The cancer-immunity cycle has been proposed, and immunotherapeutic approaches, such as vaccines using self-antigens and adjuvant, have been employed for a long time, but their therapeutic effects have been limited. However, recent studies have demonstrated that immune checkpoint inhibitors(ICIs)are able to achieve high therapeutic efficacy, in a variety of cancer types. Today, advances in multi-omics technologies, including single-cell RNA sequencing(scRNA-seq), spatial transcriptomics, and multicolor immunostaining technologies, have made it possible to analyze immune cell dynamics at the single-cell level in a greater detail. While CD8+ T cells play a central role in the antitumor immune response, recent findings have revealed the existence of various subsets within the CD8+ T cell population. During the research on T cell exhaustion, the in vivo dynamics of T progenitor exhausted cells(Tpex cells)/stem cell memory T cells(TSCM)have also been elucidated. Tpex/TSCM cells are present in tumor-draining lymph nodes and within tumors and have reported to be an important target for ICIs. Furthermore, interactions between CD4+ T cells, dendritic cells(DCs), B cells, and CD8+ T cells within the tumor microenvironment are crucial for the induction of cytotoxic CD8+ effector T cells. In human tumor tissues, cancer cells exhibit heterogeneous characteristics and the tumor microenvironment varies depending on cancer type, subtypes, and individual patients. To enhance the anti-tumor effects of CD8+ T cells in immunotherapy, it is essential to achieve a more precise understanding of the in vivo dynamics of CD8+ T cells in each patient and to develop strategies for their effective intervention. This knowledge will then be applied to the development of vaccine therapies, combination immunotherapies, and cellular immunotherapy.