Renewal and release of hemopoietic stem cells: does clonal succession exist?

The term "clonal succession" was proposed 20 years ago by Kay to characterize the release of stem cells from their primary pool, followed by the expansion of each cell to a clone and the succession of new clones as the mature cells of each clone are lost because of their finite life span. The authors point out that the events described by Kay as clonal succession are necessary features of hemopoietic proliferation. Clonal succession is equivalent to the universally recognized existence of a self-replicating primary stem cell pool that continuously supplies cells for amplification and maturation to subsequent compartments. The authors object to the term "clonal succession" because it has been used by a number of investigators to characterize specific schemes rather than the general aspects of hemopoietic proliferation, thus leading to confusion. They suggest that the descriptive term, "continuous release of stem cells for differentiation," would be preferable to the use or misuse of "clonal succession."