PDCD1 and neoplasm: Used as monotherapy, neither ICB (anti-PD-1 and anti-CTLA-4) nor activating antibodies (anti-OX40 and anti-CD137) had any significant impact on ID8 tumor-bearing mouse survival [139,140], possibly due to the compensatory upregulation of additional checkpoints on T-cells, such as LAG-3 [147].