Safety outcomes and long-term effectiveness of ex vivo autologous cultured limbal epithelial transplantation for limbal stem cell deficiency

Comparative analysis of long-term results of three epithelial cell transplantation procedures for treating limbal stem cell deficiency

This study compared the long-term outcome of different epithelial transplantation techniques to treat limbal stem cell deficiency (LSCD). We conducted a retrospective 15-year comparative systematic cohort study of patients with LSCD who underwent either cultivated limbal epithelial transplantation (CLET), simple limbal epithelial transplantation (SLET), or cultivated oral mucosal epithelial transplantation (COMET). We reviewed the demographic data, etiology, LSCD severity, best-corrected visual acuity, surgical outcomes, and complications. A total of 103 eyes of 94 patients (mean age, 45.0 ± 16.4 years) with LSCD were enrolled. The most common cause of LSCD was chemical injury (42.7 %). The median follow-up time was 75 months. The success rates of CLET, SLET, and COMET were 45.5 %, 77.8 %, and 57.8 %, respectively. The 7-year survival rates after CLET, SLET, and COMET were 50.0 %, 72.2 %, and 53.2 %, respectively. Steven-Johnson syndrome (SJS) had a significantly lower survival rate than other causes (p < 0.001), but SLET had a significantly higher survival rate than CLET (p = 0.018) and COMET (p = 0.047). Visual improvement of more than four Snellen lines was achieved in 53.1 % of successful cases and 28.2 % of failed cases. SJS, Schirmer I test <5 mm, and the presence of postoperative recurrent epithelial defects were significant risk factors for a failed surgery. All epithelial transplantation techniques had favorable long-term surgical outcomes. More than half of the patients achieved a stable ocular surface and visual acuity improvement up to 7 years postoperatively. SLET tends to have a better surgical outcome than CLET and COMET, especially in patients with SJS.

New developments in the management of persistent corneal epithelial defects

A persistent epithelial defect (PED) is a corneal epithelial defect that failed to heal after 2weeks. It is a condition that carries much morbidity, and our understanding of PED remains poor, with current treatment methods often having unsatisfactory outcomes. With PEDs becoming more prevalent, more efforts are required to establish reliable treatment modalities. Our reviews describe the causes of PEDs and the different approaches developed to manage them, as well as their associated limitations. Emphasis is placed on understanding various advances in the development of new treatment modalities. We have also described a case of a woman with a background of graft-versus-host disease on long-term topical corticosteroids who developed complicated PED involving both eyes. The current approach to managing PEDs generally involves exclusion of an active infection, followed by treatment modalities that aim to encourage corneal epithelial healing. Success rates, however, remain far from desirable, as treatment remains challenging due to multiple underlying etiologies. In summary, advances in the development of new therapies may be able to facilitate progress in the understanding and treatment of PED.

Identification of the regulatory circuit governing corneal epithelial fate determination and disease

The transparent corneal epithelium in the eye is maintained through the homeostasis regulated by limbal stem cells (LSCs), while the nontransparent epidermis relies on epidermal keratinocytes for renewal. Despite their cellular similarities, the precise cell fates of these two types of epithelial stem cells, which give rise to functionally distinct epithelia, remain unknown. We performed a multi-omics analysis of human LSCs from the cornea and keratinocytes from the epidermis and characterized their molecular signatures, highlighting their similarities and differences. Through gene regulatory network analyses, we identified shared and cell type-specific transcription factors (TFs) that define specific cell fates and established their regulatory hierarchy. Single-cell RNA-seq (scRNA-seq) analyses of the cornea and the epidermis confirmed these shared and cell type-specific TFs. Notably, the shared and LSC-specific TFs can cooperatively target genes associated with corneal opacity. Importantly, we discovered that FOSL2, a direct PAX6 target gene, is a novel candidate associated with corneal opacity, and it regulates genes implicated in corneal diseases. By characterizing molecular signatures, our study unveils the regulatory circuitry governing the LSC fate and its association with corneal opacity.

Cultivated autologous limbal epithelial cell (CALEC) transplantation: Development of manufacturing process and clinical evaluation of feasibility and safety

To treat unilateral limbal stem cell (LSC) deficiency, we developed cultivated autologous limbal epithelial cells (CALEC) using an innovative xenobiotic-free, serum-free, antibiotic-free, two-step manufacturing process for LSC isolation and expansion onto human amniotic membrane with rigorous quality control in a good manufacturing practices facility. Limbal biopsies were used to generate CALEC constructs, and final grafts were evaluated by noninvasive scanning microscopy and tested for viability and sterility. Cultivated cells maintained epithelial cell phenotype with colony-forming and proliferative capacities. Analysis of LSC biomarkers showed preservation of "stemness." After preclinical development, a phase 1 clinical trial enrolled five patients with unilateral LSC deficiency. Four of these patients received CALEC transplants, establishing preliminary feasibility. Clinical case histories are reported, with no primary safety events. On the basis of these results, a second recruitment phase of the trial was opened to provide longer term safety and efficacy data on more patients.

Clinical applications of bioengineered tissue-cellular products for management of corneal diseases

PURPOSE OF REVIEW

To discuss bioengineered tissue-cellular products for treatment of corneal diseases that are currently in clinical use. These include tissue-cellular products that have received regulatory approval, are being used off-label in clinical practice, or are in active use in clinical trials.

RECENT FINDINGS

Due to the global shortage of donor corneal tissue, significant efforts have been made to develop bioengineering tissue-cellular products that can replace or augment the use of cadaveric tissue for corneal transplantation. The development of carrier substrates to support transplantation of cultivated limbal epithelial transplantation (CLET) has been a growing area of research. CLET offers a promising therapeutic alternative to conventional simple limbal epithelial transplantation and keratolimbal allografts for treatment of limbal stem cell deficiency. Engineered tissue matrices and porcine-derived corneas are potential alternatives to human donor tissue in anterior lamellar keratoplasty for corneal ulcers and scars, as well as intrastromal transplants for advanced keratoconus. For endothelial disease, substrate supported cultured endothelial cell grafts, and synthetic barrier devices are promising alternative to traditional endothelial keratoplasties.

SUMMARY

There has been increasing interest in cellular and acellular bioengineered tissue-cellular and synthetic products for treatment of corneal diseases, and many of these products have already seen clinical use. Industry and academia have important roles in advancing these products to later phase clinical trials and comparing them to conventional allograft approaches. Future development of full thickness donor corneas with cultivated epithelium, endothelium, and stromal keratocytes in a biosynthetic matrix will likely be an important next step in tissue alternatives. Continued progress in this field will be critical for addressing the global disease burden from corneal blindness.

Cultivated Autologous Limbal Epithelial Cell Transplantation: New Frontier in the Treatment of Limbal Stem Cell Deficiency

PURPOSE

Taking into consideration prior human experience with treating limbal stem cell deficiency (LSCD) with cultivated limbal epithelial cells (CLEC) from other countries, we have set a goal to optimize and standardize the techniques of CLEC preparation (called CALEC by our group) for the clinical trial in the United States.

METHODS

We performed an extensive literature review of all human trials, case series, and reports involving autologous cultivated limbal epithelial cell transplantation. Allogeneic cultivated limbal epithelial cell transplantations were reported only when combined with autologous studies. We also searched prior animal data aiding in detailing regulatory toxicology requirements.

RESULTS

Between 1997 and 2020, the analysis of human trials revealed 21 studies on autologous grafts, and 13 studies analyzing both autologous grafts and allogeneic grafts. Of a total of 34 studies, 6 studies used good manufacturing process (GMP) facilities, and 11 studies had no animal-derived products or murine feeder layers, whereas only 1 study had both. Overall, the treatment with autologous CLEC grafts was 68.9% successful. In total there were 6 preclinical studies using rabbits, serving as surrogate studies to assess the safety and toxicity of cultivated limbal epithelial cells for human trials. Based on prior human experience, we further optimized the manufacturing conditions with GMP-grade and serum and animal-free reagents, and developed cell characterization assays for the CALEC product release.

CONCLUSIONS

These data were used to develop a novel and consistent manufacturing process using only qualified and validated reagents for performing the first clinical trial on CALEC transplantation to treat LSCD in the United States.

Goals and Challenges of Stem Cell-Based Therapy for Corneal Blindness Due to Limbal Deficiency

Corneal failure is a highly prevalent cause of blindness. One special cause of corneal failure occurs due to malfunction or destruction of the limbal stem cell niche, upon which the superficial cornea depends for homeostatic maintenance and wound healing. Failure of the limbal niche is referred to as limbal stem cell deficiency. As the corneal epithelial stem cell niche is easily accessible, limbal stem cell-based therapy and regenerative medicine applied to the ocular surface are among the most highly advanced forms of this novel approach to disease therapy. However, the challenges are still great, including the development of cell-based products and understanding how they work in the patient's eye. Advances are being made at the molecular, cellular, and tissue levels to alter disease processes and to reduce or eliminate blindness. Efforts must be coordinated from the most basic research to the most clinically oriented projects so that cell-based therapies can become an integrated part of the therapeutic armamentarium to fight corneal blindness. We undoubtedly are progressing along the right path because cell-based therapy for eye diseases is one of the most successful examples of global regenerative medicine.

Corneal supply and the use of technology to reduce its demand: A review

Recovery and access to end-of-life corneal tissue for corneal transplantation, training and research is globally maldistributed. The reasons for the maldistribution are complex and multifaceted, and not well defined or understood. Currently there are few solutions available to effectively address these issues. This review provides an overview of the system, key issues impacting recovery and allocation and emphasises how end-user ophthalmologists and researchers, with support from administrators and the wider sector, can assist in increasing access long-term through sustaining eye banks nationally and globally. We posit that prevention measures and improved surgical techniques, together with the development of novel therapies will play a significant role in reducing demand and enhance the equitable allocation of corneas.

Surgical Management and Recent Advances in Chemical Injury: A 5-year Review

Purpose: To review the surgical management options in ocular chemical burn, including newer advances.Methods: Online literature search of published articles over last 5 years on surgical management of ocular chemical burn and newer advances were performed on December 30, 2020.Results: Following literature search and screening using adequate filters, 67 review articles on surgical management of ocular chemical burns were retrieved. The review talks about the surgical management options starting from Debridement in acute stage to various visual rehabilitative procedures in the chronic stage. The review also highlights the evolving surgical advances in this field.Conclusion: It is imperative to choose adequate surgical tool wherever applicable; current review discusses the role of each surgical option at different clinical stages in detail.

Economic, clinical and social impact of simple limbal epithelial transplantation for limbal stem cell deficiency

Aims

To report the global uptake of simple limbal epithelial transplantation (SLET) and compare the economic, clinical and social outcomes of SLET with those of cultured limbal epithelial transplantation (CLET).

Methods

A comprehensive literature review and an online survey of eye surgeons were conducted to understand the efficacy and current uptake of SLET surgery. A de novo economic model was developed to estimate the cost savings with SLET compared with CLET. Our economic analysis is conducted from an Indian perspective, as this is where the technique originated. A scenario analysis using the UK cost data and a user-friendly Excel model is included to allow users to input the costs from their setting to estimate the cost savings with using SLET compared with using CLET

Results

The anatomical success with SLET in adults (72.6% (range 62%–80%)) was the same as CLET (70.4% (range 68%–80.9%)). For children, the outcome for SLET (77.8% (range 73%–83%)) was better than with CLET (44.5% (range 43%–45%)). In response to our informal questionnaire, 99 surgeons reported to have performed SLET on 1174 patients in total. They appreciated that SLET negates the requirement for costly tissue engineering facilities. Results of economic analysis suggested that SLET provided an estimated cost-savings of US$6470.88 for adults and US$6673.10 for children. In broad terms, the cost of SLET is approximately 10% of the cost of CLET for adults and 8% for children.

Conclusion

SLET offers a more accessible and financially attractive alternative to CLET to treat limbal stem cell deficiency.

Systematic review of clinical research on regenerative medicine for the cornea

PURPOSE

To conduct a systematic review of clinical research on the use of regenerative medicine for the cornea in human patients.

METHODS

A systematic literature search of MEDLINE and the Cochrane Library was performed in May 2020.

RESULTS

Forty-two articles were identified. Thirty-eight of those articles focused on the treatment for limbal stem cell deficiency (LSCD), of which 17 articles involved autologous cultured limbal epithelial cell sheet transplantation (CLET), 13 involved allogeneic CLET, and 14 involved autologous cultured oral mucosal epithelial cell sheet transplantation (COMET). For autologous CLET, the median ocular surface reconstruction rate, visual recovery rate, incidence of immunologic rejection, infectious keratitis, and ocular hypertension/glaucoma were 74.1%, 54.5%, 0%, 4.6%, and 6.3%, respectively. For allogeneic CLET, they were 71.4%, 71.4%, 7.1%, 12.0%, and 7.1%, respectively. For autologous COMET, they were 66.7%, 66.7%, 0%, 5.3%, and 8.1%, respectively. Systemic immunosuppressants and steroid medications were predominantly used following allogeneic CLET, whereas they were not routinely used after autologous CLET. Three studies focused on the treatment of keratoconus using autologous adipose-derived adult stem cells and reported no marked adverse events. One study reported on the treatment of bullous keratopathy using allogeneic cultured corneal endothelial cells. All patients achieved an endothelial cell density of >500 cells, and the corrected distance visual acuity improved in 82% of the treated eyes.

CONCLUSIONS

The results show that regenerative medicine for the cornea demonstrated a satisfactory efficacy and safety. Through translational research, we are expecting to establish a new treatment for waiting patients.

Increased Cell Survival of Human Primary Conjunctival Stem Cells in Dimethyl Sulfoxide-Based Cryopreservation Media

Glycerol and dimethyl sulfoxide (DMSO) are widely used cryoprotectants for freezing human cell cultures. During the manufacturing process of ocular stem cell-based autographs, ex vivo cultivated ocular cells are cryopreserved for quality control purposes in accordance with regulatory requirements. The efficiency of the cryopreservation methods is limited by their effect on cell survival and quality. We compared two cryopreservation reagents, glycerol and DMSO, for their influence on the survival and quality of human primary conjunctival cultures. We found increased cell viability after cryopreservation in DMSO compared to cryopreservation in glycerol. The clonogenic and proliferative capacity was unaffected by the cryopreservation reagents, as shown by the colony forming efficiency and cumulative cell doubling. Importantly, the percentage of p63α- and keratin 19 (K19)-positive cells following cryopreservation in DMSO or glycerol was comparable. Taken together, our results demonstrate that cryopreservation in DMSO improves cell survival compared to cryopreservation in glycerol, with no subsequent effect on cell proliferative-, clonogenic-, or differentiation capacity. Therefore, we advise the use of a 10% DMSO-based cryopreservation medium for the cryopreservation of human primary conjunctival cells, as it will improve the number of cells available for the manufacturing of conjunctival stem cell-based autografts for clinical use.

Outcomes of Limbal Stem Cell Transplant: A Meta-analysis

Importance

Limbal stem cell transplant (LSCT) can be categorized as direct autologous limbal transplant (AULT), direct allogenic limbal transplant (ALLT), cultivated autologous limbal stem cells transplant (cAULT), and cultivated allogenic limbal stem cells transplant (cALLT). To our knowledge, there is no study directly comparing the outcomes and complications of these procedures.

Objective

To evaluate the outcomes of different LSCT procedures.

Data Source

We searched PubMed, EMBASE, Web of Science, and Cochrane without language filter for peer-reviewed articles about LSCT. The latest search was performed on June 30, 2019.

Study Selection

Clinical studies with the outcome of at least 20 eyes after LSCT were included. Animal studies and studies of other surgical interventions were excluded.

Data Extraction and Synthesis

Two reviewers independently abstracted the data from each study. Heterogeneity was evaluated with the I2 statistic, and a meta-analysis was performed using the random-effects model.

Main Outcomes and Measures

Outcome measures included the improvement of ocular surface, visual acuity (VA), and adverse events of recipient eyes and donor eyes.

Results

Forty studies (2202 eyes) with a mean (SD) follow-up of 31.3 (20.9) months met the inclusion criteria. The mean (SD) age of study participants was 38.4 (13.1) years, and men accounted for 74%. The number of eyes that underwent AULT, ALLT, cAULT, and cALLT were 505, 742, 771, and 184, respectively. Improvement of the ocular surface was achieved in 74.5% of all eyes, 85.7% of eyes after AULT (95% CI, 79.5%-90.3%), 84.7% after cAULT (95% CI, 77.2%-90.0%), 57.8% after ALLT (95% CI, 49.0%-66.1%), and 63.2% after cALLT (95% CI, 49.3%-75.2%). Autologous limbal transplantation resulted in a greater VA improvement rate (76%) than did the other 3 procedures (cAULT: 56.4%; ALLT: 52.3%; cALLT: 43.3%; all P < .001). The most common adverse events in all recipient eyes were recurrent/persistent epithelial erosion (10.5%; 95% CI, 7.2%-23.3%) and elevated intraocular pressure (intraocular pressure, 1.7%; 95% CI, 0.5%-7.8%). Patients who underwent ALLT had the highest rate of recurrent epithelial erosion (27.8%; 95% CI, 17.1%-41.9%) and intraocular pressure elevation (6.3%; 95% CI, 1.8%-19.4%).

Conclusions and Relevance

These findings suggest LSCT can improve or stabilize the corneal surface with a low rate of severe ocular complications and that autologous LSCT may have a higher success rate and fewer complications than allogenic LSCT.

A systematic review of cellular therapies for the treatment of limbal stem cell deficiency affecting one or both eyes

PURPOSE

This systematic review (SR) assessed the efficacy, safety and cost-effectiveness of cell-based therapy to manage limbal stem cell deficiency (LSCD), a sight-threatening orphan condition most frequently associated with severe chemical or thermal burns. LSCD has historically been treated by transplanting limbal tissue. In 1997, a new treatment, cultured limbal epithelial autografts, was described for unilateral LSCD. In cases of bilateral disease cultured autologous oral mucosa stem cells have been used. The relative efficacy of different cultured tissue procedures is unknown.

METHODS

A protocol was registered with PROSPERO (CRD42017081117). Searches were conducted in 14 databases and 6 conference websites. Two reviewers independently selected studies, conducted data extraction and assessed risk of bias. One reviewer extracted individual patient data (IPD); a second checked extracted data. Data were assessed to determine the feasibility of statistical analysis, with Bayesian synthesis used to estimate improvement achieved by different treatments.

RESULTS

Fifty-two studies were eligible for inclusion (1113 eyes); 41 studies (716 eyes) reported IPD. No evidence was identified on cost-effectiveness. This SR was unable to confirm that any of the types of ex vivo cultured stem cell transplants identified for LSCD treatment were statistically superior when assessed against the outcomes of interest.

CONCLUSIONS

We believe this SR is the first to include IPD analysis of LSCD data. There is no evidence for the superiority of any method of limbal stem cell transplant. Confirmation of the safety and efficacy of this treatment modality is challenging due to heterogeneity within and between the studies identified. Therefore, recommendations for future research are proposed.

In Vivo Confocal Microscopy of the Corneal-Conjunctival Transition in the Evaluation of Epithelial Renewal after SLET

Examination of the corneal surface by in vivo confocal microscopy (IVCM) allows for objective identification of corneal and conjunctival cell phenotypes to evaluate different epithelialization patterns. Detection of a corneal-conjunctival epithelial transition could be considered as a sign of restored epithelial function following simple limbal epithelial transplantation (SLET). This is a prospective, interventional case series. We assessed patients with limbal stem cell deficiency (LSCD) by IVCM, preoperatively and at monthly intervals following SLET. Sectors in the central and peripheral cornea were scanned. Immediately upon detection of multi-layered cells with the epithelial phenotype in the central cornea and confirmation of epithelial transition in all corneal sectors, the decision for keratoplasty was taken. Ten patients were enrolled. After SLET, epithelial phenotype in the central cornea and an epithelial transition were identified within six and nine months in seven and one patients, respectively. One patient was a partial success and one failed. Five patients underwent keratoplasty, with stable results up to 12 months. Identification of the epithelial transition zone by IVCM permits assessment of the efficacy of SLET, enabling subsequent planning of keratoplasty for visual rehabilitation. The stability of the corneal surface following keratoplasty confirms that the renewal of the corneal epithelium was effectively retained.

A new standardized immunofluorescence method for potency quantification (SMPQ) of human conjunctival cell cultures

The aim of this study is to set up a standardized and reproducible method to determine the potency (= stem cell content) of human conjunctival cell cultures by means of immunofluorescence-based analyses. This will help the development of new Advanced Therapy Medicinal Products (ATMPs) to use in future cell therapy clinical studies when fewer cells are available to perform the quality controls. To achieve this purpose, a reference standard was investigated and the expression levels of ΔNp63α (considered as a marker of conjunctival stem cells) was correlated to cell size. The limbal hTERT cells were used as reference standard to define the expression value of ΔNp63α. The mean intensity value of limbal hTERT cells ranging between 15 and 20 µm in diameter was used to distinguish between ΔNp63α bright and not bright cells. As ΔNp63α bright expression was mainly seen in the smaller cell size group (10-15 µm), we defined as conjunctival stem cells (= potency) those cells which were bright and with sizes between 10 and 15 µm. Assays on cells from clonal analyses were used to validate the method, as they do allow to observe a decrease in potency (Holoclones > Meroclones > Paraclones). The stem cell content of conjunctival grafts was found to be 11.3% ± 5.0 compared to 21.9% ± 0.6, 9.0% ± 8.1 and 0% from Holoclones, Meroclones and Paraclones, respectively. This new method, here named as Standardized Method for Potency Quantification, will allow to detect the potency in conjunctival cell cultures, thus obtaining a quality control assay responding to the GMP standards required for ATMP release.

KIT ligand produced by limbal niche cells under control of SOX10 maintains limbal epithelial stem cell survival by activating the KIT/AKT signalling pathway

Homeostasis and function of limbal epithelial stem cells (LESCs) rely on the limbal niche, which, if dysfunctional, leads to limbal epithelial stem cell deficiency (LSCD) and impaired vision. Hence, recovery of niche function is a principal therapeutic goal in LSCD, but the molecular mechanisms of limbal niche homeostasis are still largely unknown. Here, we report that the neural crest transcription factor SOX10, which is expressed in neural crest‐derived limbal niche cells (LNCs), is required for LNCs to promote survival of LESCs both in vivo and in vitro. In fact, using mice with a Sox10 mutation and in vitro coculture experiments, we show that SOX10 in LNCs stimulates the production of KIT ligand (KITL), which in turn activates in LESCs the KIT‐AKT signalling pathway that protects the cells against activated CASPASE 3‐associated cell death. These results suggest that SOX10 and the KITL/KIT‐AKT pathway play key roles in limbal niche homeostasis and LESC survival. These findings provide molecular insights into limbal niche function and may point to rational approaches for therapeutic interventions in LSCD.

Corneal epithelial biology: Lessons stemming from old to new

The anterior surface of the eye functions as a barrier to the external environment and protects the delicate underlying tissues from injury. Central to this protection are the corneal, limbal and conjunctival epithelia. The corneal epithelium is a self-renewing stratified squamous epithelium that protects the underlying delicate structures of the eye, supports a tear film and maintains transparency so that light can be transmitted to the interior of the eye (Basu et al., 2014; Cotsarelis et al., 1989; Funderburgh et al., 2016; Lehrer et al., 1998; Pajoohesh-Ganji and Stepp, 2005; Parfitt et al., 2015; Peng et al., 2012b; Stepp and Zieske, 2005). In this review, dedicated to James Funderburgh and his contributions to visual science, in particular the limbal niche, corneal stroma and corneal stromal stem cells, we will focus on recent data on the identification of novel regulators in corneal epithelial cell biology, their roles in stem cell homeostasis, wound healing, limbal/corneal boundary maintenance and the utility of single cell RNA sequencing (scRNA-seq) in vision biology studies.

Corneal graft melting: a systematic review

Corneal graft melting is a severe complication of keratoplasty. This review is to summarize the incidence, the pathogenesis, the risk factors, the prognosis and the prevention of corneal graft melting after keratoplasty. We systematically searched PubMed, Web of Science and WanFang database to retrieve potentially eligible articles about relevant clinical reports and animal experiments. We read the full texts to identify eligible articles. The selection of studies and data extraction were performed independently by two reviewers. In conclusion, the pathogenesis of corneal graft melting is complicated, and many risk factors are closely related to corneal graft melting. Analysis of pathogenesis and risk factors of corneal graft melting can facilitate the development of targeted therapies to better guide clinical practice.

Long-term outcomes of conjunctival limbal autograft in patients with unilateral total limbal stem cell deficiency

PURPOSE

To investigate the long-term clinical outcomes of conjunctival limbal autograft (CLAU) in patients with unilateral total limbal stem cell deficiency (LSCD).

METHODS

In this retrospective interventional case series, the medical charts of patients with unilateral total LSCD were reviewed. Patients who underwent CLAU and no other allograft ocular stem cell transplantation with a minimum follow-up of 1 year were included. Main outcome measures were ocular surface stability, best-corrected visual acuity (BCVA), and postoperative complications.

RESULTS

27 eyes fulfilled the inclusion criteria with a mean follow-up period of 49.8 ± 36.6 months (4.15 years; range 12-186.72 months; 1-15.56 years). Ocular surface stability was achieved in 77.8% (n = 21) of eyes at last follow-up, while 22.2% (n = 6) developed partial surface failure. Optical penetrating or deep lamellar anterior keratoplasty was performed in 44.45% (n = 12). BCVA improved from 1.42 ± 0.95 mean LogMAR (equivalent to 20/400) preoperatively to 0.53 ± 0.47 mean LogMAR (equivalent to 20/70) at last follow-up (p < 0.001). BCVA ≥20/40 was achieved in 44.45% (n = 12) at last follow-up. Microbial keratitis occurred in 14.81% (n = 4). Ocular hypertension secondary to corticosteroid use developed in 25.9% (7/27) eyes. There were no other complications in the donor or recipient eyes.

CONCLUSIONS

CLAU can provide long-term ocular surface stability and successful visual outcomes in patients with unilateral LSCD.

Diagnostic criteria for limbal stem cell deficiency before surgical intervention-A systematic literature review and analysis

An accurate diagnosis of limbal stem cell deficiency (LSCD) is the premise of an appropriate treatment; however, there is no consensus about the diagnostic criteria for LSCD. We performed a systematic literature search of the peer-reviewed articles on PubMed, Medline, and Ovid to investigate how LSCD was diagnosed before surgical intervention. The methods used to diagnose LSCD included clinical presentation, impression cytology, and in vivo confocal microscopy. Among 131 eligible studies (4054 eyes), 26 studies (459 eyes, 11.3%) did not mention the diagnostic criteria. In the remaining 105 studies, the diagnosis of LSCD was made on the basis of clinical examination alone in 2398 eyes (62.9%), and additional diagnostic tests were used in 1047 (25.8%) eyes. Impression cytology was used in 981 eyes (24.2%), in vivo confocal microscopy was used in 29 eyes (0.7%), and both impression cytology and in vivo confocal microscopy were used in 37 eyes (0.9%). Our findings suggest that only a small portion of patients underwent a diagnostic test to confirm the diagnosis of LSCD. Treating physicians should be aware of the limitations of clinical examination in diagnosing LSCD and perform a diagnostic test whenever possible before surgical intervention.

Autologous limbal stem cell transplantation: a systematic review of clinical outcomes with different surgical techniques

PURPOSE

To conduct a systematic review on outcomes of three different techniques of autologous limbal stem cell transplantation (LSCT): conjunctival-limbal autografting (CLAu), cultivated limbal epithelial transplantation (CLET) and simple limbal epithelial transplantation (SLET), in unilateral limbal stem cell deficiency (LSCD).

METHODS

Literature searches were conducted in MEDLINE (Ovid), Embase, Web of Science and Cochrane Central Register. Standard systematic review methodology was followed using Meta-analysis of Observational Studies in Epidemiology guidelines. Studies with a sample size of more than 10 eyes were included. The primary outcome measure of efficacy was restoration of a completely epithelised, stable and avascular corneal surface (anatomical success). The secondary outcome measure of efficacy was improvement in best-corrected visual acuity of two-lines or greater (functional success).

RESULTS

The review identified 22 non-comparative case series, which included 1023 eyes. Ocular burns were the major (88%) indication for surgery. Overall, at a median postoperative follow-up of 1.75 years, autologous LSCT for unilateral LSCD showed anatomical and functional success rates of 69% and 60%, respectively, without any serious adverse events in the donor eye. The follow-up duration and indications for surgery were comparable across all groups (p>0.05). The anatomical and functional success rates of SLET (78%; 68.6%) and CLAu (81%; 74.4%) were comparable, and significantly better than those of CLET (61.4%; 53%; p=0.0048).

CONCLUSION

Autologous LSCT is a safe and effective treatment for unilateral LSCD. In the absence of randomised controlled trials, existing evidence clearly suggests that clinical outcomes are better with SLET and CLAu as compared with CLET.

Inflammation, vascularization and goblet cell differences in LSCD: Validating animal models of corneal alkali burns

Limbal stem cell deficiency (LSCD) is one of the serious cause of visual impairment and blindness with loss of corneal clarity and vascularization. Factors such as ocular burns (acids, lime, thermal), genetic disorders or infections results in the loss of limbal stem cells leading to LSCD. Reliable animal models of LSCD are useful for understanding the pathophysiology and developing novel therapeutic approaches. The purpose of the present study was to validate small and large animal models of LSCD by immunohistochemcal, clinical and histopathological comparison with human. The animal models of LSCD were created by topical administration of sodium hydroxide on the ocular surface of C57BL/6 mice (m, n = 12) and New Zealand white rabbits (r, n = 12) as per the standard existing protocol. Human corneal specimens (h, n = 12) were obtained from tissue bank who had chemical burn-induced LSCD. All samples were either paraffin embedded or frozen in cryogenic medium and the sections were processed for Hematoxylin-Eosin and Periodic Acid-Schiff staining to analyse the morphology and histopathological features of the corneal surface such as vascularization, inflammation, presence of goblet cells, epithelial hyperplasia and keratinization. Immunofluorescence was performed to distinguish between corneal (CK3+), conjunctival (CK19+) and epidermal (CK10+) epithelial phenotype. Histological analysis of corneal specimens from the three groups showed the presence of goblet cells (h:83%, m:50%, r:50%, p = 0.014), epithelial hypertrophy (h:92%, m:50%, r:66.6%, p = 0.04), epithelial hyperplasia (h:50%, m:17%, r:17%, p = 0.18), intra epithelial edema (h:42%, m:33%, r:100%, p = 0.02), stromal inflammation (h:100%, m:67%, r:67%, p = 0.01) and stromal vascularization (h:100%, m:50%, r:67%), in varying proportions. Immunostaining showed presence of total LSCD (CK19 + and/or CK10+, CK3-) in 92% of human and 50% of animal specimens. While partial LSCD (CK19 + and/or CK10+, CK3+) was seen in 8% of human and 50% of animal specimens. Our study shows the significant differences in the extent of vascularization, inflammation, epithelial thickness and goblet cell formation in mice and rabbit models of LSCD when compared to post-chemical burn LSCD in human corneas. In both mice and rabbit models complete LSCD developed in only 50% of cases and this important fact needs to be considered when working with animal models of LSCD.

Recovering vision in corneal epithelial stem cell deficient eyes

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Corneal limbal epithelial stem cells deficiencies cause severe ocular surface instability and visual impairment.

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These conditions, caused by injury or disease, are very difficult to treat.

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Laboratory-grown epithelial cell sheets expanded from healthy limbal tissue can be used to reconstruct the ocular surface.

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Other epithelia, such as the oral mucosa, can be used to generate the therapeutic cell sheets.

A healthy corneal epithelium, which is essential for proper vision and protection from external pathogens, is continuously replenished throughout life by stem cells located at the limbus. In diseased or injured eyes, however, in which stem cells are deficient, severe ocular problems manifest themselves. These are notoriously difficult to manage and as a result the last 20 or so years has seen a number of therapeutic strategies emerge that aim to recover the ocular surface and restore vision in limbal stem cell deficient eyes. The dominant concept involves the generation of laboratory cultivated epithelial cell sheets expanded from small biopsies of the epithelial limbus (for patient or donors) or another non-corneal epithelial tissue such as the oral mucosa. Typically, cells are grown on sterilised human amniotic membrane as a substrate, which then forms part of the graft, or specially formulated plastic culture dishes from which cells sheets can be released by lowering the temperature, and thus the adherence of the plastic to the cells. Overall, clinical results are promising, as is discussed, with new cultivation methodologies and different cell lineages currently being investigated to augment the treatment options for visual disturbance caused by a corneal epithelial limbal stem cell deficiency.

Systematic review and meta-analysis investigating autograft versus allograft cultivated limbal epithelial transplantation in limbal stem cell deficiency

PURPOSE

Currently, regenerative medicine has attracted much attention among researchers investigating new methods to treat ocular surface diseases. Based on this new concept, cultivated limbal epithelial transplantation (CLET), whether in the form of autograft or allograft, has emerged as a promising surgical procedure for treating limbal stem cell deficiency (LSCD). Given that there is no updated comparison between autograft and allograft CLETs, the present review and meta-analysis aims to compare and determine the efficacy of two different CLET techniques, autologous versus allogeneic, based on a literature review of relevant studies.

METHODS

A comprehensive search of electronic databases, including PubMed, Web of Science, Cochrane Library, Embase and Scopus, for related articles was performed in March 2018 to obtain relevant articles and to conduct a meta-analysis investigating the success rate of ocular surface regeneration and two-line improvement in best-corrected visual acuity (BCVA) using autograft versus allograft transplantations.

RESULTS

A total of 30 studies, including 1306 eyes from 1288 patients with LSCD, with a sample size ranging from 6 to 200 and follow-up period of 0.6-156 months, were reviewed. Of 1306 eyes, 982 (75.2%) underwent autograft and 324 (24.8%) received allografts from living or deceased donors. Meta-analysis revealed that there was no significant difference between autograft and allograft CLETs in terms of success rate and two-line BCVA improvement. The prospective studies showed a zero difference between the two groups; only two retrospective studies included in the analysis pulled the autografts up to 1.82 and 1.2 times more than allografts in terms of success rate and two-line BCVA improvement, respectively [pooled OR 1.82 (95% CI 0.80-4.11); pooled OR 1.2 (95% CI 0.54-2.65)]. There was no statistically significant evidence of bias in the meta-analysis in terms of success rates and two-line BCVA improvement.

CONCLUSIONS

The present analysis revealed no significant differences in success rates or visual improvement between autograft and allograft surgical techniques.

The application of human amniotic membrane in the surgical management of limbal stem cell deficiency

The application of human amniotic membrane (AM) has a wide spectrum of indications in the treatment of ocular surface disorders. Transplantation of AM has been incorporated routinely as a component of ocular surface reconstruction in a variety of ocular pathologies. The application of human AM can be combined with nearly all types of limbal transplantation in treating limbal stem cell deficiency (LSCD). AM provides support and possible protection to the transplanted limbal tissues and limbal stem cells owing to its mechanical and biological properties, and these properties are thought to enhance the success rate of LSC transplantation. This paper reviews the current literature on the applications of AM in the surgical management of LSCD and summarizes the outcome of different surgical approaches. The current literature contains mostly low-level evidences in supporting the role of AM. The efficacy of AM in LSC transplantation needs to be confirmed by randomized controlled clinical trials.

Infectious Keratitis After Ocular Surface Stem Cell Transplantation

PURPOSE

To describe the rate, clinical/microbiological characteristics, and outcomes of infectious keratitis in eyes with limbal stem cell deficiency after ocular surface stem cell transplantation (OSST).

METHODS

In this retrospective chart review of 278 eyes that underwent OSST between January 2006 and December 2016, eyes treated for previous infectious keratitis (bacterial, fungal, or viral) were included. Demographics, risk factors, course, microbiological characteristics, and outcomes were assessed.

RESULTS

A total of 52 eyes (18.7%) of 48 patients (28 men and 20 women) developed 75 episodes (culture-proven or presumed) of infectious keratitis (range 1-4 episodes) with mean follow-up of 5.3 ± 3.6 years after OSST. The most common limbal stem cell deficiency etiologies included chemical/thermal (27 episodes), Stevens-Johnson syndrome (19 episodes), aniridia (8 episodes), and mucous membrane pemphigoid (8 episodes). There were 44 (58.7%) bacterial keratitis episodes, 24 (32%) fungal keratitis episodes, and 7 (9.3%) HSV keratitis episodes. Gram-positive bacteria (79%) and Candida species (73%) were the most common bacterial and fungal pathogens. Before infection, 33% had an epithelial defect, 69% had a bandage contact lens, 91% were on systemic immunosuppression, and 25% recently had undergone ocular surgery (<3 months). Although 75% resolved with antimicrobial treatment, 25% required a therapeutic keratoplasty (TPK; 2 cases needed multiple TPK).

CONCLUSIONS

Despite successful OSST surgery, infectious keratitis is relatively common, and aggressive medical/surgical therapy is warranted. Prophylactic topical antibiotics and a cicatrizing conjunctivitis diagnosis may account for the high proportion of fungal keratitis in this population.

The current state of stem cell therapy for ocular disease

Herein, we review the safety, efficacy, regulatory standards and ethical implications of the use of stem cells in ocular disease. A literature review was conducted, registered clinical trials reviewed, and expert opinions sought. Guidelines and codes of conduct from international societies and professional bodies were also reviewed. Collated data is presented on current progress in the field of ocular regenerative medicine, future challenges, the clinical trial process and ethical considerations in stem cell therapy. A greater understanding of the function and location of ocular stem cells has led to rapid advances in possible therapeutic applications. However, in the context of significant technical challenges and potential long-term complications, it is imperative that stem cell practices operate within formal clinical trial frameworks. While there remains broad scope for innovation, ongoing evidence-based review of potential interventions and the development of standardized protocols are necessary to ensure patient safety and best practice in ophthalmic care.

Simple limbal epithelial transplantation (SLET) in failed cultivated limbal epithelial transplantation (CLET) for unilateral chronic ocular burns

AIMS

Cultivated limbal epithelial transplantation (CLET) fails in around 20%-30% of cases. This study aimed to report the clinical outcomes of autologous simple limbal epithelial transplantation (SLET) in eyes with recurrent unilateral limbal stem cell deficiency (LSCD) due to failure of CLET.

METHODS

This was a prospective case series which included 30 eyes of 30 patients who underwent SLET between 2010 and 2016 after failure of one (n=24) or two (n=6) previous CLET procedures for chronic unilateral ocular burns. The primary outcome measure was success of SLET defined on the basis of relative improvement in five objective criteria: best corrected visual acuity (BCVA), and grades of symblepharon, corneal conjunctivalisation, vascularisation and opacification.

RESULTS

At a mean follow-up of 2.3 years, 24 (80%) of the 30 eyes maintained a successful outcome. Kaplan-Meier analysis showed a 5-year survival probability of 77%±8%. At 1 year postoperatively statistically significant improvement was noted in BCVA (logarithm of the minimum angle of resolution of 3 to 1) and in the median grades of corneal conjunctivalisation (2 to 0), vascularisation (2 to 0) and opacification (2 to 1) (P≤0.0026). In 62.5% of successful cases, BCVA improved to 20/200 or better. The success rate of SLET in failed CLET was better than that of repeat CLET (53.5%, P=0.011). None of the donor eyes developed any complications.

CONCLUSION

SLET is an effective alternative to CLET in eyes with recurrence of LSCD after previously failed CLET procedures. Since SLET is single-staged and less expensive, it is probably preferable to repeating CLET.

Limbal Stem Cell Transplantation and Complications

Corneal epithelial stem cells are adult somatic stem cells located at the limbus and represent the ultimate source of transparent corneal epithelium. When these limbal stem cells become dysfunctional or deficient, limbal stem cell deficiency (LSCD) develops. LSCD is a major cause of corneal scarring and is particularly prevalent in chemical and thermal burns of the ocular surface. LSCD leads to conjunctivalization of the corneal surface, neovascularization, recurrent or persistent epithelial defects, ocular surface inflammation, and scarring that, in turn, lead to decreased vision, pain, and impaired quality of life. Several techniques have been reported for limbal stem cell transplantation (LSCT). We introduce the surgical techniques, examine the success rate, and discuss the postoperative complications of conjunctival limbal autograft (CLAU), cultivated limbal stem cell transplantation (CLET), simple limbal epithelial transplantation (SLET), and limbal allograft, including keratolimbal allografts (KLAL) and living-related conjunctival allograft (LR-CLAL).