Our finding of downregulated PD-1 expression in CD8+ T cells of aged Ae2a,b−/− mice replicate the findings in autoreactive CD8+ T cells from PBC patients which upon in vitro CD3/CD28 stimulation displayed lower PD-1 expression and decreased apoptosis compared with the same phenotypic subset of CD8+ T cells from healthy controls [4]. This evidence concerns the gene CD28 and primary biliary cholangitis.