British and Canadian researchers have manipulated human skin cells to make them act like embryonic stem cells, without using viruses, making them safer to use in humans.
In a report in Nature they describe how the cells are reprogrammed by inserting four genes, which are removed once the process is complete.
Much of the work on stem cells has focused on those taken from embryos as they have an unlimited capacity to become any of the 220 types of cell in the human body - a so-called pluripotent state.
But campaigners have objected to their use on the grounds that it is unethical to destroy embryos in the name of science.
In 2007, teams in Japan and the US managed to genetically modify skin cells to be pluripotent, opening the way for a new source of stem cells for use in research.
However, the technique used viruses to genetically modify the cells, which means there was a risk they could become cancerous and so would not be safe for medical use.
The latest study reports a way of delivering foreign genes to reprogramme the cells without using viruses in mouse and human cells. Furthermore, the team was able to remove the genes afterwards.
