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+ MDSC in melanoma lesions associated with both increased concentrations of CCR5 ligands and tumor progression. Tumor-infiltrating CCR5+ MDSC 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+ MDSC were enriched at the tumor site and correlated with enhanced production of CCR5 ligands. Moreover, they exhibited stronger immunosuppressive pattern compared to CCR5- MDSC. Blocking CCR5/CCR5 ligand interactions increased survival of tumor-bearing mice and was associated with reduced migration and immunosuppressive potential of MDSC in tumor lesions. Our findings define a critical role for CCR5 in recruitment and activation of MDSC, suggesting a novel strategy for melanoma treatment.