Identification and isolation of candidate human keratinocyte stem cells based on cell surface phenotype

Despite the central role of human epidermal stem cells in tissue homeostasis, wound repair, and neoplasia, remarkably little is known about these cells, largely due to the absence of molecular markers that distinguish them from other proliferative cells within the germinative/basal layer. Epidermal stem cells can be distinguished from other cells in the basal layer by their quiescent nature in vivo and their greater overall proliferative capacity. In this study, we demonstrate enrichment and isolation of a subpopulation of basal epidermal cells from neonatal human foreskin based on cell surface phenotype, which satisfy these criteria. These putative stem cells are distinguished from other basal cells by their characteristic expression of high levels of the adhesion molecule alpha6, a member of the integrin family (alpha6bri), and low levels of a proliferation-associated cell surface marker recognized by recently described mAb 10G7 (10G7(dim)). We conclude that cells with the phenotype alpha6bri10G7(dim) represent the epidermal stem cell population based on the demonstration that these cells (i) exhibit the greatest regenerative capacity of any basal cells, (ii) represent a minor subpopulation (approximately 10%) of immature epidermal cells, which (iii) are quiescent at the time of isolation from the epidermis, as determined by cell cycle analysis.