TUMOUR-DERIVED SOLUBLE FACTORS INDUCE DIFFERENTIATION OF MONOCYTES INTO M2-POLARIZED MACROPHAGES

Blood monocytes are recruited at the tumour site where they differentiate into macrophages having, mostly, pro-tumoral functions. To investigate the role of the tumor micro-environment on the macrophage differentiation, we cultured freshly isolated human monocytes with pancreatic cancer cell line supernatants. After 5 days, about 50% of the monocytes were differentiated into macrophages in the absence of exogenous cytokine addition. Tumour supernatants did not contain detectable IL-6 or IL-10. The role of known growth and differentiation factors such as IL-3, GM-CSF and M-CSF was considered and excluded. The phenotype analysis of tumour-conditioned macrophages (TC-macro) demonstrated high expression of the mannose receptor, scavenger receptor, CD68 and low levels of MHC class II. The functional activity as APC of TC-macro in MLR and Antigen presentation assay was remarkably impaired. TC-macro produced IL-10, IL-6 and, after LPS stimulation, TNF but not IL-12. Moreover, TC-macro produced a panel of chemokines including CCL2, CXCL8, CCL17 and CXCL10. The transcriptional profile of TC-macro is currently under evaluation; several genes in line with an M2 polarization are highly expressed. The nature of the tumour-derived factors inducing macrophage differentiation is at present under investigation. Initial biochemical studies indicated that the biological activity is excluded from exosomes and have a high molecular weight (>100.000 KDa). A differential proteomic analysis of tumour supernatants from cell lines with and without differentiating ability suggested a high number of proteins as possible differentiating factors. The identification of novel tumour-derived factors inducing macrophage differentiation may shed new light in the cross-talk between tumor cells and macrophages and identify candidate targets for novel anti-tumour therapies.