Scientists at Stanford report that they can turn human skin cells directly into functioning nerve cells in the lab dish. The process does not involve an intermediate step of forming a stem cell, but directly converts skin cells into neurons. Last year this group showed that they could accomplish this direct conversion with mouse cells. The new results, reported in the journal Nature, accomplish this conversion for the first time with human cells by adding four genes to the skin cells. Other researchers have obtained similar direct conversion results in the formation of blood, heart, and insulin-secreting cells.

The direct conversion technique is similar in some respects to the method used to create induced pluripotent stem cells (iPS cells), in which genes are added to normal cells to convert them to stem cells that behave similarly to embryonic stem cells. But pluripotent stem cells such as embryonic stem cells also have a significant risk of tumor formation. This out-of-control growth problem with pluripotent stem cells makes the direct conversion technique preferable when it comes to deriving new cells from normal cells. Likewise, using native adult stem cells is both safer and effective, e.g., in repair of stroke damage.