CCR5+ Myeloid-Derived Suppressor Cells Are Enriched and Activated in Melanoma Lesions

Accumulation of myeloid-derived suppressor cells (MDSC) in melanoma microenvironment is supported by chemokine receptor/chemokine signaling. Although different chemokines were suggested to be involved in this process, the role of CCR5 and its ligands is not established. Using a Ret transgenic mouse melanoma model, we found an accumulation of CCR5(+) MDSCs in melanoma lesions associated with both increased concentrations of CCR5 ligands and tumor progression. Tumor-infiltrating CCR5(+) MDSCs displayed higher immunosuppressive activity than their CCR5(-) counterparts. Upregulation of CCR5 expression on CD11b(+)Gr1(+) myeloid cells was induced in vitro by CCR5 ligands and other inflammatory factors. In melanoma patients, CCR5(+) MDSCs were enriched at the tumor site and correlated with enhanced production of CCR5 ligands. Moreover, they exhibited a stronger immunosuppressive pattern compared with CCR5(-) MDSCs. Blocking CCR5/CCR5 ligand interactions increased survival of tumor-bearing mice and was associated with reduced migration and immunosuppressive potential of MDSCs in tumor lesions. Our findings define a critical role for CCR5 in recruitment and activation of MDSCs, suggesting a novel strategy for melanoma treatment. (C) 2017 AACR.