Supernatant derived from a human hepatocellular carcinoma cell line (PLC/PRF/5) depresses natural killer (NK) cell activity.

Harvest fluid derived from a human primary hepatocellular carcinoma cell line (PLC/PRF/5) inhibited normal peripheral blood NK-cell activity when either PLC/PRF/5 or K562 cells were employed as targets. MN cells incubated with the PLC/PRF/5 supernatant for only 6 h demonstrated depressed NK-cell activity, which was partially reversible if the cells were washed and incubated in fresh medium for 24 h. Enriched NK cells obtained on discontinuous Percoll gradients employing human tonsillar cells also showed depressed cytotoxicity when treated directly with the tumour harvest fluid. Furthermore, the binding of these cells to the tumour targets could be inhibited by prior treatment of the NK cells with the tumour supernatant. It is suggested that materials produced by tumours may inhibit NK-cell activity by blocking a receptor site on the effector cell, thereby allowing the tumour to proliferate.