Recently, there is a growing interest in research techniques for studying the function of human T cells, as immuno-oncology studies have become popular. However, there are many difficulties in studying T cells in human patients. Mouse studies have largely addressed the difficulty of studying antigen-specific T cells with T cell receptor transgenic mice, but this method could not be applied to human studies. Recently, various techniques for studying human T cells have been developed to allow the direct ex vivo analysis of antigen-specific T cells obtained from patients. This lecture introduces recent advances in the study of human T cells and how they can be applied to immuno-oncology studies.