CXCL12 and chronic myelogenous leukemia, BCR-ABL1 positive: It has been established that leukemic stem cells (LSC) in CML express CXCR4 and utilize the CXCL12–CXCR4 signaling pathway; CXCL12 from mesenchymal stromal cells helps to maintain the LSC in a quiescent G0 state, which renders these BCR-ABL+ LSC resistant to tyrosine kinase inhibitors (TKI).