Therefore, we utilized our previously reported high-efficiency knock-in strategy, ‘CHASE knock-in’ (Hyle et al., 2019), to deliver the P2A-mCherry cassette upstream of the HOXA9 stop codon in a patient-derived human B-ALL cell line, SEM, which has a typical B-ALL signature along with a t(4;11) translocation and maintains one single allele expression of the HOXA gene cluster (Figure 1—figure supplement 1D). This evidence concerns the gene HOXA9 and acute lymphoblastic leukemia.