A method for producing red blood cells in the laboratory could one day help solve the shortage of donated blood.
Blood supplies are stretched
University of Paris researchers have developed a way to produce large numbers of cells.
The three-stage process involves combining stem cells with another group called stromal cells and then adding a growth factor to stimulate them.
It is hoped the Nature Biotechnology study will eventually enable the mass production of man-made red blood cells.
However, it is not yet clear whether lab-grown blood is a suitable replacement for donated blood for transfusion.
The NHS in England and Wales needs up to 9,000 units of blood every day.
The National Blood Service regularly campaigns for more blood donations to maintain sufficient stocks.
It is currently urging people from the ethnic minorities to donate more blood to help sick children recover from illness.
Several groups of scientists around the world are looking at how stem cells can be manipulated to produce red blood cells.
But previous attempts to produce blood cells in the laboratory have failed because the cells were not an exact match for naturally occurring cells.
In the latest study, the Paris University team devised a technique using mouse cells for maximising production of blood cells.
The first step is to take haematopoietic stem cells, which are known to evolve into blood cells. These are treated with a liquid to make them proliferate.
Then scientists created an environment to mimic the conditions found in bone marrow by using stromal cells, which provide the structure inside bone marrow.
Once a growth factor called erythropoietin is added, the stem cells are given a signal to begin the transformation into red blood cells.
Professor Luc Douay, who led the research, said the stem cells can be autologous, which means they are harvested from the blood of the person who will receive the transfusion.
"This is the best immunological situation because there is no risk of rejection," he said.
But the technique may also work with blood harvested from umbilical cords. These are known to be a rich source of supply for stem cells.
Stem cells are cells at an immature stage of development that have not yet committed to becoming any one specific type.
In the right conditions, it's thought they can be expanded to large numbers so that they can grow into replacement tissue for damaged bodies.
Professor Robin Lovell-Badge, head of stem cell biology and developmental genetics at the National Institute for Medical Research in north London, said the results looked promising.
"It sounds good and it seems as if they can produce substantial amounts of cells that are usable.
"But they have not solved the problem of being able to grow stem cells indefinitely. If they could that then they would be able to have a fairly permanent supply of red blood cells."