Unlike normal bone marrowenriched progenitors which form almost no erythroid colonies or only tiny ones in the absence of EPO as shown in the examples in Figures 2(a), 2(b), and 2(c), CML progenitors often produce erythroid colonies of varying sizes, some very large, after stimulation with various single cytokines or combinations of cytokines without EPO. Here, EPO is linked to chronic myelogenous leukemia, BCR-ABL1 positive.