A British and a Japanese scientist have won the Nobel Prize for medicine or physiology for work on creating stem cells, opening the door to new methods of diagnosing and treating disease.
John Gurdon of the Gurdon Institute in Britain and Shinya Yamanaka of Kyoto University, Japan, have been praised for determining that adult cells can be transformed back to an infant, versatile stem-cell state.
As far back as 1962, Professor Gurdon became the first scientist to clone an animal, making a healthy tadpole from the egg of a frog with DNA from another tadpole's intestinal cell, Reuters reports.
That showed that developed cells carry the information to make every cell in the body - decades before other scientists made world headlines by cloning the first mammal from adult DNA, Dolly the sheep.
More than 40 years later, Professor Yamanaka produced mouse stem cells from adult mouse skin cells by inserting a small number of genes.
His breakthrough in 2006 effectively showed that the development that takes place in adult tissue could be reversed, turning adult tissue back into cells that behave like embryos.
All of the body starts as stem cells, before developing into tissue like skin, blood, nerves, muscle and bone. The big hope is that stem cells can grow to replace damaged tissue in cases from spinal cord injuries to Parkinson's disease.
Scientists once thought it was impossible to turn adult tissue back into stem cells. That meant new stem cells could only be created by taking them from embryos, which raised ethical objections that led to research bans in some countries.
Discouraging school report
Professor Gurdon, 79, says he is surprised by the honour, since his research was done more than 40 years ago. He says when he first took an interest in science at school his biology teacher described his scientific ambitions as a waste of time.
He still keeps the old school report in a frame on his desk: "I believe he has ideas about becoming a scientist... This is quite ridiculous," his teacher wrote. "It would be a sheer waste of time, both on his part and of those who have to teach him."
Asked why he still keeps the discouraging report, Professor Gurdon said: "When you're having problems, like when an experiment doesn't work - which often happens - it's nice to remind yourself that perhaps after all you're not so good at this job and the schoolmaster may have been right."
Thomas Perlmann, Nobel Committee member and professor of Molecular Development Biology at the Karolinska Institute said: "Thanks to these two scientists, we know now that development is not strictly a one-way street."
"There is lot of promise and excitement, and difficult disorders such as neurodegenerative disorders, like perhaps Alzheimer's and, more likely, Parkinson's disease, are very interesting targets."
For now, both men said their scientific work continues.