Differences in the ability of MDSCs to suppress polyclonal T-cell activation are tumor driven. (A) OT-1 splenocytes were stimulated with OVA in the presence of BW-Sp3– or EG7-induced F1 MO- or PMN-MDSCs (1:1 ratio). One representative experiment of 2 is shown. (B) OT-1 splenocytes were stimulated with OVA in the presence of EG7 F1 MO- or PMN-MDSCs (1:1 ratio) with or without 0.5 mM L-NMMA. One representative experiment of 2 is shown. *P < .05 (C) BW-Sp3 and EG7 tumors were grown in (AKR × C57BL/6)F1 mice and total MDSCs were purified from mice with similar tumor diameters. Subsequently, BW-Sp3– and EG7-induced F1 MDSCs were added in various amounts to naive F1 splenocytes, which were subjected to the long-term culture protocol. One representative experiment of 3 is shown. (D) MO- and PMN-MDSCs were individually purified from BW-Sp3 tumor–bearing F1 mice and were added in various amounts to naive F1 splenocytes, which were subjected to the long-term culture protocol.