Here, tumor-infiltrating CD11b(+) myelomonocytoid cells in murine colon adenocarcinoma-38 and GL261 murine glioma were phenotypically characterized. Over 90% were of the CD11b(+)F4/80(+) monocyte/macrophage lineage. They also had a myeloid-derived suppressor cell (MDSC) phenotype, as they suppressed the proliferation of activated splenic CD8(+) T cells and had a CD11b(+)CD11c(+)Gr-1(low)IL-4Ralpha(+) phenotype. In addition, the cells expressed CX(3)CR1 and CCR2 simultaneously, which are the markers of an inflammatory monocyte. The MDSCs expressed CD206, CXCL10, IL-1beta, and TNF-alpha mRNAs. They also simultaneously expressed CXCL10 and CD206 proteins, which are typical, classical (M1) and alternative (M2) macrophage activation markers, respectively. Peritoneal exudate cells (PECs) strongly expressed CD36, CD206, and TGF-beta mRNA, which is characteristic of deactivated monocytes. The MDSCs also secreted TGF-beta, and in vitro culture of MDSCs and PECs with anti-TGF-beta antibody recovered their ability to secrete NO. However, as a result of secretion of proinflammatory cytokines, MDSCs could not be categorized into deactivated monocyte/macrophages. Thus, tumor-infiltrating MDSCs bear pleiotropic characteristics of M1 and M2 monocytes/macrophages. Furthermore, CD206 expression by tumor-infiltrating MDSCs appears to be regulated by an autocrine mechanism that involves TGF-beta.

T cells in mice treated with PC61 was approximately twice that in mice treated with PBS. The numbers of tumor-infiltrating CD4+ and natural killer cells were also increased significantly. To test the antimetastatic effects of IL-2 treatment in combination with Treg-cell depletion, human recombinant IL-2 (rIL-2) and PC61 were administered to mice implanted with MC38/ mock cells in the spleen, and hepatic metastasis was investigated. The average liver weight in mice treated with rIL-2 plus PC61 was 1.04 ± ± ± ± 0.03 g, less than that in mice treated with rIL-2 (2.04 ± ± ± ± 0.51 g) or PC61 alone (1.81 ± ± ± ± 0.38 g). We conclude that IL-2-induced antitumor immunity is enhanced by Treg-cell depletion and is due to expansion of the tumor-infiltrating cytotoxic CD8 + T-cell population. (Cancer Sci 2007; 98: [416][417][418][419][420][421][422][423]

Mononuclear phagocytes (MPCs) at the tumor site can be divided into subclasses, including monocyte-lineage myeloid-derived suppressor cells (MDSCs) and the immunosuppressive tumor-infiltrating macrophages (TIMs). Cancer growth coincides with the expansion of MDSCs found in the blood, secondary lymphoid organs, and tumor tissue. These MDSCs are thought to mature into macrophages and to promote tumor development by a combination of growth-enhancing properties and suppression of local antitumor immunoresponses. As little is known about either subset of MPCs, we investigated MPCs infiltrating into murine adenocarcinoma MCA38 tumors. We found that these MPCs displayed immunosuppressive characteristics and a MDSC cell-surface phenotype. Over 70% of the MPCs were mature (F4/80(+)Ly6C(-)) macrophages, and the rest were immature (F480(+) Ly6C(+)) monocytes. MPC maturation was inhibited when the cells infiltrated a tumor variant expressing IL-2 and soluble TNF type II receptor (sTNFRII). In addition, the IL-2/sTNFRII MCA38 tumor microenvironment altered the MPC phenotype; these cells did not survive culturing in vitro as a result of Fas-mediated apoptosis and negligible M-CSFR expression. Furthermore, CD4(+) tumor-infiltrating lymphocytes (TILs) in wild-type tumors robustly expressed IL-13, IFN-gamma, and GM-CSF, and CD4(+) TILs in IL-2/sTNFRII-expressing tumors expressed little IL-13. These data suggest that immunotherapy-altered Th cell balance in the tumor microenvironment can affect the differentiation and maturation of MPCs in vivo. Furthermore, as neither the designation MDSC nor TIM can sufficiently describe the status of monocytes/macrophages in this tumor microenvironment, we believe these cells are best designated as MPCs.

Abstract. In order to evaluate host immune response to cancer, many methods have been applied. However, in the field of oral squamous cell carcinoma, evaluation of host immune response on the basis of proliferative activity of tumor-infiltrating T-cells (TIL) has not been reported. Therefore, we applied double immunohistochemical staining of proliferation markers Ki-67 and CD8 to surgically resected and paraffin-embedded tissue sections for 35 cases of oral squamous cell carcinoma. With this method, there was a significant correlation between the percentage of Ki-67 + CD8 + TIL and the intra-tumor epithelium infiltration rate of CD8 + TIL (P=0.0237). In the process of analysis, we found that the proliferative activity of CD8 + TIL tended to correlate (P=0.0859) with clinical N factor (lymph node metastasis), which was previously reported to suppress host immune response. We therefore assumed there was another factor inducing host immune response. The proliferative activity of CD8 + TIL was well correlated with preoperative radiotherapy (P=0.0200) while there was no significant correlation between the proliferative activity of CD8 + TIL and other clinical factors; age, tumor size, clinical stage, pathological N factor (P=0.5410, 0.7769, 0.1041, and 0.1072, respectively). Our present results strongly imply that preoperative radiotherapy is a very important factor in oral squamous cell carcinoma inducing host immune response regardless of the clinical factors present.

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