PDCD1 and rheumatoid arthritis: Inhibitory/regulatory molecules, such as cytotoxic‐T‐lymphocyte antigen 4 (CTLA‐4), PD‐1/programmed cell death-ligand 1 (PD‐L1), lymphocyte activation gene 3 (LAG3), T cell immunoglobulin and mucin domain 3 (TIM3), T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT), V‐domain immunoglobulin suppressor of T cell activation (VISTA), and BTLA play a key role in the modulation of the activation and tolerance of T cells in rheumatoid arthritis (19).