TP53 and malignant colon neoplasm: To investigate the role of p53 in PDL1 regulation, we used three different cell systems and determined whether the specific induction or depletion of p53 affects PDL1 expression: 1) isogenic HCT116 p53-/- and p53+/+ colon cancer cells treated with the p53 stabilizer nutlin 3 (26), 2) p53-inducible H1299 lung cancer cells treated with ponasterone A (PoA) (27,28), and 3) H460 lung cancer cells transfected with a p53-specific or a scrambled shRNA.