Fig. 3.

Approaches to erasing tissue-specific epigenetic memory and evaluating the resulting pluripotent stem cells. Extended tissue culture after iPSC reprogramming (top) and modification of the iPSC reprogramming procedure (bottom) have been suggested to increase the quality of the resulting iPSC. In both cases, the resulting cells need to be compared not only with iPSC from different tissues but also with ESC as the gold standard of pluripotency. Genetic and epigenetic stability and alteration rates will be different during extended tissue culture and with variations in iPSC reprogramming; therefore, rigorous verification procedures are required to evaluate the potential therapeutic utility of the resulting cells.