Nivolumab is an anti-PD-1 monoclonal antibody acting to activate T-lymphocyte-mediated anti-tumor activity by blocking the PD-1-PD-L1 T-cell regulation pathway. Tumor-secreted cytokines recruit myeloid-derived suppressor cells, which cause immunosuppression to counteract the effects of nivolumab. Pro-angiogenic factors secreted by myeloid-derived suppressor cells stimulate angiogenesis and subsequent tumor growth. These contribute to mechanisms of resistance.

Abbreviations: ICI, Immune checkpoint inhibitor; PD-1, programmed cell death protein-1; PD-L1, programmed death-ligand 1; IL-10, interleukin-10.