PDCD1 and non-small cell lung carcinoma: CD8+ T cells expressing BTLA in NSCLC microenvironment exhibit exhausted phenotype and are correlated with clinical response to anti-PD-1 therapy in NSCLC patients, suggesting that BTLA+CD8+ T cells might serve as biomarkers to predict the responsiveness to anti-PD-1 therapy in NSCLC patients.