Not All They're Cracked Up to Be?

In the past couple of months, researchers have sounded some alarms about induced pluripotent stem cells, says Not Exactly Rocket Science's Ed Yong. There have always been reasons to think that iPSCs aren't exactly like human embryonic stem cells, but now researchers have reason to be concerned about the differences. Last year, researchers found that iPSCs "carry a memory of their past identities," and last month, researchers found there were many more epigenetic changes in the cells than anyone previously thought, Yong says. Now, two other teams have published studies in Nature, producing their work that found that reprogramming cells changes their DNA — this discovery isn't new, but researchers have changed their methods to make it less likely. Now, however, a team from UCSD has found that no matter what method is used to reprogram the cell — whether it be using a virus, using RNA molecules, or not working with the cancer gene c-Myc as Shinya Yamanaka did — "all of these methods still mutate the genes of the resulting cells," Yong says. Meanwhile, another team of researchers has found that the genome of iPSCs have twice as many CNVs as hESCs or adult skin cells. Both studies found that about half of these changes only became high enough to detect once the cells had been reprogrammed into iPSCs. The process to reprogram the cells may be to blame here, Yong says, and the good news is that we have the right tools to screen for the abnormalities in the cells before they're used. Researchers also believe the fast pace of progress in the field will help produce more knowledge and better cells.