PDCD1 and Autoimmunity: Given the role of PD-1/PD-L1 in limiting autoimmunity 9, 10, 14, patients with preexisting autoimmune Hashimoto's thyroiditis (HT) and/or an asymptomatic elevated titer of thyroid autoantibodies are at-risk of disease worsening or de novo irAEs 16, 17.