As revealed by the punctate staining pattern for MMP-9 by immunohistochemistry, however, these high levels of MMP-9 in healthy controls and CML patients were likely due to MMP-9 production by myeloid cells compared with a more diffuse staining pattern in B-ALL patients (Fig. S11C). This evidence concerns the gene MMP9 and precursor B-cell acute lymphoblastic leukemia.