Immunotherapy has received the expectation that it should contribute to the therapy of cancer patients for >100 years. At long last, recent clinical trials of immunotherapy with immune checkpoint inhibitors and adoptive cell therapy with genetically engineered T cells have reported their remarkable efficacies. Nowadays, it is expected that T-cell adoptive immunotherapy can not only control tumor progression but even cure cancer in some patients. Conversely, severe adverse events associated with efficacy have frequently been reported in clinical trials, suggesting that the assessment and control of safety will be indispensable in the future development of the therapy. New approaches in T-cell adoptive immunotherapy such as reduction of adverse events, targeting of new antigens or utilization of allogeneic cells will open a new gate for less harmful and more effective immunological treatment of cancer patients.