The distribution of colony‐forming cells among spleen colonies

Progenitor cells that are recognized by their ability to form colonies of descendants in the spleens of irradiated mice have the capacity for self-renewal. The distribution of new colony-forming cells per colony is extremely heterogeneous, indicating lax control of self-renewal. The capacities of colony-forming cells for self-renewal, for extensive proliferation, and for giving rise to differentiated descendants, fulfill three requirements for studies of stem cells. Thus, colony-forming cells may be considered to be class (though not necessarily the only class) of such progenitor cells, and the spleen colony method is a quantitative method for their detection. Journal of Cellular and Comparative Physiology copyright 1963 Wiley-Liss, Inc., A Wiley Company (www.interscience.Wiley.com).