Cancer cell-expressed B7-H3 regulates the differentiation of tumor-associated macrophages in human colorectal carcinoma

Co-stimulatory molecule B7 homolog 3 protein (B7-H3) has been described as an important tumor antigen in various human tumors. The exact role of B7-H3 in tumor progression and its receptor are still ambiguous. The phenotype and the function of tumor-associated macrophages (TAMs) in human solid tumors are complicated and could contribute to the shaping of the tumor microenvironment. In the present study, B7-H3 expression and lymphocyte infiltration were investigated by immunohistochemistry in 117 colorectal carcinoma (CRC) patients. B7-H3 expression was positively associated with the infiltrating density of macrophage in CRC tissues, and B7-H3 expression and the infiltrating density of macrophages were negatively associated with the overall survival rate of patients. The putative B7-H3 receptor was found on activated monocytes and macrophages, indicating the direct function of B7-H3 signal on macrophages. Additional results revealed that during the differentiation of TAMs, B7-H3 promoted the polarization of type 2 macrophages (M2s) and switch of the M1 phenotype to the M2 phenotype. Thus, B7-H3 signaling promotes M2 differentiation via the putative receptor on monocytes and macrophages. Targeting the manipulation of TAMs through the B7-H3 pathway may be valuable for the development of novel immunotherapeutic strategies against human CRC.