BACKGROUND AIMS: Cytokine-induced killer (CIK) cells have shown cytolytic activity against several tumor cells in vitro and in animal tumor models. Furthermore, CIK cells activated by dendritic cell (DC) stimulation show increased anti-tumor activity. This study aimed to evaluate the clinical efficacy of DC-activated CIK cell treatment following regular chemotherapy and the effects of this therapy on immune responses in patients with non-small cell lung cancer (NSCLC) after surgery. METHODS: A paired study, with 42 patients in each group with stage I-IIIa NSCLC after surgery, was performed. Patients received chemotherapy alone (CT) or chemotherapy and DC-activated CIK cell treatment (immuno-CT). Disease-free survival (DFS) and overall survival were evaluated. CIK cell cytotoxicity against tumor cells was detected using a lactate dehydrogenase-based method. Serum cytokine levels in the immuno-CT group were detected using cytokine antibody arrays. RESULTS: The cytotoxicity of CIK cells was significantly enhanced by DC activation. The 2-year overall survival rate in the immuno-CT group was significantly improved compared with the CT group (94.7 +/- 3.6% versus 78.8 +/- 7.0%, P < 0.05). The 2-year DFS of these two groups showed no significant difference. DC-activated CIK cell treatment increased production of cytokines that have known anti-tumor effects, including IFN-gamma, MIG, TNF-alpha and TNF-beta, in patients who had no progression, but they were not found in patients who developed recurrence/metastasis. CONCLUSIONS: This study suggests that the role of DC-activated CIK cells in improvement of chemotherapy for malignant tumor treatment is associated with up-regulation of the production of cytokines involved in the anti-tumor effect.