Human embryonic stem cells appear to be much more stable than scientists had feared, research suggests.
Stem cells have huge potential
The cells hold great potential for use in repairing tissues damaged by trauma and disease.
There was concern the cells' genes might be liable to undergo changes that would make them unsafe for use in therapeutic treatments.
But a Cambridge University report published in Nature Genetics appears to show that these fears are unfounded.
Embryonic stem cells are at an early stage of development, and have the ability to become almost any tissue type in the body.
It is hoped they will eventually be used to treat a range of diseases, from diabetes to Parkinson's.
However, their use is opposed by some campaigners on ethical grounds.
Scientists were concerned about biochemical - or epigenetic - factors, which play a key role in controlling genetic activity during development.
These factors help to ensure the activity of our genes remains balanced by subtly changing their physical structure.
As we inherit two copies of every gene, one from each parent, there is a danger that in combination some of them might become too potent.
Epigenetic factors work to shut down activity of one of the paired genes, ensuring that genetic activity remains in kilter.
This is known as imprinting. It only applies to a small fraction of the total number of genes, but is crucial to normal development nonetheless.
However, scientists are concerned that epigenetic factors may alter the function of stem cell genes grown in the lab in unpredictable ways, which would be impossible to control.
The Cambridge team examined six "imprinted" genes from four lines of human embryonic stem cells.
They found they were highly stable. Unlike similar cells from mice, their epigenetic status hardly altered at all while they were grown in culture.
Researcher Professor Roger Pederson said it was vital that human stem cells were shown to be stable before research could forge ahead.
"We know from mouse stem cells that these kinds of genes are altered in the course of mouse embryo development.
"The fact that human stem cells are so stable is good news."
The Cambridge team only looked at stem cells taken from spare embryos. It is still not known whether stem cells derived from cloning techniques are also stable.
Professor Robin Lovell-Badge, of the MRC Research Council National Institute for Medical Research, said the study "had to be done".
He said it was not known exactly what effect using unstable stem cells would have, but it was possible that the cells would either over-grow, or not grow at all, rendering treatments useless.
This month a team of South Korean scientists announced the creation of the first human embryonic stem cells tailored to match individual patients.