Tumor-associated macrophages—additional effectors at anti-PD-1/PD-L1 therapy?

Immunotherapies that target programmed cell death protein 1 (PD-1) or one of its ligands, programmed cell death ligand 1 (PD-L1), are a recent breakthrough in treatment of human malignant diseases (1), including non-small cell lung cancers (NSCLCs) (2). Monoclonal antibody drugs that target the interaction between PD-1 and PD-L1 have shown dramatic and/or durable responses in a subset of NSCLC patients (3-6), leading to FDA approvals of three agents (nivolumab, pembrolizumab, and atezolizumab) for treatment of metastatic NSCLC patients. Other agents that also target this pathway, such as durvalumab (7) and avelumab (8), are currently under clinical development.