Cytokine-enhanced cytolytic activity of Exosomes from NK Cells

Natural killer (NK) cells are a type of innate lymphocytes that play key roles in immune surveillance against tumors and viral infection. NK cells distinguish abnormal cells from healthy cells by cell-cell interaction with cell surface proteins and then attack target cells via multiple mechanisms involving TRAIL, Fas Ligand, cytokine secretion, perforin, and granzymes. In addition, extracellular vesicles (EVs), including exosomes derived from NK cells (NK-EVs), possess cytotoxic capacity against tumor cells, but their characteristics and regulation by cytokines remain unknown. Here, we report that EVs derived from human NK-92 cells stimulated with IL-15 + IL-21 show enhanced cytotoxic capacity against tumor cells in a granzyme B independent manner. In addition, small RNA-seq and mass spectrometry analyses indicate that miRNA and protein profiles in EVs are altered by cytokine stimulation. We also show NK-EVs are taken up by target cells via macropinocytosis. Collectively, our findings reveal novel characteristics of NK-EVs and the mechanism of their incorporation into target cells.