PDCD1 and neoplasm: According to previous studies (24, 25), the mechanism in which regulatory T cells could secrete suppressive immune-related cytokines, while myeloid and stromal cells could stimulate immune inhibitory checkpoints (PD-1, CTLA4 and TIM-3) has been adopted by many cancers to evade immune surveillance (24–26), which contributes to aggressive tumor proliferation and low ICI efficacy.