The progress of tissue resident memory T-cells against tumors

Most effector T cells are known to die as only a few of them became memory T cells following immune responses. According to their distribution, function, and transcription factors, memory T cells can be divided into effector memory T cells, central memory T cells, and tissue resident memory T cells (T_RM). The tissue resident memory T cells do not circulate in the blood and lymph nodes but are found in non-lymphoid tissues, which includes the skin and mucous membranes, urogenital system, brain, respiratory system, lung, and liver tissues. The form of memory T cells can play the defense response directly and quickly when the pathogens invade the tissues. In addition, the tissue resident memory T cells also play a very important role in the immune responses to tumors, allergic, and autoimmune diseases. The tissue resident memory T cells include the CD4⁺ and CD8⁺ T cells that express cell surface molecules CD69 and/or CD103 and produce cytokines and/or play killing functions during the immune response as well as linking original and adaptive immunity to initiate a systemic immune response. In addition, studies have shown that the function of the tissue resident memory T cells is controlled by the regulatory T (Treg) cells in tissues. In this paper, the differentiation of the tissue resident memory T cells cells and their role in tumors are reviewed.