Further, the percentage of BCR-ABL1+ (GFP+) BP-1+ cells in BM (P = 0.05, Fig. 3a) was reduced, which is likely causative of the survival prolongation in secondary recipient mice transplanted with BM from MMP-9-deficient mice with B-ALL (Fig. 1d). Here, MMP9 is linked to precursor B-cell acute lymphoblastic leukemia.