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English: Figure 1. Mechanism of action of nivolumab.

The TCR signaling pathway is a major component of immune defense against tumors. Under normal circumstances, TCR recognition of the MHC on APCs will trigger a cascade of events causing activation of T cells and thus immune response against tumor cells. This signal is inhibited by tumor cells with activation of the PD-1/PD-L1 inhibitor co-signaling pathway, which ameliorates T-cell activation. Nivolumab acts by binding onto the PD-L1 on T cells, thus preventing inhibitor co-signaling and restoring T-cell activation.

APC, antigen presenting cell; MHC, major histocompatibility complex; PD-1, programmed death-1; PD-L1, programmed death-1 ligand; TCR, T-cell receptor.