Programmed Cell Death-1 (PD-1)
Aliyah Weinstein, Ph.D.
Article
Programmed cell death-1 (PD-1) is an immune checkpoint molecule that belongs to the CD28 family, which also includes CTLA-4. PD-1 is expressed on T cells and functions as a negative regulator of helper and effector T cell activity. Its ligands, PD-L1 and PD-L2, are members of the B7 family and are expressed by antigen presenting cells as well as tissue type-specific cells throughout the body and cancer cells. Binding of PD-1 to its ligands activates an intracellular signaling cascade that results in the dephosphorylation of the T cell receptor or of CD281, and the consequent reduction in T cell activity. In healthy individuals, this pathway tunes the immune system to protect against autoimmunity by suppressing effector T cells and promoting the activity of regulatory T cells (Tregs)2, 3.