Heart muscle and brain cells have been made for the first time in a test tube from human skin, marking a breakthrough in stem-cell research that could end the need to clone human embryos.
Scientists believe the development could soon lead to the growing of "spare part" tissue from a patient's skin cells for transplant surgery, which could lead to new treatments for a range of incurable illnesses, from Parkinson's to heart disease.
It may also resolve the controversy over the use of human embryos for medical research, because the findings could eventually end the need to use human eggs for creating stem cells in so-called "therapeutic cloning" – which has been opposed by powerful bodies ranging from the White House to the Vatican.
Two independent teams of researchers have shown that a relatively simple technique is able to turn skin cells from adult volunteers into apparently functioning nervous tissue and beating heart muscle. Other tests have shown that the stem cells are just as good as those derived from early embryos and that they can develop into any of the 220 specialised tissues of the body, such as mature nerve cells for mending spinal-cord injuries.
Creating so-called "pluripotent" stem cells which can be used to produce many different kinds of specialist tissue has been a holy grail of medical research. If the technique can be refined and made safe, it will mean anyone who needs replacement tissue for transplant surgery could have the necessary cells grown in the laboratory from their own skin and transplanted a few weeks later with little risk of tissue rejection.
It could also provide scientists with an unparalleled opportunity to create human tissue banks from patients suffering from a spectrum of incurable diseases in order to study each condition in detail and so open the way to developing new drugs and treatments, and provide new alternatives to animal testing.
The work was carried out by Shinya Yamanaka, of Kyoto University in Japan, whose findings follow a previous study published a year ago showing that stem cells can be derived from the skin of mice. His latest study on skin cells taken from a 46-year-old woman is published in the journal Cell.
Professor James Thomson of the University of Wisconsin-Madison, who conducted the second study confirming the findings, which is to be published in the journal Science, said: "The world has changed because of this new result."
Both teams of researchers took adult skin cells and genetically engineered them with four human genes that almost miraculously "reprogrammed" them back to the state of being a stem cell from an early embryo with the power of developing into any specialised cells of the body.
"The induced cells do all the things embryonic stem cells do. It's going to completely change the field. The idea of cells becoming things they don't normally become suddenly becomes viable," Professor Thomson said.
"The new results may not eliminate the controversy [over cloned human embryos] but it may be the beginning of the end of that controversy," added Professor Thomson, who in 1998 was the first person to isolate stem cells from human embryos and so began the controversy over embryonic cloning.
The scientists warned, however, that further work was needed before the technique could be used widely in medicine. In the meantime, it would continue to be necessary to use stem cells derived from human embryos. "They are the gold standard we need to compare against," Professor Thomson said.
Specialists in the field said the breakthrough was very important and could lead to new ways of studying the genetic causes of disease as well as bringing closer the day when stem-cell transplants became a routine part of treating incurable conditions. "It is relatively easy to grow an entire plant from a small cutting, something that seems inconceivable in humans," said Professor Azim Surani, a stem-cell expert at Cambridge University. "Yet this study brings us tantalisingly close to using skin cells to grow many different types of human tissues,"
Professor Robin Lovell-Badge, a developmental geneticist at the National Institute for Medical Research in north-west London, said the findings came much sooner than anyone had predicted and they could accelerate the pace of developing human stem cells in all sorts of fields.
"It doesn't remove the need to do the cloning approach but if it really works as well as it might, it's going to make it a lot easier to make pluripotent, patient-specific stem-cell lines," Professor Lovell-Badge said.
"We always said there was a hope that research would lead to direct reprogramming to avoid the use of embryos. This has just come sooner than any of us thought. This unpredictability is one of the fantastic things about science, and it is the reason that research avenues should always be open."