The formation of CD8+/MHC‐I complexes around muscle fibers triggers the release of perforin granules, leading to muscle lysis [219]. Transcriptomic analyses of CD4+ and CD8+ T cells from peripheral blood of DM and PM patients reveal minimal gene expression differences in CD4+ T cells but substantial differences in CD8+ T cells, mainly involving lymphocyte migration and T cell differentiation pathways [221]. The gene discussed is CD8A; the disease is diabetes mellitus.