Anti-human CTLA-4 Monoclonal Antibody (Tremelimumab)

CTLA-4 (Cytotoxic T-Lymphocyte-Associated Protein 4) is a 223-amino-acid transmembrane glycoprotein receptor expressed mainly on activated CD4+ and CD8+ T cells that functions as a critical negative regulator of immune responses by out-competing CD28 for binding to the costimulatory ligands CD80 (B7-1) and CD86 (B7-2) on antigen-presenting cells, thereby transducing inhibitory signals that attenuate T-cell proliferation, cytokine production, and cell cycle progression; the protein’s signal peptide is cleaved to yield a disulfide-linked homodimer whose extracellular Ig-like V-type domain mediates high-avidity ligand engagement, while its cytoplasmic tail contains a tyrosine-based motif that recruits phosphatases such as SHP-2 and PP2A to propagate inhibitory cascades, and genetic polymorphisms or therapeutic blockade of CTLA-4 (e.g., the monoclonal antibody ipilimumab) can enhance antitumor immunity but also precipitate autoimmune toxicities, underscoring its pivotal role in maintaining immune homeostasis.