In vitro repolarized tumor macrophages inhibit gastric tumor growth

Gastric cancer is the second most frequent cause of cancer-related death worldwide. Combined surgery and chemo/radiotherapy give only a limited 5-year survival rate. Alternative therapeutic strategies such as immunotherapy are needed to improve this survival rate. Macrophages are functionally plastic cells. Type 1 macrophages (M1) inhibit, whereas type 2 macrophages (M2) promote, tumor growth. In this study, we examined the effects of in vitro repolarized tumor macrophages on gastric tumor growth in vivo. We demonstrated that peritoneal macrophages isolated from mouse forestomach carcinoma (MFC) tumor-bearing mice (TPM) displayed a M2 functional phenotype as indicated by a characteristic cytokine production profile and expression pattern of inducible nitric oxide synthase (iNOS) and arginase (Arg) of M2 macrophages. Treatment of TPM with type 1 cytokine IL-12 and IFN-gamma repolarized TPM toward the M1 phenotype as confirmed by a cytokine production profile and expression pattern of iNOS and Arg of typical M1 macrophages. Repolarized TPM significantly inhibits the growth of MFC tumors implanted subcutaneously compared to peritoneal macrophage (PM) isolated from normal animals, TPM, or M2 macrophages. Our study supports in vitro repolarization of macrophages as a potential immunotherapeutic strategy for gastric cancer.