CXCR4 and precursor B-cell acute lymphoblastic leukemia: As a second approach, we mutated endogenous CXCR4 in two B-ALL cell lines cells using CRISPR/Cas9 with Green fluorescent protein (GFP), a marker of cell transfection with the CRISPR-Cas9 plasmid targeting CXCR4 (CRISPR-Cxcr4) (Supplementary Fig. 16t).