γδ T cell-based cancer immunotherapy is attracting attention for the treatment of various malignancies because these cells secrete Th1-type cytokines, exert potent cytotoxicity against a variety of cancer cells. We have established a large-scale in vitro expansion method for Vγ9Vδ2 T cells using zoledronate and interleukin-2. We conducted phase I clinical trials to evaluate safety and anti-tumor effects of intravenous injection of Vγ9Vδ2 T cells in patients with various cancers, and intraperitoneal injection of Vγ9Vδ2 T cells for the treatment of gas- tric cancer with malignant ascites. γδ T cell therapy trials are being conducted with safety and response results already reported for selected cases. Despite the limited number of patients in the phase I studies, the clinical response is thus far promising and warrants further study.