Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4) is a cell surface molecule that is closely related to CD28, and a powerful negative regulator of T cell activation. Structurally, CTLA-4 is a member of the Ig superfamily, having a single extracellular V-like domain , homology with CD28; The overall sequence homology between CD28 and CTLA-4 is about 20%, but they share a 27%(murine) to 31%(human) identity at the amino acid level. Inhibitory receptor acting as a major negative regulator of T-cell responses. The affinity of CTLA-4 for its natural B7 family ligands, CD80 and CD86, is considerably stronger than the affinity of their cognate stimulatory coreceptor CD28.  
Recombinant Human CTLA-4 Fc Chimera produced in CHO cells is a polypeptide chain containing 378 amino acids with the C-termimal human IgG1 Fc fragment. A fully biologically active molecule, rhCTLA-4 has a molecular mass of 45-48 kDa analyzed by reducing SDS-PAGE and is obtained by chromatographic techniques at ExCell Bio.