Key Points Mutational trajectories are defined by complex patterns of molecular heterogeneity in MDS, including lower-risk cases. Therapeutic intervention dynamically reshapes mutational patterns often resulting in branched or independent evolution of MDS clones.

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 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 CD11bGr1 myeloid cells was induced 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. These findings validate the importance of the CCR5/CCR5 ligand axis not only for MDSC recruitment but also for further activation of their immunosuppressive functions in the tumor microenvironment, with potentially broad therapeutic implications, given existing clinically available inhibitors of this axis. .