A transcriptomic map of murine and human alopecia areata.

Alopecia areata (AA) is a common autoimmune condition, presenting initially with loss of hair without other overt skin changes. The unremarkable appearance of the skin surface contrasts with the complex immune activity occurring at the hair follicle. AA pathogenesis is due to the loss of immune privilege of the hair follicle, leading to autoimmune attack. Although the literature has focused on CD8+ T cells, vital roles for CD4+ T cells and antigen-presenting cells have been suggested. Here, we use single-cell sequencing to reveal distinct expression profiles of immune cells in murine AA. We found clonal expansions of both CD4+ and CD8+ T cells, with shared clonotypes across varied transcriptional states. The murine AA data were used to generate highly predictive models of human AA disease. Finally, single-cell sequencing of T cells in human AA recapitulated the clonotypic findings and the gene expression of the predictive models.