We then cocultured these cells with a HER2-overexpressing breast cancer cell line, SK-BR-3 cells, and found that the characteristics of NK cells, including trastuzumab-induced IFN-γ secretion and rapid degranulation, as evidenced by CD107a externalization24, remained unchanged after expansion (Supplementary Fig. S2c, d). This evidence concerns the gene IFNG and breast cancer.