Cytokine-induced killer (CIK) cells have shown antitumor activity against several tumor cells both in vitro and in vivo. This study reports on the large-scale expansion of CIK cells and also present preliminary results from a pilot clinical trial. Sixteen (16) patients with renal cell carcinoma (RCC), all of whom had metastases after radical nephrectomy and adjuvant therapy using interferon-alpha (IFN-alpha) and/or interleukin-2 (IL-2), were treated with CIK cells. CIK cells were generated from peripheral blood mononuclear cells (PBMCs) and incubated in the presence of IFN-gamma followed by OKT3 and IL-2. Treatment schedule consisted of two to three cycles of CIK cell infusions at an interval of 3 weeks. A total of 46 infusions were administered to 16 metastatic RCC (mRCC) patients. The median number of transferred cells per treatment was 6.7 x 10(9) (range, 2.5-12.3). At a 60:1 effector-target cell ratio, CIK cells killed 51.4% and 32.1% of two human kidney tumor cell lines (293 and SK-RC-42), respectively. After CIK cell infusion, the percentage of CD3(+), CD8(+), CD3(+)CD56(+), and NKG2D(+) cells and the intracellular products of two type 1 cytokines (IFN-gamma and tumor necrosis factor alpha) significantly increased in the patients' PBMCs. Toxicity was minimal, and there were no immediate adverse reactions to the infusions. Three (3) patients had complete response, 1 patient had partial response, and 6 patients had stable disease. These results showed that adoptive CIK cell immunotherapy is a safe and effective treatment, which may have essential benefits for the improvement of the immunologic function in mRCC patients and play an important role in the treatment of mRCC.