CXCR4 and leukemia: CXCR4 has been shown to play a key role in normal HSCs in the bone marrow niche (Nie et al., 2008; Sugiyama et al., 2006; Zou et al., 1998) and has been explored as a therapeutic target in leukemia (Abraham et al., 2017; Liu et al., 2017; Tavor et al., 2008).