The Role of PD-1 and PD-L1

Julie R. Brahmer, MD, from Johns Hopkins University School of Medicine, Sidney Kimmel Comprehensive Cancer Center, explains the role of the PD-1 pathway and the ligands PD-L1 and PD-L2 in the regulation of the immune system.

Clinical Pearls

• The program death 1 (PD-1) pathway is a checkpoint pathway that controls immune response in the body to prevent extreme inflammation or other problems during illness
• PD-1 is a receptor on a T cell while its ligand, PD-L1, is expressed on peripheral tissues or tumor cells. PD-L2, another ligand, is also thought to be present on antigen-presenting cells or tumor cells, though research is ongoing
• When the T cell binds to one of its ligands, it deactivates the T cell. This protects the tumor from the body’s immune system
• When that response is blocked, the T cell can remain active and kill the tumor