Regulation of programmed death-ligand 1 expression in response to DNA damage in cancer cells: Implications for precision medicine

Anti-programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) therapy, which is one of the most promising cancer therapies, is licensed for treating various tumors. Programmed death-ligand 1, which is expressed on the surface of cancer cells, leads to the inhibition of T lymphocyte activation and immune evasion if it binds to the receptor PD-1 on CTLs. Anti-PD-1/PD-L1 Abs inhibit interactions between PD-1 and PD-L1 to restore antitumor immunity. Although certain patients achieve effective responses to anti-PD-1/PD-L1 therapy, the efficacy of treatment is highly variable. Clinical trials of anti-PD-1/PD-L1 therapy combined with radiotherapy/chemotherapy are underway with suggestive evidence of favorable outcome; however, the molecular mechanism is largely unknown. Among several molecular targets that can influence the efficacy of anti-PD-1/PD-L1 therapy, PD-L1 expression in tumors is considered to be a critical biomarker because there is a positive correlation between the efficacy of combined treatment protocols and PD-L1 expression levels. Therefore, understanding the mechanisms underlying the regulation of PD-L1 expression in cancer cells, particularly the mechanism of PD-L1 expression following DNA damage, is important. In this review, we consider recent findings on the regulation of PD-L1 expression in response to DNA damage signaling in cancer cells.