Schematic representation of the proposed tumor-promoting role of monocytes in BCP-ALL via the CXCL10/CXCR3 axis. The figure shows BCP-ALL cells to “condition” monocytes for elevated expression of the chemokine CXCL10. Increased CXCL10 release by these monocytes would possibly set up a chemokine gradient across which the CXCR3⁺ BCP-ALL cells migrate (into the tissue), invade, and possibly lead to metastatic spread. It may be noted that CXCL10 induced MMP9 expression and activity in the BCP-ALL cells, which may explain its role in promoting their invasion. In addition, the “conditioned” monocytes also show elevated MMP9 expression and activity, which can as well contribute to the invasion and spread of BCP-ALL cells.