Stem Cells: The Black Box of Reprogramming

Eggs and sperm do it when they combine to make an embryo. John Gurdon did it in the 1960s, when he used intestinal cells from tadpoles to generate genetically identical frogs. Ian Wilmut did it too, when he used an adult mammalian cell to make Dolly the sheep in 1996. Reprogramming — reverting differentiated cells back to an embryonic state, with the extraordinary ability to create all the cells in the body — has been going on for a very long time.

Scientific interest in reprogramming rocketed after 2006, when scientists showed that adult mouse cells could be reprogrammed by the introduction of just four genes, creating what they called induced pluripotent stem (iPS) cells¹. The method was simple enough for almost any lab to attempt, and now it accounts for more than a thousand papers per year. The hope is that pluripotent cells could be used to repair damaged or diseased tissue — something that moved closer to reality this year, when retinal cells derived from iPS cells were transplanted into a woman with eye...