CXCR4 and leukemia: Apart from Cxcr4, the screen also identified Cd47 and Cd244 (also referred to as 2B4) as positive regulators of MLL-AF9 leukemia cells in vivo; both are known to play a role in immune regulation in normal hematopoiesis and to promote AML cell growth and survival (Majeti et al., 2009; Zhang et al., 2017).