Both MDSC subfractions have the capacity to suppress antigen-driven T-cell responses. (A) OT-1 splenocytes were stimulated with either 1 μg/mL anti-CD3 or 250 μg/mL ovalbumin protein (OVA), in the presence of various amounts of purified total EG7 CD11b⁺Gr-1⁺ MDSCs, in a short-term culture (“Methods”). Graphs represent the average level of ³H-thymidine incorporation plus or minus SD, expressed as counts per minute (CPM), for each MDSC/splenocyte ratio. One representative experiment of 3 is shown. (B) Similar experiment as panel A, whereby OT-1 splenocytes were activated by OVA in the presence of various amounts of purified EG7 MO-MDSCs or PMN-MDSCs. One representative experiment of 8 is shown. (C) Percentage suppression induced by EG7 MO-MDSC and PMN-MDSC fractions at a 1:1 MDSC/splenocyte ratio, as observed in 8 individual experiments. (D) MO- and PMN-MDSCs were purified from EG7 tumor–bearing β2-microglobulin–deficient C57BL/6 mice and added to OT-1 cultures together with OVA. Percentage suppression represents the mean of 3 individual experiments. (E) OT-1 splenocytes were stimulated with OVA in the presence of BW-Sp3–induced AKR MO- or PMN-MDSCs (1:1 ratio) and percentage suppression was calculated. One representative experiment of 2 is shown. *P < .05; **P < .01.