MUC1/sec-expressing tumor cells (DA-3/sec) accumulate less MDSCs, relative to MUC1/TM-expressing cells (DA-3/TM). BALB/c^nu/nu mice were implanted with 10⁶ DA-3/sec or DA-3/TM cells s.c. (A) Single-cell suspensions were produced from tumors and spleens of mice harboring tumors with volumes of 900 to 1000 mm³, then stained for myeloid-derived suppressor cell (MDSC) markers (CD11b⁺ and GR-1⁺) and analyzed by flow cytometry. (B) Blood from mice at different stages in tumor development was collected, and cells were stained and analyzed by flow cytometry for MDSC markers. (C) Blood from animals harboring similar sized DA-3/sec or DA-3/TM tumors was collected, and cells were stained and analyzed by flow cytometry for MDSC markers. (D) Plasma from normal animals and tumor bearers was assayed for urokinase plasminogen activator (uPA). Error bars representing SEM and P values are provided.