PDCD1 and lung cancer: Additionally, an upregulation of the expression of multiple inhibitory receptor genes, including PD-1, CTLA-4, TIM-3, lymphocyte activation gene-3 (LAG-3), T cell immunoreceptor with Ig and ITIM domains (TIGIT), and 2B4, was observed in lung cancer samples that developed resistance to PD-1 pathway blockade therapy compared with their corresponding pretreatment samples (66).