Several inhibitory checkpoints have been recognized and are being tested as promising new targets for cancer immunotherapy in addition to PD-1 (L1) blockade, including LAG-3, TIM-3 (T cell immunoglobulin and mucin domain-containing molecule-3), and TIGIT (T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain) are highly anticipated (39). Here, PDCD1 is linked to cancer.