Blood stem cell discovery may revolutionise transplants

Canadian scientists have identified a master stem cell that is capable of becoming any of the different types of cells found in blood. The discovery offers hope of alternative treatments for people who would normally require bone marrow transplants to replenish their blood supply, for example those with cancer or blood disorders.

Scientists have known about the existence of haematopoietic stem cells (HSCs) for many years, but this is the first time they have been able to isolate and study them. Dr John Dick, who led the study, said: 'We have isolated a single cell that makes all arms of the blood system, which is key to maximising the potential power of stem cells for use in more clinical applications. Stem cells are so rare that this is a little like finding a needle in a haystack'.

HSCs are found in umbilical cord blood and adult bone marrow, and are essential for the generation of new blood. Patients with leukaemia and other blood disorders require bone marrow transplants from healthy donors to replace their diseased blood cells. However, around two-thirds of all patients requiring a bone marrow transplant do not find a matching donor, and many die as a result.

Despite the fact it was known that HSCs were required for replacing blood cells, it had been impossible to identify them from the many other cell types found in the blood and bone marrow. 'No one has ever gotten a glimpse of them within the mass of cells used when someone gets a transplant', explained Dr Dick.

The research team at the University of Toronto carefully sorted cord blood, separating the different cell types, and were able to identify a tiny population of HSCs. Mice were used in experiments that mimic the bone marrow transplant process, the group found that these cells alone were able to regenerate all the components of human blood. Additionally, cord blood without these cells could not successfully replace the blood system in the mice.

Crucially, the researchers were able to identify proteins that were uniquely present on the surface of the HSCs, in particular one called CD49f. These findings, reported in the journal Science, will enable easy identification of HSCs in the future. It is hoped this will eventually allow scientists to generate large blood supplies in the laboratory for use in transplants. Alternatively, they may one day be able to tailor-make blood supplies for a patient using their own HSCs.