 we compared bona - fide human induced pluripotent stem cells ( ipsc ) derived from umbilical cord blood ( cb ) and neonatal keratinocytes ( k ) . as a consequence of both incomplete erasure of tissue - specific methylation and aberrant de novo methylation , cb - ipsc and k - ipsc are distinct in genome - wide dna methylation profiles and differentiation potential . 
 extended passage of some ipsc clones in culture did n't improve their epigenetic resemblance to esc , implying that some human ipsc retain a residual  epigenetic memory  of their tissue of origin . 
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