BACKGROUND AIMS: Cytokine-induced killer cells (CIKs) were shown to be a promising tool in the quest for new therapeutic approaches in the setting of metastatic solid tumors refractory to standard treatments. However, there is a practical clinical problem of different expansion rates and cell function as individual variability exists. Stimulatory molecular 4-1BB could promote division and survival of T cells and enhance effector activity including cytokine production. This study aimed to invest the contribution of co-stimulation signal to CIKs production for exploring new strategies, which increase the expansion and reliability of CIKs generation to improve access to CIKs therapy. METHODS: We studied the larger-scale expansion of CIKs cultured with engineered cells for costimulatory enhancement (ECCE) consisting of K562 cells that expressed 4-1BBL in heavily pretreated patients with solid tumor. The proliferation and cytotoxic capacity of CIKs were evaluated. Phenotypes of CIKs were analyzed using flow cytometry. Cytokine levels of interferon (IFN)-γ and tumor necrosis factor (TNF)-α were detected using enzyme-linked immunosorbent assay (ELISA). RESULTS: The proliferation and cytotoxic activity of CIKs were significantly up-regulated by ECCE. The percentages of CD3(+)CD8(+) and CD3(+)CD56(-) CIKs were significantly increased while the percentage of CD3(+)CD56(+) CIKs was decreased. In addition, the secretion of IFN-γ and TNF-α by CIKs could also be enhanced significantly when ECCE were added into the culture system. CONCLUSIONS: This study suggests that ECCE may improve the efficacy of CIKs therapy and make CIKs therapy possible for the patients whose CIKs would be hard to be cultured using conventional methods.