Fig. 1

T cell activation signals. The main signal is mediated by T cell receptor. Co-stimulatory signal is provided by CD28. Co-inhibitory signals are mediated by CTLA-4, PD-1, LAG-3, or TIM-3. TIM-3 T cell immunoglobulin and mucin domain-containing protein-3. LAG-3 lymphocyte activation gene-3, PD-1 programmed death-1, CTLA-4 cytotoxic T-lymphocyte antigen-4, TCR T cell receptor, HMGB1 high mobility group protein B1, MHC major histocompatibility complex, PD-L1 programmed death-ligand 1, PD-L2 programmed death-ligand 2