Tissue-resident memory T cells in the skin.

PURPOSE: Tissue-resident memory T (TRM) cells are a newly described subset of memory T cells. The best characterized TRM cells are CD8+ and express CD103 and CD69. These cells are non-recirculating and persist long term in tissues, providing immediate protection against invading pathogens. However, their inappropriate activation might contribute to the pathogenesis of autoimmune and inflammatory disorders. In the skin, these cells have been described in psoriasis, vitiligo, and melanoma among other diseases.

METHODS: Literature review was done to highlight what is currently known on the phenotype and function of TRM cells and summarizes the available data describing their role in various cutaneous conditions.

RESULTS: Resolved psoriatic skin and disease-naïve non-lesional skin contain a population of IL-17-producing TRM cells with shared receptor sequences that recognize common antigens and likely contribute to disease recurrence after cessation of therapy. In vitiligo, TRM cells produce perforin, granzyme B, and interferon-γ following stimulation by interleukin-15 and collaborate with recirculating memory T cells to maintain disease. In melanoma, increased accumulation of TRM cells was recently shown to correlate with improved survival in patients undergoing therapy with immune checkpoint inhibitors.