Molecular regulatory network of PD-1/PD-L1 in non-small cell lung cancer

Lung cancer remains the most common cancer and the leading cause of cancer death worldwide. Despite effective chemotherapy and molecular-based therapies, the median and overall survival remains poor. Immune checkpoint inhibitors have changed the treatment landscape for patients with non-small cell lung cancer (NSCLC) by inhibiting negative T cell regulators, including programmed death 1 (PD-1, CD279) and programmed death ligand 1 (PD-L1, also known as B-H1, CD274) inhibitors. Nonetheless, most patients do not respond to these inhibitors. Recently, PD-L1 expression has been demonstrated to influence the anti-tumor efficacy of immune checkpoint inhibitors. However, the mechanisms of PD-L1 regulation are not clearly understood. This review thus aims to summarize the current knowledge and recent developments in the regulatory mechanisms of PD-L1 expression levels and attempts to clarify its latent function in anti-tumor activity, with the goal of guiding better designs for future NSCLC immunotherapies.