Tissue-resident memory CD8⁺ T cells in cancer immunology and immunotherapy

Memory T cells can be generated and remain long-term in different tissues following infection or immunization. Tissue-resident memory T (T_RM) cells are a unique group of memory T cells that form and persist mainly in peripheral non-lymphoid organs. Unlike effector or central memory T (T_EM or T_CM) cells, T_RM cells do not circulate to the blood but can provide a rapid and robust local response to re-infection. Recently, a large body of clinical studies has shown that CD103⁺ CD8⁺ T_RM-like cells also exist intratumorally and strongly correlate with favorable prognosis in cancer patients. Cancer vaccine-induced CD103⁺ CD8⁺ T_RM cells have been reported to suppress tumor growth in mouse models. This suggests that CD8⁺ T_RM-like cells play a crucial role in cancer immunosurveillance and immunotherapy. In this review, we focus on the features and cytotoxic mechanisms of CD8⁺ T_RM-like cells in multiple solid tumors and discuss their potential implications for cancer immunotherapy. We believe a better understanding of the generation, function, and longevity of CD8⁺ T_RM-like cells in the tumor microenvironment will provide new insights for cancer immunotherapies.