PRF1 and hepatocellular carcinoma: To further study the role of ICAM-1 in the NK resistance of HCC cells, we transfected SMMC-7721 and QGY-7703 with pcDNA3.1-ICAM-1 plasmid (Fig. 5J–L), and examined their susceptibility to NK cells through the calcein release assay (Fig. 5M, N), perforin polarization assay (Fig. 5O, P) and conjugation assay (Fig. 5Q, R).