The persistence of memory

people in need of regenerative medicine. The generation of induced pluripotent stem cells (iPSCs) from adult cells is a promising alternative to stem cells derived from embryos. Two recent studies by Jose Polo et al.1 and K. Kim et al.2 now show that iPSCs—but not embryonic stem cells (ESCs)—obtained through reprogramming with transcription factors, which render adult cells pluripotent, retain epigenetic traits from the cell of origin. Compared with ESCs, these iPSCs were relatively limited in their ability to differentiate to lineages other than those that are similar to the original cell. The authors proved that multiple divisions of iPSCs over time or treatment with drugs that modify epigenetic-related proteins may confer complete pluripotency to generate any tissue. We asked three experts about the consequences of carrying ‘epigenetic memory’ in the use of iPSCs in therapy and drug development. com m u n i t y co r n e r