KLRK1 and hepatocellular carcinoma: The CAR-T cells with extracellular domains containing human NKG2D, 4-1BB, and CD3 ζ signal domain (BBZ) had effective kill effects on hepatoma cell lines SMMC-7721 and MHCC97H cell lines with high expression of NKG2DL in vitro and in vivo, but had ineffective cytotoxic effects on SMMC-7721 or Hep3B cell lines with negative NKG2DL.