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Cells on stems.

Blood cells, like blossoms of a floribunda, arise together from a single branch. Clinicians have long assumed that granulocytes, megakaryocytes and erythroid cells have a common origin because all three cell lines may be involved to a varying degree in the many forms of myeloproliferative disease. Studies of the marker chromosone Ph1 in chronic myelocytic leukemia support the idea since this abnormal chromosome is found in erythroid precursors, megakaryocytes and myeloid cells, but not in skin fibroblasts or lymphocytes,1 suggesting a single pluripotent stem cell that becomes committed to erythroproliferation, megakaryocyte production or granulopoiesis. There might be, in fact, a . . .