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

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

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

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

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

An investigation of donor and culture parameters which influence epithelial outgrowths from cultured human cadaveric limbal explants

Limbal stem cell deficiency is a blinding disease which affects the cornea at the front of the eye. The definitive cure involves replacing the corneal epithelial (limbal) stem cells, for example by transplanting cultured limbal epithelial cells. One method of performing cultures is to grow a sheet of epithelial cells from a limbal explant on human amniotic membrane. The growth of limbal tissue can be variable. The aim of this study is to investigate how different donor and culture factors influence the ex vivo growth of cadaveric limbal explants. Limbal explant cultures were established from 10 different cadaveric organ cultured corneo-scleral discs. The growth rate and the time taken for growth to be established were determined. Statistical analysis was performed to assess correlation between these factors and donor variables including donor age, sex, time from donor death to enucleation, time from enucleation to organ culture storage and duration in organ culture. Growth curves consistently showed a lag phase followed by a steeper linear growth phase. Donor age, time between death and enucleation, and time between enucleation and organ culture were not correlated to the lag time or the growth rate. Time in organ culture had a significant correlation with the duration of lag time (P = 0.003), but no relationship with the linear growth rate. This study shows that an important factor correlating with growth variation is the duration of corneo-scleral tissue in organ culture. Interestingly, donor age was not correlated with limbal explant growth.

The impact of age on the physical and cellular properties of the human limbal stem cell niche

The limbal niche in the corneoscleral junction of the eye, habitat of the limbal epithelial stem cells (LESC), facilitates corneal epithelial regeneration by providing physical support and chemical signalling. Anatomical structures within the limbus, namely, limbal epithelial crypts and focal stromal projections, are believed to function as a putative niche for LESCs. In this study, the impact of age on the topography of this niche was investigated. Also, the relationship between niche topography and limbal epithelial cell phenotype was assessed. Ex vivo imaging of the limbus in cadaveric tissue of donors aged from infancy to 90 years was carried out using electron and confocal microscopy. The data suggested that the area occupied by the crypts was sharply reduced after the age of 60 years. The niche microstructures also became smoother with donor age. The phenotypic assessment of cultured limbal epithelial cells harvested from donors of different ages showed that the levels of putative stem cell markers as well as telomerase activity and telomere length remained unchanged, regardless of niche topography. However, the colony forming efficiency of the cultures was significantly reduced with age (p < 0.05). This is the first comprehensive study of the effect of age on the structural and phenotypic characteristics of the human limbal niche. The results have a significant biological value as they suggest a correlation of limbal architecture with decline of re-epithelialisation rate in older patients. Overall, the data also suggest that LESCs harvested from younger donors may be more suitable for cultured LESC therapy production.

Characteristics of immune rejection after allogeneic cultivated limbal epithelial transplantation

PURPOSE

To investigate the characteristics and prognosis of immune rejection after allogeneic cultivated limbal epithelial transplantation (CLET).

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Forty-two eyes of 41 patients undergoing allogeneic CLET for total limbal stem cell deficiency who completed a follow-up of at least 12 months.

METHODS

Allogeneic cultivated limbal epithelial cells using human amniotic membrane as a carrier were transplanted into the recipient eye. Immune rejection occurred in 10 eyes; the medical records of these patients were reviewed.

MAIN OUTCOME MEASURES

Best-corrected visual acuity, corneal opacification and neovascularization, immunofluorescence staining of CD4 and CD8 T cells, and distribution of Langerhans cells (LCs) in the corneal epithelium.

RESULTS

The corneal epithelium became edematous with epithelial rejection lines and peripheral epithelial defects in 6 eyes. Circumlimbal vessels were hyperemic and extended up to the corneal stroma, thus resulting in aggravation of corneal neovascularization in 8 eyes. Corneal stromal opacification was observed in 9 eyes. CD4(+) or CD8(+) T cells were detected in 5 of 6 eyes from which impression cytology specimens were obtained. In vivo confocal microscopy examination revealed an accumulation of LCs in the central and peripheral corneal epithelium. All patients responded to antirejection therapy. One eye developed a second episode.

CONCLUSIONS

The diagnosis of immune rejection after allogeneic CLET mainly depends on typical clinical manifestations. Delayed recognition can result in worsening corneal opacification and neovascularization. Reasonable use of topical immunosuppressives and a close follow-up within 6 months after allogeneic CLET are critical to improve the prognosis.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

[Ocular surface reconstruction in limbal stem cell deficiency : Transplantation of cultivated limbal epithelium]

Various ocular surface diseases are caused by loss of corneal epithelial stem cells or dysfunction of the limbal stem cell niche. Besides conventional transplantation of autologous or allogenic limbal tissue, recent advances in tissue engineering have led to the development of new culture and expansion techniques of human limbal stem and progenitor cells (LSPC) as a new strategy to successfully treat limbal stem cell deficiency (LSCD). From a small autologous limbal biopsy with a limited amount of LSPC an epithelium ready for transplantation is achieved. Autologous grafting of cultured limbal epithelium led in most of the treated cases to a successful reconstruction of the corneal surface. Alternative methods which have recently been introduced to treat LSCD use other stem cell sources including the transplantation of oral mucosal epithelium. In this article the challenges and controversies associated with these stem cell culture techniques for ocular surface reconstruction are reviewed.

Limbal epithelial cell therapy: past, present, and future

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

Progenitor cells for ocular surface regenerative therapy

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

Current status and future prospects for cultured limbal tissue transplants in Australia and New Zealand

Cultured limbal tissue transplants have become widely used over the last decade as a treatment for limbal stem cell deficiency (LSCD). While the number of patients afflicted with LSCD in Australia and New Zealand is considered to be relatively low, the impact of this disease on quality of life is so severe that the potential efficacy of cultured transplants has necessitated investigation. We presently review the basic biology and experimental strategies associated with the use of cultured limbal tissue transplants in Australia and New Zealand. In doing so, we aim to encourage informed discussion on the issues required to advance the use of cultured limbal transplants in Australia and New Zealand. Moreover, we propose that a collaborative network could be established to maintain access to the technology in conjunction with a number of other existing and emerging treatments for eye diseases.

Cultivation and characterization of cornea limbal epithelial stem cells on lens capsule in animal material-free medium

A simple, reproducible, animal-material free method for cultivating and characterizing cornea limbal epithelial stem cells (LESCs) on human lens capsule (LC) was developed for future clinical transplantation. The limbal tissue explants (2×2×0.25 mm) were harvested from 77 cadavers and expanded ex vivo on either cell culture plates or LC in medium containing human serum as the only growth supplement. Cell outgrowth at the edge of the explants was observed within 24 hours of cultivation and achieved viable outgrowth (>97% viability as measured by MTT assay and flow cytometry) within two weeks. The outgrowing cells were examined by genome-wide microarray including markers of stemness (p63α, ABCG2, CK19, Vimentin and Integrin α9), proliferation (Ki-67), limbal epithelial cells (CK 8/18 and 14) and differentiated cornea epithelial cells (CK 3 and 12). Immunostaining revealed the non-hematopoietic, -endothelial and -mesenchymal stem cell phenotype of the LESCs and the localization of specific markers in situ. Cell adhesion molecules, integrins and lectin-based surface carbohydrate profiling showed a specific pattern on these cells, while colony-formation assay confirmed their clonal potency. The LESCs expressed a specific surface marker fingerprint (CD117/c-kit, CXCR4, CD144/VE-Cadherin, CD146/MCAM, CD166/ALCAM, and surface carbohydrates: WGA, ConA, RCA, PNA and AIL) which can be used for better localization of the limbal stem cell niche. In summary, we report a novel method combining the use of a medium with human serum as the only growth supplement with LC for cultivating, characterizing and expanding cornea LESCs from cadavers or alternatively from autologous donors for possible treatment of LESC deficiency.

Autologous stem cells for personalised medicine

Increasing understanding of stem cell biology, the ability to reprogramme differentiated cells to a pluripotent state and evidence of multipotency in certain adult somatic stem cells has opened the door to exciting therapeutic advances as well as a great deal of regulatory and ethical issues. Benefits will come from the possibility of modelling human diseases and develop individualised therapies, and from their use in transplantation and bioengineering. The use of autologous stem cells is highly desirable, as it avoids the problem of tissue rejection, and also reduces ethical and regulatory issues. Identification of the most appropriate cell sources for different potential applications, development of appropriate clinical grade methodologies and large scale well controlled clinical trials will be essential to assess safety and value of cell based therapies, which have been generating much hope, but are by and large not yet close to becoming standard clinical practice. We briefly discuss stem cells in the context of tissue repair and regenerative medicine, with a focus on individualised clinical approaches, and give examples of sources of autologous cells with potential for clinical intervention.

Clinical outcomes of repeat autologous cultivated limbal epithelial transplantation for ocular surface burns

PURPOSE

To report the clinical outcomes of repeat autologous cultivated limbal epithelial transplantation in patients with recurrence of limbal stem cell deficiency after a failed primary procedure.

DESIGN

Retrospective case series.

METHODS

This study included 50 patients, above 8 years of age, with clinically diagnosed unilateral limbal stem cell deficiency following ocular surface burns, treated between 2001 and 2010. Following failure of primary surgery all patients underwent a repeat limbal biopsy from the unaffected eye. The limbal cells were expanded ex vivo on a human amniotic membrane substrate for 10 to 14 days using a completely xeno-free explant culture technique. The resulting cultured epithelial monolayer and amniotic membrane were transplanted onto the patient's affected eye. All patients underwent a comprehensive ophthalmic examination of both eyes at every follow-up visit. Postoperative corneal surface stability, change in visual acuity, and complications were objectively analyzed.

RESULTS

At a mean follow-up of 2.3±1.4 (median: 1.96, range: 1 to 7.5) years, 33 of the 50 recipient eyes (66%) maintained a completely epithelialized, avascular, and clinically stable corneal surface. A 2-line improvement in visual acuity was seen in 38 of the 50 recipient eyes (76%). None of the donor eyes developed any clinical features of ocular surface disease, conjunctival overgrowth of the donor site, or decrease in vision throughout the follow-up period.

CONCLUSIONS

Repeat autologous cultivated limbal epithelial transplantation successfully restores corneal epithelial stability and improves vision in eyes with recurrence of limbal stem cell deficiency, following failed primary surgery for ocular burns, without adversely affecting donor eyes.

Concise review: limbal epithelial stem cell therapy: controversies and challenges

Limbal epithelial stem cells (LESCs) are a population of stem cells responsible for maintenance and repair of the corneal surface. Injury and disease can result in a deficiency of these stem cells, the vision affecting condition called limbal stem cell deficiency (LSCD) in which the cornea becomes opaque, vascularized, and inflamed. Cultured LESC therapy was first described in 1997;29:19231932-19231932.and LESCs cultured from either patients or donors have been used to successfully treat LSCD. In this review, some of the challenges and controversies associated with cultured LESC therapy will be discussed including alternative stem cell sources.

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

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

Characterization of ocular surface epithelial and progenitor cell markers in human adipose stromal cells derived from lipoaspirates

PURPOSE

The goal of this study was to characterize and compare mesenchymal stem cells from adult human adipose tissue (ADS cells) with progenitor cell lines from the human corneoscleral limbus and to analyze their potential for the expression of epithelial markers.

METHODS

Stem cell markers (CD34, CD90, p63, and ABCG2) and epithelial cell markers (CK3/76, CK12, CK76, CK19, and CK1/5/10/14) were analyzed by immunostaining, flow cytometry, Western blot analysis, and PCR methods. The authors assayed adhesion and proliferation on different extracellular matrix proteins.

RESULTS

ADS cells expressed a set of progenitor cell markers, including p63 and ABCG2. CK12 expression in ADS cell cultures increased spontaneously and progressively by differential adhesion, which demonstrates the cells' potential and capability to acquire epithelial-like cell characteristics. The authors observed an increase in the adhesion and proliferation of ADS cells seeded onto different basement membrane extracellular matrix proteins. Laminin substrates reduced the proliferative state of ADS cells.

CONCLUSIONS

The expression of putative stem cell markers (CD90, ABCG2, and p63) and cytokeratins (CK12 and CK76) supports the hypothesis that ADS cells have self-renewal capacity and intrinsic plasticity that enables them to acquire some epithelial-like characteristics. Therefore, adult ADS cells could be a potential source for cell therapy in ocular surface regeneration.

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

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

Clinical outcomes of penetrating keratoplasty after autologous cultivated limbal epithelial transplantation for ocular surface burns

PURPOSE

To report the clinical outcomes of penetrating keratoplasty (PK) after autologous cultivated limbal epithelial transplantation in eyes with limbal stem cell deficiency (LSCD) after ocular surface burns.

DESIGN

Retrospective case series.

METHODS

This study included 47 patients with unilateral LSCD treated by autologous cultivated limbal epithelial transplantation and PK between 2001 and 2010. PK was performed either along with (single-stage; n = 12) or at least 6 weeks after (2-stage; n = 35) limbal transplantation. The primary outcome measure was corneal allograft survival, and failure was defined clinically as loss of central graft clarity. Secondary outcomes were postoperative Snellen visual acuity and complications.

RESULTS

Most patients were young (mean age, 18 ± 11.4 years) males (76.6%) with LSCD resulting from alkali burns (78.7%) and with visual acuity less than 20/200 (91.5%). The mean follow-up was 4.2 ± 1.9 years. Kaplan-Meier corneal allograft survival rate at 1 year was significantly greater in eyes undergoing 2-stage limbal and corneal transplantation (80 ± 6%; median survival, 4 years) compared with single-stage limbal and corneal transplantation (25 ± 13%; median survival, 6 months; P = .0003). Visual acuity of 20/40 or better was attained by 71.4% of eyes with clear corneal grafts. Allograft failure occurred in 26 (60.5%) eyes as a result of graft rejection (57.7%), graft infiltrate (26.9%), or persistent epithelial defects (15.4%). Recurrence of LSCD was more common after single-stage (58.3%) than 2-stage (14.3%) surgery (P = .008).

CONCLUSIONS

The 2-stage approach of autologous cultivated limbal epithelial transplantation followed by PK successfully restores ocular surface stability and vision in eyes with chronic ocular burns. The single-stage approach is associated with poorer clinical outcomes and should be avoided.

Ocular epithelial transplantation: current uses and future potential

Visual loss may be caused by a variety of ocular diseases and places a significant burden on society. Replacing or regenerating epithelial structures in the eye has been demonstrated to recover visual loss in a number of such diseases. Several types of cells (e.g., embryonic stem cells, adult stem/progenitor/differentiated epithelial cells and induced pluripotent cells) have generated much interest and research into their potential in restoring vision in a variety of conditions: from ocular surface disease to age-related macular degeneration. While there has been some success in clinical transplantation of conjunctival and particularly corneal epithelium utilizing ocular stem cells, in particular, from the limbus, the replacement of the retinal pigment epithelium by utilizing stem cell sources has yet to reach the clinic. Advances in our understanding of all of these cell types, their differentiation and subsequent optimization of culture conditions and development of suitable substrates for their transplantation will enable us to overcome current clinical obstacles. This article addresses the current status of knowledge concerning the biology of stem cells, their progeny and the use of differentiated epithelial cells to replace ocular epithelial cells. It will highlight the clinical outcomes to date and their potential for future clinical use.

Corneal stem cells in the eye clinic

INTRODUCTION OR BACKGROUND

Corneal opacity is a common cause of blindness. The majority of cases result from ulceration and scarring following infection or trauma, but in a proportion corneal epithelial stem cell (SC) deficiency leads to an inability to maintain a healthy corneal surface.

SOURCES OF DATA

This review includes systematic reviews and individual case series of treatments for corneal epithelial SC deficiency.

AREAS OF AGREEMENT

Two techniques such as transplantation of large segments of cornea from a healthy eye and ex vivo expansion of corneal SCs in the laboratory were compared. Both have merits and their clinical outcomes are similar. The smaller biopsy in the cell expansion approach has less risk for the donor eye, which is a significant advantage.

AREAS OF CONTROVERSY

Treatment algorithms for different aetiologies of SC failure are evolving. The proportion of true corneal epithelial SCs in ex vivo culture is unclear and it is unknown whether these cells survive long term.

GROWING POINTS

In this study, the optimum method of cell culture and transplantation is being intensively investigated.

AREAS TIMELY FOR DEVELOPING RESEARCH

Development of tissues using multiple cell types, genetic modification to treat hereditary corneal disorders and development of cell therapy for other eye diseases are future possibilities.