A new study has raised doubts about the creation of "ethical" all-purpose stem cells for use in research and treatments.
Embryonic stem cells have the power to develop into any of the 220 cell types that make up the different tissues of the human body, but they are mired in controversy because they must be extracted from cannibalised early-stage human embryos.
However, recent advances have made it possible to "reprogram" ordinary skin cells, giving them the properties of embryonic stem cells.
These cells, known as induced pluripotent stem (iPS) cells, are seen by many experts and pro-life groups as a potential solution to the problem of having to destroy human embryos.
But new brain research published today suggests that iPS cells have serious shortcomings not shared by "real" embryonic stem cells.
Scientists compared the ability of induced cells and embryonic stem cells to transform into immature neurons - a key process for any future treatment of brain diseases such as Parkinson's or Alzheimer's.
They found that the iPS cells differentiated less efficiently and less faithfully.
Professor Su-Chun Zhang, from the University of Wisconsin-Madison School of Medicine in the US, who led the study, said: "Embryonic stem cells can pretty much be predicted. Induced cells cannot. That means that at this point there is still some work to be done to generate ideal induced pluripotent stem cells for application."
The scientists used different methods to coax five human embryonic stem cell lines and 12 iPS cell lines to start down the path of development to becoming neurons.
The results, published yesterday in the journal Proceedings of the National Academy of Sciences, suggest that unknown factors may undermine their usefulness both as laboratory research tools and potential treatments.
To their surprise, the scientists found that whether or not iPS cells differentiated successfully did not depend on the presence or absence of genes used to create them.
Some of the iPS cells tested by the researchers were made using techniques that bypassed gene reprogramming.
"It tells us the techniques for generating induced pluripotent stem cells are still not optimal," said Prof Zhang.
Nevertheless he believed the problems identified by his team were technical hurdles that would ultimately be resolved.
"It appears to be a technical issue. Technical things can usually be overcome," he said.Reuse content