Limbal allografting from related live donors for corneal surface reconstruction

A Review of Contact Lens-Induced Limbal Stem Cell Deficiency

Limbal stem cell deficiency (LSCD) is a pathologic condition caused by the dysfunction and destruction of stem cells, stem cell precursors and limbal cell niche in the corneal epithelium, leading to severe conjunctivalization of the cornea. Etiologies for LSCD span from congenital (aniridia), traumatic (chemical or thermal injuries), autoimmune (Stevens-Johnson syndrome) and iatrogenic disease to contact lens (CL) wear. Of these, CL wear is the least understood and is often a subclinical cause of LSCD. Even with recent advances in LSCD research, limitations persist in establishing the pathogenesis and treatment guidelines for CL-induced LSCD. A literature search was conducted to include original articles containing patients with CL-induced LSCD. This review will critically discuss the complex pathophysiology behind CL-induced LSCD, the underlying risk factors and epidemiology of the disease as well as methods to obtain a diagnosis. Various treatment options will be reviewed based on proposed treatment strategies.

Outcomes of Combined Penetrating Keratoplasty and Limbal Stem Cell Transplantation: A Meta-Analysis on Simultaneous Versus Sequential Surgery

PURPOSE

The objective of this study is to perform a systematic review and meta-analysis of the published studies on limbal stem cell transplantation (LSCT) combined with penetrating keratoplasty (PK) performed either simultaneously or sequentially.

METHODS

An extensive search was conducted in the MEDLINE and Google Scholar databases. Prospective and retrospective trials and case series reporting on the outcomes of LSCT with PK were included. Primary outcomes were the stability of the ocular surface and the rejection and/or failure of the corneal graft.

RESULTS

A total of 209 eyes from 13 studies were included in the simultaneous group and 489 eyes from 33 studies in the sequential group. Ocular surface stability was 88% [95% confidence interval (CI), 79%-96%] for sequential cases and 64% (95% CI, 43%-82%) for simultaneous cases ( P = 0.001). The graft failure rate was 15% (95% CI, 6%-26%) for sequential cases and 44% (95% CI, 31%-58%) for simultaneous cases ( P < 0.001). For cases performed sequentially, subgroup analysis revealed a stable ocular surface in 97% (95% CI, 91%-100%) of autograft cases and 63% (95% CI, 45%-80%) of allograft cases ( P < 0.001). The graft failure rate in sequential cases was 7% (95% CI, 0%-18%) for autografts and 34% (95% CI, 18%-52%) for allografts ( P < 0.001).

CONCLUSIONS

Sequential LSCT followed by PK demonstrated superior results in terms of ocular surface stability and graft retention compared with simultaneous LSCT and PK. Limbal stem cells of autologous origin fare better than allogeneic ones in sequential cases.

Global Consensus on the Management of Limbal Stem Cell Deficiency

PURPOSE

In recent decades, the medical and surgical treatment of limbal stem cell deficiency (LSCD) has evolved significantly through the incorporation of innovative pharmacological strategies, surgical techniques, bioengineering, and cell therapy. With such a wide variety of options, there is a need to establish a global consensus on the preferred approaches for the medical and surgical treatment of LSCD.

METHODS

An international LSCD Working Group was established by the Cornea Society in 2012 and divided into subcommittees. Four face-to-face meetings, frequent email discussions, and teleconferences were conducted since then to reach agreement on a strategic plan and methods after a comprehensive literature search. A writing group drafted the current study.

RESULTS

A consensus in the medical and surgical management of LSCD was reached by the Working Group. Optimization of the ocular surface by eyelid and conjunctival reconstruction, antiinflammatory therapy, dry eye and meibomian gland dysfunction treatment, minimization of ocular surface toxicity from medications, topical medications that promote epithelialization, and use of a scleral lens is considered essential before surgical treatment of LSCD. Depending on the laterality, cause, and stage of LSCD, surgical strategies including conjunctival epitheliectomy, amniotic membrane transplantation, transplantation of limbal stem cells using different techniques and sources (allogeneic vs. autologous vs. ex vivo-cultivated), transplantation of oral mucosal epithelium, and keratoprosthesis can be performed as treatment. A stepwise flowchart for use in treatment decision-making was established.

CONCLUSIONS

This global consensus provides an up-to-date and comprehensive framework for the management of 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.

Surgical Management of Limbal Stem Cell Deficiency

Treatment of limbal stem cell deficiency is challenging. Multiple options can be adopted according to the underlying cause and the patient and physician preferences. Stem cell transplant is a common treatment modality and several techniques have been described with outcomes varying by the laterality of the condition. Keratoprosthesis is a preferred option for bilateral conditions. Indications for type 1 and type 2 keratoprosthesis differ and the past 2 decades have seen a revolution in the field of keratoprosthesis with encouraging and improved outcomes. Management also includes preventive measures and measures to optimize/stabilize the ocular surface that would go a long way in reducing the deterioration of the ocular surface. The aim of this review is to provide an overview of the currently available techniques and to present a comprehensive algorithm to assist in decision making for unilateral and bilateral limbal stem cell deficiency.

Allogenic simple limbal epithelial transplantation (alloSLET) from cadaveric donor eyes in patients with persistent corneal epithelial defects

BACKGROUND/AIM

To describe the clinical outcome of allogenic simple limbal epithelial transplantation (alloSLET) utilising tissue from cadaveric donor eyes after failed re-epithelialisation of the corneal surface.

METHODS

Medical records of 14 eyes from 14 patients treated for persistent corneal epithelial defects with alloSLET were reviewed. The primary outcome measure was complete epithelialisation of the corneal surface. Secondary outcome measures were best corrected visual acuity (BCVA) and postoperative side effects due to surgery or medical therapy.

RESULTS

Of the 14 eyes, 7 received alloSLET only and 7 alloSLET together with penetrating keratoplasty (PK). Thirteen (92.9%) of 14 eyes had an epithelialised corneal surface 3 and 6 months after surgery and 10 (71.4%) of 14 eyes displayed an epithelialised corneal surface 12 months after surgery. In both subgroups, alloSLET only and alloSLET with PK, respectively, 5 (71.4%) of 7 eyes had a stable corneal epithelium 12 months after surgery, respectively. Postoperatively, BCVA improved markedly in the whole patient collective. However, the increase was not significant when looking at the two individual subgroups. One patient lost his bandage contact lens several times within the first postoperative month and had a partial detachment of the amniotic membrane. The ocular surface of this patient failed to epithelialise. In three patients, limbal donor pieces translocated to the centre of the cornea, which possibly prolonged the improvement of BCVA.

CONCLUSION

AlloSLET appears to be an effective treatment option in eyes with non-healing corneal epithelial defects when autologous limbal tissue is not available.

Limbal niche cells: a novel feeder cell for autologous cultivated oral mucosal epithelial transplantation

AIM

To establish a culture system using conspecific limbal niche cells (LNCs) as feeders for autologous cultivated oral mucosal epithelial transplantation (COMET).

MATERIALS & METHODS

Rabbit oral epithelial sheets, harvested from culture systems containing LNCs or 3T3 cells, were transplanted onto limbal stem cell-deficient rabbit eyes (COMET-3T3 or COMET-LNCs).

RESULTS

After COMET, corneas were relatively restored, with the exception of mild neovascularization in one cornea of the COMET-3T3 group. CD34 was detected in COMET-3T3 group corneas. Corneas of the COMET-LNCs group expressed high levels of PEDF and sFlt-1, but low levels of bFGF, compared with expression in COMET-3T3 corneas.

CONCLUSION

The culture system containing conspecific LNC feeders could substitute for the 3T3 cell system and decrease the risk of neovascularization after COMET.

Limbal Stem Cell Transplantation: Clinical Results, Limits, and Perspectives

Limbal stem cell deficiency (LSCD) is a clinical condition characterized by damage of cornea limbal stem cells, which results in an impairment of corneal epithelium turnover and in an invasion of the cornea by the conjunctival epithelium. In these patients, the conjunctivalization of the cornea is associated with visual impairment and cornea transplantation has poor prognosis for recurrence of the conjunctivalization. Current treatments of LSCD are aimed at replacing the damaged corneal stem cells in order to restore a healthy corneal epithelium. The autotransplantation of limbal tissue from the healthy, fellow eye is effective in unilateral LSCD but leads to depauperation of the stem cell reservoir. In the last decades, novel techniques such as cultivated limbal epithelial transplantation (CLET) have been proposed in order to reduce the damage of the healthy fellow eye. Clinical and experimental evidence showed that CLET is effective in inducing long-term regeneration of a healthy corneal epithelium in patients with LSCD with a success rate of 70%–80%. Current limitations for the treatment of LSCD are represented by the lack of a marker able to unequivocally identify limbal stem cells and the treatment of total, bilateral LSCD which requires other sources of stem cells for ocular surface reconstruction.

Surgical management of severe ocular surface injury due to Roman candle explosion accidents

PURPOSE

To report the clinical features, management, and outcomes of patients with ocular surface damage secondary to Roman candle explosion accidents.

METHODS

Retrospective, noncomparative, interventional case series of 11 patients with Roman candle explosion-related ocular surface injuries referred to the Cincinnati Eye Institute between 2007 and 2016.

RESULTS

Eleven patients (10 male, 1 female, mean age 22.4 years) sustained unilateral ocular surface injuries with presenting visual acuity ranging from count fingers to light perception. All patients had severe limbal stem cell deficiency with total ocular surface failure. Eight eyes received a conjunctival-limbal autograft (CLAU) with a keratolimbal allograft (KLAL), 1 eye received a living related-conjunctival limbal allograft (lr-CLAL) with a KLAL, and 2 eyes received a CLAU with lr-CLAL. Nine eyes underwent subsequent penetrating keratoplasty, and 7 eyes had reconstructive eyelid surgery. Nine eyes demonstrated improved visual acuity at last follow-up; seven eyes demonstrated a stable ocular surface at last follow-up. Nonadherence was noted in 7 patients, either with poor adherence with post-operative treatment or poor follow-up; this portended a worse visual result.

CONCLUSIONS

Roman candle-related accidents can lead to severe ocular surface injury. Despite total ocular surface failure, these eyes can achieve good postoperative visual results following limbal stem cell transplantation and subsequent keratoplasty with appropriate compliance.

Preserving Basement Membranes during Detachment of Cultivated Oral Mucosal Epithelial Cell Sheets for the Treatment of Total Bilateral Limbal Stem Cell Deficiency

Total bilateral limbal stem cell deficiency leading to loss of corneal clarity, potential vision loss, pain, photophobia, and keratoplasty failure cannot be treated by autologous limbal transplantation, and allogeneic limbal transplantation requires subsequent immunosuppressive treatment. Cultured autologous oral mucosal epithelial cells have been shown to be safe and effective alternatives. These cells can be transplanted on supports or without support after detachment from the culture dishes. Dispase, known for epidermal sheet detachment, is reported as not usable for oral mucosa. The objective was to find an optimized detachment method providing a sufficiently resistant and adhesive cultured oral mucosal epithelium (COME), which can be grafted without sutures. Enzymatic treatments (dispase or collagenase at different concentrations) were compared to enzyme-free mechanical detachment. Histological immunofluorescence (IF) and Western blotting (WB) were used to examine the impact on adhesion markers (laminin-332, β1-integrin, and type VII collagen) and junctional markers (E-cadherin, P-cadherin). Finally, the COME ability to adhere to the cornea and produce a differentiated epithelium 15 d after grafting onto an ex vivo porcine stroma model were investigated by histology, IF, and transmission electron microscopy. Collagenase at 0.5 mg/mL and dispase at 5 mg/mL were selected for comparative study on adhesive expression marker by IF and WB showed that levels of basement membrane proteins and cell-cell and cell-matrix junction proteins were not significantly different between the 3 detachment methods. Collagenase 0.5 mg/mL was selected for the next step validation because of the better reproducibility, 100% success (vs. 33% with dispase 5 mg/mL). Grafted onto porcine de-epithelialized corneal stroma, collagenase 0.5 mg/mL detached COME were found to adhere, stratify, and continue to ensure renewal of the epithelium. For COME, collagenase 0.5 mg/mL enzymatic detachment was selected and validated on its resistance and adhesive marker expression as well as their anchorage onto our new ex vivo de-epithelialized stroma model.

Limbal stem cell and oral mucosal epithelial transplantation from ex vivo cultivation in LSCD-induced rabbits: histology and immunologic study of the transplant epithelial sheet

PURPOSE

To evaluate the results of cultivated limbal epithelial and oral mucosal epithelial transplantation (CLET and COMET) in limbal stem cell deficiency (LSCD)-induced rabbit model.

MATERIALS AND METHODS

Six New Zealand white rabbits were divided into two groups of three rabbits each. Limbal tissue was harvested from the first group, and oral mucosal biopsy was obtained from the second group. The tissues were cultured using an explant technique with amniotic membrane as a substrate and co-culture with the 3T3 fibroblast and air-lifting method. The right eye of each rabbit was induced to have LSCD using alkali burns. After three weeks, the LSCD-induced rabbit eyes were transplanted with the cultivated limbal and oral mucosal epithelial sheet in the first and second group, respectively. The transplanted eye was evaluated weekly post-operation. After 2 months, all transplanted eyes were enucleated and the epithelial morphology and phenotype of ocular surfaces were studied and compared with normal corneal and oral mucosal tissue.

RESULTS

At 2-month post-transplantation, the eyes of four animals recovered with corneal transparency, one partially recovered, and one failed. The histology of the majority of transplanted eyes was stratified layers of corneal epithelia similar to normal rabbit cornea with some different findings such as goblet cells in the limbal region. Corneal epithelial thickening and stromal vascularization in two animals were observed. Phenotypic characterization of transplanted eyes showed a similar pattern of marker expression with the absence of p63 expression in the limbal or corneal epithelium in the COMET group.

CONCLUSIONS

The histology and phenotype of transplanted eyes after CLET and COMET were most likely to have similar characteristics as a normal healthy rabbit eye even though the COMET eyes have some inferior characteristics to the CLET eyes.

Diagnostic criteria for limbal stem cell deficiency-a systematic literature review

The diagnosis of limbal stem cell deficiency (LSCD) is often based on clinical manifestations with or without the use of tests to demonstrate the presence of goblet cells or of specific epithelial markers on the corneolimbal surface. This systematic review looks at the various diagnostic methods used in the diagnosis of LSCD in published interventional studies. The design is a systematic literature review. We did a systematic search on MEDLINE and PUBMED for articles published in English between January 1, 2003, and December 31, 2013. We collected data on diagnostic methods used to diagnose LSCD (clinical findings, impression cytology, immunohistochemistry for various epithelial markers, or in vivo confocal microscopy). Forty-six studies (mostly retrospective/interventional case series) met the inclusion criteria. All of the studies used clinical features as evidence of LSCD: discomfort, impaired vision, irregular epithelium, unstable tear film, persistent epithelial defects, scarring, fibrovascular pannus, neovascularization, keratinization, calcification, and opacification of the cornea. Eighteen studies (39.1%) used an additional test for the diagnosis; 17 studies (37.0%) used impression cytology for goblet cells, 4 studies (8.7%) used immunohistochemistry for epithelial markers, and 2 studies (4.3%) use in vivo confocal microscopy. The diagnosis of LSCD was made in most cases on clinical grounds alone. In some studies, diagnostic tests were used, but these varied considerably from study to study. Comparison of effectiveness of various interventions requires standardized diagnostic methods. Consensus on the diagnostic criteria for LSCD is essential and needs to be reached by the interested care providers.

Acute and Chronic Ophthalmic Involvement in Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis - A Comprehensive Review and Guide to Therapy. II. Ophthalmic Disease

Our purpose is to comprehensively review the state of the art with regard to Stevens- Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), with particular attention to improving the management of associated ocular surface complications. SJS and TEN are two ends of a spectrum of immune-mediated disease, characterized in the acute phase by a febrile illness followed by skin and mucous membrane necrosis and detachment. Part I of this review focused on the systemic aspects of SJS/TEN and was published in the January 2016 issue of this journal. The purpose of Part II is to summarize the ocular manifestations and their management through all phases of SJS/TEN, from acute to chronic. We hope this effort will assist ophthalmologists in their management of SJS/TEN, so that patients with this complex and debilitating disease receive the best possible care and experience the most optimal outcomes in their vision and quality of life.

Limbal Stem Cell Transplantation for Soft Contact Lens Wear-Related Limbal Stem Cell Deficiency

PURPOSE

To describe the outcomes of limbal stem cell transplantation in eyes with limbal stem cell deficiency related to soft contact lens wear.

DESIGN

Retrospective interventional case series.

METHODS

Institutional database search at the Cincinnati Eye Institute revealed 9 patients (14 eyes) who underwent limbal stem cell transplantation with systemic immunosuppression for soft contact lens wear-related limbal stem cell deficiency. Outcome measures included patient demographics, symptoms, best-corrected visual acuity, ocular surface stability, adverse events, and additional surgeries required.

RESULTS

Average patient age at time of surgery was 46.6 ± 11.1 years (range 20-60 years). Average duration of follow-up was 28 ± 19.1 months (range 12-70 months). Preoperative best-corrected visual acuity (BCVA) was 20/40 or worse in all eyes (average 20/70, range 20/40-20/250) and patient symptoms included foreign body sensation, tearing, redness, and/or pain. Four eyes (29%) underwent living-related conjunctival limbal allograft and 10 eyes (71%) underwent cadaver-donor keratolimbal allograft surgery. Topical and systemic immunosuppression was used in all patients. At final follow-up after limbal stem cell transplantation, there was a stable ocular surface in 12 of 14 eyes (86%) and improvement in BCVA to 20/30 or better and complete resolution of patient symptoms in all except 1 patient who had significant rosacea blepharokeratoconjunctivitis, whose BCVA remained at 20/150 and 20/60, in right and left eyes, respectively. The most common adverse event was an increase in intraocular pressure in 8 of 14 eyes (57%), requiring topical antiglaucoma treatment. Ten of 14 eyes (71%) underwent cataract extraction related to topical steroid use. No eyes required subsequent penetrating keratoplasty.

CONCLUSION

Limbal stem cell transplantation is a viable option for the management of soft contact lens wear-related limbal stem cell deficiency in young healthy patients. Early intervention prior to subepithelial fibrosis can lead to good visual outcomes with no need for subsequent cornea transplant. Co-management with a solid organ transplant specialist is helpful for the monitoring and management of systemic adverse events related to patient systemic immunosuppression.

Successful application of ex vivo expanded human autologous oral mucosal epithelium for the treatment of total bilateral limbal stem cell deficiency

Ocular surface reconstruction with ex vivo expanded limbal stem cells (LSCs) is a widely used clinical treatment for patients with limbal stem cell deficiency (LSCD). This is not applicable to patients with bilateral LSCD where there are no remaining LSCs. Cultivated oral mucosa epithelium (OME) has been used as an alternative source of autologous epithelial stem cells for ocular reconstruction in few clinical trials. However, successful generation of stratified OME epithelium has only been achieved in the presence of animal feeder cells and/or animal-derived products in the culture media, likely to contribute to increased risk of pathogen transmission and graft rejection. In this study, we report generation of multilayered OME epithelium that shares many of the characteristics of corneal epithelium using a fully compliant good manufacturing practice, feeder- and animal product-free method. Proof of concept was achieved by transplantation of autologous ex vivo expanded OME in two patients with histologically confirmed bilateral total LSCD that resulted in successful reversal of LSCD in the treated eye up to 24 months.

Clinical Spectrum and Treatment Approaches in Corneal Burns

Objectives:

To evaluate the clinical findings, treatment modalities and long-term prognosis of chemical and thermal burns of the cornea.

Materials and Methods:

Twenty-one patients (27 eyes) who were followed at two centers for corneal chemical and thermal burns between 2001 and 2013 were included. Eyes were grouped into four grades according to the severity of burn using Roper-Hall classification. Age, gender, type of burn, follow-up duration, corrected visual acuity before and after treatment, treatment modalities and complications were recorded. Patients received medical treatment or combined surgical treatment including amniotic membrane transplantation (AMT), conjunctivolimbal autograft/allograft (CLAU/CLAL) transplantation, keratolimbal allograft (KLAL) or penetrating keratoplasty (PKP).

Results:

Patients had a mean age of 27.1±15.5 years (range, 6 months-56 years) and were followed for a mean 63.2±58.6 weeks (4-160 weeks). Significant improvement was achieved with medical treatment alone in patients with grade I (4 eyes) and 2 burns (8 eyes). Patients with grade III burns (11 eyes) underwent CLAU (6 eyes), combined AMT/CLAU (3 eyes), AMT/CLAL (1 eye), or CLAL+PKP (1 eye), while patients with grade IV burns (4 eyes) had keratectomy+CLAL/AMT (1 eye), keratectomy+CLAL+PKP after recurrence with CLAU/AMT (1 eye), CLAU+PKP (1 eye), and AMT/KLAL+PKP (1 eye). All patients except the latter showed ocular surface stabilization with these procedures.

Conclusion:

Ocular burns cause severe impairment of the ocular surface. It is possible to achieve good results with appropriate medical treatment and surgeries including ocular surface reconstruction.

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

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

Transforming ocular surface stem cell research into successful clinical practice

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

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.

Cultivation and phenotypic characterization of rabbit epithelial cells expanded ex vivo from fresh and cryopreserved limbal and oral mucosal explants

PURPOSE

To compare the morphology of cultured rabbit epithelial sheets and the expression of stem cells with differentiated cell markers of cultivated epithelial cells from fresh and cryopreserved limbal and oral mucosal biopsies.

MATERIALS AND METHODS

Six New Zealand white rabbits were divided into two groups of three, from which limbal and oral mucosal biopsies were taken. Harvested tissues from each rabbit were brought to immediate cultivation, while another set of tissues was cryopreserved. Cultivation was performed by the explant culture technique using human amniotic membrane as a culture substrate, co-culturing with 3T3 fibroblasts and using the air-lifting method. Cells were cultured for three weeks; then cultured epithelial sheets were stained with hematoxylin-eosin and examined for expression patterns of p63, keratin 3 (K3) and connexin 43 (Cx43). Cryopreservation was carried out using the vitrification method. Tissues were preserved in liquid nitrogen using 25% dimethyl sulfoxide combined with 25% propylene glycol in Dulbecco's Modified Eagle's Medium containing 20% fetal bovine serum. After two months, the tissues were warmed, cultured and stained using the same processes as for fresh tissue cultures.

RESULTS

Cultivation of fresh limbal and fresh oral mucosal tissues showed epithelial stratification, with two to five cell layers. Immunohistochemical staining showed p63-positive cells in basal and intermediate cell layers. K3 staining was observed in cells in the suprabasal layer, while expression of Cx43 was scattered throughout all layers of the epithelia. All culture sheets expressed p63, K3 and Cx43 with the exception of one sheet from the oral mucosal culture that was p63-negative. Cultured epithelial sheets from cryopreserved tissues showed results similar to those from fresh tissue culture.

CONCLUSIONS

This study found that cells in cultivated fresh limbal and oral mucosal tissues had similar morphology to cells in cultivated cryopreserved limbal and oral mucosal tissues, both containing a heterogeneous population of cells including stem cells and differentiated cells.

Surgical rehabilitation following ocular chemical injury

PURPOSE

The purpose of this study is to evaluate the management of limbal stem cell deficiency (LSCD) secondary to chemical ocular burns.

MATERIALS AND METHODS

The charts of 48 eyes of 40 patients with grade 2 or higher chemical injury were evaluated retrospectively. Subjects with follow-up longer than 1 year were included. Medical treatment, surgical correction of abnormalities of ocular adnexial structures, limbal stem cell transplantation from patient's fellow eye, from living relatives or from cadaveric donor, amniotic membrane transplantation, conjunctival epitheliectomy, chelation with ethylenediaminetetraacetic acid and penetrating keratoplasty were the treatment modalities. Outcome measures were ocular surface stability and corrected distance visual acuity (CDVA). Failure was defined as the appearance of persistent epithelial defect (nonhealing epithelial defect for more than 2 weeks) with progressive corneal conjunctivalization/vascularization and thinning, and also progression of conjunctivalization to the central 6 mm of the cornea in eyes with subsequent keratoplasty.

RESULTS

The mean age of 31 male and 9 female patients were 32.32 ± 12.6 years. LSCD was bilateral in 8 cases. The mean follow-up was 77.2 ± 35.1 months. The presentations were in acute phase in 37.5%, in subacute phase in 32.5% and in chronic phase in 30% of the patients. Only 13 of 48 (27.1%) eyes obtained sufficient ocular surface stability through medical treatment; however, only 5 of these eyes achieved CDVA of less than 0.7 logMAR. Limbal stem cell transplantation was performed in 26 eyes as conjunctival limbal autograft, living-related conjunctival limbal allograft and keratolimbal allograft or as a combination of these transplantations. At the last visit, 30 eyes (62.5%) had an intact and stable ocular surface. Clear cornea was achieved in 11 (78.6%) of 14 eyes with grade 2 injury, in 9 (60%) of 15 eyes with grade 3 injury, in 5 (50%) of 10 eyes with grade 4 injury, in 1 (16.6%) of 6 eyes with grade 5 injury and in 1 (33.3%) of 3 eyes with grade 6 injury. The CDVA that was 1.66 ± 0.99 logMAR initially improved to 0.87 ± 0.85 logMAR at the last visit (p < 0.001).

CONCLUSION

While patients with low-grade chemical injury seem to benefit quite well from the medical treatment, amniotic membrane transplantation, limbal graft transplantation and subsequent keratoplasty; patients with severe injuries seem to be more prone to failure after all of the available treatment modalities.

Successful management of immunological rejection following allogeneic simple limbal epithelial transplantation (SLET) for bilateral ocular burns

A 41-year-old woman presented with bilateral total limbal stem cell deficiency, one year after chemical injury. She underwent allogeneic simple limbal epithelial transplantation (SLET) from a cadaveric donor in her right eye. One month later her unaided visual acuity (VA) improved to 20/100 from hand-motions. The corneal surface was avascular and epithelialised. Three months later, she presented with acute pain in right eye with peripheral corneal neovascularisation encircling the transplants, engorged and tortuous perilimbal vessels and diffuse epithelial haze. For a diagnosis of allograft rejection, pulse doses of intravenous methyl prednisolone with intensive topical steroids were administered. Her symptoms resolved in a week, confirming the diagnosis. She recovered her pre-rejection VA. She was maintained on systemic immunosuppressive agents. Her ocular surface continues to be stable. This case describes hitherto unknown clinical features of allograft rejection following SLET and emphasises the importance of continued immunosuppression in allogeneic limbal 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.

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.

Limbal stem cell disease: Treatment and advances in technology

Anterior segment stem cell technology, due to its already well-defined corneal limbal stem cells with greater ease of evaluation, has been at the forefront of ophthalmic stem cell treatment and technology since 1997. This paper provides an overview of the current standard of care for treatment of limbal stem-cell deficient conditions and reviews recent treatment technologies using ex vivo expansion of cultivated limbal stem cells of the cornea.

Donor site complications in autolimbal and living-related allolimbal transplantation

OBJECTIVE

To study the long-term changes at donor sites and safety implications for donor eyes used for harvesting tissue for autologous and living-related donor limbal transplants.

DESIGN

Retrospective, observational, consecutive case series.

PARTICIPANTS

We examined 50 donor sites of limbal tissue belonging to 25 healthy eyes (23 human subjects).

METHODS

The corneas and limbus of donor eyes were assessed for symptoms and visual acuity and examined by slit-lamp biomicroscopy and in vivo confocal microscopy with particular emphasis on the donor sites and central cornea.

MAIN OUTCOME MEASURES

In the donor eyes, we assessed visual acuity, persistence of symptoms, stability of the corneal epithelium, and the clinical and microscopic changes that occurred at the donor sites.

RESULTS

Mean follow-up was 41±38 months (median, 24; range, 3-127). All eyes had symptoms of ocular discomfort up to 4 weeks postoperatively and remained asymptomatic thereafter. No patient reported subjective reduction in visual acuity. Mean best-corrected visual acuity (logarithm of the minimum angle of resolution fraction) preoperatively was 0.076±0.19 and postoperatively was 0.09±0.17 (P = 0.57). All donor sites showed re-epithelialization of the peripheral denuded limbus within 2 weeks. Observed complications were filamentary keratitis and subconjunctival hemorrhage in 4 eyes. In vivo confocal microscopy confirmed that the central corneal epithelium remained normal in all eyes. The re-epithelialized donor site was covered with conjunctival epithelium in 17 sites of 10 eyes and with corneal epithelium in 7 sites of 5 eyes.

CONCLUSIONS

Limbal donation of 2 clock-hours of the superior and inferior limbus with 3×3 mm of adjacent conjunctiva was a safe procedure in this group of patients, demonstrating stable vision and an intact corneal epithelium during the follow up period. Donor sites can be re-epithelized by multiple layers of either corneal or conjunctival epithelium and is associated with deep stromal scarring.

Evaluation of molecular markers in corneal regeneration by means of autologous cultures of limbal cells and keratoplasty

PURPOSE

To determine the epithelial phenotype in patients with a limbal stem cell deficiency (LSCD) after ocular surface reconstruction with autologous cultured stem cells. To correlate the epithelial phenotype with the clinical outcome.

METHODS

Six eyes affected by LSCD, verified and graded by impression cytology, were treated with an autologous fibrin-cultured limbal stem cell graft. The clinical outcome was defined as a "success" or a "failure," depending on ocular surface stability. To improve their visual function, 4 patients underwent lamellar or penetrating keratoplasty after the stem cell graft. The phenotype of the regenerated corneal epithelium was determined by immunofluorescence of the corneal button to detect CK12, CK3, CK19, and Muc1 as corneal and conjunctival markers.

RESULTS

After a mean follow-up of 24 months, 5 cases were defined as successes; 1 case presented an epithelial defect 4 months after grafting and was defined as a failure. Immunofluorescence performed on 4 patients after lamellar and penetrating keratoplasty confirmed the presence of epithelial corneal markers (CK12 and CK3) in 2 of the success cases and the presence of conjunctival markers (CK19 and Muc1) in the 1 failure case. In one of the success cases, both corneal and conjunctival markers were detected on the corneal button. All success cases showed maintenance of marker accounting for high proliferative potential (DeltaNp63alpha) after transplantation.

CONCLUSIONS

Autologous cultures of limbal stem cells can regenerate a functional corneal epithelium in patients affected by unilateral LSCD. We showed a correlation between the clinical outcome and the molecular marker expression.

A new surgical technique: a femtosecond laser-assisted keratolimbal allograft procedure

PURPOSE

To evaluate the feasibility of a femtosecond (FS) laser-assisted keratolimbal allograft (KLAL) technique.

DESIGN

Interventional case series.

METHODS

This study included 3 patients with extensive limbal stem cell deficiency. The donor cornea was dissected with an FS laser (IntraLase FS laser, 60 kHz) using a ring procedure, without outer side cutting for the limbal graft, after a penetrated dissection of the donor cornea prior to penetrating keratoplasty (PKP). The depth and width of the ring procedure were adjusted for each individual patient. Further extension to the periphery of the sclerocorneal tissue of the donor graft was performed with a diamond knife. In a case of KLAL alone, the unhealthy limbal tissue of the recipient was removed with the FS laser by the same method employed in donor preparation. One patient underwent KLAL alone, and 2 patients underwent KLAL combined with PKP. The patients were followed up for a maximum of 10 months.

RESULTS

Limbal grafts were even and thin, as expected. The case with KLAL alone showed the fastest epithelization of the recipient cornea. The 2 cases of combined KLAL and PKP showed excellent approximation between recipient and donor tissue. The ocular surfaces have been stable for 8 months in case 1 and 10 months in cases 2 and 3.

CONCLUSION

FS laser-assisted KLAL has potential advantages in terms of simplicity and speed as compared with conventional techniques.

Ex vivo cultured limbal epithelial transplantation. A clinical perspective

The term ex vivo cultured limbal epithelial transplantation (CLET) refers to the process of culturing a sheet of human limbal epithelium in the laboratory and transplanting this sheet back onto the limbal stem cell-deficient cornea of the same patient or another recipient. This emerging technology represents one of the earliest successes in regenerative medicine. CLET is, at present, best suited to patients who have unilateral total limbal stem cell deficiency arising from chemical injury and who are suitable for autologous cell culture and transplantation. Although the results of allogeneic cell transplantation are encouraging and superior to conventional stem cell transplantation techniques, insufficient follow-up precludes conclusions regarding the long-term outcomes. Other tissues, such as oral mucosal epithelium, are emerging as viable alternative sources of cells, especially for patients with bilateral disease.

Corneal Epithelial Cultures Generated from Organ-Cultured Limbal Tissue: Factors Influencing Epithelial Cell Growth

PURPOSE

To explore the in vitro proliferative potential of human limbal epithelial cells after 31 degrees C organ-culture storage and to investigate putative factors influencing it.

METHODS

185 cultures of limbal explants were carried-out either from full-thickness explants (n = 102) or from enzymatically dissociated cells (n = 83) seeded on a feeder layer of human keratocytes. Epithelial outgrowth was assessed by phase contrast microscopy using a computerized image analysis software. Cell phenotype was evaluated by transmission electron microscopy and immunocytology. Univariate and multivariate analysis were performed to determine factors influencing epithelial growth in culture.

RESULTS

An epithelial outgrowth of 100 square mm or more was observed in 52% of cultures, (average growth area: 440 +/- 256 mm at three weeks). Corneal epithelial phenotype was confirmed by transmission electron microscopy, and cytokeratin pattern. Cytokeratine 19, deltaNp63, nestin and vimentin positive staining revealed undifferentiated epithelial cells in both explant and cell suspension cultures at three weeks. Short death to cornea retrieval time (p < 0.03) and female donors (p < 0.01) were associated with higher cell growth. Enzymatic treatment of explants by trypsin, but not dispase, decreased cell proliferation at two (p < 0.03) and three weeks (p < 0.04). Donor age, duration of corneal storage, and source of the explant did not influence the cell growth.

CONCLUSION

Organ-culture conditions can preserve limbal cell mitotic potential if limbal tissue is excised early after circulatory arrest. Human keratocytes can be used as a feeder layer allowing epithelial cells to maintain poorly differentiated phenotype in culture. Further investigations are needed to explain the influence of the donor sex on epithelial cell growth in culture.

[Ocular burns]

Ocular or thermal burns account for 7.7%-18% of ocular trauma. The majority of victims are young. The burns occur in the setting of accidents at work or in the home, or during a physical attack. Chemical burns by strong acids or bases are responsible for the most serious injuries. Associated with the destruction of limbal stem cells, they present as recurrent epithelial ulcerations, chronic stromal ulcers, deep stromal revascularization, conjunctival overlap, or even corneal perforation. The initial clinical exam is sometimes difficult to perform in the presence of burning symptoms. Nevertheless, it enables the physician to classify the injury, establish a prognosis, and most importantly, guide the therapeutic management. The Roper-Hall modification of the Hughes classification system is the most widely utilized, broken down into stages based on the size of the stromal opacity and the extent of possible limbal ischemia. This classification is now favorably supplemented by those proposed by Dua and Wagoner, which are based on the extent of the limbal stem cell deficiency. The prognosis of the more serious forms of ocular burns has markedly improved over the last decade because of a better understanding of the physiology of the corneal epithelium. Surgical techniques aimed at restoring the destroyed limbal stem cells have altered the prognosis of severe corneal burns. In order to decrease the incidence of burns, prevention, particularly in industry, is essential.

[Porous matrix and primary-cell culture: a shared concept for skin and cornea tissue engineering]

Skin and cornea both feature an epithelium firmly anchored to its underlying connective compartment: dermis for skin and stroma for cornea. A breakthrough in tissue engineering occurred in 1975 when skin stem cells were successfully amplified in culture by Rheinwald and Green. Since 1981, they are used in the clinical arena as cultured epidermal autografts for the treatment of patients with extensive burns. A similar technique has been later adapted to the amplification of limbal-epithelial cells. The basal layer of the limbal epithelium is located in a transitional zone between the cornea and the conjunctiva and contains the stem cell population of the corneal epithelium called limbal-stem cells (LSC). These cells maintain the proper renewal of the corneal epithelium by generating transit-amplifying cells that migrate from the basal layer of the limbus towards the basal layer of the cornea. Tissue-engineering protocols enable the reconstruction of three-dimensional (3D) complex tissues comprising both an epithelium and its underlying connective tissue. Our in vitro reconstruction model is based on the combined use of cells and of a natural collagen-based biodegradable polymer to produce the connective-tissue compartment. This porous substrate acts as a scaffold for fibroblasts, thereby, producing a living dermal/stromal equivalent, which once epithelialized results into a reconstructed skin/hemicornea. This paper presents the reconstruction of surface epithelia for the treatment of pathological conditions of skin and cornea and the development of 3D tissue-engineered substitutes based on a collagen-GAG-chitosan matrix for the regeneration of skin and cornea.

Comparison of characteristics of cultured limbal cells on denuded amniotic membrane and fresh conjunctival, limbal and corneal tissues

This study aimed to evaluate proposed molecular markers related to eye limbal stem cells (SC) and to identify novel associated genes. The expression of a set of genes potentially involved in stemness was assessed in freshly prepared limbal, corneal and conjunctival tissues. PAX6, AC133, K12 and OCT4 were detected in all the tissues and p63(+)/K3(-)/K12(+)/Nodal(+)/Cx43(+) were expressed in conjunctival, p63(-)/K3(+)/K12(+)/Nodal(-)/Cx43(+) in corneal, and p63(+)/K3(-)/K12(-)/Nodal(-)/Cx43(-) in limbal tissues. Limbal explants were cultured on human amniotic membrane for 21 days. The cells expressed p63 but not K3, K12, Nodal and Cx43, however, the expression of K3, K12 and Cx43 was detected, and p63 and the high BrdU-labeling index decreased with more culture. Ultrastructure analysis of the cultured cells showed typically immature organization of intracellular organelles and architecture. Our data suggest that limbal, corneal and conjunctival tissues are heterogeneous with some progenitors. Also, the expression of traditional SC markers may not be a reliable indicator of limbal SC and there is an increasing need to determine factor(s) involved in their stemness.