Furthermore, Bcl-XL is preferentially required for CML progression [34], while the anti-apoptotic MCL1 is essential for the survival of normal and Ph+ leukemic stem cell populations [35,36], suggesting that ALX must act on additional signaling pathways to target CSLs. This evidence concerns the gene BCL2L1 and chronic myelogenous leukemia, BCR-ABL1 positive.