Optimization of Ex Vivo Expansion of Limbal Epithelial Progenitors by Maintaining Native Niche Cells on Denuded Amniotic Membrane

Purpose: Transplantation of ex vivo expanded limbal epithelial progenitor cells (LEPCs) on epithelially denuded amniotic membrane (dAM) in supplemented hormonal epithelial medium (SHEM) is an alternative solution for treating corneal blindness due to limbal stem cell (SC) deficiency. Because the phenotype of limbal niche cells (NCs) is preserved better in serum-free modified embryonic stem cell (ESC) medium (MESCM) than SHEM, we question whether the aforementioned expansion protocol can be further optimized by maintaining limbal NCs using MESCM. Methods: Collagenase-isolated limbal clusters were cultured on dAM in SHEM or MESCM for 8 to 10 days. Epithelial outgrowth sheets removed by dispase were subjected to real-time quantitative polymerase chain reaction (qPCR) and immunostaining for expression of corneal epithelial markers (p63, pax6, and K12) and NC markers (FLK-1, CD34, CD31, PDGFR-B, and -SMA). A total of 1000 single cells were seeded on 6-well dish containing 3T3 feeder layers for 12 to 14 days before rhodamine B staining. Results: Epithelial outgrowth in SHEM showed a significant loss of corneal SC and ESC markers when compared with freshly collagenase-isolated limbal clusters. Although the epithelial outgrowth was slower in MESCM, epithelial cell size was consistently smaller than that found in SHEM. Furthermore, MESCM maintained a significantly higher percentage of PCK-/Vim+ cells and exhibited a significant upregulation of NC markers and corneal epithelial SC markers (K15, Bmi-1, and Msi-1) than SHEM. Furthermore, the number of purported holoclones was significantly promoted in MESCM than SHEM. Conclusion: These data collectively suggest that MESCM can be used to replace SHEM to further promote expansion of LEPC by maintaining limbal native NCs. Translational Relevance: Effective ex vivo expansion of limbal epithelial SC is a first and important step toward the success of treating corneal blindness caused by limbal stem cell deficiency and paves the way for future applications in regenerative medicine.