Abstract: ObjectiveTo analyse the effects of IL-15 on the expression of NKG2D and the cytotoxicity of cytokine-induced killer (CIK) cells against human esophagus carcinoma cell EC9706 in vitro. MethodsPeripheral blood mononuclear cells were isolated from healthy donors then divided into two groups: the control group ( cells were cultured in the presence of IFN-γ, anti-CD3 antibody and IL-2) and IL-15 group (cells were cultured in the presence of IFN-γ, anti-CD3 antibody, IL-2 and 10 ng/ml IL-15). Phenotypic characteristics of CIK cells and the expression of NKG2D were analyzed by flow cytometry. After 14 days culture, cytotoxicity of CIK cells against EC9706 cells was measured by using a standard LDH releasing assay. Effector cells were added to target cells at E∶T radios of 20∶1, 30∶1. In blocking experiments, NKG2D monoclonal antibody was added to CIK cells for 15 min before plating at 30∶1 E∶T ratio. ResultsNKG2D molecules were significantly up-regulated during the culture period on CD3+ cells (the CIK cells population) and the CD56+cells. The differences of NKG2D expressions were significant between IL-15 group and the control group (P＜0.05). Cytotoxicity of CIK cells treated by the IL-15 group was higher than that of the control group, both at 20∶1 E∶T ratios and at 30∶1 E∶T ratios (P＜0.05). When the NKG2D molecules on CIK cell ular membrance were blocked by the NKG2D monoclonal antibody, the cytolytic activity in the control group cells and IL-15 group cells was significantly inhibited. ConclusionIL-15 up-regulated the expression of NKG2D on CIK cells, which enhanced the NKG2D mediated cytotoxicity against EC9706 cells.CIK cells played a role through the NKG2D molecules.