The activating receptors on the surface of NK cells co-cultured with HCC cells was significantly increased by the treatment of rhIL-21 (Fig. 6, NKG2D+; control 18.18%, rhIL-21 23.37%, NKp44+; control 18.82%, rhIL-21 22.29%, NKp30+; 39.81%, 52.34%, NKG2C+; control 6.32%, rhIL-21 7.98%, *p < 0.05). This evidence concerns the gene KLRK1 and hepatocellular carcinoma.