PD-L1

The immune system employs a series of checkpoints to protect normal, healthy tissue from an immune response. These consist of receptors on the surface of activated T cells and their corresponding ligands on the surface of antigen presenting cells. A key immune checkpoint is triggered when PD-1 (programmed cell death protein 1) engages its ligand PD-L1. As a result of this interaction, T cell activation is attenuated and an active immune response is prevented(1).

This mechanism is often co-opted by tumors. PD-L1 is upregulated in several tumor types and contributes to the malignancy of these cancers by interacting with PD-1 and inhibiting T cell activation. In this way, the tumors avoid detection and destruction by the immune system(1-3). Accordingly, PD-1 and PD-L1 have garnered much attention for their roles in tumor immunology and as immune-based therapeutic targets(4,5).