Dr. Julie Brahmer Explains 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.

Brahmer says 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, Brahmer says. PD-1 has another ligand, PD-L2, which 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, Brahmer says, protecting the tumor from the body’s immune system. When that response is blocked, the T cell can remain active and kill the tumor.