A distinct CD8+ T cell subset derived from virtual memory T cells causes alopecia areata through innate-like cytotoxicity [scRNA-seq]

Virtual memory T (TVM) cells are a T-cell subtype that exhibit a memory phenotype without prior exposure to a foreign antigen. Although several recent studies suggest that TVM cells exert anti-viral and anti-bacterial function, pathological roles of TVM cells causing inflammatory diseases have not been studied. Here, we identified a novel CD8+ T-cell subset (CD44s-hiCD49dlo CD8+ T cells), which is originated from TVM cells and can cause a chronic inflammatory disease, alopecia areata (AA). In the skin of alopecic mice, we detected a distinct TVM-cell subpopulation characterized by superior expression of CD44 and features of tissue residency, which was transcriptionally, phenotypically, and functionally distinct from conventional CD8+ TVM cells. Mechanistically, this cell population could be induced from conventional TVM cells by IL-12, IL-15, and IL-18 stimulation. Moreover, the pathological activity of CD44s-hiCD49dlo CD8+ T cells was mediated by NKG2D-depedent innate-like cytotoxicity against target cells, which was further augmented by IL-15 stimulation and triggered the onset of disease. Collectively, our results suggest a new immunological mechanism through which TVM cells can cause chronic inflammatory disease by innate-like cytotoxicity. Comparative gene expression profiling analysis of scRNA-seq data for alopecia areata and naïve mice