Abatacept

Abatacept (marketed as Orencia) is drug used to treat autoimmune diseases like rheumatoid arthritis, by interfering with the immune activity of T cells. It is a modified antibody.

Abatacept is a fusion protein composed of the Fc region of the immunoglobulin IgG1 fused to the extracellular domain of CTLA-4. In order for a T cell to be activated and produce an immune response, an antigen presenting cell must present two signals to the T cell. One of those signals is the major histocompatibility complex (MHC), combined with the antigen, and the other signal is the CD80 or CD86 molecule (also known as B7-1 and B7-2). Abatacept binds to the CD80 and CD86 molecule, and prevents the second signal. Without the second signal, the T cell can't be activated.