Tumor-associated macrophages recruit CCR6+ regulatory T cells and promote the development of colorectal cancer via enhancing CCL20 production in mice (66.33)

Abstract

Abstract Background: Tumor-associated macrophages (TAMs) remodel the colorectal cancer (CRC) microenvironment. Yet, findings on the role of TAMs in CRC seem to be contradictory compared with other cancers. Regulatory T (Treg)-cells dominantly infiltrate CRC. However, the underlying molecular mechanism in which TAMs may contribute to the trafficking of Treg-cells to the tumor mass remains unknown. Methodology/Principal Findings: CRC was either induced by MNU and H. pylori or established by subcutaneous injection of mouse colorectal tumor cell line (CMT93) in mice. Recruitment of FoxP3GFP+ Treg-cells was assessed using the IVIS Imaging System. A role for macrophages in trafficking of Treg-cells and in the development of CRC was investigated in CD11b diphtheria toxin receptor (CD11b-DTR) transgenic mice in which macrophages can be selectively depleted. Treg-cells remarkably infiltrated solid tumor, and predominantly expressed the homing chemokine receptor (CCR) 6 in the induced CRC model. Macrophages produced a large amount of CCL20, the sole ligand of CCR6 when co-cultured with CRC cells. Injection of recombinant CCL20 into tumor sites promoted its development with a marked recruitment of Treg-cells. Conditional macrophage ablation decreased CCL20 levels, blocked Treg-cell recruitment and inhibited tumor growth in CD11b-DTR mice. Conclusions/Significance: TAMs recruit CCR6+ Treg-cells to tumor mass and promote its development via enhancing the production of CCL20 in a CRC mouse model.