reprogramming factors are not needed forever. Indeed, once the cells are reprogrammed, they express endogenous pluripotency genes and silence the exogenous ones. Thus, like ESCs or other pluripotent cells, iPSCs should readily differentiate into appropriate lineages and respond in a manner indistinguishable from ESCs. Indeed, this observation has been utilized cleverly by several groups to develop zero-footprint technology [20,21] that allows one to reprogram somatic cells using factors or genes that can then be permanently eliminated leaving cells that theoretically, at least, should be indistinguishable from ESCs derived in a conventional fashion, and thus media and reagents developed for ESCs should work with iPSCs.
