Stem cell breakthrough could end shortage of vital blood cells

Patients undergoing chemotherapy or organ transplants may soon be treated with a vital blood-clotting agent derived from the stem cells of human embryos.

Scientists have produced blood platelets from human embryonic stem cells and have shown for the first time that these "donor-less" platelets can repair damaged tissues in laboratory mice.

People undergoing certain forms of medical treatment, such as cancer therapies or transplant surgery, often need transfusions of platelets in order to repair damaged tissues and blood vessels and to prevent uncontrolled bleeding. The scientists believe that the technique could result in unlimited quantities of platelets being produced on an industrial scale without the need for human blood donors.

Platelets play a key role in the complex process of blood clotting. Without them, damaged tissues would not heal properly and quickly, and there would be a risk of death from internal bleeding. Platelets derived from blood donations, however, cannot be frozen and have a short shelf life of between seven and 10 days. The constant demand for platelets can lead to shortages – which is why medical researchers are trying to devise ways of producing unlimited supplies from stem cells to replace conventional blood donors.

Scientists in the United States have not only produced platelets from human embryonic stem cells on a clinically useful scale, but have shown that they work when injected into mice, as they would do normally in the human body.

The researchers believe that platelets that are produced in this way could rapidly find their way into clinics, because they do not contain any genetic material, which largely eliminates the risk of introducing cancerous tumours into the recipient.

Robert Lanza, chief scientific officer at Advanced Cell Technology (ACT), the stem cell company behind the work, said the platelets looked and behaved just like ordinary ones derived from blood donations, including being activated by the natural clotting agent of the blood, thrombin. He said: "Amazingly, we show that they're even biconcave-shaped disks just like the real thing. Importantly, we demonstrated the platelets incorporated into thrombi, or blood clots, in living mice in a manner similar to that observed for normal blood platelets. These results represent an important step towards generating a potentially unlimited supply of functional platelets for transfusion."

The platelets were made from a line of stem cells derived from a spare IVF embryo. The stem cells were first coaxed to develop into specialised cells called megakaryocytes, which were then cultivated in the laboratory to make fully mature platelets. Dr Lanza said that an alternative method of making stem cells that does not involve using human embryos could be used to make platelets. Known as induced pluripotent stem cells (iPS), the technique involves the genetic modification of a patient's skin cells to make embryonic-like stem cells.

Safety concerns over using such iPS-derived material could be overcome in the case of platelets because they would not pose a cancer risk, Dr Lanza suggested. "Since platelets contain no genetic material – and can be irradiated before use – they're ideal candidates for early clinical translation involving iPS cells," he said.