CXCR4 and acute myeloid leukemia: Activation of TGF-β signaling as a resistance mechanism is supported by our previous data that demonstrated a potential role of TGF-β signaling in modulating the sensitivity of AML cells to chemotherapeutic agents, in which the blockade of TGF-β1 enhanced the response to the combination of cytarabine and CXCR4 inhibitor (plerixafor) in vitro and prolonged survival in an in vivo leukemia model [42].