Blood donations could one day become unnecessary, after the discovery of a way to grow potentially unlimited supplies of blood in the lab.

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An American team has found a way to turn the parent cells of other types, human embryonic stem cells, into significant quantities of functional oxygen-carrying red blood cells.
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Tests could start on patients by the end of next year and the advance holds out the promise that one day "blood farms" could provide a versatile source.

The research, which appears in the journal Blood, was carried out by Advanced Cell Technology, Worcester Massachusetts, and its collaborators at the Mayo Clinic and the University of Illinois, shows for the first time that the oxygen-carrying capacity of these blood cells is comparable to that of normal blood transfusions.

And it should be easier to ensure that blood created this way is free of contamination by disease agents, such as Aids and variant CJD.

"Limitations in the supply of blood can have potentially life-threatening consequences for patients with massive blood loss," said Dr Robert Lanza, Chief Scientific Officer at ACT, and senior author.

"Embryonic stem cells represent a new source of cells that can be propagated and expanded indefinitely, providing a potentially inexhaustible source of red blood cells for human therapy. We can currently generate 10 to 100 billion red blood cells from a single six-well plate of stem cells."

He added that, if his company can obtain sufficient resources and depending on the outcome of safety studies, "we could be in a position . . . to begin clinical trials by the end of next year."