Keratinocytes are reprogrammed faster, approximately in 1-2 weeks in contrast to the duration of 3-4 weeks for fibroblasts. In addition, fibroblasts show much lower expression of C-MYC and KLF4 compared with other cell types [71, 72]. An already high base level of these genes, as observed in keratinocytes, may contribute to a more efficient reprogramming process. Keratinocytes have been described to exhibit a 100-fold higher reprogramming efficiency (about 1-2%) compared to fibroblasts [17, 73]. A successful reprogramming strategy using episomal vectors was recently described, making keratinocytes even more interesting in the future of iPSC generation [74].
