CD197, also known as CCR7 or BLR2, is a protein that belongs to the G protein-coupled receptor family and is a subset of chemokines. It is identified as being induced by the Epstein-Barr virus （EBV） and is considered a mediator of the effects of EBV on B lymphocytes. CCR7 is expressed in blood, bone marrow, lymph nodes, and the gastrointestinal tract, particularly on lymphoid tissues and activated B and T lymphocytes. It has been shown to control the migration of memory T cells to inflamed tissues and the maturation of dendritic cells. The chemokine （C-C motif） ligand 19 （CCL19/ECL） is reported to be a specific ligand for this receptor. CD197 is involved in the cellular response to cytokine stimuli, myeloid dendritic cell chemotaxis, and the positive regulation of neutrophil chemotaxis. In the context of T cell maturation, CD197 is expressed on recent thymic emigrants （RTEs） that mature into naive T lymphocytes. These cells differentiate into short-term effector T cells and further into memory T cells, which include central memory T cells （expressing CCR7 and CD62L） and effector memory T cells （which do not migrate to lymph nodes）. In cancer immunology, particularly in lung cancer, the presence of memory T cells in metastatic lymph nodes has been shown to be an independent positive prognostic factor. Tregs, which play a significant role in regulating the immune response to tumors, can be differentiated into naive, effector, and terminal effector subtypes based on the expression of the CD45RO marker.