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

Wnt activation as a potential therapeutic approach to treat partial limbal stem cell deficiency

Limbal epithelial stem/progenitor cells (LSCs) are adult stem cells located at the limbus, tightly regulated by their niche involving numerous signaling pathways, such as Wnt. Wnt proteins are secreted morphogens that play critical roles in embryonic development, stem cell proliferation, self-renewal, tissue regeneration, and remodeling in adults. It has been shown that a small molecule Wnt mimic could improve LSCs expansion ex vivo. Damage to the LSCs and/or their niche can lead to limbal stem cell deficiency (LSCD), a condition that can cause corneal blindness and is difficult to treat. This study explored if repopulating residual LSCs in partial LSCD through Wnt activation could be a novel therapeutic approach. To mimic LSCD due to a chemical injury, single cultured LSCs were exposed to various concentrations of sodium hydroxide. A progressive loss of the LSCs phenotype was observed: the percentage of p63bright cells and cytokeratin (K)14+ cells decreased while the percentage of K12+ increased. Wnt activation was attained by treating the LSCs with lithium chloride (LiCl) and a small-molecule Wnt mimic, respectively. After 18 h of treatment, LSCs proliferation was increased, and the LSCs phenotype was recovered, while the untreated cells did not proliferate and lost their phenotype. The percentage of p63bright cells was significantly higher in the Wnt mimic-treated cells compared with untreated cells, while the percentage of K12+ cells was significantly lower. These findings suggest that local Wnt activation may rescue LSCs upon alkaline injury.

Outcomes of keratolimbal allograft from ABO compatible donors for severe bilateral limbal stem cell deficiency

PURPOSE

To report outcomes of keratolimbal allograft (KLAL) compatible for both human leukocyte (HLA) and/or blood type using oral prednisone, mycophenolate, and tacrolimus, with basiliximab if panel reactive antibodies (PRA) are present. Intravenous immunoglobulin (IVIG) was used post-operatively if donor-specific anti-HLA antibodies (DSA) were present.

METHODS

Retrospective interventional series of consecutive patients with KLAL for limbal stem cell deficiency (LSCD) from HLA and/or blood type compatible deceased donors with a minimum follow-up time of 12 months. Main outcome measures were ocular surface stability, visual acuity and systemic immunosuppression (SI) adverse events.

RESULTS

Eight eyes of eight patients with mean age of 48.6 ± 10.1 years (range 34-65 years) were included. Mean follow-up time was 37.3 ± 22.7 months (range 12-71 months) following KLAL; four (50%) had combined LR-CLAL surgery. The etiologies of LSCD were Stevens-Johnson Syndrome (n = 4/8), aniridia (n = 2/8), chemical injury (n = 1/8) and atopic eye disease (n = 1/8). All patients had PRA present and received basiliximab infusions. 5/8 patients received IVIG based on DSA identified pre-operatively. At last follow-up, 7 eyes (87.5%) had a stable ocular surface; 1 eye (12.5%) developed failure and had keratoprosthesis implantation. There was a significant improvement in visual acuity from 1.65 ± 0.48 to 0.68 ± 0.34 logMAR (p = 0.01). SI was tolerated well with minimal adverse events.

CONCLUSIONS

Preliminary outcomes of KLAL with ABO compatible tissue using the Cincinnati protocol, preoperative basiliximab (when PRA present) and post-operative IVIG (when DSA present) are encouraging. This protocol may allow for utilization of deceased donor tissue with results approximating those of living donor tissue transplanted for severe bilateral LSCD.

Human limbal epithelial stem cell regulation, bioengineering and function

The corneal epithelium is continuously renewed by limbal stem/progenitor cells (LSCs), a cell population harbored in a highly regulated niche located at the limbus. Dysfunction and/or loss of LSCs and their niche cause limbal stem cell deficiency (LSCD), a disease that is marked by invasion of conjunctival epithelium into the cornea and results in failure of epithelial wound healing. Corneal opacity, pain, loss of vision, and blindness are the consequences of LSCD. Successful treatment of LSCD depends on accurate diagnosis and staging of the disease and requires restoration of functional LSCs and their niche. This review highlights the major advances in the identification of potential LSC biomarkers and components of the LSC niche, understanding of LSC regulation, methods and regulatory standards in bioengineering of LSCs, and diagnosis and staging of LSCD. Overall, this review presents key points for researchers and clinicians alike to consider in deepening the understanding of LSC biology and improving LSCD therapies.

Limbal stem cell diseases

The function of limbal stem/progenitor cells (LSCs) is critical to maintain corneal epithelial homeostasis. Many external insults and intrinsic defects can be deleterious to LSCs and their niche microenvironment, resulting in limbal stem cell dysfunction or deficiency (LSCD). Ocular comorbidities, frequent in eyes with LSCD, can exacerbate the dysfunction of residual LSCs, and limit the survival of transplanted LSCs. Clinical presentation and disease evolution vary among different etiologies of LSCD. New ocular imaging modalities and molecular markers are now available to standardize the diagnosis criteria and stage the severity of the disease. Medical therapies may be sufficient to reverse the disease if residual LSCs are present. A stepwise approach should be followed to optimize the ocular surface, eliminate the causative factors and treat comorbid conditions, before considering surgical interventions. Furthermore, surgical options are selected depending on the severity and laterality of the disease. The standardized diagnostic criteria to stage the disease is necessary to objectively evaluate and compare the efficacy of the emerging customized therapies.

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.

Central corneal basal cell density and nerve parameters in ocular surface disease and limbal stem cell deficiency: a review and meta-analysis

OBJECTIVE

To conduct a review and meta-analysis for investigating the relative reduction of central corneal basal cell density (BCD) and nerve parameters in ocular surface disease (OSD) and limbal stem cell deficiency (LSCD).

METHODS

A systematic literature search using the terms ((1) "ocular surface disease" or "ocular surface disorder"; (2) "in vivo confocal microscopy"; (3) "limbal stem cell deficiency"; (4) "basal cell density" or "corneal basal cell density" or "central corneal basal cell density"; (5) "corneal nerves" or "corneal nerve parameters" or "central corneal nerve parameters") was performed. The results are presented as weighted mean difference (WMD) with corresponding 95% CI.

RESULTS

16 studies that reported the central corneal BCD and 21 studies that reported the central corneal nerve parameters in OSD (including LSCD) were included. A significant reduction in central corneal BCD was observed in patients with various OSDs (WMD=-9.50, 95% CI -14.04 to -4.97, p<0.01) as well as in patients with LSCD (WMD=-22.14, 95% CI -37.91 to -6.37, p<0.01) compared with healthy controls, however, no significant difference in BCD was observed between the two groups (WMD=-11.61, 95% CI -15.96 to -7.26, p=0.13). There was no conclusive difference in various central corneal nerve parameters between OSDs and LSCD.

CONCLUSION

Central corneal BCD and nerve parameters are reduced in LSCD, there is a similar reduction in other OSDs.