Normal adult cells have been reprogrammed to become stem cells inside live mice for the first time.
As stem cells can be coaxed into developing into almost any kind of cell, being able to prompt this behaviour in the body could one day be used to repair ailing organs including the heart, liver, spinal cord and pancreas.
"By doing it in situ, the cells are already there in the tissue, in the right position," says Manuel Serrano at the Spanish National Cancer Research Centre in Madrid, and co-leader of the new work.