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Figure 2. Mechanisms that may either alone, or in combination lead to de novo or acquired resistance to immune checkpoint inhibition (A); Primary and acquired mechanisms of resistance at different points in the cancer immunity cycle and potential therapeutic strategies to overcome them (B). PD-1: programmed death 1; PD-L1: programmed cell death ligand 1; IDO: Indoleamine 2,3-dioxygenase; VEGF: vascular endothelial growth factor
