CXCR4 and acute myeloid leukemia: Human MSCs are potent feeder cells that are able to maintain AML cells in long-term culture. Co-culture of AML cells on MSCs results in a significantly higher proliferation capacity than on MS-5 or liquid culture. This favourable co-existence seems to be due, in part, to molecules important for communication within the niche. Blockade of TGF-β1 increases AML cell proliferation and chemosensitivity, while the CXCR4 antagonist plerixafor shows anti-proliferative effects and does not change cytarabine-induced cell death compared to control.