In vitro plating of B-ALL cells from vehicle- versus MMP-9-inhibitor-treated mice on wild type MSC in limiting dilution to test proliferation of B-ALL cells demonstrated reduced cell proliferation if the cells were derived from an MMP-9 inhibitor-derived BMM (P = 0.009, Fig. S9D). Here, MMP9 is linked to precursor B-cell acute lymphoblastic leukemia.