Since expression of the immune checkpoints PD-1 and PD-L1 is correlated with infiltrating immune cells and Bcl9 depletion is synergistic with anti-PD-1 treatment in mouse tumor models, we studied the relationship among CD226, PD-1 (or PDCD1), and PD-L1 (or CD274) in CRC, lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC) and triple-negative breast cancer (TNBC). Here, PDCD1 is linked to squamous cell lung carcinoma.