New immunotherapies targeting the PD-1 pathway.

Ligands from the B7 family bind to receptors of the CD28 family, which regulate early T cell activation in lymphoid organs and control inflammation and autoimmunity in peripheral tissues. Programmed death-1 (PD-1), a member of the CD28 family, is an inhibitory receptor on T cells and is responsible for their dysfunction in infectious diseases and cancers. The complex mechanisms controlling the expression and signaling of PD-1 and programmed death ligand 1 (PD-L1) are emerging. Recently completed and ongoing clinical trials that target these molecules have shown remarkable success by generating durable clinical responses in some cancer patients. In chronic viral infections, preclinical data reveal that targeting PD-1 and its ligands can improve T cell responses and virus clearance. There is also promise in stimulating this pathway for the treatment of autoimmune and inflammatory disorders.