PD-L1

PD-L1 is a protein that acts as a kind of “brake” to keep the body’s immune response under control.

PD-L1 may be found on some normal cells and in higher-than-normal amounts on some types of cancer cells.

When PD-L1 binds to another protein called PD-1 (found on T cells), it keeps T cells from killing the PD-L1-containing cells, including the cancer cells.

Anticancer drugs called immune checkpoint inhibitors bind to PD-L1 and block its binding to PD-1. This releases the “brakes” on the immune system and leaves T cells free to kill cancer cells. Tumors have adopted the PD-1/PD-L1 axis for immune escape to facilitate tumor growth, which can be leveraged as a potential target for immune checkpoint inhibitors.

On this basis, PD-L1 expression on tumor or immune cells has emerged as the first potential predictive biomarker for sensitivity to immune checkpoint blockade.