Mechanistically, to find how PD-L1 is affected by p53, three systems are used: first being the isogenic HCT116 p53−/− and p53+/+ colon cancer cells treated with the p53 stabilizer nutlin 3, second being the p53-inducible H1299 lung cancer cells treated with ponasterone A (PoA) and third being the H460 lung cancer cells transfected with a p53-specific or a scrambled shRNA. The gene discussed is TP53; the disease is lung cancer.