Tissue-resident memory T cell induction

Tissue-resident memory T (T_RM_) cell induction refers to the biological process by which circulating T cell precursors differentiate into tissue-resident memory T (T_RM_) cells, a non-recirculating subset of memory T cells that persist in peripheral tissues like skin, mucosa, lung, liver, and gut to provide rapid frontline immunity against pathogens.[1][2][3] Tissue-resident memory T (T_RM_) cell induction is the differentiation process converting circulating effector T cell precursors into long-lived, non-recirculating T_RM_ cells that occupy epithelial and mucosal barrier tissues such as skin, lung, gut, liver, and reproductive tract.[1][3][4] This process is triggered by antigen exposure in non-lymphoid tissues, where local signals like TGF-β drive upregulation of residency markers including CD69, CD103 (αEβ7 integrin), and CD49a, preventing egress via suppression of S1PR1 and promotion of tissue anchoring.[1][2][3] T_RM_ cells develop early during immune responses from KLRG1-low precursors, guided by transcription factors like Runx3, Hobit, Blimp1, and Notch, which confer hybrid effector-memory properties with constitutive granzyme B, rapid IFN-γ production, and in situ proliferation upon re-challenge.[2][3][5] They provide superior tissue-specific protection against reinfection compared to circulating memory T cells, rapidly clearing pathogens at entry sites and coordinating broader responses via cytokines and chemokines.[1][3][6] In disease, T_RM_ cells contribute to antitumor immunity within tumors but can drive chronic inflammation, autoimmunity (e.g., psoriasis, mycosis fungoides), and liver pathologies like viral hepatitis or hepatocellular carcinoma when dysregulated.[2][4][5] While not a molecular target like a receptor or enzyme, modulating T_RM_ induction via cytokines, checkpoint inhibitors, or vaccines is explored in immunotherapy to enhance antitumor surveillance or combat infections, though challenges include ensuring persistence without exhaustion in tumor microenvironments.[2][6] No direct small-molecule drugs target this process, as it involves complex transcriptional and environmental cues rather than a single protein.[1][2][3]