CD274 and rheumatoid arthritis: Increased serum sCTLA‐4 concentrations have been reported in several autoimmune diseases,15, 18 and a reduced PD‐1/PD‐L1 signaling has been detected in the synovial microenvironment of patients with rheumatoid arthritis (RA), leading to the recent development of drugs stimulating this endogenous immune‐inhibitory pathway.19, 20