By performing engraftment studies in SCID (severe combined immunodeficiency) mice, Cobaleda et al. showed that the self-renewal and phenotypic properties of leukemia-initiating cells (SL-ICs) in BCR-ABL p190 Ph-ALL were similar to those of normal stem cells, suggesting that HSCs act as cell of origin in CML [10]. Here, ABL1 is linked to acute lymphoblastic leukemia.