Negative regulation of tumor-infiltrating NK cell in clear cell renal cell carcinoma patients through the exosomal pathway.

Natural killer cells are the key components in tumor immunity and defects in function are necessary for tumor immune escape. Emerging studies on tumor cell-derived exosomes have shown the biological significance in tumor microenvironment, but the underlying role of exosomes in regulating natural killer cells functions in clear cell renal cell carcinoma patients remains unknown. Firstly, we precisely characterized the phenotype and function of natural killer cells in clear cell renal cell carcinoma patients vs healthy controls. With an inhibitory phenotype, tumor-infiltrating natural killer cells exhibited poor cytotoxic capacity and deficient potential to produce cytokines compared with natural killer cells from tumor margin tissue and non-tumor tissue. Next, we revealed that primary tumor cells trigged natural killer cell dysfunction in an exosome-dependent manner. Interestingly, exosomes from primary tumor cells were preferentially enriched with TGF-β1 which acted as important mediator of natural killer cell functional deficiency. In vitro culture of exosomes induced natural killer cell dysfunction mediated by activation of the TGF-β/SMAD signaling pathway, and abrogated by knockdown TGF-β. Our data indicate that exosomes from clear cell renal cell carcinoma induce natural killer cells dysfunction by regulating the TGF-β/SMAD pathway to evade innate immune surveillance.