To investigate whether the upregulation of ABCG1 contributes to the MTX resistance in ALL, we employed lentiviral shRNAs (Figures 3A,B) and the CRISPR-Cas9 system (Supplementary Figure S2A) to knock down ABCG1 in Reh and Reh-MTXR cells. The gene discussed is ABCG1; the disease is acute lymphoblastic leukemia.