Targeting tumor-infiltrating CCR8+ regulatory T cells induces antitumor immunity through functional restoration of CD4+ Tconvs and CD8+ T cells in colorectal cancer

Background Chemokine (C-C motif) receptor 8 (CCR8) is a chemokine receptor selectively expressed on tumor-infiltrating regulatory T cells (Tregs). Strong immunosuppression mediated byCCR8(+) Tregs observed in breast and lung malignancies suggest for their functional significance in cancer therapy. To date, detailed characterization of tumor-infiltrating CCR8(+) Tregs cells in colorectal cancer (CRC) is limited. Methods To study the presence and functional involvement of CCR8(+) Tregs in CRC, we analyzed the proportions of CCR8-expressing T cells in different T cell subsets in tumor and adjacent normal tissues and peripheral blood mononuclear cells (PBMCs) from CRC patients by Flow cytometry. Also, we compared the distribution of CCR8(+) T cells in malignant tissues and peripheral lymphoid organs from a subcutaneous CRC murine model. Bioinformatic analysis was performed to address the significance of CCR8 expression levels in CRC prognosis, immune regulatory gene expression profiles and potential molecular mechanisms associated with CCR8(+) Tregs in CRC tumors. Further, we administrated an anti-CCR8 monoclonal antibody to CT26 tumor-bearing mice and examined the antitumor activity of CCR8-targeted therapy both in vivo and in an ex vivo confirmative model. Results Here, we showed that Tregs was predominantly presented in the tumors of CRC patients (13.4 +/- 5.8, p < 0.0001) and the CRC subcutaneous murine model (35.0 +/- 2.6, p < 0.0001). CCR8 was found to be preferentially expressed on these tumor-infiltrating Tregs (CRC patients: 63.6 +/- 16.0, p < 0.0001; CRC murine model: 65.3 +/- 9.5, p < 0.0001), which correlated with poor survival. We found that majority of the CCR8(+) Tregs expressed activation markers and exhibited strong suppressive functions. Treatment with anti-CCR8 antibody hampered the growth of subcutaneous CRC tumor through effectively restoring the anti-tumor immunity of CD4+ conventional T cells (CD4(+) T-convs) and CD8(+) T cells, which was confirmed in the ex vivo examinations. Conclusions Collectively, these findings illustrate the importance of CCR8(+) Tregs for an immunosuppressive microenvironment in CRC tumors by functional inhibition of CD4(+) T-convs and CD8(+) T cells, and suggest for the applicable value of CCR8-targeted therapy for CRC.