Abstract
Natural killer (NK) and CD56(+) T cells are thought to play a central role in antitumour immunity. Their cytolytic activities are controlled by a variety of receptors including CD94 and killer immunoglobulin-like receptors (KIR), which bind to major histocompatibility complex (MHC) class I molecules on target cells and mediate cell activation or inhibition. We have examined the numbers, phenotypes and antitumour cytotoxic functions of hepatic NK and CD56(+) T cells isolated from 22 patients with hepatic malignancy and 19 healthy donors. Flow cytometry revealed that NK cell numbers were increased among hepatic mononuclear cells in malignancy compared to histologically normal livers (mean: 38% vs 27%; P=0.03), but CD56(+) T cell numbers were not (28% vs 27%). NK cells and CD56(+) T cells from tumour-bearing livers exhibited lymphokine-activated killing of K562 targets and T cell receptor-mediated lysis of P815 cells. The expression of CD94 and the KIR isotypes CD158a, CD158b and KIR3DL1 by CD56(+) T cells and NK cells was significantly and consistently reduced in tumour-bearing livers compared to healthy livers ( P<0.05 in all cases). Simultaneous ligation of CD158a, CD158b and KIR3DL1 caused an overall partial inhibition of CD56(+) T cell cytotoxic activity, suggesting that the observed reductions in KIR(+) cell numbers in malignancy are likely to lead to enhanced cytotoxicity. Our results suggest that, while hepatic CD56(+) T cells are not expanded in malignancy, downregulation of KIR and CD94 expression may be a mechanism by which the hepatic immune system can be activated to facilitate tumour rejection.