Are iPS cells better than embryonic stem cells? For anyone interested in the ethical dimension of regenerative medicine, this is a hot topic. Gretchen Vogel weighs up the latest research in the March 5 issue of the journal Science. Some recent papers suggest that induced pluripotent stem cells – which have less ethical baggage because they do not involve the destruction of embryos – have less medical potential than iPS cells.

In one of these, Robert Lanza, of Advanced Cell Technology, found that iPS cells were capable of producing far fewer cells than human embryonic stem cells (hESCs). In one experiment, the difference was a thousand to one. The iPS cells also aged more quickly and died sooner than hESCs. “These cells are pretty screwed up,” Lanza commented.

However, James Thomson, of the University of Wisconsin, the scientist who first isolated hESCs, is more optimistic. “The differences are real, but one shouldn’t overinterpret them. When you go back and tweak the conditions, [iPS cells] seem to have the same potential” as ES cells, he says. The differences may be due to imperfections in the reprogramming process that morphs a skin cell into an iPS cell. “There’s going to be a lot of noise” in the data as scientists work to diagnose and overcome reprogramming’s weak spots, Thomson says.

He tried to turn both hESCs and iPS cells into neural cells and found that 90% of the hESCs made the transition. Of the iPS cells, 79% of one line and only 15% of another line did. However, another leading stem cell scientist, Hans Schöler, of the Max Planck Institute for Molecular Biomedicine in Münster, Germany, says he has noticed no differences between hESCs and iPS cells when they changed into neural stem cells. But he, too, acknowledges that reprogramming is still an inexact science.

Shinya Yamanaka, of Kyoto University, who was the first to successfully reprogram mature mouse cells into iPS cells, has also observed that iPS and hESCs vary from line to line, thought not systematically. He told Science that adding factors to the reprogramming mix should produce more dependable iPS cells. ~ Science, Mar 5