Lysis of tumor cells in vitro and in vivo is dependent on NKG2D ligands expressed on the tumor cells. (A) Staining of tumor cells by PE-labeled NKG2D tetramer. As a control, cells were incubated with PE-conjugated streptavidin. (B) Cytotoxicity of NK cells isolated from naive or DC-treated mice against A20, MPC11, and YAC cells. Cytotoxicities against CT26 and against MPC11 were identical. In some experiments, A20 cells were blocked with NKG2D tetramer. □ indicates naive mouse, A20 target; ▵, DC mouse, A20 target; ▴, DC mouse, YAC target; ⋄, DC mouse, A20 target + tetramer; and ×, DC mouse, MPC11 target. E/T ratio indicates effector-target ratio. (C) Preincubation of A20 cells with NKG2D tetramer abrogates the protective effect of DC. indicates DC + A20; ▴, DC + A20 + tetramer; and ×, tumor control.