Detailed methods are described in the Supplementary Materials, including immunohistochemical staining (IHC), transient transfection and drug treatment, clinical sample collection and NK cell isolation, RNA extraction and real-time quantitative PCR analysis, ligand expression analysis, Annexin V and propidium iodide staining analysis, flow cytometry analysis of cell cycle, western blotting assay, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, vector constructs, statistical analysis and ethics statement.