Elsevier

Survey of Ophthalmology

Volume 52, Issue 5, September–October 2007, Pages 483-502
Survey of Ophthalmology

Diagnostic and Surgical Techniques
Transplantation of Ex Vivo Cultured Limbal Epithelial Stem Cells: A Review of Techniques and Clinical Results

https://doi.org/10.1016/j.survophthal.2007.06.013Get rights and content

Abstract

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.

Section snippets

Limbal Epithelial Stem Cells and Corneal Epithelial Homeostasis

The corneal epithelium is essential in maintaining the clarity and the regular refractive surface of the cornea. As with other epithelial surfaces there is a continuous loss of cells from the surface of the corneal epithelium.52, 103 Desquamated cells are replenished by a small population of LESCs located in the basal layer of the limbal epithelium, which also play a central role in corneal epithelial regeneration and repair following injury.13, 14, 24, 26, 57, 81, 103 Clinically LSCD is

Etiology

A deficiency of LESCs occurs in a variety of disorders. Some, such as aniridia, are the result of a genetic disorder and are heritable.41, 70 More commonly, however, LSCD results from acquired factors such as chemical or thermal injury, ultraviolet and ionizing radiation, Stevens Johnson syndrome, advanced ocular cicatricial pemphigoid, contact lens wear, multiple surgeries, radiation, antimetabolites, or extensive microbial infection.9, 24, 27, 29, 33, 35, 40, 42, 92 If LESCs are depleted by

Characteristics of Reported Studies

We identified 17 peer-reviewed publications reporting the use of ex vivo cultured LECs18, 37, 55, 56, 63, 64, 67, 76, 80, 87, 89, 90, 91, 94, 95, 96, 102 and four publications reporting the transplantation of ex vivo cultured oral mucosal epithelial cells.46, 47, 62, 71 The main characteristics of these studies are listed in Table 1.

Methods Employed by Studies

The methods used to diagnose LSCD and produce ex vivo cultured LEC grafts varied widely.

Evidence for Presence of Stem Cells in Cultures and Grafts

The evidence for the presence of stem cells in the transplanted cell population is based upon the following: functional assays of the colony forming ability of transplanted cells (only stem cells can give rise to large colonies in culture4, 75), immunohistological analysis of grafts, and evidence of donor cell survival.

Three studies provided colony forming efficiency data that strongly support the presence of stem cells in these transplanted cell populations.76, 80, 95 Schwab et al estimated

Surgical Transplantation of Ex Vivo Cultured Epithelial Sheets

The surgical technique for transplanting ex vivo cultured LECs was similar in all the studies. Following 360° conjunctival peritomy, the fibrovascular pannus and ingrowing conjunctival tissue was dissected from the cornea and limbus. Hemostasis was achieved using cautery with or without topical 10% phenylephrine. In an attempt to prevent conjunctival ingrowth in the postoperative period some authors applied mitomycin C (0.04% for 5 minutes) to the subconjunctival space followed by vigorous

Postoperative Management

The basic principles are immediate control of inflammation, prophylaxis against infection, mechanical protection of the graft, and prevention of allograft rejection. In all studies topical unpreserved steroid and a broad spectrum antibiotic (ofloxacin37, 55, 56, 64, 67 or chloramphenicol18, 76, 80) were administered four times daily starting immediately after transplantation and continuing for 1 to 3 months. A 1-month course of oral corticosteroids (e.g., betamethasone or prednisolone 1

Donor Screening

Ex vivo LEC culture carries a risk of transfer of bacteria, viruses, and prions, both to the patient but also to the laboratory staff processing the tissue. For these reasons consideration must be given to the screening of tissue donors and the risk of cross-contamination of cultures. Screening should include HIV (human immunodeficiency virus), hepatitis B and C, syphilis and HTLV (human T lymphotrophic virus), and prion-related disease. This can be achieved through a combination of

Improvement in Ocular Surface

The outcome measures used to define successful treatment were poorly described by most studies. Rama et al devised a scoring system to grade the severity of stem cell deficiency.80 This was based on defined clinical and impression cytology findings. These were assessed and scored before and after treatment and statistical analysis of the difference was performed. This provided a reliable objective assessment of treatment success. Koizumi et al55 and Daya et al18 defined a set of clinical

Regulatory Considerations

Until recently, groups providing this treatment only required a local ethics committee's approval. However, groups providing cellular therapies in Europe will soon be required to comply with new mandatory European Union (EU) regulations. The Department of Health in the UK introduced a voluntary “Code of Practice for Tissue Banks Providing Tissues of Human Origin for Therapeutic Purposes” in 2001 (ISBN 1 84182 329 5). This code of practice applies to all non-commercial tissue banks. Currently

Discussion and Conclusions

Ex vivo expansion and transplantation of limbal epithelium has been performed by several unrelated groups in a number of countries. It has been used to treat a variety of ocular surface disorders that are thought to be the result of limbal stem cell failure.

Despite a substantial number of experimental models of this technique, and an ever-growing body of laboratory data on limbal epithelial stem cell biology, the scientific understanding of this procedure is poor. Some key questions still need

Method of Literature Search

This article was prepared by searching the National Library of Medicine database 1975–October 2006 using the following search words: tissue engineering, cultured cells, stem cell transplantation, deficiency, stem cell deficiency, cornea, amnion, corneal limbus, limbal stem cell, ocular surface. Additional sources included the textbooks referenced herein. The search was restricted to publications in English and other-language publications with English abstracts. The reference lists of published

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    The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article. Supported by the National Institute of Health Biomedical Research Centre at Moorfields Eye Hospital and UCL Institute of Ophthalmology, Medical Research Council UK (AJS) and Moorfields Eye Hospital Special Trustees (AJS, JTD).

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