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

Five- to Twelve-Year Outcomes of Autologous Simple Limbal Epithelial Transplantation: Long-Term Corneal Epithelial Imaging and Phenotypic Analysis

PURPOSE

To objectively assess the long-term corneal epithelial recovery after autologous simple limbal epithelial transplantation (SLET) for ocular chemical burn (OCB)-induced unilateral limbal stem cell deficiency (LSCD).

DESIGN

Prospective, fellow-eye controlled, cross-sectional imaging and diagnostic study.

SUBJECTS

The study included 47 patients, who were 5 to 12 years postautologous SLET done for OCB-induced unilateral LSCD.

METHODS

The donor and recipient eyes of all patients were assessed at a single follow-up visit with slit-lamp biomicroscopy (SLB), in vivo confocal microscopy (IVCM), impression cytology (IC), anterior segment optical coherence tomography (ASOCT), and Scheimpflug imaging (SI). The objective parameters that were assessed were corneal epithelial phenotype (CEP), thickness (CET), reflectivity (CER), and densitometry (CED). Median values with inter-quartile ranges were assessed for all parameters and analyzed using non-parametric tests.

MAIN OUTCOME MEASURES

The primary outcome measure was successful restoration of normal CEP on SLB, IVCM, and IC. Secondary outcome measures were comparison of CET and CER on ASOCT, and CED on SI between the eyes with successful and failed CEP restoration, and donor eyes.

RESULTS

The study analyzed 94 eyes of 47 patients, with a median follow-up of 5.75 years post-SLET. Successful restoration of CEP on SLB, IVCM, and IC was observed in 32 (68%) recipient eyes, while failure was seen in 15 (32%) eyes. The CEP was normal in all 47 (100%) donor eyes. The median CET was similar in healthy donor eyes, eyes with successful CEP restoration (55.9 microns, 50.3-59.2 vs. 57.8, 49.9-63.1; P = .47) and eyes with failure (57.7 microns, 50.9-66.2; P ≥ .59). Although, the median CER (100.72, 89.9-111.2 vs. 121.6, 109.7-139.8; P = .001) and CED (14.7, 13.4-17.1 vs. 26.5, 20.1-30.2; P = .02) values were significantly lower in eyes with successful CEP restoration as compared to eyes with failure, they were still significantly greater than corresponding values in the healthy donor eyes for CER (90.33, 84.9-96.9; P = .02), and CED (13.5, 11.4-15.1; P = .03), respectively.

CONCLUSIONS

Long-term 5-12 year successful restoration of the corneal epithelial phenotype was seen in two-thirds of eyes postautologous SLET. While corneal epithelial reflectivity, and densitometry were relatively better in eyes with successful outcomes, corneal epithelial thickness was similar in all eyes.

Can Stem Cell Therapy Revolutionize Ocular Disease Treatment? A Critical Review of Preclinical and Clinical Advances

Stem cell therapy in regenerative medicine has a scope for treating ocular diseases. Stem cell therapy aims to repair damaged tissue and restore vision. The present review focuses on the advancements in stem cell therapies for ocular disorders, their mechanism of action, and clinical applications while addressing some outstanding challenges. Stem cells that include embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and retinal progenitor cells have regenerative potential for ocular repair. They differentiate into specialized ocular cell types, conduct neuroprotection, and modulate immune responses. It is emphasized in preclinical and clinical studies that stem cell therapy can treat corneal disorders such as limbal stem cell deficiency, retinal diseases like dry age macular degeneration and retinitis pigmentosa, and diabetic retinopathy. Various studies suggested that stem cells have considerable scope in glaucoma treatment by supporting retinal ganglion cell survival and optic nerve regeneration. Advanced approaches such as gene editing, organoid generation, and artificial intelligence enhance these therapies. Effective delivery to target areas, engraftment, orientation, and long-term survival of transplanted cells need optimization. Issues such as immune rejection and tumorigenicity must be addressed. This approach is further hindered by regulatory issues and overly complicated approval processes and trials. Ethical issues related to sourcing embryonic stem cells and patient consent complicate the issue. The cost of manufacturing stem cells and their accessibility are other factors posing potential barriers to widespread application. These regulatory, ethical, and economic issues must be tackled if stem cell treatments are to be made safe, accessible, and effective. Future studies will include refining therapeutic protocols, scaling manufacturing processes, and overcoming socio-economic barriers, eventually improving clinical outcomes.

Limbal stem cell deficiency approaches and limbal niche restoration

Approaches to limbal stem cell deficiency remain challenging, especially in bilateral cases, where healthy limbal stem cells are not accessible. While living-related allogeneic and allogeneic limbal stem cell sources have been utilized, their dependence on immunosuppression and its associated side effects pose significant limitations. Mucosal and mesenchymal stem cells have shown potential for differentiation into limbal stem cells and promoting corneal healing, primarily when cultured on the amniotic membrane or fibrin. However, none can fully replicate the original limbus. Innovations in surgical techniques, such as simple oral mucosal transplantation and subconjunctival or intrastromal mesenchymal stem cell injections, are emerging approaches. For successful limbal regeneration, both appropriate cells and suitable scaffolds are essential. Recent studies on decellularized and acellularized limbus models have demonstrated the potential to provide a three-dimensional native structure for cell seeding, retention, and differentiation. Creating a thin, evenly decellularized scaffold is a critical step in ensuring proper corneo-limbal slope formation, facilitating cell migration to the ocular surface. Harvesting the limbus, decellularization, and cell seeding are the three main steps in limbal reconstruction. Recent studies focus on microkeratome-assisted limbal harvesting to create a thin, even, and 360-degree limbal graft. This technique helps form an attached corneo-limbal interface, facilitating limbal stem cell migration. In the second step, acellularization is performed to preserve the extracellular matrix as much as possible, maintaining hemostasis and supporting paracrine interactions. The final steps involve recellularization and transplantation onto the eye. We summarize various limbal decellularization methods, their outcomes, and their potential in limbal reconstruction. More clinical studies are needed to validate this phase of limbal deficiency treatment.

Midterm results after allogeneic simple limbal epithelial transplantation from deceased-donor eyes in patients with persistent corneal epithelial defects due to limbal stem cell deficiency

BACKGROUND

This study aims to characterize the clinical outcomes after allogeneic simple limbal epithelial transplantation (alloSLET) utilizing tissue from cadaveric donor eyes to address persistent corneal epithelial defects caused by limbal stem cell deficiency.

METHODS

We conducted a retrospective analysis of medical records from 20 patients, encompassing 24 eyes, who underwent alloSLET at least 2 years prior. The primary endpoint was the achievement of complete epithelialization of the corneal surface by corneal epithelium. Secondary endpoints included corrected distance visual acuity (CDVA) and postoperative adverse events.

RESULTS

The median postoperative follow-up period was 36 months (range, 24-74 months). At 1, 3 and 6 months post-surgery, 96% of eyes demonstrated epithelialized corneal surfaces, which declined to 71% at 12 months, to 54% at 24 and 36 months after surgery, and to 50% thereafter. There were no significant differences in graft survival between alloSLET performed alone versus in combination with penetrating keratoplasty. However, instances of graft failure were associated with postoperative elevated intraocular pressure (IOP) and a history of multiple amniotic membrane and corneal graft transplants.

CONCLUSIONS

AlloSLET emerges as a viable mid-term intervention for limbal stem cell deficiency-associated non-healing corneal epithelial defects in the absence of autologous limbal tissue. Our findings underscore the increased risk of graft failure in patients with elevated IOP and a background of multiple previous amniotic membrane and corneal graft procedures.

Unveiling the Molecular Mechanisms Underlying the Success of Simple Limbal Epithelial Transplantation (SLET)

Simple limbal epithelial transplantation (SLET) has emerged as an effective treatment option for limbal stem cell deficiency (LSCD). However, the precise molecular mechanisms underlying its success remain incompletely understood. This review delves into the proposed mechanisms involving the donor limbus, host microenvironment, and the amniotic membrane as a scaffold in SLET. The donor limbus contributes to SLET efficacy through various factors secreted by limbal epithelial stem cells, including hepatocyte growth factor (HGF), soluble Fms-like tyrosine kinase-1 (sFLT-1), and pigment epithelium-derived factor (PEDF), which support corneal healing and transparency. Additionally, the presence of melanocytes, immune cells, limbal fibroblasts, and adhesion molecules within the donor tissue helps preserve the integrity of the limbal niche. The host environment plays a critical role in supporting the transplanted stem cells, with mesenchymal stem cell-secreted factors promoting proliferation and differentiation. Although the amniotic membrane has traditionally been used as a scaffold, emerging evidence suggests that it may not always be necessary. Further studies are needed to validate this scaffold-free approach and to evaluate the vitality and functional contributions of individual components used in SLET. Understanding these complex interactions and molecular mechanisms sheds light on the importance of the donor tissue, host microenvironment, and scaffold in SLET, paving the way for the optimization of this technique for the effective treatment of LSCD.

Biology and medicine on ocular surface restoration: Advancements and limits of limbal stem cell deficiency treatments

Ocular vision can be hampered by corneal damages, sensibly reducing patients' quality of life and having important social and economic consequences. Ocular surface diseases, which often lead to corneal opacities with visual impairment are the most severe forms of the Limbal Stem Cell Deficiency (LSCD). The present review provides an updated perspective on the available treatments for LSCD, focusing on clinical and biological features, as well as critical points to monitor during clinical translation. Recently developed surgical treatments for LSCD are described, along with their benefits and limitations, with the aim of addressing the issue of correct patient selection. Autologous surgical approaches have been attempted, such as conjunctival limbal autograft (CLAU), simple limbal epithelial transplantation (SLET), and others. Allogeneic limbal stem cell transplantation represents an alternative but carries risk of rejection and requires immunosuppression. Other potential treatments are based on induced pluripotent stem cells (iPSCs), but they require further investigation. The development of advanced therapy medicinal products (ATMPs) such as cultivated limbal epithelial transplantation (CLET), or the use of other epithelia as cultivated oral mucosal epithelial cell transplantation (COMET), has opened additional therapeutic possibilities. Some common critical issues in clinical translation are described, such as patient selection, biopsy procurement, or the use of human/animal derived components, which require rigorous validation to ensure safety and efficacy. Personalized medicine is a promising field for ocular surface restoration, where long-term follow-up studies and standardized criteria are crucial to evaluate the efficacy of these treatments and their cost-effectiveness in providing high-value healthcare.

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.

Induction of human ESC-derived and adult primary multipotent limbal stem cells into retinal pigment epithelial cells and corneal stromal stem cells

Human embryonic stem cell (hESC)- and human induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (RPE) therapies are promising alternatives for the treatment of retinal degenerative diseases caused by RPE degeneration. The generation of autologous RPE cells from human adult donors, which has the advantage of avoiding immune rejection and teratoma formation, is an alternative cell resource to gain mechanistic insight into and test potential therapies for RPE degenerative diseases. Here, we found that limbal stem cells (LSCs) from hESCs and adult primary human limbus have the potential to produce RPE cells and corneal stromal stem cells (CSSCs). We showed that hESC-LSC-derived RPE cells (LSC-RPE) expressed RPE markers, had a phagocytic function, and synthesized tropical factors. Furthermore, during differentiation from LSCs to RPE cells, cells became pigmented, accompanied by a decrease in the level of LSC marker KRT15 and an increase in the level of RPE marker MITF. The Wnt signaling pathway plays a role in LSC-RPE fate transition, promotes MITF expression in the nucleus, and encourages RPE fate transition. In addition, we also showed that primary LSCs (pLSCs) from adult human limbus similar to hESC-LSC could generate RPE cells, which was supported by the co-expression of LSC and RPE cell markers (KRT15/OTX2, KRT15/MITF), suggesting the transition from pLSC to RPE cells, and typical polygonal morphology, melanization, RPE cell marker genes expression (TYR, RPE65), tight junction formation by ZO-1 expression, and the most crucial phagocytotic function. On the other hand, both hESC-LSCs and pLSCs also differentiated into CSSCs (LSC-CSSCs) that expressed stem cell markers (PAX6, NESTIN), presented MSC features, including surface marker expression and trilineage differentiation capability, like those in human CSSCs. Furthermore, the capability of pLSC-CSSC to differentiate into cells expressing keratocyte marker genes (ALDH3A1, PTGDS, PDK4) indicated the potential to induce keratocytes. These results suggest that the adult pLSC is an alternative cell resource, and its application provides a novel potential therapeutic avenue for preventing RPE dysfunction-related retinal degenerative diseases and corneal scarring.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clinical efficacy of a new surgical technique of oral mucosal epithelial transplantation for severe ocular surface disorders

BACKGROUND

Severe ocular surface disorders are one of the major blinding diseases, and a paucity of original tissue obscures successful reconstruction. We developed a new surgical technique of direct oral mucosal epithelial transplantation (OMET) to reconstruct severely damaged ocular surfaces in 2011. This study elaborates on the clinical efficacy of OMET.

METHODS

A retrospective review of patients with severe ocular surface disorders who underwent OMET from 2011 to 2021 at the Department of Ophthalmology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine was conducted. Patients who were followed up for at least 3 months postoperatively and had sufficient pre or postoperative records were included. Surgical efficacy was evaluated by comparing the best-corrected visual acuity (BCVA), corneal transparency, neovascularization grade, and symblepharon grade. Additionally, postoperative ocular surface impression cytology was used to study the morphology of the newborn epithelial cells.

RESULTS

Forty-eight patients (49 eyes; mean age: 42.55 ± 12.40 years, range:12-66 years) were enrolled in the study. The etiology included chemical burns (30 eyes), thermal burns (16 eyes), explosive injuries (1 eye), Stevens-Johnson syndrome (1 eye), and multiple pterygiums (1 eye). The mean follow-up period was 25.97 ± 22.99 months. Postoperatively, 29 eyes (59.18%) showed improved corneal transparency, 26 eyes (53.06%) had improved BCVA, 47 eyes (95.92%) had a stable epithelium until the final follow-up, 44 eyes (89.80%) had a reduced neovascularization grade. Of the 20 eyes with preoperative symblepharon, 15 (75%) were completely resolved, and five (25%) were partially resolved. Impression cytological studies showed no postoperative conjunctival invasion onto the corneal surface.

CONCLUSIONS

OMET is a safe and effective surgical technique for reconstruction in severe ocular surface disorder by maintaining a stable epithelium and reducing the neovascularization and symblepharon grade.

Genetic analysis of allogenic donor cells after successful allo-limbal epithelial transplantation in simple and cultivated limbal epithelial transplantation procedures

This non-comparative cohort study investigated long-term donor cell survival after allogenic simple/cultivated limbal epithelial transplantations (allo-SLET/allo-CLET, respectively) by genetic analysis. Transplanted corneal epithelial cells, which underwent impression cytology and/or corneal-button biopsy, were examined for personal identities of autosomal short-tandem repeats; the percentages of donor cells were calculated based on matching recipient or donor buccal-DNA references. Twelve patients were included; 4 underwent allo-CLET, 8 underwent allo-SLET. Eight patients (67%) had total limbal stem cell deficiency (LSCD). Genetic analysis was performed postoperatively (mean, 55.3 months). Donor cells were detected in 4 of 12 patients (25%), all of whom underwent allo-SLET; 1 patient had a donor genotype and 3 patients had a mixed donor/recipient genotype. The longest time of donor cell detection was 30 months. Seven patients (58%) used systemic immunosuppressives at the time of genetic analysis (mean use, 22.5 months). Allogenic donor cells survived in both procedures for the long term postoperatively, which encourages the long-term use of systemic immunosuppressives. Donor cells may not be the only factor in graft survival, in that most successful cases had a recipient profile. Their presence for a specific time may promote niches for the patients' own cells to repopulate, especially for partial LSCD.

A Review of the Diagnosis and Treatment of Limbal Stem Cell Deficiency

Limbal stem cell deficiency (LSCD) can cause significant corneal vascularization and scarring and often results in serious visual morbidity. An early and accurate diagnosis can help prevent the same with a timely and appropriate intervention. This review aims to provide an understanding of the different diagnostic tools and presents an algorithmic approach to the management based on a comprehensive clinical examination. Although the diagnosis of LSCD usually relies on the clinical findings, they can be subjective and non-specific. In such cases, using an investigative modality offers an objective method of confirming the diagnosis. Several diagnostic tools have been described in literature, each having its own advantages and limitations. Impression cytology and in vivo confocal microscopy (IVCM) aid in the diagnosis of LSCD by detecting the presence of goblet cells. With immunohistochemistry, impression cytology can help in confirming the corneal or conjunctival source of epithelium. Both IVCM and anterior segment optical coherence tomography can help supplement the diagnosis of LSCD by characterizing the corneal and limbal epithelial changes. Once the diagnosis is established, one of various surgical techniques can be adopted for the treatment of LSCD. These surgeries aim to provide a new source of corneal epithelial stem cells and help in restoring the stability of the ocular surface. The choice of procedure depends on several factors including the involvement of the ocular adnexa, presence of systemic co-morbidities, status of the fellow eye and the comfort level of the surgeon. In LSCD with wet ocular surfaces, autologous and allogeneic limbal stem cell transplantation is preferred in unilateral and bilateral cases, respectively. Another approach in bilateral LSCD with wet ocular surfaces is the use of an autologous stem cell source of a different epithelial lineage, like oral or nasal mucosa. In eyes with bilateral LSCD with significant adnexal issues, a keratoprosthesis is the only viable option. This review provides an overview on the diagnosis and treatment of LSCD, which will help the clinician choose the best option amongst all the therapeutic modalities currently available and gives a clinical perspective on customizing the treatment for each individual case.

Longitudinal Changes in Corneal Epithelial Thickness and Reflectivity following Simple Limbal Epithelial Transplantation: An Optical Coherence Tomography-Based Study

PURPOSE

To describe the changes in corneal epithelial thickness and reflectivity following simple limbal epithelial transplantation (SLET) using anterior segment optical coherence tomography (ASOCT).

METHODS

This was a prospective imaging study of 31 eyes of 29 patients who had undergone autologous or allogeneic SLET for limbal stem cell deficiency and had stable, avascular surfaces postoperatively. ASOCT scans of all four quadrants were taken preoperatively and at 1-week, 1-month, 3-month, 6-month, and 1-year postoperative time points in the eyes undergoing SLET. Baseline scans were also taken from the normal eye in unilateral cases. The following parameters were obtained from the scans: (i) epithelial thickness (ET), (ii) stromal thickness, (iii) total corneal thickness, (iv) epithelial reflectivity (ER), (v) stromal reflectivity, and (vi) epithelial/stromal (ES) reflectivity ratio.

RESULTS

Chemical injury (24 eyes, 77.4%) was the most common indication for surgery. There was a significant improvement in the ET (184.8 ± 117.1 vs 60.3 ± 10 µm, p < .0001) and ER (144.5 ± 26.4 vs 120.9 ± 28.9, p < .0001) within the initial postoperative period following SLET, which remained stable at the end of 1 year follow-up. There was no difference in the ET of the post-SLET and normal eyes after the 3-month timepoint and this normalization was maintained until the end of the first year. A significant normalization was also noted in the ES reflectivity ratio at the end of 1 year (2.1 ± 0.8 vs 1 ± 0.2, p < .001). A significant correlation was found between the final visual acuity and the total corneal thickness (r = 0.942, p = .005).

CONCLUSION

There is a significant improvement in the epithelial thickness and reflectivity of the cornea in eyes undergoing SLET. ASOCT provides a reliable objective measure of these changes and can be used to monitor the outcomes in these eyes postoperatively.