Isolation, Cultivation, and Differentiation of Normal Human Epidermal Keratinocytes in Serum-Free Medium

The outer layer of human skin is the epidermis. More than 90% of the epidermal cells are keratinocytes, which originate from stem cells, located in the basal cell layer (Stratum basale ). Keratinocytes in the basal layer divide, differentiate, and migrate to the outer layer of the epidermis, the horny layer (Stratum corneum). The horny layer consists of terminally differentiated keratinocytes (corneocytes) embedded in multilamellar lipid sheets (1 ). Finally, corneocytes are shed from the surface of the skin by desquamation. Keratinocytes are an ideal target for gene therapy (2 ,3 ) to treat desquamation disorders (4 ,5 ). In addition, keratinocytes are secretory cells (6 ), which opens the possibility for systemic delivery (7 ,8 ).