Targeting MO-MDSC infiltration by inhibiting CSF1R signaling. 3LL tumor cells were subcutaneously implanted in C57BL/6 mice, and mice were treated with control diluent or 160 mg/kg GW2580 once daily. At day 14, single-cell suspensions of tumors were analyzed by flow cytometry. Representative images and quantification of total CD11b⁺Gr-1⁺ MDSCs (A), Gr-1^loLy6C^hi MO-MDSCs and Gr-1^hiLy6C^lo PMN-MDSCs (B) are shown (n = 4/group). May-Grunwald-Giemsa staining of sorted MDSC populations within the tumor (Bi-ii). (C) Mice were implanted with 3LL tumors and treated with GW2580 once 24 hours before harvesting tumors for flow cytometric analysis. Total MDSCs, MO-MDSCs, and PMN-MDSCs were quantified (n = 3-4/group). RT-PCR analysis of Arg1 (D) and Inos (E) expression in tumors from control and GW2580-treated mice. Relative mRNA expression was normalized to β-actin (n = 6/group). Scale bars represent 50 um.