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

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

A Review of Contact Lens-Induced Limbal Stem Cell Deficiency

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

Safety and Efficacy of Contact Lenses in Eyes After Simple Limbal Epithelial Transplantation

PURPOSE

The aim of this study was to evaluate the safety and efficacy of contact lenses (CLs) in eyes after simple limbal epithelial transplantation (SLET) for limbal stem cell deficiency (LSCD).

METHODS

This retrospective study included 61 eyes with partial or total LSCD which underwent SLET and were fitted with corneal or scleral rigid gas-permeable CLs. The primary outcome measure was best-corrected visual acuity (BCVA) with CLs.

RESULTS

The median age at presentation was 22 years. The most common cause of LSCD was chemical injury [47/61 eyes (77%)]. Twenty-seven eyes (44%) were fitted with corneal rigid gas-permeable lenses, while 34 eyes (56%) were prescribed scleral lenses. The median duration of interval between SLET and CL trial was 10 months (interquartile range: 4-17). The median preoperative BCVA was logarithm of minimal angle of resolution (logMAR) 1.8. This improved to logMAR 1 ( P < 0.001) after SLET and to logMAR 0.6 ( P < 0.001) with CLs. Eyes with chemical injury (logMAR 1 vs. 0.6, P = 0.0001), grade 1 (logMAR 0.8 vs. 0.4, P < 0.0001), and grade 2 (logMAR 0.9 vs. 0.6, P = 0.004) corneal scarring had better improvement in BCVA with CLs. No complications were noted until the last follow-up visit.

CONCLUSIONS

CLs, both corneal and scleral lenses, provide significant visual improvement in eyes after SLET with residual corneal scarring. These can be safely prescribed in such eyes without any adverse effects. This option can be considered before offering keratoplasty in these eyes.

Culturing Limbal Epithelial Cells of Long-term Stored Corneal Donors (Organ Culture) In Vitro - A Stepwise Linear Regression Algorithm

PURPOSE

To assess various potential factors on human limbal epithelial cell (LEC) outgrowth in vitro using corneal donor tissue following long-term storage (organ culture) and a stepwise linear regression algorithm.

METHODS

Of 215 donors, 304 corneoscleral rings were used for our experiments. For digestion of the limbal tissue and isolation of the limbal epithelial cells, the tissue pieces were incubated with 4.0 mg/mL collagenase A at 37 °C with 95% relative humidity and a 5% CO2 atmosphere overnight. Thereafter, limbal epithelial cells were separated from limbal keratocytes using a 20-µm CellTricks filter. The separated human LECs were cultured in keratinocyte serum-free medium medium, 1% penicillin/streptomycin (P/S), 0.02% epidermal growth factor (EGF), and 0.3% bovine pituitary extract (BPE). The potential effect of donor age (covariate), postmortem time (covariate), medium time (covariate), size of the used corneoscleral ring (360°, 270°180°, 120°, 90°, less than 90°) (covariate), endothelial cell density (ECD) (covariate), gender (factor), number of culture medium changes during organ culture (factor), and origin of the donor (donating institution and storing institution, factor) on the limbal epithelial cell outgrowth was analyzed with a stepwise linear regression algorithm.

RESULTS

The rate of successful human LEC outgrowth was 37.5%. From the stepwise linear regression algorithm, we found out that the relevant influencing parameters on the LEC growth were intercept (p < 0.001), donor age (p = 0.002), number of culture medium changes during organ culture (p < 0.001), total medium time (p = 0.181), and size of the used corneoscleral ring (p = 0.007), as well as medium time × size of the corneoscleral ring (p = 0.007).

CONCLUSIONS

The success of LEC outgrowth increases with lower donor age, lower number of organ culture medium changes during storage, shorter medium time in organ culture, and smaller corneoscleral ring size. Our stepwise linear regression algorithm may help us in optimizing LEC cultures in vitro.

Evaluation of Limbal Stem Cell Transplant Success in Ocular Chemical Injury

OBJECTIVES

We evaluated limbal stem cell transplant success in limbal stem cell deficiency due to chemical injury at a tertiary eye care center in Turkey with a novel system for describing limbal stem cell deficiency, as developed by the Limbal Stem Cell Working Group.

MATERIALS AND METHODS

Medical records of 80 eyes of 80 patients after limbal stem cell transplant for limbal stem cell deficiency secondary to chemical injury were included, with patients grouped according to surgical procedure, ie, limbal autograft, limbal allograft, and cultivated limbal epithelial cell transplant. Surgical success was defined as improvement in postoperative year 1 of limbal stem cell deficiency stage.

RESULTS

Patients' mean age was 37.9 ± 15.7 years (range, 4-71 years). Male/female ratio was 2.4. Forty-five patients (56.3%) were injured with alkaline substance, and 16 (20%) with acid substance. Mean follow-up time was 60.3 ± 30.6 months (range, 6-118.6 months). Limbal autograft, allograft, and cultivated limbal epithelial cell transplants were performed in 58 (72.5%), 12 (15%), and 10 (12.5%) eyes, respectively. Intervals between injury and surgery in limbal autograft, limbal allograft, and cultivated limbal epithelial cell transplants were 43.3 ± 94.1 months (range, 0.5-592 months), 14.5 ± 10.6 months (range, 2.4-32.5 months), and 122.8 ± 158.9 months (range, 21.1-504 months),respectively (P = .02); and surgical success rates in each group were 65.5%, 41.7%, and 90%, respectively (P = .03). Overall surgical success rate was 65%.

CONCLUSIONS

Accurate determination of the limbal stem cell deficiency stage is crucial for proper evaluation of surgical success. Surgery type and interval between injury and surgery were the most important factors associated with higher surgical success rates. Despite the limited number of patients in the subgroups, the results were remarkable to emphasize the significance of a novel limbal stem cell deficiency scoring system.

The role of eye banking with cell-based therapies

PURPOSE OF REVIEW

Cell-based therapies are an exciting new frontier in managing corneal diseases. The introduction of these novel therapies may provide new alternatives to corneal transplantation and decrease the dependence on donor corneal tissue. These changes have the potential to significantly impact eye banking in the future.

RECENT FINDINGS

The current article reviews current research involving cell-based therapy for treating corneal disorders, including cultivated limbal stem cell transplantation, limbal mesenchymal stem cells for stromal regeneration, and the use of human-cultivated endothelial cells. We will look at barriers to the development and implementation of these therapies.

SUMMARY

As corneal surgery expands to include cell-based therapies; eye banks will need to redefine their role to support the everchanging landscape of corneal surgery and the decreased demand for corneal donor tissue.

Advancements in Ocular Regenerative Therapies

The use of stem cells (SCs) has emerged as a promising avenue in ophthalmology, offering potential therapeutic solutions for various vision impairments and degenerative eye diseases. SCs possess the unique ability to self-renew and differentiate into specialised cell types, making them valuable tools for repairing damaged tissues and restoring visual function. Stem cell-based therapies hold significant potential for addressing conditions such as age-related macular degeneration (AMD), retinitis pigmentosa (RP), corneal disorders, and optic nerve damage. Therefore, researchers have explored different sources of stem cells, including embryonic stem cells (ESC), induced pluripotent stem cells (iPSCs), and adult stem cells, for ocular tissue regeneration. Preclinical studies and early-phase clinical trials have demonstrated promising outcomes, with some patients experiencing improved vision following stem cell-based interventions. However, several challenges remain, including optimising the differentiation protocols, ensuring transplanted cells' safety and long-term viability, and developing effective delivery methods. The field of stem cell research in ophthalmology witnesses a constant influx of new reports and discoveries. To effectively navigate these tons of information, it becomes crucial to summarise and systematise these findings periodically. In light of recent discoveries, this paper demonstrates the potential applications of stem cells in ophthalmology, focusing on their use in various eye tissues, including the cornea, retina, conjunctiva, iris, trabecular meshwork, lens, ciliary body, sclera, and orbital fat.

Future regenerative therapies for corneal disease

PURPOSE OF REVIEW

To highlight the progress and future direction of stem-cell based regenerative therapies for the treatment of corneal disease.

RECENT FINDINGS

Corneal stem cell-based therapies, such as limbal stem cell transplantation, corneal stromal stem cell transplantation, endothelial stem cell transplantation, and stem cell-derived extracellular vesicles have demonstrated promising results in the laboratory. Although most are still in preclinical development or early phase clinical trials, these stem cell-based therapies hold potential to facilitate tissue regeneration, restore native function, and inhibit pathologic disease processes such as fibrosis, inflammation, and neovascularization.

SUMMARY

Stem cell-based therapy offers a promising therapeutic option that can circumvent several of the challenges and limitations of traditional surgical treatment. This concise review summarizes the progress in stem-cell based therapies for corneal diseases along with their history, underlying mechanisms, limitations, and future areas for development.

Derivation of Limbal Stem Cells from Human Adult Mesenchymal Stem Cells for the Treatment of Limbal Stem Cell Deficiency

Approximately 10 million individuals have blindness due to limbal stem cell (LSCs) deficiency, one of the most challenging problems in ophthalmology. To replenish the LSC pool, an autologous extraocular cell source is appropriate, thereby avoiding the risk of immune rejection, the need for immunosuppression and the risk of damaging the contralateral eye. In recent years, adipose-derived mesenchymal stem cells (ADSCs) have been a key element in ocular regenerative medicine. In this study, we developed a protocol for deriving human LSCs from ADSCs compatible with the standard carrier human amniotic membrane, helping provide a stem cell pool capable of maintaining proper corneal epithelial homeostasis. The best protocol included an ectodermal induction step by culturing ADSCs with media containing fetal bovine serum, transforming growth factor-β inhibitor SB-505124, Wnt inhibitor IWP-2 and FGF2 for 7 days, followed by an LSC induction step of culture in modified supplemental hormonal epithelial medium supplemented with pigment epithelium-derived factor and keratinocyte growth factor for 10 additional days. The optimal differentiation efficiency was achieved when cells were cultured in this manner over vitronectin coating, resulting in up to 50% double-positive αp63/BMI-1 cells. The results of this project will benefit patients with LSC deficiency, aiding the restoration of vision.

Corneal stem cells niche and homeostasis impacts in regenerative medicine; concise review

The limbal stem cells niche (LSCN) is an optimal microenvironment that provides the limbal epithelial stem cells (LESCs) and strictly regulates their proliferation and differentiation. Disturbing the LSCN homeostasis can lead to limbal stem cell dysfunction (LSCD) and subsequent ocular surface aberrations, such as corneal stromal inflammation, persistent epithelial defects, corneal neovascularisation, lymphangiogenesis, corneal opacification, and conjunctivalization. As ocular surface disorders are considered the second main cause of blindness, it becomes crucial to explore different therapeutic strategies for restoring the functions of the LSCN. A major limitation of corneal transplantation is the current shortage of donor tissue to meet the requirements worldwide. In this context, it becomes mandatory to find an alternative regenerative medicine, such as using cultured limbal epithelial/stromal stem cells, inducing the production of corneal like cells by using other sources of stem cells, and using tissue engineering methods aiming to produce the three-dimensional (3D) printed cornea. Limbal epithelial stem cells have been considered the magic potion for eye treatment. Epithelial and stromal stem cells in the limbal niche hold the responsibility of replenishing the corneal epithelium. These stem cells are being used for transplantation to maintain corneal epithelial integrity and ultimately sustain optimal vision. In this review, we summarised the characteristics of the LSCN and their current and future roles in restoring corneal homeostasis in eyes with LSCD.

Outcome of keratolimbal allograft transplantation with deep anterior lamellar keratoplasty for bilateral limbal stem cell deficiency

OBJECTIVES

To evaluate and compare the outcome of keratolimbal allograft (KLAL) transplantation with or without deep anterior lamellar keratoplasty (DALK) for bilateral severe limbal stem cell deficiency (LSCD).

METHODS

This retrospective review included 49 eyes of 46 patients who underwent KLAL transplantation at the Department of Ophthalmology of Chinese PLA general hospital, 2009-2020, for bilateral severe LSCD were examined for corneal clarity and corneal scarring to determine whether to combine DALK with KLAL transplantation. Preoperative information, surgical decision tree, surgical procedures, and postoperative data were collected for each eye.

RESULTS

All patients had preoperative severe or total LSCD. Twenty-four eyes underwent KLAL transplantation only, 25 KLAL transplantation plus DALK. The mean follow-up was 46.80 ± 31.22 months (18-158 months). Overall KLAL survival (with or without DALK) was 71.43% at the final follow-up (KLAL-only 66.67%, KLAL-DALK 76%). Kaplan-Meier survival analysis showed that the 3-year survival probability of all grafts was 70.53 ± 10.89% (KLAL-only 64.86 ± 10.11%, KLAL-DALK 75.79 ± 8.62%). The proportion of BCVA ≥ 20/200 eyes among all KLAL transplantations increased from 11 eyes (22.45%) preoperatively to 25 eyes (51.02%) after 1 year and 24 eyes (48.98%) at the last follow-up (P = 0.01). The proportion of BCVA ≥ 20/200 eyes in the KLAL-DALK group increased significantly (P = 0.04), from 16.0% at baseline to 48.0% after 1 year to 44.0% at the last follow-up. Seventeen eyes (34.69%) had postoperative complications.

CONCLUSION

KLAL-DALK is an effective option to restore a stable ocular surface and visual acuity rapidly in patients with bilateral, late-stage, severe LSCD.

[Regenerative medicine for the corneal epithelium : Cell therapy from bench to bedside]

In the case of thermal or caustic burns of the ocular surface, loss of limbal epithelial stem cells leads to compromised self-renewal of the corneal epithelium. This results in permanent loss of vision. In these situations, transplantation of cultured limbal epithelial cells on an amniotic membrane or fibrin gel as substrate (Holoclar®) can help to regenerate the corneal surface. The required cells are obtained from the healthy partner eye, if available. Adult stem cells from other parts of the body potentially serve as alternative cell sources: hair follicles, oral mucosa, mesenchymal stromal cells, or induced pluripotent stem cells (originally, e.g., skin fibroblasts). The reprogramming of such cells can be achieved with the help of transcription factors. In addition, work is being done on biosynthetic or synthetic matrices, which not only serve as substrate material for the transplantation but also support the functional properties of these cells (self-renewal, corneal epithelial-typical phenotype).

Influence of the Postmortem/Storage Time of Human Corneas on the Properties of Cultured Limbal Epithelial Cells

Besides being a powerful model to study the mechanisms of corneal wound healing, tissue-engineered human corneas (hTECs) are sparking interest as suitable substitutes for grafting purposes. To ensure the histological and physiological integrity of hTECs, the primary cultures generated from human cornea (identified as human limbal epithelial cells (hLECs) that are used to produce them must be of the highest possible quality. The goal of the present study consisted in evaluating the impact of the postmortem/storage time (PM/ST) on their properties in culture. hLECs were isolated from the entire cornea comprising the limbus and central cornea. When grown as monolayers, short PM/ST hLECs displayed increased daily doublings and generated more colonies per seeded cells than long PM/ST hLECs. Moreover, hLECs with a short PM/ST exhibited a markedly faster wound closure kinetic both in scratch wound assays and hTECs. Collectively, these results suggest that short PM/ST hLECs have a greater number of highly proliferative stem cells, exhibit a faster and more efficient wound healing response in vitro, and produce hTECs of a higher quality, making them the best candidates to produce biomaterial substitutes for clinical studies.

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.

Signaling Pathways Impact on Induction of Corneal Epithelial-like Cells Derived from Human Wharton’s Jelly Mesenchymal Stem Cells

Corneal epithelium, the outmost layer of the cornea, comprises corneal epithelial cells (CECs) that are continuously renewed by limbal epithelial stem cells (LESCs). Loss or dysfunction of LESCs causes limbal stem cell deficiency (LSCD) which results in corneal epithelial integrity loss and visual impairment. To regenerate the ocular surface, transplantation of stem cell-derived CECs is necessary. Human Wharton’s jelly derived mesenchymal stem cells (WJ-MSCs) are a good candidate for cellular therapies in allogeneic transplantation. This study aimed to test the effects of treatments on three signaling pathways involved in CEC differentiation as well as examine the optimal protocol for inducing corneal epithelial differentiation of human WJ-MSCs. All-trans retinoic acid (RA, 5 or 10 µM) inhibited the Wnt signaling pathway via suppressing the translocation of β-catenin from the cytoplasm into the nucleus. SB505124 downregulated the TGF-β signaling pathway via reducing phosphorylation of Smad2. BMP4 did not increase phosphorylation of Smad1/5/8 that is involved in BMP signaling. The combination of RA, SB505124, BMP4, and EGF for the first 3 days of differentiation followed by supplementing hormonal epidermal medium for an additional 6 days could generate corneal epithelial-like cells that expressed a CEC specific marker CK12. This study reveals that WJ-MSCs have the potential to transdifferentiate into CECs which would be beneficial for further applications in LSCD treatment therapy.

Substance P/neurokinin-1 receptor pathway blockade ameliorates limbal stem cell deficiency by modulating mTOR pathway and preventing cell senescence

Severe ocular surface diseases can lead to limbal stem cell deficiency (LSCD), which is accompanied by defective healing. We aimed to evaluate the role of the substance P (SP)/neurokinin-1 receptor (NK1R) pathway in corneal epithelium wound healing in a pre-clinical model of LSCD. SP ablation or NK1R blockade significantly increased epithelial wound healing (p < 0.001) and corneal transparency (p < 0.001), compared with wild type (WT). In addition, a reduced number of infiltrating goblet and conjunctival cells (p < 0.05) and increased number of epithelial stem cells (p < 0.01), which also expressed NK1R, was observed. The mammalian target of rapamycin (mTOR) pathway was significantly inhibited (p < 0.05) and expression of γH2AX was significantly reduced (p < 0.05) after SP ablation. These results suggest that excessive expression of SP is associated with LSCD and results in accelerated senescence and exhaustion of residual stem cells. Topical treatment with NK1R antagonist ameliorates clinical signs associated with LSCD and could be used as an adjuvant treatment in LSCD.

Evaluating the clinical translational relevance of animal models for limbal stem cell deficiency: A systematic review

PURPOSE

Animal models are pivotal for elucidating pathophysiological mechanisms and evaluating novel therapies. This systematic review identified studies that developed or adapted animal models of limbal stem cell deficiency (LSCD), assessed their reporting quality, summarized their key characteristics, and established their clinical translational relevance to human disease.

METHODS

The protocol was prospectively registered (PROSPERO CRD42020203937). Searches were conducted in PubMed, Ovid EMBASE and Web of Science in August 2020. Two authors screened citations, extracted data, assessed the reporting quality of eligible studies using the ARRIVE guidelines, and judged the clinical translational relevance of each model using a custom matrix.

RESULTS

105 studies were included. Rabbits were the most common animal species. Overall, 97% of studies recapitulated LSCD to a clinical etiology, however 62% did not provide sufficient methodological detail to enable independent reproduction of the model. Adverse events and/or exclusion of animals were infrequently (20%) reported. Approximately one-quarter of studies did not produce the intended severity of LSCD; 34% provided insufficient information to assess the fidelity of disease induction. Adjunctive diagnostic confirmation of LSCD induction was performed in 13% of studies.

CONCLUSIONS

This is the first systematic review to assess the reporting quality and clinical translational relevance of animal models of LSCD. Models of LSCD have evolved over time, resulting in variable reporting of the characteristics of animals, experimental procedures and adverse events. In most studies, validation of LSCD was made using clinical tests; newer adjunctive techniques would enhance diagnostic validation. As most studies sought to evaluate novel therapies for LSCD, animal models should ideally recapitulate all features of the condition that develop in patients.

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 Epithelial Stem Cells-Physiology, Pathophysiology and Therapeutic Options

In the human cornea, regeneration of the epithelium is regulated by the stem cell reservoir of the limbus, which is the marginal region of the cornea representing the anatomical and functional border between the corneal and conjunctival epithelium. In support of this concept, extensive limbal damage, e.g., by chemical or thermal injury, inflammation, or surgery, may induce limbal stem cell deficiency (LSCD) leading to vascularization and opacification of the cornea and eventually vision loss. These acquired forms of limbal stem cell deficiency may occur uni- or bilaterally, which is important for the choice of treatment. Moreover, a variety of inherited diseases, such as congenital aniridia or dyskeratosis congenita, are characterized by LSCD typically occurring bilaterally. Several techniques of autologous and allogenic stem cell transplantation have been established. The limbus can be restored by transplantation of whole limbal grafts, small limbal biopsies or by ex vivo-expanded limbal cells. In this review, the physiology of the corneal epithelium, the pathophysiology of LSCD, and the therapeutic options will be presented.

Characterisation of corneas following different time and storage methods for their use as a source of stem-like limbal epithelial cells

The transplantation of expansions of limbal epithelial stem cells (LESC) remains one of the most efficient therapies for the treatment of limbal stem cell deficiency (LSCD) to date. However, the available donor corneas are scarce, and the corneas conserved for long time, under hypothermic conditions (after 7 days) or in culture (more than 28 days), are usually discarded due to poor viability of the endothelial cells. To establish an objective criterion for the utilisation or discarding of corneas as a source of LESC, we characterized, by immunohistochemistry analysis, donor corneas conserved in different conditions and for different periods of time. We also studied the potency of LESCs isolated from these corneas and maintained in culture up to 3 cell passages. We hoped that the study of markers of LESCs present in both the corneoscleral histological sections and the cell cultures would show the adequacy of the methods used for cell isolation and how fit the LESC enrichment of the obtained cell populations to be expanded was. Thus, the expressions of markers of the cells residing in the human limbal and corneal epithelium (cytokeratin CK15 and CK12, vimentin, Collagen VII, p63α, ABCG2, Ki67, Integrin β4, ZO1, and melan A) were analysed in sections of corneoscleral tissues conserved in hypothermic conditions for 2-9 days with post-mortem time (pmt) < 8 h or for 1 day with pmt > 16 h, and in sclerocorneal rims maintained in an organ culture medium for 29 days. Cell populations isolated from donor corneoscleral tissues were also assessed based on these markers to verify the adequacy of isolation methods and the potential of expanding LESCs from these tissues. Positivity for several putative stem cell markers such as CK15 and p63α was detected in all corneoscleral tissues, although a decrease was recorded in the ones conserved for longer times. The barrier function and the ability to adhere to the extracellular matrix were maintained in all the analysed tissues. In limbal epithelial cell cultures, a simultaneous decrease in the melan A melanocyte marker and the putative stem cell markers was detected, suggesting a close relationship between the melanocytes and the limbal stem cells of the niche. Holoclones stained with putative stem cell markers were obtained from long-term, hypothermic, stored sclerocorneal rims. The results showed that the remaining sclerocorneal rims after corneal transplantation, which were conserved under hypothermic conditions for up to 7 days and would have been discarded at a first glance, still maintained their potential as a source of LESC cultures.

Current perspectives of limbal-derived stem cells and its application in ocular surface regeneration and limbal stem cell transplantation

Limbal stem cells are involved in replenishing and maintaining the epithelium of the cornea. Damage to the limbus due to chemical/physical injury, infections, or genetic disorders leads to limbal stem cell deficiency (LSCD) with partial or total vision loss. Presently, LSCD is treated by transplanting limbal stem cells from the healthy eye of the recipient, living-related, or cadaveric donors. This review discusses limbal-derived stem cells, the importance of extracellular matrix in stem cell niche maintenance, the historical perspective of treating LSCD, including related advantages and limitations, and our experience of limbal stem cell transplantation over the decades.

Efficacy and outcome of simple limbal epithelial transplantation for limbal stem cell deficiency verified by epithelial phenotypes integrated with clinical evaluation

PURPOSE

To evaluate the efficacy and outcome of simple limbal epithelial transplantation (SLET) for limbal stem cell deficiency (LSCD) using epithelial phenotype detection integrated with clinical manifestation.

METHODS

This prospective multicenter study included patients with LSCD who underwent autologous SLET (autoSLET) and living-related allogenic SLET (Lr-alloSLET). All patients were assessed by slit-lamp biomicroscopy, in vivo confocal microscopy (IVCM), and impression cytology with immunofluorescence staining (ICIF) before and after surgery. The criteria for success were the presence of a clinically non-conjunctivalized cornea and corneal epithelium detected by IVCM or ICIF. Otherwise, the case would be considered a failure. Visual improvement and risk factors for SLET failure were analyzed.

RESULTS

A total of 28 eyes of 26 patients (11 autoSLET and 17 Lr-alloSLET) were included. The median age was 53 years (range, 35-63), and the follow-up time was 29.5 months (range, 17.5-39.8). The overall survival rate was 89.3% at 2 years and 75.6% at 3 years with no difference between autoSLET and Lr-alloSLET (p = 0.24). Seven eyes subsequently underwent penetrating keratoplasty. Immunohistochemistry analysis showed that all corneal buttons had corneal epithelium and limbal stem cell markers. Visual improvement was achieved in both SLET groups (p < 0.001). Failed SLET developed between 5 and 32 months postoperatively. However, absolute risk factors for SLET failure were unidentified.

CONCLUSION

The efficacy of autoSLET and Lr-alloSLET for LSCD was excellent. Limbal explants can regenerate and restore the corneal surface while maintaining the characteristics of limbal stem cells as shown by epithelial phenotype detection and immunohistochemistry integrated with clinical evaluation.

Priming human adipose-derived mesenchymal stem cells for corneal surface regeneration

Limbal stem cells (LSC) maintain the transparency of the corneal epithelium. Chemical burns lead the loss of LSC inducing an up-regulation of pro-inflammatory and pro-angiogenic factors, triggering corneal neovascularization and blindness. Adipose tissue-derived mesenchymal stem cells (AT-MSC) have shown promise in animal models to treat LSC deficiency (LSCD), but there are not studies showing their efficacy when primed with different media before transplantation. We cultured AT-MSC with standard medium and media used to culture LSC for clinical application. We demonstrated that different media changed the AT-MSC paracrine secretion showing different paracrine effector functions in an in vivo model of chemical burn and in response to a novel in vitro model of corneal inflammation by alkali induction. Treatment of LSCD with AT-MSC changed the angiogenic and inflammatory cytokine profile of mice corneas. AT-MSC cultured with the medium that improved their cytokine secretion, enhanced the anti-angiogenic and anti-inflammatory profile of the treated corneas. Those corneas also presented better outcome in terms of corneal transparency, neovascularization and histologic reconstruction. Priming human AT-MSC with LSC specific medium can potentiate their ability to improve corneal wound healing, decrease neovascularization and inflammation modulating paracrine effector functions in an in vivo optimized rat model of LSCD.

A single cell atlas of human cornea that defines its development, limbal progenitor cells and their interactions with the immune cells

Purpose

Single cell (sc) analyses of key embryonic, fetal and adult stages were performed to generate a comprehensive single cell atlas of all the corneal and adjacent conjunctival cell types from development to adulthood.

Methods

Four human adult and seventeen embryonic and fetal corneas from 10 to 21 post conception week (PCW) specimens were dissociated to single cells and subjected to scRNA- and/or ATAC-Seq using the 10x Genomics platform. These were embedded using Uniform Manifold Approximation and Projection (UMAP) and clustered using Seurat graph-based clustering. Cluster identification was performed based on marker gene expression, bioinformatic data mining and immunofluorescence (IF) analysis. RNA interference, IF, colony forming efficiency and clonal assays were performed on cultured limbal epithelial cells (LECs).

Results

scRNA-Seq analysis of 21,343 cells from four adult human corneas and adjacent conjunctivas revealed the presence of 21 cell clusters, representing the progenitor and differentiated cells in all layers of cornea and conjunctiva as well as immune cells, melanocytes, fibroblasts, and blood/lymphatic vessels. A small cell cluster with high expression of limbal progenitor cell (LPC) markers was identified and shown via pseudotime analysis to give rise to five other cell types representing all the subtypes of differentiated limbal and corneal epithelial cells. A novel putative LPCs surface marker, GPHA2, expressed on the surface of 0.41% ± 0.21 of the cultured LECs, was identified, based on predominant expression in the limbal crypts of adult and developing cornea and RNAi validation in cultured LECs. Combining scRNA- and ATAC-Seq analyses, we identified multiple upstream regulators for LPCs and demonstrated a close interaction between the immune cells and limbal progenitor cells. RNA-Seq analysis indicated the loss of GPHA2 expression and acquisition of proliferative limbal basal epithelial cell markers during ex vivo LEC expansion, independently of the culture method used. Extending the single cell analyses to keratoconus, we were able to reveal activation of collagenase in the corneal stroma and a reduced pool of limbal suprabasal cells as two key changes underlying the disease phenotype. Single cell RNA-Seq of 89,897 cells obtained from embryonic and fetal cornea indicated that during development, the conjunctival epithelium is the first to be specified from the ocular surface epithelium, followed by the corneal epithelium and the establishment of LPCs, which predate the formation of limbal niche by a few weeks.

Conclusions

Our scRNA-and ATAC-Seq data of developing and adult cornea in steady state and disease conditions provide a unique resource for defining genes/pathways that can lead to improvement in ex vivo LPCs expansion, stem cell differentiation methods and better understanding and treatment of ocular surface disorders.

Understanding cornea epithelial stem cells and stem cell deficiency: Lessons learned using vertebrate model systems

Animal models have contributed greatly to our understanding of human diseases. Here, we focus on cornea epithelial stem cell (CESC) deficiency (commonly called limbal stem cell deficiency, LSCD). Corneal development, homeostasis and wound healing are supported by specific stem cells, that include the CESCs. Damage to or loss of these cells results in blindness and other debilitating ocular conditions. Here we describe the contributions from several vertebrate models toward understanding CESCs and LSCD treatments. These include both mammalian models, as well as two aquatic models, Zebrafish and the amphibian, Xenopus. Pioneering developments have been made using stem cell transplants to restore normal vision in patients with LSCD, but questions still remain about the basic biology of CESCs, including their precise cell lineages and behavior in the cornea. We describe various cell lineage tracing studies to follow their patterns of division, and the fates of their progeny during development, homeostasis, and wound healing. In addition, we present some preliminary results using the Xenopus model system. Ultimately, a more thorough understanding of these cornea cells will advance our knowledge of stem cell biology and lead to better cornea disease therapeutics.

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.

Subconjunctival injection of mesenchymal stem cells for corneal failure due to limbal stem cell deficiency: state of the art

Mesenchymal stem cells (MSCs) have unique and beneficial properties and are currently used to treat a broad variety of diseases. These properties include the potential for differentiation into other cell types, secretion of different trophic factors that promote a regenerative microenvironment, anti-inflammatory actions, selective migration to damaged tissues, and non-immunogenicity. MSCs are effective for the treatment of ocular surface diseases such as dry eye, corneal burns, and limbal stem cell deficiency (LSCD), both in experimental models and in humans. LSCD is a pathological condition in which damage occurs to the limbal epithelial stem cells, or their niche, that are responsible for the continuous regeneration of the corneal epithelium. If LSCD is extensive and/or severe, it usually causes corneal epithelial defects, ulceration, and conjunctival overgrowth of the cornea. These changes can result in neovascularization and corneal opacity, severe inflammation, pain, and visual loss. The effectiveness of MSCs to reduce corneal opacity, neovascularization, and inflammation has been widely studied in different experimental models of LSCD and in some clinical trials; however, the methodological disparity used in the different studies makes it hard to compare outcomes among them. In this regard, the MSC route of administration used to treat LSCD and other ocular surface diseases is an important factor. It should be efficient, minimally invasive, and safe. So far, intravenous and intraperitoneal injections, topical administration, and MSC transplantation using carrier substrata like amniotic membrane (AM), fibrin, or synthetic biopolymers have been the most commonly used administration routes in experimental models. However, systemic administration carries the risk of potential side effects and transplantation requires surgical procedures that could complicate the process. Alternatively, subconjunctival injection is a minimally invasive and straightforward technique frequently used in ophthalmology. It enables performance of local treatments using high cell doses. In this review, we provide an overview of the current status of MSC administration by subconjunctival injection, analyzing the convenience, safety, and efficacy for treatment of corneal failure due to LSCD in different experimental models. We also provide a summary of the clinical trials that have been completed, are in progress, or being planned.

A Review on Modifications of Amniotic Membrane for Biomedical Applications

The amniotic membrane (AM) is the innermost layer of the fetal placenta, which surrounds and protects the fetus. Its unique structure, in addition to its physical and biological properties, makes it a useful substance in many applications related to regenerative medicine. The use of this fantastic substance with a century-old history has produced remarkable results in vivo, in vitro, and even in clinical studies. While the intact or preserved AM is widely used for these purposes, the addition of further modifications to AM can be considered as a relatively new subject in its applications. These modifications are applied to improve AM properties, ease of handling, and durability. Here, we will discuss the cases in which AM has undergone additional modifications besides the required processes for sterilization and preservation. In this article, we have categorized these modifications and discussed their applications and results.

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.

Recent Advances in Stem Cell Therapy for Limbal Stem Cell Deficiency: A Narrative Review

Destruction of the limbus and depletion of limbal stem cells (LSCs), the adult progenitors of the corneal epithelium, leads to limbal stem cell deficiency (LSCD). LSCD is a rare, progressive ocular surface disorder which results in conjunctivalisation and neovascularisation of the corneal surface. Many strategies have been used in the treatment of LSCD, the common goal of which is to regenerate a self-renewing, transparent, and uniform epithelium on the corneal surface. The development of these techniques has frequently resulted from collaboration between stem cell translational scientists and ophthalmologists. Direct transplantation of autologous or allogeneic limbal tissue from a healthy donor eye is regarded by many as the technique of choice. Expansion of harvested LSCs in vitro allows smaller biopsies to be taken from the donor eye and is considered safer and more acceptable to patients. This technique may be utilised in unilateral cases (autologous) or bilateral cases (living related donor). Recently developed, simple limbal epithelial transplant (SLET) can be performed with equally small biopsies but does not require in vitro cell culture facilities. In the case of bilateral LSCD, where autologous limbal tissue is not available, autologous oral mucosa epithelium can be expanded in vitro and transplanted to the diseased eye. Data on long-term outcomes (over 5 years of follow-up) for many of these procedures is needed, and it remains unclear how they produce a self-renewing epithelium without recreating the vital stem cell niche. Bioengineering techniques offer the ability to re-create the physical characteristics of the stem cell niche, while induced pluripotent stem cells offer an unlimited supply of autologous LSCs. In vivo confocal microscopy and anterior segment OCT will complement impression cytology in the diagnosis, staging, and follow-up of LSCD. In this review we analyse recent advances in the pathology, diagnosis, and treatment of LSCD.

Standard Gamble to Derive Utility Health States for Limbal Stem Cell Deficiency

Purpose

To generate UK health-related quality-of-life (HRQoL) data for adult patients with moderate-to-severe limbal stem cell deficiency (LSCD), unilateral or bilateral, due to physical or chemical ocular burns to help inform economic evaluations of treatments.

Patients and Methods

EQ-5D-3L with vision bolt-on scores was prospectively measured for one of five clinical scenarios of LSCD described in vignettes in a demographically representative population of 520 UK adults. These were converted to health state utilities using three different UK value sets. A standard gamble (SG) was then undertaken using 12 SG scenarios to examine the component drivers of health utility for the treatment of LSCD.

Results

For the EQ-5D-3L scenarios, the mean disutility for LSCD with poor visual acuity, pain and disfigurement in both eyes compared to one eye was −0.084 (range=−0.156 to −0.045 across the value sets). The mean disutility of bilateral LSCD with pain, disfigurement, and poor visual acuity compared to unilateral LSCD with only poor visual acuity in one eye was −0.104 (range=−0.151 to −0.078). Similarly, where one eye was affected, pain and disfigurement in combination were associated with a greater mean disutility than improvements in visual acuity alone: −0.011 (range=−0.04 to 0.005). Mean SG utilities were within a narrow range (0.682–0.765). Where one eye was affected, the main driver was disfigurement: mean utility was 0.731 (0.709–0.753) compared to 0.682 (0.659–0.704) when disfigurement was removed compared to vision restored to normal. For bilateral LSCD, mean utilities were 0.693 (0.672–0.715) for normal vision and 0.75 (0.73–0.771) when disfigurement and pain were removed.

Conclusion

Improvements in pain and disfigurement appeared to be the main factors driving differences in health utilities associated with symptom profiles in LSCD, with improvements in visual acuity having lesser impact.

Expansion of Human Limbal Epithelial Stem/Progenitor Cells Using Different Human Sera: A Multivariate Statistical Analysis

Transplantation of human cultured limbal epithelial stem/progenitor cells (LESCs) has demonstrated to restore the integrity and functionality of the corneal surface in about 76% of patients with limbal stem cell deficiency. However, there are different protocols for the expansion of LESCs, and many of them use xenogeneic products, being a risk for the patients’ health. We compared the culture of limbal explants on the denuded amniotic membrane in the culture medium—supplemental hormone epithelial medium (SHEM)—supplemented with FBS or two differently produced human sera. Cell morphology, cell size, cell growth rate, and the expression level of differentiation and putative stem cell markers were examined. Several bioactive molecules were quantified in the human sera. In a novel approach, we performed a multivariate statistical analysis of data to investigate the culture factors, such as differently expressed molecules of human sera that specifically influence the cell phenotype. Our results showed that limbal cells cultured with human sera grew faster and contained similar amounts of small-sized cells, higher expression of the protein p63α, and lower of cytokeratin K12 than FBS cultures, thus, maintaining the stem/progenitor phenotype of LESCs. Furthermore, the multivariate analysis provided much data to better understand the obtaining of different cell phenotypes as a consequence of the use of different culture methodologies or different culture components.

The Surgical Outcomes of Limbal Allograft Transplantation in Eyes Having Limbal Stem Cell Deficiency

Purpose:

To report the limbal allograft transplantation and penetrating keratoplasty (PK) results in limbal stem cell deficiency (LSCD)-developed eyes because of chemical or thermal injury.

Methods:

Medical records of 18 eyes of 14 patients who had undergone keratolimbal allograft (KLAL) or living-related conjunctival limbal allograft (lr-CLAL) with or without PK and followed up at least 1 year postoperatively were evaluated retrospectively. The preoperative LSCD grade was noted in all patients. Rejection incidents, recurrence of LSCD, and corneal graft clarity along with a visual improvement during the follow-up were noted. The complications rate due to surgery or injury itself, for instance, glaucoma and cataract, were evaluated. The limbal allograft tissue survival analysis and corneal allograft survival analysis were done to reveal the differences in both the procedures. The existence of normal corneal epithelium and improvement in visual acuity were accepted as the surgical success criteria.

Results:

In the limbal allograft transplantation group, the survival rates of the allograft tissue were 65 ± 10.7% at 1 year and 36.6 ± 11.4% at 3 years in lr-CLAL and 66.7 ± 15.7% at 12 months and 53.3 ± 17.3% at 18 months in KLAL-transplanted eyes. The survival rate of corneal allograft at the 5^th postoperative year was lower in the simultaneous procedure compared to the staged procedure, but it was not statistically significant (25.7 ± 25.8% vs. 62.5 ± 17.1%, P = 0.75). The ambulatory vision was achieved in 10 eyes (56%) after a mean follow-up time of 93.8 ± 37.8 months. The visual acuity level has increased in 12 eyes (67%) in which the limbal allograft transplantation was applied. The ambulatory visual acuity level was achieved (≤1.0 logMar [20/200]) in 10 eyes (56%). In addition, two or more Snellen lines’ gain in the best corrected visual acuity was observed in 12 eyes of 18 (67%) at the last follow-up, and there was not any significant difference between the KLAL and lr-CLAL.

Conclusions:

Ocular surface integrity was longer in KLAL than in lr-CLAL transplantation, but it was not statistically significant. The staged procedure was more convenient than the simultaneous procedure in terms of corneal allograft clarity maintenance in limbal allograft-employed eyes.

Topical cell-free conditioned media harvested from adipose tissue-derived stem cells promote recovery from corneal epithelial defects caused by chemical burns

Corneal chemical burns can lead to blindness following serious complications. As most of these complications are caused by failure of reepithelization during the acute phase, treatment at this stage is critical. Although there have been some studies on corneal injury recovery using adipose tissue-derived stem cells (ADSCs), none has reported the effect of topical cell-free conditioned culture media (CM) derived from ADSCs on corneal epithelial regeneration. Here, the best conditions for CM were selected and used for in vitro and in vivo experiments. Corneal burn in rats was induced using 100% alcohol. The chosen CM was administered to corneal burn rats (CM-treated [CT] group) four times a day for three days and this group was compared with the normal control and corneal burn (CB) groups. Biomicroscopic fluorescence images and the actual physical corneas were taken over time and used for analysis. mRNA levels of hepatocyte growth factor and epidermal growth factor (EGF) were significantly increased, whereas those of vascular endothelial growth factor, interleukin (IL)-1β, IL-6, IL-10, and matrix metalloproteinase-9 were significantly decreased in the CT group compared with those in the CB group. The numbers of proliferating cell nuclear antigen- and zonular occludens-1-positive cells in the CT group were significantly higher than those in the CB group. The macrophage-infiltrating corneas in the CT group expressed significantly more of the M2 marker arginase than corneas in the CB group. Optimal CM (× 0.5 concentration) treatment significantly accelerated the migration of corneal epithelial cells and induced upregulation of the expression of IL-6, EGF, and C-X-C chemokine receptor type 4 mRNAs. Overall, in this study, topical administration of cell-free CM promoted regeneration of the corneal epithelium after induction of chemical burns.

Tissue engineered corneal epithelium derived from clinical-grade human embryonic stem cells

PURPOSE

To construct tissue engineered corneal epithelium from a clinical-grade human embryonic stem cells (hESCs) and investigate the dynamic gene profile and phenotypic transition in the process of differentiation.

METHODS

A stepwise protocol was applied to induce differentiation of clinical-grade hESCs Q-CTS-hESC-1 and construct tissue engineered corneal epithelium. Single cell RNA sequencing (scRNA-seq) analysis was performed to monitor gene expression and phenotypic changes at different differentiation stages. Immunostaining, real-time quantitative PCR and Western blot analysis were conducted to detect gene and protein expressions. After subcutaneous transplantation into nude mice to test the biosafety, the epithelial construct was transplanted in a rabbit corneal limbal stem cell deficiency (LSCD) model and followed up for eight weeks.

RESULTS

The hESCs were successfully induced into epithelial cells. scRNA-seq analysis revealed upregulation of ocular surface epithelial cell lineage related genes such as TP63, Pax6, KRT14, and activation of Wnt, Notch, Hippo, and Hedgehog signaling pathways during the differentiation process. Tissue engineered epithelial cell sheet derived from hESCs showed stratified structure and normal corneal epithelial phenotype with presence of clonogenic progenitor cells. Eight weeks after grafting the cell sheet onto the ocular surface of LSCD rabbit model, a full-thickness continuous corneal epithelium developed to fully cover the damaged areas with normal limbal and corneal epithelial phenotype.

CONCLUSION

The tissue engineered corneal epithelium generated from a clinical-grade hESCs may be feasible in the treatment of limbal stem cell deficiency.

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.

Oral Mucosa Tissue Equivalents for the Treatment of Limbal Stem Cell Deficiency

Cultured limbal and oral epithelial cells have been successfully used to treat patients with limbal stem cell deficiency (LSCD). The most common culture method for these cell therapies utilizes amniotic membrane as a cell support and/or murine 3T3s as feeder fibroblasts. The aim of this study is to refine the production of autologous oral mucosal cell therapy for the treatment of LSCD. Real architecture for 3D tissue (RAFT) is used as an alternative cell culture support. In addition, oral mucosal cells (epithelial and fibroblast) are used as autologous alternatives to donor human limbal epithelial cells (HLE) and murine 3T3s. The following tissue equivalents are produced and characterized: first, for patients with bilateral LSCD, an oral mucosa tissue equivalent consisting of human oral mucosal epithelial cells on RAFT supported by human oral mucosal fibroblasts (HOMF). Second, for patients with unilateral LSCD, HLE on RAFT supported by HOMF. For both tissue equivalent types, features of the cornea are observed including a multi-layered epithelium with small cells with a stem cell like phenotype in the basal layer and squamous cells in the top layers, and p63α and PAX6 expression. These tissue equivalents may therefore be useful in the treatment of LSCD.

Short-Term Results Analysis in the Allogenic Transplantation of Limbal Stem Cells Expanded on Amniotic Membrane in Patients with Bilateral Limbal Stem Cell Deficiency

Purpose: The objective of this study was to describe the short-term results of allogenic transplantation of limbal stem cells expanded on amniotic membrane for the ocular surface reconstruction. Methods: Prospective nonrandomized, nonmasked study in a single ophthalmological center. Ten patients with bilateral total limbal stem cell deficiency (LSCD) were included. Expression and presence of ABCB5 and Δp63α in amniotic membrane-cultured limbal epithelial stem cells were analyzed, in relationship with clinical changes after allogenic transplantation. An objective evaluation was performed to determine corneal transparency and superficial vascularization. Results: In a median follow-up time of 11.6 months, 7 patients (70%) were considered as failure compared with the preoperative status. ABCB5 and Δp63α are expressed in similar amount in the limbal epithelial cells expanded in vitro and transplanted in patients with bilateral LSCD. Conclusions: Transplantation of allogenic epithelial limbal cells expanded in amniotic membrane could be considered in patients with LSCD due to burns or congenital etiologies such as aniridia, but its benefit is limited for patients with immunologic diseases.

Optimization of Human Limbal Stem Cell Culture by Replating a Single Limbal Explant

Cultured limbal epithelial stem cell transplantation is a clinical procedure used to regenerate the corneal epithelium in patients with limbal stem cell deficiency. The protocols used to expand limbal epithelial cells in vitro need to be optimized, since the scarcity of human ocular tissue donors is limiting the potential use of this procedure. Here, we describe a method to consecutively expand a single human limbal explant. With this method it is possible to obtain up to three limbal epithelial primary cultures from the same explant, thus increasing the efficiency of the in vitro cell culture.

Expansion processes for cell-based therapies

Living cells are emerging as therapeutic entities for the treatment of patients affected with severe and chronic diseases where no conventional drug can provide a definitive cure. At the same time, the promise of cell-based therapies comes with several biological, regulatory, economic, logistical, safety and engineering challenges that need to be addressed before translating into clinical practice. Among the complex operations required for their manufacturing, cell expansion occupies a significant part of the entire process and largely determines the number, the phenotype and several other critical quality attributes of the final cell therapy products (CTPs). This review aims at characterizing the main culture systems and expansion processes used for CTP production, highlighting the need to implement scalable, cost-efficient technologies together with process optimization strategies to bridge the gap between basic scientific research and commercially available therapies.

Aniridia and Axenfeld-Rieger Syndrome: Clinical presentations, molecular genetics and current/emerging therapies

Aniridia and Axenfeld-Rieger Syndrome are related, human ocular disorders that are typically inherited in an autosomal dominant manner. Both result from incorrect development of the eye and have, as their most serious consequences, elevated risk to develop the blinding condition glaucoma. This review will focus on describing the clinical presentations of Aniridia and Axenfeld-Rieger Syndrome as well as the molecular genetics and current and emerging therapies used to treat patients.

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.

A proof-of-concept clinical trial using mesenchymal stem cells for the treatment of corneal epithelial stem cell deficiency

Ocular stem cell transplantation derived from either autologous or allogeneic donor corneoscleral junction is a functional cell therapy to manage extensive and/or severe limbal stem cell deficiencies that lead to corneal epithelial failure. Mesenchymal stem cells have been properly tested in animal models of this ophthalmic pathology, but never in human eyes despite their potential advantages. We conducted a 6- to 12-month proof-of-concept, randomized, and double-masked pilot trial to test whether allogeneic bone marrow-derived mesenchymal stem cell transplantation (MSCT], n = 17) was as safe and as equally efficient as allogeneic cultivated limbal epithelial transplantation (CLET), (n = 11) to improve corneal epithelial damage due to limbal stem cell deficiency. Primary endpoints demanded combination of symptoms, signs, and the objective improvement of the epithelial phenotype in central cornea by in vivo confocal microscopy. This proof-of-concept trial showed that MSCT was as safe and efficacious as CLET. Global success at 6-12 months was 72.7%-77.8% for CLET cases and 76.5%-85.7% for MSCT cases (not significant differences). Central corneal epithelial phenotype improved in 71.4% and 66.7% of MSCT and CLET cases, respectively at 12 months (P = 1.000). There were no adverse events related to cell products. This trial suggests first evidence that MSCT facilitated improvement of a diseased corneal epithelium due to lack of its stem cells as efficiently as CLET. Consequently, not only CLET but also MSCT deserves more preclinical investigational resources before the favorable results of this proof-of-concept trial could be transformed into the larger numbers of the multicenter trials that would provide stronger evidence. (ClinicalTrials.gov number, NCT01562002.).

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.

Allogeneic Ex Vivo Expanded Corneal Epithelial Stem Cell Transplantation: A Randomized Controlled Clinical Trial

Limbal stem cell deficiency (LSCD) is a disease resulting from the loss or dysfunction of epithelial stem cells, which seriously impairs sight. Autologous limbal stem cell transplantation is effective in unilateral or partial bilateral disease but not applicable in total bilateral disease. An allogeneic source of transplantable cells for use in total bilateral disease can be obtained from culture of donated cadaveric corneal tissue. We performed a controlled multicenter study to examine the feasibility, safety, and efficacy of allogeneic corneal epithelial stem cells in the treatment of bilateral LSCD. Patients were randomized to receive corneal epithelial stem cells cultured on amniotic membrane (AM): investigational medicinal product (IMP) or control AM only. Patients received systemic immunosuppression. Primary endpoints were safety and visual acuity, secondary endpoint was change in composite ocular surface score (OSS). Sixteen patients were treated and 13 patients completed all assessments. Safety was demonstrated and 9/13 patients had improved visual acuity scores at the end of the trial, with no significant differences between IMP and control groups. Patients in the IMP arm demonstrated significant, sustained improvement in OSS, whereas those in the control arm did not. Serum cytokine levels were measured during and after the period of immune suppression and we identified strongly elevated levels of CXCL8 in the serum of patients with aniridia, which persisted throughout the trial. This first randomized control trial of allogeneic corneal epithelial stem cells in severe bilateral LSCD demonstrates the feasibility and safety of this approach. stem cells translational medicine2019;8:323–331