Functional heterogeneity of human skin-resident memory T cells in health and disease

The human skin is populated by a diverse pool of memory T cells, which can act rapidly in response to pathogens and cancer antigens. Tissue-resident memory T cells (T-RM) have been implicated in range of allergic, autoimmune and inflammatory skin diseases. Clonal expansion of cells with T-RM properties is also known to contribute to cutaneous T-cell lymphoma. Here, we review the heterogeneous phenotypes, transcriptional programs, and effector functions of skin T-RM. We summarize recent studies on T-RM formation, longevity, plasticity, and retrograde migration and contextualize the findings to skin T-RM and their role in maintaining skin homeostasis and altered functions in skin disease.