CXCR4 and acute myeloid leukemia: Refractory/relapsed AML shows relatively higher abundance of clusters enriched with expression of the inhibitory receptor KLRG1, a marker of antigen-experienced and senescent cells (99, 100), while newly diagnosed AML displays relative higher percentage of clusters expressing cell-migratory receptor CXCR4 and AP-1 transcription factor FOSB (94).