Functions and features of circulating memory T cells.

Memory T (TMEM) cells in the circulation (Tcircm cells) comprise a spectrum of populations that vary in their differentiation, durability, and function. While recirculation was once considered a feature of all TMEM cells, considerable advances in understanding the role of non-circulating resident memory (Trm) T cells have raised the question of how Tcircm populations integrate and complement Trm cells in mediating responses to pathogens and tumors. This review discusses current understanding about the functional properties of Tcircm subsets, their identifying characteristics and distinct pathways of differentiation and homeostasis, and the role of Tcircm cells in providing versatile, safe, and effective immunity.