ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: In the early 1990s, the first convincing evidence of CML stem cells came from early observations in which transfusion of unirradiated white blood cells obtained by leukapheresis from CML patients with high granulocyte counts into severely neutropenic recipients, resulting in the transient repopulated Ph+/BCR-ABL+ cells [16].