{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Programmed death 1 (PD-1 or CD279) is a type I membrane protein composed of 268 amino acids. PD-1 is a member of the extended CD28/CTLA-4 family of T-cell regulators. PD-1 is expressed on most T-cells, macrophage, and a small subset of B-cells in the light zone of germinal centers, but not elsewhere in the tonsil. On that basis, it was postulated that PD-1 may play a role in the process of clonal selection of centrocytes, which occurs in this sub-anatomic site in germinal centers. In comparison to CTLA-4, PD-1 more broadly negatively regulates T cell immune responses. Studies show expression of PD-L1 on tumor cells inhibits anti-tumor activity through engagement with PD-1 on effector T-cells. Expression of PD-L1 on tumors is correlated with reduced survival in several types of cancers."}]}]}