The characteristics of human NKT cells in lung cancer--CD1d independent cytotoxicity against lung cancer cells by NKT cells and decreased human NKT cell response in lung cancer patients

The activation of human Valpha24+Vbeta11+natural killer T cells (NKT) cells (Valpha24 NKT cells) induces effective antitumor responses with secondary immune effects through activation of conventional T cells and natural killer cells. In this study, we attempted to analyze the characteristics of human NKT cells in lung cancer patients. Valpha24 NKT cells stimulated with alpha-GalCer from healthy volunteers exhibited direct cytotoxic activity against two (RERF-LC-OK and PC-3) of seven human lung cancer cell lines studied. Cytotoxicity by Valpha24 NKT cells against human lung cancer cells was dependent on the perforin pathway and independent of Fas/FasL pathway. Intracellular adhesion molecule (ICAM)-1 expression on tumor cells was clearly associated with the cytotoxicity of Valpha24 NKT cells. On the other hand, the proportion of Valpha24 NKT cells in the patients with lung cancer was lower than that in the healthy volunteers. Furthermore, the proliferative response of Valpha24 NKT cells to alpha-GalCer was significantly lower in the peripheral blood mononuclear cells in the patients with lung cancer. Addition of granulocyte colony-stimulating factor moderately restored the low proliferative response of Valpha24 NKT cells in the patients with lung cancer, however the percentage by which the response was restored in these patients was still lower than the natural response in healthy volunteers. These results suggest that Valpha24 NKT cells may play a pivotal role or the antitumor response in lung cancer.