PDCD1 and lung cancer: Consequently, this promotes immune evasion by tumor cells (i.e., tumor immune tolerance) and facilitates the metastasis and progression of lung cancer (41, 42).PD-1 contributes to the persistence of PD-1+TIM-3+ T cells by binding with TIM-3 ligand galectin-9 (Gal-9), and mitigates Gal-9/TIM-3-induced cell death.