brain, and head and neck, among others. The first documented ophthalmological application was in the 1940s when it was used in the treatment of ocular burns. Following initial reports, its use in ocular surgery abated until recently when it was re-discovered in the Soviet Union and South America. Its introduction to North America in the early 1990s heralded a massive surge in the ophthalmic applications of this membrane. The reintroduction of amniotic membrane in ophthalmic surgery holds great promise; however, although it has been shown to be a useful and viable alternative for some conditions, it is currently being used far in excess of its true useful potential. In many clinical situations it offers an alternative to existing management options without any distinct advantage over the others. Further studies will undoubtedly reveal the true potential of the membrane, its mechanism(s) of action, and the effective use of this tissue in ophthalmology.

Ex vivo expansion of corneal limbal epithelial/stem cells for corneal surface reconstruction

PURPOSE

The management of severe ocular surface disease due to limbal stem cell deficiency has changed dramatically. The concept of limbal stem cells, as the source of corneal epithelium revolutionised the therapeutic approach of ocular surface reconstruction. Deficiency of limbal stem cells results in blinding ocular surface diseases. Grafting viable limbal tissue, from either fellow healthy eye or a donor eye, with the resident stem cell population may replenish limbal stem cells and can restore the corneal surface to normality. Transplanting the limbal tissue can be achieved through a variety of procedures that include cadaveric keratolimbal allograft (KLAL), live or living related conjunctival limbal allograft (Ir-CLAL) and limbal autograft. Advances in tissue engineering techniques have offered a viable alternative to overcome the limitation of limbal tissue available for transplantation. Epithelial stem cells harvested from a small limbal biopsy can be expanded in vitro on a suitable carrier and then transplanted to the diseased cornea to successfully restore the corneal surface. This article is a chronological review of the important steps that brought ex vivo expanded stem cell transplantation in ocular, particularly corneal surface reconstruction.

METHODS

The MEDLINE data base was searched for the years 1966-2002, using key words cornea, cell culture, ex-vivo expansion, limbus, stem cell, ocular surface and transplantation. Several articles that were not found by MEDLINE search were taken from references from other articles. Inclusion or exclusion of article was based on the relevance to the subject.

CONCLUSIONS

Corneal epithelial reconstruction with ex vivo expanded limbal cells is a potential tool in ocular surface reconstruction, although the technique is currently investigational. Strategies to achieve conjunctival epithelial restoration and tear film replenishment will allow ophthalmic surgeons to truly reconstruct the ocular surface.

Idiopathic limbal stem cell deficiency

PURPOSE

To describe and to characterize the clinical findings and prognosis of patients with idiopathic limbal stem cell deficiency (LSCD).

DESIGN

Retrospective case series.

PARTICIPANTS/METHODS

We reviewed records from seven patients whose LSCD had been diagnosed clinically and confirmed by impression cytology and in whom the cause of LSCD was never identified. A detailed history, clinical records, and results of slit-lamp biomicroscopy, photography, vital staining, and impression cytology were evaluated.

RESULTS

Six of seven patients (86%) were women, indicating a female predominance. Two patients were from the same family, whereas one other had a positive family history. Severe photophobia was noted in all patients and reduced vision in three patients. The main clinical findings included superficial vascularization, worse in the superior followed by the inferior and nasal cornea. The limbal regions showed a loss of limbal palisades of Vogt, and the adjacent peripheral cornea revealed an irregular and hazy epithelium with positive late fluorescein staining and the presence of conjunctival goblet cells by impression cytology. LSCD was bilateral in all patients but asymmetric in four. During a mean follow-up of 6.1+/- 3.8 years, the visual acuity decreased in both eyes of one patient after cataract extraction and in both eyes of two other patients without surgery. The process of conjunctivalization advanced in four patients (57%) and remained stable in three (43%) without surgical intervention.

CONCLUSIONS

Idiopathic LSCD is a rare and as yet poorly recognized clinical entity, and the findings reported herein may help explore how progressive loss of limbal stem cells occurs. Correct diagnosis of idiopathic LSCD is important so that the patient will not be subjected to unnecessary surgeries, which may actually severely worsen the clinical course.

Management of primary and recurrent pterygium using amniotic membrane transplantation

This review discusses the relative merits of the various techniques used in pterygium surgery with particular reference to the growing interest in the use of amniotic membrane transplantation (AMT) because it is safe, effective, and may be employed in conjunction with other techniques, such as limbal transplantation. The efficacy of AMT is comparable to the established method of conjunctival autograft transplantation (CG) and it is especially indicated when there exists a very large conjunctival defect to cover as in primary double-headed pterygium, or in the context of preserving superior bulbar conjunctiva for future glaucoma surgeries. The authors explain how current management principles (eg, use of anti-inflammatory agents, adequate removal of fibrovascular tissue) are based on known differences in pathogenesis and clinical behavior between primary and recurrent pterygium.

Amniotic membrane transplantation for reconstruction after excision of large ocular surface neoplasias

AIM

To evaluate the clinical outcome of patients in whom ocular surface reconstruction was performed using amniotic membrane transplantation (AMT) after the excision of large (>20 mm square) ocular surface neoplasias (OSN).

METHODS

A non-comparative interventional case series. In 16 eyes of 16 patients, excision of large OSN including conjunctival intraepithelial neoplasia (CIN), primary acquired melanosis, and malignant melanoma was followed by adjunctive cryotherapy and suturing of a single layer of amniotic membrane (AM) with the basement membrane side facing up to the healthy bordering tissue. Epithelial healing, complications, and tumour recurrences were analysed.

RESULTS

During a mean follow up of 23.7 (SD 11, range 11-43) months, ocular surface healing was rapid and complete in all cases. One complication of pyogenic granuloma was noted. Tumour recurrence occurred in one out of 10 CIN cases (10%), no recurrences were observed in the patients with melanotic lesions.

CONCLUSIONS

AMT in lieu of conjunctival or mucosal autograft is an effective substrate for reconstructing the ocular surface following excision of large OSN. AMT is effective in managing large OSN by avoiding the complications that may be associated with conventional removal, specifically in cases where the limbal architecture is destroyed by surgical resection or adjuvant therapies.

Nonpreserved human amniotic membrane transplantation in acute and chronic chemical eye injuries

PURPOSE

To evaluate the safety and efficacy of nonpreserved amniotic membrane transplantation (AMT) with or without limbal autograft transplantation (LAT) in management of acute and chronic chemical eye injuries.

METHODS

Amniotic membrane transplantation or AMT + LAT was performed on nine eyes of seven consecutive patients, five eyes with acute chemical burn and four eyes with limbal stem cell deficiency secondary to previous chemical burn. Nonpreserved amniotic membrane was used in all procedures.

RESULTS

Five patients (71.5%) were men and two (28.5%) were women. The average age at the time of surgery was 32.7 +/- 10.9 years (range, 20-45). Mean follow-up after last surgery was 8.9 +/- 3.2 months (range, 6-14). The average epithelial healing time was 24.6 +/- 17.3 days (range, 3-45). At the end of the follow-up period, visual acuity improved in all eyes, inflammation subsided, and the subjective complaints decreased remarkably.

CONCLUSION

AMT with nonpreserved amniotic membrane promoted epithelial healing, reduced surface inflammation, increased patient comfort, and decreased the extent and severity of vascularization when used in patients with acute chemical burns. When used in limbal stem cell deficiency owing to past chemical burns, AMT alone or in combination with LAT aided in ocular surface reconstruction. Infectious, inflammatory, or toxic/allergic reactions were not encountered in any patient owing to the use of nonpreserved amniotic membrane. Further studies are required to establish the safety and efficacy of preserved and nonpreserved AMT in ocular surface reconstruction.

Amniotic membrane surgery

Human amniotic membrane (AM) is composed of three layers: a single epithelial layer, a thick basement membrane, and an avascular stroma. Amniotic membrane has anti-adhesive properties and is felt to promote epithelialization and decrease inflammation, neovascularization, and fibrosis. Amniotic membrane transplantation (AMT) is currently being used for a continuously widening spectrum of ophthalmic indications. Amniotic membrane transplantation has been shown to be effective in the reconstruction of the corneal surface in the setting of persistent epithelial defects, sterile corneal ulcerations, and partial limbal stem cell (LSC) deficiency states, including those secondary to chemical or thermal burns. Amniotic membrane transplantation also has been used in conjunction with limbal stem cell transplantation (LSCT) both in a concurrent fashion as well as in preparation for LSCT. Amniotic membrane transplantation also has been used in place of conjunctival autografting after pterygium excision and to reconstruct the conjunctival surface after removal of conjunctival lesions. Most recently, ex vivo cultivation and expansion of limbal epithelial cells has been performed utilizing AM as a matrix. However, the superiority of AMT over other treatment modalities in many of these settings needs to be substantiated by controlled clinical trials.