Synergistic cytotoxicity of ex vivo expanded natural killer cells in combination with monoclonal antibody drugs against cancer cells

► An ex vivo feeder-cell-free method was established for large-scale NK cell expansion. ► The expanded NK cells showed higher cytokine production in response to cancer cell. ► The expanded NK cells showed higher cytotoxicity against various cancer cells. ► The expanded NK cells showed synergistic cytotoxicity when combined with mAb drug. ► Cancer therapy by combination of expanded NK cells with mAb drugs is a useful tool.