Natural killer T (NKT) cells are CD1d-restricted lymphoid cells and are characterized by an invariant T-cell receptor, which in humans consists of a Va24 chain paired with a Vb11 chain. These cells are known for their rapid production of large amounts of cytokines (e.g.,
Vb11+ NKT cell numbers in both healthy controls and cancer patients and demonstrate that in both groups females have higher NKT cell levels compared to males. In a large group of 120 cancer patients, we show that circulating Va24+ NKT cell numbers are about 50% lower than in ageand gender-matched healthy controls and that this decrease is independent of tumor type or tumor load. This decrease was not restored upon tumor removal by means of surgery or radiotherapy. Even though the percentage of NKT cells that secrete IFN-g, as detected by ELISPOT, is normal in cancer patients, the absolute number of circulating IFN-g-secreting NKT cells is reduced. Together, our results suggest that the reduced circulating Va24 +
Vb11+ NKT cell numbers in cancer patients are not affected by tumor load, but might actually reflect a risk factor for tumor development, e.g., by hampering efficient tumor immunosurveillance. ' 2005 Wiley-Liss, Inc.