Prof Sir Ian Wilmut FRS, Director, MRC Centre for Regenerative Medicine, University of Edinburgh, said:

"These papers remind us that there is still a great deal to learn about the production of stem cells from adult tissues.

"The expectation is that it will be possible to develop methods that enable us to obtain from adult tissues such as skin, stem cells that will be equivalent to embryo stem cells. That is they will divide in culture for a very long time, so that it is possible to have many millions of the cells, while they retain the ability to form all of the different tissues of an adult.

"These new results show that during their isolation these cells retain some of the characteristics of the adult tissues from which they are produced. However, the authors each describe a simple method for overcoming this tendency.

"It is also important to remember that at an earlier stage in the use of embryo stem cells many lines also showed a similar tendency to form some tissues rather than others. These new results will come to be considered as reflecting the fact that we are still at an early stage of developing this exciting new source of stem cells.

"There are already a number of papers that have used these new cells to study inherited diseases and it is probable that in future this will be an important opportunity to develop treatments for at least some inherited diseases.

"The moral for each of us who use these new cells is that we should be cautious in their use either for research or in the future for therapy.

"Shinya Yamanaka called them induced pluripotent stem cells. These very important new papers show that in fact with present procedures the cells retain come of the characteristics of the source tissue."