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**48**

Until recently, T cells were thought to remain in circulation until recruitment of the inflammation and only a small number of T cells remained in the peripheral tissues without inflammation. However, studies have found that a group of T cells settled in the tissues and remained there for a long time. Those cells are named as tissue-resident memory T cells (TRM). TRM cells are transcriptionally, phenotypically, and functionally distinct from other T cells, which recirculate between blood, secondary lymphoid organs, and non-lymphoid tissues. They undergo a distinct proliferation that discriminates them from circulating T cells and their main cell surface markers are CD69, CD103, and CD49a. Upon exposure to the same or similar diseases, TRM cells provide a first line of adaptive cellular defense against infection in peripheral non-lymphoid tissues, such as skin, lungs, digestive, and urogenital tracts. This approach forms the basis of a novel vaccination strategy called "prime and pull", which ensures long-term local immunity. On the other hand, abnormal activated and malignant TRM may contribute to numerous human inflammatory diseases such as psoriasis and vitiligo. Here in this chapter, we aimed to emphasize TRM cell location, migration, phenotypic structure, maintenance, and diseases associated with TRM cells.

**Keywords:** resident memory T cell, CD8+ TRM, CD69, CD103, CD49a, prime and pull, autoreactive human disease
