Keratinocytes are propagated and infected while still in the growth phase. After infection, keratinocytes are transferred onto a feeder layer (e.g., murine or human mitotically inactivated fibroblasts) until primary colonies with an obvious stem cell morphology reach the appropriate size to be picked mechanically and to be subsequently cultured in, for example, a feeder-free system (Figure 1). After testing newly generated cell lines for stem cell characteristics, such as pluripotency marker expression, genetic coherence, and differentiation capacity, iPSCs can be propagated and used for further applications.
