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. .

Timely and reliable distinction of sepsis from non-infectious systemic inflammatory response syndrome (SIRS) supports adequate antimicrobial therapy and saves lives but is clinically challenging. Blood transcriptional profiling promises to deliver insights into the pathomechanisms of SIRS and sepsis and to accelerate the discovery of urgently sought sepsis biomarkers. However, suitable reference genes for normalizing gene expression in these disease conditions are lacking. In addition, variability in blood leukocyte subtype composition complicates gene profile interpretation. Here, we aimed to identify potential reference genes in natural killer (NK) cells and granulocytes from patients with SIRS and sepsis on intensive care unit (ICU) admission. Discovery by a two-step probabilistic selection from microarray data followed by validation through branched DNA assays in independent patients revealed several candidate reference genes in NK cells including AKIRIN1, PPP6R3, TAX1BP1, and ADRBK1. Initially, no candidate genes could be validated in patient granulocytes. However, we determined highly similar AKIRIN1 expression also in SIRS and sepsis granulocytes and no change by in vitro LPS challenge in granulocytes from healthy donors. Inspection of external neutrophil transcriptome datasets further support unchanged AKIRIN1 expression in human systemic inflammation. As a potential new reference gene in NK cells and granulocytes in infectious and inflammatory diseases, AKIRIN1 may improve our pathomechanistic understanding of SIRS and sepsis and help identifying new sepsis biomarkers.

Natural killer (NK) cells are among the first innate immune cells to arrive at sites of tissue inflammation and regulate the immune response to infection and tumors by the release of cytokines including interferon (IFN)γ. In vitro exposure to the innate cytokines interleukin 15 (IL-15) and IL-12/IL-18 enhances NK cell IFNγ production which, beyond 16 h of culture, was shown to depend on metabolic switching to glycolysis. NK effector responses are, however, rapid by comparison. Therefore, we sought to evaluate the importance of glycolysis for shorter-term IFNγ production, considering glucose deprivation and hypoxia as adverse tissue inflammation associated conditions. Treatments with IL-15 for 6 and 16 h were equally effective in priming early IFNγ production in human NK cells in response to secondary IL-12/IL-18 stimulation. Short-term priming was not associated with glycolytic switching but induced the release of IFNγ and, additionally, CCL3, CCL4 and CCL5 from both normoxic and hypoxic NK cells in an equally efficient and, unexpectedly, glucose independent manner. We conclude that release of IFNγ and CC chemokines in the early innate immune response is a metabolically autonomous NK effector program.