Co-inhibitory-receptors such as CTLA-4 (cytotoxic T-lymphocyte–associated protein 4), LAG-3 (lymphocyte activation gene 3; or CD223), TIM-3 (T-cell immunoglobulin and mucin domain–containing 3), PD-1 (PDCD1; programmed cell death 1), and TIGIT (T-cell immunoreceptor with Ig and ITIM domains) are key factors in maintaining immune homeostasis and play a central role in regulating autoimmune diseases (5–7). This evidence concerns the gene PDCD1 and autoimmune disease.