PD‐1 is primarily expressed on the surface of activated T cells, and is an important regulator of immune homeostasis.[11] The absence of PD‐1 can lead to the development of autoimmune disease; blockade of the PD‐1 checkpoint exacerbates autoimmune diseases in both human and mouse models.[12] However, depletion of PD‐1+ cells ameliorates autoimmune murine models of diabetes and encephalomyelitis.[12b] Herein we demonstrate the clonal expansion of functionally activated PD‐1+CD8+ T cells in the livers of dnTGFβRII Aire−/− mice, which play a pathogenic role in the progression of disease. The gene discussed is PDCD1; the disease is autoimmune disease.