Cytotoxic T lymphocyte associated ANTIgen-4 (CTLA-4), also known as CD152, is a kind of leukocyte differentiation antigen and a transmembrane receptor on T cells, sharing B7 ligand with CD28. The binding of CTLA-4 with B7 induces T cells to be non-reactive and participates in the negative regulation of immune response. The recombinant CTLA-4 Ig can effectively and specifically inhibit cellular and humoral immune responses in vivo and in vitro, and has significant therapeutic effects on transplant rejection and various autoimmune diseases with very low toxicity. It is considered as a promising new immunosuppressive drug at present.