Cell Stem Cell doi:10.1016/j.stem.2009.04.005 (2009)

Ever since Kyoto University's Shinya Yamanaka showed that cultured skin cells could be made to behave like embryonic stem cells by the addition of a handful of genes, researchers have been trying to repeat the trick without introducing DNA to the cells. Now, Sheng Ding at the Scripps Research Institute in La Jolla, California, and his colleagues say they can reprogram cells — in this case mouse embryonic fibroblasts — with those genes' protein products, specifically engineered to cross the cellular and nuclear membranes.

The resulting cells are “morphologically indistinguishable” from embryonic stem cells, the authors say, and express similar markers.

Although such work has not yet been reported in human cells, Ding predicts that similar techniques will replace those requiring DNA or viruses, which are deemed risky in therapeutic applications.