Cultivation, serial transfer, and differentiation of epidermal keratinocytes in serum-free medium

We describe serum-free culture conditions for human epidermal keratinocytes using lethally treated 3T3 cells as feeder layers and normal Ca++ concentrations (1.2 mM), in a DMEM/F12-Ham nutrient mixture supplemented with several additives, and 10 mg/ml bovine serum albumin instead of animal serum. Keratinocytes were serially grown to 15-18 cell generations (4 subcultivations) and formed a stratified squamous epithelium that could be detached as a graftable epithelial sheet. EGF and TGF alpha significantly increased keratinocyte proliferation under these conditions; EGF reduced the expression of keratin K1, which is specific for stratified and terminally differentiated epidermal keratinocytes. In contrast with previous reports, the serum-free medium we describe here supports serial growth and normal differentiation of human epidermal keratinocytes, and the formation of graftable stratified epithelia; it also supports the assay of a variety of cytokines or compounds that modulate epidermal keratinocyte proliferation and differentiation.