Hemopoietic Progenitor Cells of the Mouse Incapable of Self-Replication

Small numbers of transplanted marrow cells generate both differentiating hemic cell progeny and new undifferentiated progenitor cells. Comparable grafts of spleen cells generate only the former. Thus, hemopoietic progenitor cells consist of at least two compartments: “precursor cells” which do not self-replicate and their more primitive precursors called “stem cells.” The pool size of stem cells relative to that of precursor cells is much greater in bone marrow than in spleen of adult mice.