Characterization of a unique technique for culturing primary adult human epithelial progenitor/“stem cells”

BACKGROUND Primary keratinocytes derived from epidermis, oral mucosa, and urothelium are used in construction of cell based wound healing devices and in regenerative medicine. This study presents in vitro technology that rapidly expands keratinocytes in culture by growing monolayers under large volumes of serum-free, essential fatty acid free, low calcium medium that is replaced every 24 hrs. METHODS Primary cell cultures were produced from epidermal skin, oral mucosa and ureter by trypsinization of tissue. Cells were grown using Epilife medium with growth factors under high medium volumes. Once densely confluent, the keratinocyte monolayer produced cells in suspension in the overlying medium that can be harvested every 24 hrs. over a 7-10 day period. The cell suspension (approximately 8 X 105 cells/ml) is poured into a new flask to form another confluent monolayer over 2-4 days. This new culture, in turn produced additional cell suspensions that when serially passed expand the cell strain over 2-3 months, without the use of enzymes to split the cultures. The cell suspension, called epithelial Pop Up Keratinocytes (ePUKs) were analyzed for culture expansion, cell size and glucose utilization, attachment to carrier beads, micro-spheroid formation, induction of keratinocyte differentiation, and characterized by immunohistochemistry. RESULTS The ePUKs expanded greatly in culture, attached to carrier beads, did not form micro-spheroids, used approximately 50% of medium glucose over 24 hrs., contained a greater portion of smaller diameter cells (8-10 microns), reverted to classical appearing cultures when returned to routine feeding schedules (48 hrs. and 15 ml/T-75 flask) and can be differentiated by either adding 1.2 mM medium calcium, or essential fatty acids. The ePUK cells are identified as cycling (Ki67 expressing) basal cells (p63, K14 expressing). CONCLUSIONS Using this primary culture technique, large quantities of epithelial cells can be generated without the use of the enzyme trypsin to split the cultures. The cells are small in diameter and have basal cell progenitor/"stem" (P/SC) cell characteristics induced by daily feeding with larger than normal medium volumes. The ePUK epithelial cells have the potential to be used in regenerative medicine and for basic studies of epithelia P/SC phenotype.