Donor cell type can influence the epigenome and differentiation potential of human induced pluripotent stem cells

Mouse induced pluripotent stem (iPS) cells have been shown to retain an epigenetic 'memory' of their cell type of origin. Kim et al . study this question in human cells and document both incomplete erasure of methylation and aberrant de novo methylation during reprogramming. We compared bona fide human induced pluripotent stem cells (iPSCs) derived from umbilical cord blood (CB) cells and neonatal keratinocytes (K). As a consequence of both incomplete erasure of tissue-specific methylation and aberrant de novo methylation, CB-iPSCs and K-iPSCs were distinct in genome-wide DNA methylation profiles and differentiation potential. Extended passage of some iPSC clones in culture did not improve their epigenetic resemblance to embryonic stem cells, implying that some human iPSCs retain a residual 'epigenetic memory' of their tissue of origin.