Induced pluripotent stem cell

An induced pluripotent stem cell, or iPS cell, starts out as an ordinary specialized cell, often a skin fibroblast or a blood cell. Scientists switch on a few genes for transcription factors, proteins that control which other genes are active, and some of the treated cells are reprogrammed to an embryo-like state. The resulting cells divide indefinitely and can be guided to form cells of all three germ layers, just as embryonic stem cells can.

Shinya Yamanaka's team at Kyoto University reported the method in mouse cells in 2006, using four factors: Oct3/4, Sox2, Klf4 and c-Myc. Human iPS cells followed in 2007. The work proved that cell specialization can be reversed, and Yamanaka shared the 2012 Nobel Prize in Physiology or Medicine with John Gurdon, whose frog experiments decades earlier had shown that the nucleus of a mature cell can still direct the development of a whole tadpole.

Because iPS cells can be made from anyone, they avoid the use of embryos and can match a patient's own tissue. They are used to model diseases in a dish, to test drugs and in early trials of cell therapy. Concerns include genetic changes during reprogramming and the cancer risk linked to c-Myc.