Reversing the polarization of tumor-associated macrophages inhibits tumor metastasis

Objective: The M2 phenotype is dominant in tumor associated macrophages (TAM), and plays a key role in promoting tumor growth, invasion and metastasis. Converting TAM polarization from M2 to M1 may contribute to eliciting anti-tumor-specific immune responses and inhibiting tumor metastasis. In this study, the effect of reversing the polarization of TAM on tumor metastasis was investigated. Methods: Peritoneal macrophages were obtained from BABL/c mice, and M2 polarization was induced by IL-4. In an in vivo experiment, BABL/c mice were transplanted with 4 T1 tumor cells. In vitro and in vivo experimental studies, M2 macrophage polarization was reversed with CpG-DNA or CpG-DNA combined with anti-IL-10R Ab. CD68, MHCII and FR beta molecular expression in macrophages were examined with immunofluorescence staining. The mRNA expression of IL-2, IL-6, IL-13, VEGF and MMP-9 were detected with RT-PCR. VEGF and MMP-9 protein expression of tumors in situ was measured by western blot assay. Lung-metastasis of the tumor was observed and assessed by micro-CT. Results: CpG-DNA and CpG-DNA combined with anti-IL-10R Ab could promote MHCII, IL-2, IL-6 and IL-13 molecular expression, and suppress the expression of FRP, MMP-9 and VEGF, in both freshly isolated peritoneal macrophages and M2 macrophages. In the CpG-DNA combined with anti-IL-10R Ab injecting group, the percentage of CD68(+) MHCII+ cells were significantly higher than that of CD68(+) FR beta(+) cells (P < 0.05). This was distinct from the result of the control group, which CD68(+) FR beta(+) was higher than CD68(+) MHCII+ cells (P < 0.01). Furthermore, VEGF-A and MMP-9 level in primary tumor tissues in the experimental group was significantly lower (P < 0.01), compared to the control group. Moreover, the number of detectable lung metastasis foci was significantly lower in the experimental group than in the control group (P < 0.05). Conclusion: Reversing the polarization of TAM from M2 to M1 phenotype can inhibit tumor metastasis.