NK Cell Exosomes Alleviate PD-L1 Expression and Facilitate Tumor Immunity by Repressing PI3K-AKT-mTOR Signaling

BACKGROUND: Liver cancer (LC) is a deadly malignancy with limited therapeutic options in recent years. Natural killer cell-derived exosomes (NK-exo), as an important bridge of information transmission between cells, also have a certain killing effect on tumor cells. On this basis, this study investigated the specific regulatory mechanism of NK-exo on LC cells. METHODS: T cells in each treatment group was determined by enzyme-linked immunosorbent assay (ELISA) kits. We employed flow cytometry to analyze the expression of PD-L1 protein on the surface of LC cells and CD8 level in mice tumor tissues. RESULTS: T cells, the proliferation ability and cytokine secretion content of T cells were considerably elevated, and the expression of PD-L1 on LC cell surface was considerably reduced. However, these effects were restored to control levels by PI3K agonists.The in vivo experiments also confirmed that NK-exo could effectively inhibit the progression of LC, and the PI3K agonist could restore this effect to the level of the control group. CONCLUSION: This study provided the first evidence that exosomes derived from NK cells inhibited the PI3K-AKT-mTOR signaling pathway in LC cells, and reduced PD-L1 expression, thereby promoting tumor immunity. In comparison to traditional immune checkpoint inhibitors, NK-exo possessed unique mechanisms of action and potential advantages. NK-exo holds the promise of becoming an innovative immunotherapy for the treatment of LC.