A supramolecular look at microenvironmental regulation of limbal epithelial stem cells and the differentiation of their progeny / Uma visão supramolecular sobre a regulação microambiental de células tronco epiteliais limbais e a diferenciação de sua progênie

ABSTRACT Various approaches have been taken to improve our knowledge of the microenvironmental regulation of limbal epithelial stem cells. Researchers have extensively investigated the roles of growth factors, survival factors, cytokines, enzymes, and permeable molecules secreted by the limbal cells. However, recent evidence suggests that stem cell fate (i.e., self-renewal or differentiation) can also be influenced by biophysical and mechanical cues related to the supramolecular organization and the liquid crystalline (mesophase) nature of the stromal extracellular matrix. These cues can be sensed by stem cells and transduced into intracellular biochemical and functional responses, a process known as mechanotransduction. The objective of this review is to offer perspectives on the supramolecular microenvironmental regulation of limbal epithelial stem cells and the differentiation of their progeny.

RESUMO Muitas abordagens têm sido utilizadas para ampliar entendimentos sobre a regulação microambiental das células tronco epiteliais limbais. Neste contexto, pesquisadores têm exaustivamente investigado a participação de fatores de crescimento, fatores de sobrevida, citocinas, enzimas e moléculas permeáveis secretadas pelas células limbais. Entretanto, evidências recentes sugerem que o destino (ie. autorrenovação ou recrutamento para a via de diferenciação) das células tronco também sofre influência de estímulos biofísicos ou mecânicos relacionados à organização supramolecular e à natureza liquido-cristalina (mesofases) da matriz extracelular estromal. Esses estímulos podem ser percebidos e traduzidos pelas células tronco em sinais bioquímicos que geram respostas funcionais, através de um processo designado de mecanotransdução. Objetiva-se, com a presente revisão, oferecer ao leitor perspectivas supramoleculares sobre a regulação microambiental das células tronco epiteliais limbais e a diferenciação de sua progênie.

Assessment of surgical outcomes of limbal transplantation using simple limbal epithelial transplantation technique in patients with total unilateral limbal deficiency / Avaliação dos resultados cirúrgicos do transplante de limbo utilizando a técnica SLET (simple limbal epithelial transplantation), em pacientes com deficiência límbica total unilateral

ABSTRACT This study aimed to evaluate the effectiveness of the novel simple limbal epithelial transplantation (SLET) technique, which reduces the risk of iatrogenic limbal stem cell deficiency in the donor eye. Four patients with total unilateral limbal stem cell deficiency received a limbal graft, measuring 4 mm × 2 mm, from the contralateral healthy eye in a single surgical procedure. The graft was divided into 10-20 pieces and distributed on the corneal surface. At 6-month follow-up, a completely avascular corneal epithelial surface was obtained in two patients, and there was improvement in visual acuity in one patient. The limbal grafts did not adhere to the cornea in one patient. No serious complications related to the surgery were observed in this study.

RESUMO Este trabalho tem como objetivo avaliar a eficácia de uma nova técnica cirúrgica denominada SLET (simple limbal epithelial transplantation), um procedimento promissor que reduz os riscos de indução de deficiência límbica iatrogênica no olho doador. Quatro pacientes com deficiência límbica total unilateral, secundária a queimadura química, receberam um enxerto de células límbicas, medindo 4 mm x 2 mm, do olho contralateral sadio, em apenas um tempo cirúrgico. Este foi divido em 10 a 20 fragmentos e distribuído sobre a superfície da córnea. Após 6 meses de cirurgia, superfície corneana totalmente epitelizada e avascular foi obtida em dois pacientes. Houve melhora da acuidade visual em um paciente. Não houve aderência dos enxertos de limbo na córnea em um paciente. Nenhum paciente apresentou efeitos colaterais graves decorrentes do procedimento cirúrgico.

Limbal transplantation at a tertiary hospital in Brazil: a retrospective study / Transplante de limbo em hospital terciário no Brasil: estudo retrospectivo

ABSTRACTPurpose:Epidemiological analysis of limbal transplantation surgeries performed in the Ophthalmologic Hospital of Sorocaba.Methods:Retrospective medical records review of 30 patients who underwent limbal stem cell transplants between January 2003 and March 2008. Cases involving conjunctival limbal autograft were classified as group I, and those involving conjunctival limbal allograft as group II.Results:Two patients were excluded due to incomplete data during postoperative follow-up. Of the total sample of 28 patients, 53.6% constituted group I, whereas 46.4% were included in group II. Males were predominant (67.9%), and right eyes were the most prevalent (67.9%). The mean age was 40.3 years. Unilateral cases accounted for 60.7%. The most frequent pathology causing limbal system failure was chemical burns (53%). The mean length of time from diagnosis to surgery was 11.18 years. The limbal graft and amniotic membrane were associated in 75% of all cases, and tarsorrhaphy in 57.1%. The average follow-up period was 24.84 months. The uncorrected visual acuity improved in 38% of the cases, was unchanged in 28.5%, and deteriorated in 33.3%. There was no persistent epithelial defect in 75% of the patients. The conjunctivalization rate was similar between the groups (53.3% and 58.3%, respectively). The transparency improved in only 38.4% of the cases, and 28.5% of the surgeries performed were successful. The most prevalent complication was persistent epithelial defect, which occurred in 25% of the patients, followed by corneal melting in 14.2%. Other complications observed included infectious ulcers, limbal graft necrosis or ischemia, perforation, and descemetocele.Conclusion:Chemical burns remain the main cause of limbal stem cell deficiency. In these cases, limbal transplantation is the standard procedure to restore the ocular surface even though the success rate is low.

RESUMOObjetivo:Análise epidemiológica dos transplantes de limbo realizados no Hospital Oftalmológico de Sorocaba.Método:Foi realizada uma análise retrospectiva através de revisão de prontuário de trinta casos de transplante de limbo realizados no período de janeiro de 2003 a março de 2008. Casos de transplante de limbo autólogo foram classificados como grupo I e alogênicos como grupo II.Resultados:Dois pacientes foram excluídos da análise por insuficiência de dados nos registros. Da amostra completa de 28 pacientes, 53,6% constituíram o grupo I enquanto 46,4% o grupo II. O olho direito (68%) e o sexo masculino (68%) foram mais acometidos, com uma média de idade de 40,3 anos. Casos unilaterais contabilizaram 60,7%. A patologia de base causadora da deficiência límbica mais prevalente foi a queimadura química (53%). A média do tempo de doença até a cirurgia foi de 11,18 anos. Na maioria dos casos o transplante foi associado a membrana amniótica (75%) e tarsorrafia (57%). O tempo médio de seguimento foi de 24,84 meses. Foi observado melhora da acuidade visual não corrigida em 38% dos casos enquanto 28,5% permaneceram inalteradas e 33,3% pioraram. Evolução sem defeito epitelial persistente ocorreu em 75% dos pacientes. A taxa de conjuntivalização foi semelhante nos 2 grupos (53,3% e 58,3%). Em apenas 38% dos casos houve melhora da transparência. A taxa de sucesso foi de cerca de 28%. A complicação mais prevalente foi defeito epitelial persistente (25%) seguida de melting (14,2%). Outras complicações observadas foram úlceras infecciosas, necrose ou isquemia do enxerto, perfuração e descemetocele.Conclusões:A queimadura química permanece como principal patologia causadora de deficiência límbica. Nestes casos o transplante de limbo é atualmente a técnica de eleição para restauração da superfície ocular, porém com baixa taxa de sucesso.

Maintenance of the corneal epithelium is carried out by germinative cells of its basal stratum and not by presumed stem cells of the limbus

The purpose of this investigation was to analyze the proliferative behavior of rabbit corneal epithelium and establish if any particular region was preferentially involved in epithelial maintenance. [3H]-thymidine was injected intravitreally into both normal eyes and eyes with partially scraped corneal epithelium. Semithin sections of the anterior segment were evaluated by quantitative autoradiography. Segments with active replication (on) and those with no cell division (off) were intermingled in all regions of the tissue, suggesting that the renewal of the epithelial surface of the cornea followed an on/off alternating pattern. In the limbus, heavy labeling of the outermost layers was observed, coupled with a few or no labeled nuclei in the basal stratum. This suggests that this region is a site of rapid cell differentiation and does not contain many slow-cycling cells. The conspicuous and protracted labeling of the basal layer of the corneal epithelium suggests that its cells undergo repeated cycles of replication before being sent to the suprabasal strata. This replication model is prone to generate label-retaining cells. Thus, if these are adult stem cells, one must conclude that they reside in the corneal basal layer and not the limbal basal layer. One may also infer that the basal cells of the cornea and not of the limbus are the ones with the main burden of renewing the corneal epithelium. No particular role in this process could be assigned to the cells of the basal layer of the limbal epithelium.

Cytological features of live limbal tissue donor eyes for autograft or allograft limbal stem cell transplantation / Características citológicas do tecido límbico de doador vivo para transplante autólogo ou alógeno de células-tronco epiteliais corneais

PURPOSE: To evaluate by impression cytology (IC) the corneal surface of live limbal tissue donor eyes for autograft or allograft limbal stem cell transplantation (LSCT). METHODS: Twenty limbal donors were enrolled (17 for autograft LSCT and 3 for allograft). Impression cytology was performed before transplantation of superior and inferior limbal grafts and after the third postoperative month. RESULTS: Impression cytology analysis showed sheets of corneal epithelial cells and goblet cell absence beyond the edge of the keratectomy sites in all patients, suggesting that conjunctival invasion towards the center did not occur in any eye. Partial conjunctivalization within 2 to 3 clock hours, confirmed by the presence of goblet cells, was limited to the keratectomy site in 10 percent of the cases. CONCLUSION: A clear central corneal surface was demonstrated in all eyes following surgery leading to the conclusion that limbal donation was a safe procedure in this group of patients. A small percentage of eyes can have donor sites re-epithelized with conjunctival cells at the periphery of the cornea.

OBJETIVO: Avaliar pela citologia de impressão a superfície da córnea de doador vivo para transplante autólogo ou alógeno de células-tronco epiteliais. MÉTODOS: Vinte pacientes doadores de tecido límbico foram avaliados (17 para transplante autólogo e 3 para alógeno). Os exames citológicos foram realizados em dois momentos: antes da ceratectomia, que removeu tecido límbico dos quadrantes superior e inferior, e após o terceiro mês pós-operatório. RESULTADOS: Invasão de células da conjuntiva em direção ao centro além da margem da ceratectomia não ocorreu em nenhum olho estudado. Uma pequena área de conjuntivalização parcial, confirmada pela presença de células caliciformes, foi detectada dentro do limite da ceratectomia em 10 por cento dos casos. CONCLUSÃO: A superfície central da córnea manteve-se transparente demonstrando que a manipulação de tecido límbico em doador vivo foi um procedimento seguro neste grupo de pacientes. Uma pequena porcentagem dos olhos pode ter o local do sítio da ceratectomia re-epitelizado com células da conjuntiva sobre a periferia da córnea.

Comparação entre membrana amniótica com e sem epitélio como substrato para cultura de células epiteliais do limbo ex vivo / Comparison between amniotic membrane with and without epithelium as a support for human limbal epithelial cells cultured ex vivo

OBJETIVO: Avaliar a eficácia e aspecto estrutural de células límbicas epiteliais humanas cultivadas sobre membrana amniótica (MA) com e sem epitélio. MÉTODOS: As culturas límbicas foram obtidas a partir de rima corneoescleral remanescentes de transplantes de córnea de 6 diferentes doadores. Cada explante foi cultivado em três diferentes grupos: MA desepitelizada por tripsina (Grupo 1), MA com epitélio íntegro (Grupo 2) e controle (Grupo 3). A migração epitelial foi avaliada por microscopia de contraste de fase. Após 15 dias, as células cultivadas sobre MA foram submetidas à microscopia eletrônica para avaliar migração e adesão epitelial. RESULTADOS: Todas as células do grupo controle cresceram até atingir confluência. Somente uma das culturas em membrana amniótica desepitelizada não apresentou crescimento epitelial. O crescimento de células epiteliais sobre membrana amniótica epitelizada foi observada em apenas uma cultura. CONCLUSÃO: Baseando-se nestes achados, o uso de membrana amniótica desepitelizada aparenta ser o melhor substrato para migração e adesão epitelial comparando com membrana amniótica epitelizada. Remover o epitélio da membrana amniótica demonstra ser um importante passo para estabelecer culturas de células sobre membrana amniótica.

PURPOSE: To evaluate the efficacy and ultrastructural aspects of human limbal epithelial cells cultured on amniotic membrane (AM) with and without epithelium. METHODS: Limbal epithelial cell cultures were established from cadaveric cor neo-scleral rim explants derived from 6 different donors. The explants from each donor were placed under 3 different groups: on human preserved AM with epithelium (Group 1), AM deepithelialized with trypsin (Group 2) and control (Group 3). The epithelial cell migration was evaluated under phase contrast microscopy. After 15 days, the amniotic membrane with cells cultures were removed and submitted to scanning and transmission electron microscopy to check for epithelial migration and adhesion. RESULTS: All epithelial cell cultures from the controls grew over the botton of the culture plate wells until reaching confluence. Epithelial cultures grew over all but one denuded amniotic membrane. In the group amniotic membrane with epithelium, epithelial cell growing was observed only in 1 well. CONCLUSIONS: Using this model, denuded amniotic membrane appeared to be the best substrate for epithelial cell migration and adhesion comparing to amniotic membrane with epithelium. Removal of amniotic membrane epithelial seems to be an important step for establishing limbal epithelial cell culture on amniotic membrane.

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

Uso de células-tronco cultivadas ex vivo na reconstrução da superfície ocular / Use of stem cells cultured ex vivo for ocular surface reconstruction

Lesões na superfície ocular podem atingir as células-tronco do limbo e causar deficiência límbica. A deficiência límbica é caracterizada pela conjuntivalização, que pode ser definida como a invasão do epitélio conjuntival sobre a córnea. Este processo é acompanhado por graus variáveis de alterações corneanas, como neovascularização, inflamação, erosões recorrentes, defeitos epiteliais persistentes, destruição da membrana basal do epitélio e cicatrização estromal. Frequentemente, estas alterações estão associadas à diminuição da acuidade visual, fotofobia e desconforto ocular. O melhor tratamento para essa afecção não é conhecido e possibilidades variam em casos uni ou bilaterais. Entre os tratamentos disponíveis, o transplante de limbo autólogo ou alógeno é um dos mais utilizados. Para melhorar os resultados dos transplantes alógenos, alguns pesquisadores utilizam o transplante de epitélio da córnea cultivado em laboratório pela expansão ex vivo de células-tronco epiteliais límbicas. Mas devido à limitada disponibilidade de tecido autólogo do limbo e o risco de complicações associadas à imunossupressão em transplante de tecido alógeno, pesquisas de outras opções de células-tronco cultivadas ex vivo têm sido descritas em fase experimental e clínica. Essa revisão descreve os novos tipos de células-tronco cultivadas ex vivo, seus resultados atuais e potencialidades futuras.

Lesions on the ocular surface can destroy the stem cells from the limbus and cause limbal stem cell deficiency. The limbal stem cell deficiency is marked by conjunctivalization, which can be defined as the invasion of conjunctival epithelium over the cornea. This process is accompanied by varying degrees of corneal changes such as neovascularization, inflammation, recurrent erosions, persistent epithelial defects, destruction of basement membrane of epithelium and stromal healing. Often, these changes are associated with poor visual acuity, photophobia and ocular discomfort. The best treatment for this disease is not known and varies in unilateral or bilateral cases. Among the treatments available, transplantation of limbal autograft or allograft is one of the most used. To improve the outcome of allotransplantation, some researchers use the transplantation of corneal epithelium cultured in the laboratory by ex vivo expansion of limbal stem cells, but due to limited availability of autologous tissue from the limbus and the risk of complications associated with immunosuppression in allogeneic tissue transplantation, researches of others options of stem cell cultured ex vivo have been described in experimental and clinical stage. This review describes the new types of stem cells cultured ex vivo, their current results and future potential.

Isolation, culture, characterization and optimization of human corneal stem cells

The effects of human versus mouse EGF on cell growth and culture duration were studied to optimize a human limbal stem cells culture method for therapeutical autologous transplantation. Limbal cells were obtained by trypsin digestion and transferred to a culture medium. The time needed to reach full confluence in culture was determined. Specific antibodies to corneal stem cell marker (P63) versus corneal epithelial differentiation marker (K3) were used for histochemical determinations. A high proportion of P63 positive cells (85 +/- 4.6%), and a correspondingly low proportion K3 positive cells (15 +/- 3.8%) indicated that most cultured cells remained undifferentiated and were considered as stem cells (mean +/- SE, n=10). Cultures reached full confluency after 17.3 +/- 1.2 days when the medium was supplemented with human EGF, while 21.7 +/- 1.5 days were needed when the medium was supplemented with mouse EGF. The results showed that limbal stem cells proliferate more easily and reach to full confluency in a shorter time if the medium is supplemented with hEGF rather than with mEGF.

Transplante de células-tronco epiteliais límbicas alógenas expandidas ex vivo sobre membrana amniótica: relato de caso / Transplantation of allogenic limbal epithelial stem cells cultivated ex vivo on amniotic membrane: case report

Paciente apresentou falência de transplante de limbo e conjuntiva de doador vivo alógeno no olho direito após ceratoconjuntivite epidêmica. Após alguns meses, foi submetida a transplante de células-tronco epiteliais límbicas alógenas cultivadas ex vivo sobre membrana amniótica (primeiro caso no Brasil), tendo evoluído com epitelização total da córnea e melhora da acuidade visual. Após o 3º mês da cirurgia, iniciou-se neovascularização superficial periférica com piora da transparência corneana. A visão manteve-se 0,1 após um ano de cirurgia.

Case report of a patient who developed failure of an allogenic living related conjunctival limbal transplantation in the right eye after an episode of epidemic keratoconjunctivitis. After a few months, she underwent transplantation of allogenic limbal epithelial stem cells cultivated ex vivo on amniotic membrane (first case in Brazil). The patient evolved with total corneal epithelialization and improvement of the visual acuity. Three months after the surgery, peripheral superficial neovascularization with worsening of the corneal transparency was observed. The vision remained 0.1 after one year of the transplantation.

Importância do co-cultivo com fibroblastos de camundongo 3T3 para estabelecer cultura de suspensão de células epiteliais do limbo humano / Importance of 3T3 feeder layer to establish epithelial cultures from cell suspension obtained from corneo-scleral rims

OBJETIVO: Avaliar a importância da presença de células 3T3 para estabelecer cultura de suspensão de células epiteliais do limbo obtido de rimas córneo-esclerais. MÉTODOS: Rimas de diferentes doadores tiveram seus estroma posterior e endotélio removidos (n=6). Cada rima foi dividida em três segmentos iguais, que foram colocados em cultura em três diferentes condições: um segmento foi colocado na placa de cultura com o lado epitelial para cima (Grupo A). Os dois segmentos restantes foram tripsinizados e a suspensão de células obtida foi cultivada com (Grupo B) ou sem (Grupo C) células 3T3 irradiadas. As células foram mantidas em meio de cultura "supplemental hormonal epithelial médium" (SHEM), a migração epitelial e a formação de clones nos grupos A, B e C foram avaliadas pela microscopia de contraste de fase e por coloração pela rodamina B. Os resultados foram comparados estatisticamente. RESULTADOS: O crescimento de células epiteliais foi observado em 4/6 rimas (Grupo A). Todas as suspensões de células epiteliais que foram cultivadas com células 3T3 (Grupo B) formaram clones. Nenhuma adesão ou formação de clones verdadeiros (holo ou meroclones) foi observada na cultura de células que foi cultivada sem 3T3 (Grupo C) (p=0,009). CONCLUSÕES: Suspensão de células epiteliais límbicas obtidas de rimas córneo-esclerais no modelo utilizado precisa ser cultivada com células 3T3 para formar clones e estabelecer colônias epiteliais com perspectivas para uso terapêutico na reconstrução da superfície ocular.

PURPOSE: To evaluate the importance of the presence of 3T3 fibroblasts for establishing limbal epithelial cultures from cell suspension obtained from corneo-scleral rims (CSR). METHODS: Corneo-scleral rims from different donors (n=6) had their posterior stroma and endothelium stripped away. Each corneo-scleral rim was divided into three equal segments that were set up in tissue culture in three different conditions: one of the segments was placed with the epithelial side up on the bottom of a 6-well culture plate (Group A). The other two fragments were trypsinized and the obtained cell suspension was cultured with (Group B) or without (Group C) irradiaded 3T3 cells. The cells were cultured in supplemental hormonal epithelial medium (SHEM), the epithelial migration and clone formation in groups A, B and C were evaluated with phase contrast microscopy and rodamine B staining. RESULTS: Epithelial cell growth was observed in 4/6 rims (Group A). All epithelial cell suspensions that were cultured with 3T3 cells (Group B) formed clones. No adhesion or true clone formation (holo- or meroclones) was observed in the cell suspensions that were cultivated without 3T3 (Group C) (p=0.009). CONCLUSIONS: Epithelial cell suspension obtained from corneo-scleral rims in this model needs to be cultivated with 3T3 cells in order to form clones and establish limbal epithelial cell colonies with the potential to be used for ocular surface reconstruction.

Caracterización fenotípica de células epiteliales limbales humanas expandidas in vitro / In vitro phenotypic characterization of human limbal epithelial cells

Introducción: Las células epiteliales limbales humanas (CELhu) han sido utilizadas en la clínica para promover la rápida reepitelización en enfermedades de la superficie ocular con la finalidad de restaurar la integridad del epitelio corneal. Sin embargo, esta técnica aún no ha sido desarrollada en nuestro país. El objetivo de este estudio fue desarrollar una técnica de cultivo de CELhu in vitro y caracterizar su fenotipo. Material y métodos: Las células fueron obtenidas de tejido limbal, cultivadas en medio KSFM y analizadas para la expresión de vimentina, K, K19, p63 y K12 por citometría de flujo e inmunofluorescencia. Resultados: El fenotipo de las células cultivadas fue vimentina+K+K19+p63+K12-. Conclusiones: Nuestros resultados sugieren que bajo estas condiciones de cultivo, las CELhu mantuvieron el fenotipo de célula pluripotencial. Esta técnica de cultivo podría ser utilizada con propósitos clínicos en nuestro país.

INTRODUCTION: Human limbal epithelial cells (huLEC) have been used for clinical purposes in ocular surface diseases to promote rapid re-epithelisation and restore corneal epithelium integrity. However, in Mexico this technique has not been fully developed. This study was conducted to characterize the huLEC phenotype expanded in vitro using a cell culture technique. MATERIAL AND METHODS: Cells were obtained from limbal tissue, cultured in KSFM medium and analyzed for the expression of vimentin, K, K19, p63, K12, by flow cytometry and immuno-fluorescence. RESULTS: The phenotype of cultured cells was vimentin+K+K19+ p63+K12-. CONCLUSIONS: Our results suggest that under these culture conditions huLEC maintained their stem cell phenotype. This culture technique could be used for clinical purposes in Mexico.

Clinical outcome of autologous cultivated limbal epithelium transplantation.

PURPOSE: To report the clinical outcome of autologous cultivated limbal epithelial transplantation. METHODS: Eighty-six patients' records and their clinical photographs were reviewed for demographics, primary etiology, type of limbal transplantation, ocular surface stability, visual acuity, final outcome and possible factors affecting outcome and complications. RESULTS: Eighty-eight eyes of 86 patients with limbal stem cell deficiency (LSCD) underwent autologous cultivated limbal epithelium transplantation between March 2001 and May 2003, with a mean follow-up of 18.3 months. The etiology of LSCD was alkali burns in 64% patients. Sixty-one eyes had total LSCD. Thirty-two of the 88 eyes had undergone amniotic membrane transplantation and 10 eyes had previously undergone limbal transplantation with unfavorable outcome. Nineteen eyes underwent penetrating keratoplasty, of which 11 grafts survived at the final follow-up. Finally, 57 eyes (73.1%, 95% CI: 63.3-82.9) had a successful outcome with a stable ocular surface without conjunctivalization, 21 eyes (26.9%, 95%CI: 17.1-36.7) were considered failures and 10 patients were lost to follow-up. CONCLUSION: LSCD can be successfully treated by autologous cultivated limbal epithelium transplantation in majority of the cases.

Isolation of Putative Corneal Epithelial Stem Cells from Cultured Limbal Tissue

PURPOSE: To investigate methods of isolating putative corneal epithelial stem cells from cultured limbal tissue. METHODS: Three extraction techniques were compared to identify an efficient method of obtaining a large number of viable corneal epithelial stem cells from the limbus. Limbal tissues were extracted by incubation at 37 degrees C or 4 degrees C for 1 or 16 hours, respectively, with 1.2U/ml dispase/trypsin or by treatment with 0.05% trypsin and 0.01% ethyldiaminetetraacetic acid (EDTA) at 37 degrees C in single procedure. Collected cells were cultured on NIH/3T3-seeded plates, and colony forming efficiency (CFE) was evaluated. Fluorescence activated cell sorting (FACS) was performed with a Coulter EPICS 753 after incubation with Hoechst 33342 and propidium iodide (PI). Hoechst negative cells were obtained using gates exhibiting low Hoechst blue with a 424/44 nm BP filter. Gated cells of each fraction were re-cultured to assess the capability of colony formation. RESULTS: The mean numbers of viable cells obtained from treatment with dispase and trypsin was 3x10(4) cell/ml and 8.06x10(5) cell/ml at 37 degrees C and 4 degrees C incubations; the number increased to 1.21x10(6) cell/ml with a trypsin/EDTA treatment (p<0.05). CFE was 9.67+/-2.13% and 6.63+/-2.35% in rabbit and human cells, respectively. Likewise, the Hoechst negative fraction was 3.61+/-0.42% and 5.21+/-4.91% in rabbit and human cells, respectively. The sorted Hoechst negative cells were cultured through four passages, forming small round colonies. In rabbit cells, the CFEs of Hoechst negative and positive fractions after FACS, were 12.67+/-2.24% and 1.17+/-6.13%, respectively (p<0.05). CONCLUSIONS: Putative corneal epithelial stem cells were efficiently isolated from limbal tissue using a trypsin/EDTA extraction and FACS. This technique may be very useful in tissue engineered stem cell therapy.

Phacoemulsification after penetrating keratoplasty with autologous limbal transplant and amniotic membrane transplant in chemical burns.

We report a patient who had earlier penetrating keratoplasty with amniotic membrane transplant and autologous limbal cell transplant for chemical injury who underwent cataract surgery by phacoaspiration. A posterior limbal incision with corneal valve was made superotemporally with extreme caution to avoid damage to the limbal graft. Aspiration flow rates and vacuum were kept low to avoid any turbulence during surgery. A 6.0 mm optic diameter acrylic foldable intraocular lens was inserted in the bag. The patient achieved a best-corrected visual acuity of 6/12 at 10 months' follow-up with a clear corneal graft. We conclude that caution during wound construction and phacoaspiration can help preserve corneal and limbal graft integrity in patients undergoing cataract surgery after corneal graft and limbal transplantation.

Amniotic membrane transplantation for reconstruction of corneal epithelial surface in cases of partial limbal stem cell deficiency.

PURPOSE: To assess the efficacy of amniotic membrane for treatment of partial limbal stem cell deficiency (LSCD). METHODS: Medical records of four patients with partial LSCD who underwent pannus resection and amniotic membrane transplantation (AMT) were reviewed for ocular surface stability and improvement in visual acuity. Clinico-histopathological correlation was done with the resected pannus tissue. RESULTS: All the eyes exhibited stable corneal epithelial surface by an average of 7 weeks postoperatively with improvement in subjective symptoms. Best corrected visual acuity improved from preoperative (range: 6/9p-6/120) to postoperative (range: 6/6p-6/15) by an average of 4.5 lines on Snellen visual acuity charts. Histopathological examination of excised tissue showed features of conjunctivalisation. CONCLUSION: Amniotic membrane transplantation appears to be an effective means of reconstructing the corneal epithelial surface and for visual rehabilitation of patients with partial limbal stem cell deficiency. It may be considered as an alternative primary procedure to limbal transplantation in these cases.

Ex-vivo potential of cadaveric and fresh limbal tissues to regenerate cultured epithelium.

PURPOSE: To evaluate and compare the ex-vivo growth potential and formation of cultured corneal epithelium from residual corneo-limbal rings obtained from the operating room after penetrating keratoplasty, and fresh limbal tissues from patients undergoing routine cataract surgery. METHODS: With the approval of the Institutional Review Board and informed consent from patients, 1-2 mm of limbal tissues from 15 patients and 31 tissues from the cadaveric limbal ring preserved in MK medium (16 tissues) and Optisol (15 tissues) were used for the study. Donor data included age, time lapse between death and collection, collection and preservation and preservation and culture. Tiny bits of the limbal tissue were explanted on the de-epithelialised human amniotic membrane prepared following standard guidelines, and cultured using Human Corneal Epithelial cell medium. Radial growth from the explant was observed and measured by phase contrast microscopy over 2-4 weeks. After adequate confluent growth, whole mount preparation of the membrane was made and stained with haematoxylin and eosin. Part of the membrane was fixed in formalin and processed for routine histologic examination. The sections were stained with haematoxylin and eosin. RESULTS: Forty-six tissues were evaluated from 42 eyes (15 from patients, 31 from cadaveric eyes) with a mean age of 55.3 years +/- 21.23 years (range 18 years - 110 years). The growth pattern observed was similar in all the positive cases with clusters of cells budding from the explant over 24-72 hours, and subsequent formation of a monolayer over the next 2-3 weeks. The stained whole mount preparation showed a radial growth of cells around explants with diameter ranging from 5 to 16mm. Histologic evaluation of the membrane confirmed the growth of 2-3 cell-layered epithelium over the amniotic membrane. Cultivated epithelium around explant cell cultures was observed in 100% (15/15) of limbal tissue obtained from patients, as against 56% (9/16) of MK medium preserved tissues and 46.7% (7/15) of Optisol preserved tissues. This was statistically significant (P=0.0131) There was no significant statistical difference in the growth properties, i.e, the mean percentage of fragments showing growth (P=0.229) or the mean diameter of growth (P=0.479) in the cultures obtained from fresh and preserved tissues. The time lapse at various stages between death and utilisation and donor age had no significant influence on the growth potential of the limbal tissues. CONCLUSION: The potential for generating cultured corneal epithelium from fresh limbal tissues obtained from living subjects is higher than that observed with preserved tissues. It would also be worthwhile to address the factors that could further enhance the proliferative potential of the cadaveric tissues obtained from eye banks.

Limbal stem cell transplantation.

The past two decades have witnessed remarkable progress in limbal stem cell transplantation. In addition to harvesting stem cells from a cadaver or a live related donor, it is now possible to cultivate limbal stem cells in vitro and then transplant them onto the recipient bed. A clear understanding of the basic disease pathology and a correct assessment of the extent of stem cell deficiency are essential. A holistic approach towards management of limbal stem cell deficiency is needed. This also includes management of the underlying systemic disease, ocular adnexal pathology and dry eye. Conjunctival limbal autografts from the healthy contralateral eye are performed for unilateral cases. In bilateral cases, tissue may be harvested from a cadaver or a living related donor; prolonged immunosuppression is needed to avoid allograft rejection in such cases. This review describes the surgical techniques, postoperative treatment regimes (including immunosuppression for allografts), the complications and their management. The short and long-term outcomes of the various modalities reported in the literature are also described.

Avaliação da presença de células caliciformes na córnea humana / Evaluation of the presence of goblet cells on the human corneal surface

OBJETIVO: Analisar pela citologia de impressão a presença de células caliciformes na superfície de córneas com sinais clínicos de conjuntivalização. MÉTODOS: Foram realizados exames de citologia de impressão do epitélio córneo-conjuntival em 65 olhos de 65 pacientes com sinais clínicos de conjuntivalização com ou sem tratamento cirúrgico prévio. Os pacientes foram divididos em dois grupos segundo a história anterior de cirurgia de reconstrução da superfície ocular com transplante de limbo e membrana amniótica de tal forma que no grupo I foram estudados 49 pacientes sem cirurgia prévia e no grupo II estudaram-se 16 pacientes após cirurgia para reconstrução da superfície e com sinais de conjuntivalização recorrente. As amostras foram colhidas do olho afetado entre fevereiro de 2000 e fevereiro de 2002 no Laboratório de Doenças Externas Oculares do Departamento de Oftalmologia da UNIFESP. Definiu-se que o diagnóstico de deficiência límbica era confirmado por citologia de impressão quando uma ou mais células caliciformes íntegras eram encontradas na superfície da córnea. RESULTADOS: No grupo I uma ou mais células caliciformes foram evidenciadas na superfície da córnea em 21 olhos (42,85 por cento). No grupo II foi possível detectá-las na superfície da córnea em 9 pacientes (56,25 por cento). CONCLUSAO: A presença de células caliciformes na superfície da córnea detectada no exame de citologia de impressão em pacientes com conjuntivalização pode confirmar o diagnóstico de deficiência de limbo no local pesquisado, porém, a ausência destas células não exclui o diagnóstico.

Cultivo primário de células epiteliais germinativas do limbo de olhos doadores / Primary culture of limb germ epithelial cells of donor eyes

OBJETIVO: Padronizar cultivo primário de células epiteliais germinativas do limbo de olhos doadores do Banco de Olhos da Santa Casa de São Paulo. MÉTODOS: Por meio de biópsias de aproximadamente 4 mm² realizadas na região do limbo cirúrgico do anel córneo-escleral remanescente de olhos doadores, foram obtidos explantes, que passaram por métodos de dissociação para obtenção de células epiteliais germinativas do limbo, as quais foram semeadas em placas de cultivo celulare encubadasna estufa a 37°C em atmosfera a 5 por cento de CO2. As placas foram observadas em 21 dias, sendo avaliadas a aderência, a morfologia e a multiplicação celular. RESULTADOS: Observamos que as células no decorrer dos 21 dias multiplicaram-se, passando da forma arredondada inicial ao processo de dissociação, para a forma poligonal como in vivo, além de demonstrarem maior aderência à placa de cultivo. CONCLUSÃO: Neste estudo foi possível demonstrar que o cultivo de células epiteliais límbicas in vitro pode ser realizado.