C-C chemokine receptor 4 (CCR4)-positive regulatory T cells interact with tumor-associated macrophages to facilitate metastatic potential after radiation.

PURPOSE: Our previous study revealed that elevated C-C motif chemokine ligand 2 (CCL2) secretion by irradiated cancer cells recruited C-C motif chemokine receptor 2 (CCR2)-positive myeloid cells and polarized M2-type tumor-associated macrophages (TAMs), promoting lung metastasis in an established mouse model. This study investigated the impact of CCL2 and TAMs on adaptive immunity. METHODS: We assessed the influence of CCL2 and TAMs on adaptive immunity through two ectopic allograft mouse models constructed with MB49 bladder cancer cells and Lewis lung carcinoma cells. Both models exhibited delayed primary tumor growth following radiation therapy (RT), but RT promoted the development of pulmonary metastases in C57BL/6 mice. Additionally, we employed a direct coculture system to investigate the interaction between macrophages and target cells in the context of adaptive immunity. RESULTS: C-C motif chemokine receptor 4 (CCR4)-positive regulatory T cells (Tregs) were recruited to the postirradiated tumor microenvironment (TME). Utilizing a CCR4 antagonist to inhibit CCL2-CCR4 activation reversed the infiltration of CCR4 + Tregs and reduced the incidence of pulmonary metastases. In addition, a positive feedback loop between M2-type TAMs and Tregs was observed. The combined blockade of the CCL2-CCR4 and CCL2-CCR2 signaling pathways further decreased the risk of RT-promoted lung metastasis. CONCLUSION: The recruitment of CCR4 + Tregs to the postirradiated TME increases the metastatic potential of tumor cells through increased interactions with M2-type TAMs. A significant reduction in post-RT lung metastases in ectopic mouse models was achieved by disrupting the recruitment of both CCR4 + Tregs and CCR2 + myeloid cells, which are TAM precursors.

Tumor-Derived C-C Motif Ligand 2 Induces the Recruitment and Polarization of Tumor-Associated Macrophages and Increases the Metastatic Potential of Bladder Cancer Cells in the Postirradiated Microenvironment.

PURPOSE: Radiation therapy (RT) is mainly used for bladder preservation in patients with muscle-invasive bladder cancer. The response of urothelial tumors to RT remains unsatisfactory. We investigated the interaction of RT and tumor-associated macrophages (TAMs) in the context of bladder cancer radioresistance. METHODS AND MATERIALS: We evaluated the therapeutic effects of RT and TAM distribution by establishing an ectopic allograft mouse model. A Transwell coculture system was used to simulate the interaction between TAMs and MB49 bladder cancer cells in the tumor microenvironment. Cytokines and chemokines were analyzed in irradiated MB49 cells. Colony formation and Boyden chamber assays were used to assess the cytotoxic effects and the effects of TAMs on MB49 cell invasion, respectively. RESULTS: Local RT delayed primary tumor growth but promoted pulmonary metastases in C57BL/6 mice. Increased secretion of C-C motif chemokine ligand (CCL2) by irradiated MB49 cells, especially in the presence of M1-type TAMs, contributed to the infiltration of bone marrow-derived C-C motif chemokine receptor 2 (CCR2)-positive myeloid cells and the polarization of M1-type TAMs toward the M2 type to promote MB49 cell invasion. Blockade of CCL2-CCR2 activation by a CCR2 antagonist reversed the phenotypic TAM transformation and suppressed pulmonary metastases. CONCLUSIONS: Bladder cancer cells responded to RT by producing CCL2, which recruited TAM precursors from bone marrow and polarized M1-type TAMs toward the M2 type. This phenotypic TAM transformation promoted the pulmonary metastasis of bladder cancer cells after RT. Disrupting the CCL2-CCR2 signaling axis in combination with RT holds promise for improving RT efficacy in bladder cancer.