Programmed cell death 1 protein (PD-1)

Programmed cell death 1 protein (PD-1), also known as CD279, is a 288 amino acid type I transmembrane receptor in the immunoglobulin superfamily, expressed primarily on activated T cells and many other immune cells[1][4][5]. PD-1 acts as an immune checkpoint receptor; upon engagement by its ligands PD-L1 or PD-L2, it negatively regulates immune responses to maintain self-tolerance and prevent autoimmunity[1][4][7][10]. This occurs via ITIM and ITSM motifs in its cytoplasmic tail, which mediate inhibitory signaling[3][4]. Tumor cells overexpress PD-L1 to evade immune surveillance, making the PD-1/PD-L1 pathway a validated target for cancer immunotherapy. Blocking this pathway with monoclonal antibodies (such as nivolumab or pembrolizumab) enhances antitumor immune responses and is approved for multiple cancer types[1][5][7][10]. However, checkpoint inhibition can cause immune-related toxicities as enhanced immune activity may target normal tissues[1][4]. PD-1 is thus a key regulator of immune homeostasis and an important biomarker and therapeutic target in oncology and autoimmune diseases[1][4][8].

Other names

CD279PDCD1

Immune checkpoint inhibition (antibody blockade of PD-1 enhances T cell responses against tumors or infections); Reversal of T cell exhaustion; Promotion of anti-tumor immune activity