Haematopoietic stem cells. Evidence for competing proliferative demands.

A HAEMATOPOIETIC stem cell must be able both to replicate itself and to differentiate into a formed blood element. The presence of a pool of multipotent, functionally important, common stem cells for the various haematopoietic formed elements has not as yet been established. There is evidence to suggest that there is a population of bone marrow cells which when transplanted into irradiated recipients is capable of differentiating into more than one mature cellular form1–3. We are interested in whether this class of cells is functionally important, and specifically whether demand for one blood element limits the ability of the animal to produce other cell types. Such a relationship would suggest competitive demands on a common stem cell pool. There is some evidence to suggest that this may be the case. Harris et al.4 have shown that after large acute haemorrhage the number of granulocyte precursors in the guinea-pig bone marrow is reduced. The present experiment demonstrates that an increased demand for red blood cell production reduces the ability of transplanted syngeneic bone marrow to make granulocytic progeny.