By Michelle Roberts
BBC News health reporter
Stem cell work may find cures for intractable diseases
US President Barack Obama has lifted restrictions on federal funding for research on embryonic stem cells.
The move will be welcomed by scientists who say this type of work will lead to medical breakthroughs and cures for debilitating diseases like Parkinson's.
They say they need support to move their therapies from the lab to the clinic to help patients.
But many groups oppose the research, not just on ethical but also on safety grounds.
As well as the possibility that stem cells may grow tumours, some fear the therapy could unwittingly pass viruses and other diseases to people who receive stem cell transplants.
But experts say their work using stem cells, which have the ability to develop into other kinds of human cells, is essential to cure some of the most intractable diseases.
Using embryos donated through IVF treatment scientists have coaxed the stem cells inside to grow different types of tissue that could be used for treatments.
One day it may be possible to eliminate diabetes and Parkinson's disease and even cure some types of blindness using stem cells, researchers believe.
But the work is still in its infancy and scientists around the world say they need support to move their therapies from the lab to the clinic to help patients.
Roger Pederson, a stem cell expert at Cambridge University in the UK, said he and many other US researchers had been forced to move to other countries to continue their work.
It is essential this work goes on to move from basic science to the clinic faster
Professor Chris Mason, a stem cell scientist at University College London
"There has been a brain drain in the US." He said it was time US research was put on an equal footing with other countries.
Stem cell scientist Dr Stephen Minger, of King's College London, said if the restrictions were lifted in the US, more researchers might opt to work there.
"There is a danger that researchers will vote with their feet and flock to the US if they thing funding is more readily available and more easy to obtain than in other countries."
Professor Chris Mason, a stem cell scientist at University College London and member of the steering committee of the UK National Stem Cell Network, agreed.
He said the UK could lose its place to the US as the world leader of stem cell research.
"We may well see a shift in the leadership. The UK has done remarkably well for the level of funding. But we many not be able to compete.
"It is essential this work goes on to move from basic science to the clinic faster. Hopefully the changes in the US will mean a bigger volume of this work happening."
Ethics and safety
But some strongly oppose this route of research.
Josephine Quintavalle of the public interest group Comment on Reproductive Ethics said: "The ethical debate surrounding the status of the human embryo will continue unabated, as will resistance to the suggestion that science exists in some kind of ethical void.
STEM CELL MILESTONES
1960s: Research begins on stem cells taken from adult tissue
1968: Adult stem cells used to treat immunodeficient patient
1998: US scientists grow stem cells from human embryos and germ cells, establishing cell lines still in use today
2001: Embryonic stem cell turned into a blood cell
2002: UK regulator issues two licences to begin research on embryonic stem cells
"But what we suggest President Obama would be well advised to do pretty sharply is to sit down and analyse objectively the scientific reality, as opposed to the hype, surrounding the use of human embryos.
"Embryonic stem cell research has been with us for over a decade now and there is very little to show for it in terms of tangible evidence of likely cures.
"On the other hand, ethically sourced stem cells, whether from adult donors or from the cord blood and placenta at birth, are already curing patients."
UK and Canadian researchers have had some success making "ethical" stem cells by manipulating human skin cells to act like embryonic stem cells.
And many centres have been successfully using stem cells from cord blood to treat patients.
However, some experts say only embryonic stem cells can generate the vast number of cells needed to cure some diseases.
Professor Mason said: "There is no doubt that for some applications adult stem cells will do a good job.
"But the problem is when we need a lot of cells to cure things like Parkinson's disease. Here, embryonic stem cells remain our only option.
"Obviously, it is very important that all safety issues are addressed and that scientists work within the law of the land and within high ethical standards."