PD1 / PDCD1 / CD279, a type 1 transmembrane protein of the Ig superfamily, consists of an extracellular N-terminal IgV-like domain, a transmembrane domain, and a cytoplasmic tail engaging in inhibitory signal transmission. Being expressed on activated immune cell types including T cells, B cells, natural killer (NK) cells, NKT cells, dendritic cells (DCs), macrophages, and host tissues, the expression on effector T cells is associated with constitutive antigen exposure and thus PD1 / PDCD1 / CD279 has become a marker of T cell unresponsiveness or exhaustion.
Mei Ji et al. PD-1/PD-L1 pathway in non-small-cell lung cancer and its relation with EGFR mutation. Journal of Translational Medicine (2015) 13:5