CD44 and lung carcinoma: To investigate if PD-L1 was involved in tumor stemness character and cell apoptosis, we overexpressed and knocked down PD-L1 in lung cancer cells, and found that PD-L1 overexpression or knockdown did not affect the expression of the CSC-related markers (CD44, OCT4) or the apoptosis-related molecules (Bax and Bcl-2) (Supplementary Fig. S2A).