CTCF and precursor B-cell acute lymphoblastic leukemia: We developed an optimized CRISPR/Cas9 with homology arm and sorting enrichment knock-in protocol, so called CHASE-knock-in, which combined HMEJ donor design (33) with flow cytometry based serial sorting to efficiently deliver the miniAID-mClover3 cassette to the endogenous CTCF locus in a human B-ALL cell line, SEM (31), and an immortal human erythroid precursor cell line, HUDEP-2 (32), each with doxycycline inducible OsTIR1 integration (Figure 1A and Supplementary Figure S1A).