Generation of Keratinocytes from Human Induced Pluripotent Stem Cells Under Defined Culture Conditions.

Differentiation of keratinocytes from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) has become an important tool for wound healing research and for studying skin diseases in instances where patient cells are not available. Several keratinocyte differentiation protocols using hiPSC colony fragments or embryoid bodies have been published with some requiring prolonged time for differentiation or extended use of reagent cocktails. In this study, we present a simplified method to efficiently generate large numbers of uniformly differentiated keratinocytes in less than 4 weeks from singularized hiPSCs with differentiation factors, retinoic acid and bone morphogenetic protein 4 (BMP4). Low seeding density of singularized iPSCs results in keratinocyte cultures with minimum cell death during differentiation and up to 96% homogeneity for keratin 14-positive cells and low percentage of keratinocyte maturation markers, comparable to early passage primary keratinocytes. hiPSC-derived keratinocytes remain in a proliferative state, can be maintained for prolonged periods of time, and can be terminally differentiated under high calcium conditions in the same way as primary human keratinocytes. Moreover, coculturing hiPSC-derived fibroblasts and keratinocytes consistently formed organotypic 3D skin equivalents. Therefore, keratinocytes generated by this method are a viable source of cells for downstream applications.