Novel enzymatic isolation of an entire viable human limbal epithelial sheet

OBJECTIVE. To develop a reproducible method of isolating an intact viable human limbal epithelial sheet. METHODS. Human pigmented limbus was incubated at 4degreesC for 18 hours in supplemental hormonal epithelial medium (SHEM) containing 50 mg/mL dispase II and 100 mM sorbitol. A loose limbal epithelial sheet was separated by a spatula. The remaining stroma was digested and subcultured. The viability of isolated cells was assessed. Isolated epithelial sheets and remaining stroma were subjected to immunostaining. Sheets 1.5 mm in length were cultured in SHEM on plastic until confluence, and cell extracts were subjected to Western blot analysis. RESULTS. Intact limbal epithelial sheets were consistently isolated. Pigmented palisades of Vogt revealed large superficial squamous cells and small basal cuboidal cells. No epithelial cells grew from the remaining stroma. Mean viability was 80.7% +/- 9.1%. The basal epithelium was negative to keratin 3 and connexin 43, but was scatter positive for p63. The epithelial sheet showed negative staining for laminin 5 and Collagen VII, but interrupted linear basal staining for Collagen IV. The remaining stroma showed negative staining for laminin 5, positive linear staining for Collagen IV in the basement membrane, and diffuse staining for Collagen VII in the superior stroma subjacent to the basement membrane. Western blot analysis revealed that cells originating from the limbal sheets expressed keratin 3 and p63. CONCLUSIONS. An intact limbal epithelial sheet can be consistently and reproducibly isolated and contains stem cell characteristics in the basal epithelium by degrading laminin 5 and part of Collagen IV, and disassembling Collagen VII.