PGE2 mediates the enhanced development of MDSCs in human cancer environment. (A) Correlation between the PGE2 production and the frequencies of cancer-infiltrating CD11b+CD33+ cells from different patients. The percentage of cancer-infiltrating CD11b+CD33+ cells was determined by flow cytometry (n = 5 patients). The regression line and corresponding R2 value are shown. (B) MDSC phenotype induced in GM-CSF+IL-4–cultured monocytes by membrane-permeable soluble factor(s) produced by cancer-infiltrating cells. Similar data were obtained using the CM from cancer-infiltrating cells and in a Transwell system (see supplemental Figure 3 for experimental design). Left panel: Suppression of DC differentiation by CM from cancer-infiltrating cells (manifested by loss of the DC marker CD1a). Right panel: Induction of the CD1a−CD14+DCSIGN−CD80−CD83− MDSC phenotype. (C) mRNA levels of IL-10, arginase 1 (ARG1), IDO1, IL-4Rα, and COX2 in cancer-induced MDSCs. (D) Suppressed CD3/CD28–induced proliferation of granzyme B+ CTL (percentages) in the presence of cancer-induced MDSCs. Left panel: Percentages indicate the fraction of proliferating granzyme B+CD8+ cells. Right panel: Percentage of proliferating CD8+ T cells in the presence of cancer-induced MDSCs (cancer d0) and cancer-conditioned DCs (cancer d6). (E) Induction of immunosuppressive factors by cancer-associated PGE2. (F) Induction of CD14+ MDSCs by CM from cancer-infiltrating cells is suppressed by COX2 inhibition and restored by synthetic PGE2. (G) Regulation of COX1 and COX2 expression by CM from cancer-infiltrating cells generated in the presence or absence of celecoxib and/or synthetic PGE2 and analyzed after 6-10 hours. (H) Immunosuppressive effects of cancer-induced MDSCs on naive CFSE-labeled CD8+ T cells primed by CD3/CD28 and stained for granzyme B. Cancer-infiltrating primary cell CM was generated in the presence or absence of the COX2 inhibitor celecoxib. (I) Induction of immunosuppressive factors by PGE2, the EP4 agonist CAY10598, the EP2 agonist butaprost, but not the EP3/1 agonist sulprostone. All data (panels A-I) were confirmed in 3-7 independent experiments. Histograms present data from a single representative experiment with different donors as mean ± SD.