KLRK1 and prostate cancer: To determine whether NKG2D-CAR T cells can recognize and lyse prostate cancer cells such as PC-3, DU 145 and C4-2, which expresses a high level of NKG2DLs (Additional file 1: Figure S1), the cytotoxicity of NKG2D-CAR T cells against the NKG2DLs+ prostate cancer cells was determined by detection of the apoptosis of the target cells.