PDCD1 and pneumonia: Even the cutting-edge innovations, such as anti programmed cell death protein 1 (PD-1), anti programmed cell death protein (PD-L1) or anti cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), while greatly improving tumor killing rates and prolonging survival period of patients, their unique immune adverse events such as skin toxicity, gastrointestinal toxicity, pneumonia and endocrine toxicity also limit their use (10, 11).