One way the immune system attacks harmful substances in the body is by making antibodies that are proteins secreted by white blood cells called B cells. Antibodies recognize unique parts of a toxin, foreign substance, or other protein that is attached to the surface of cells, called antigens. Antigens cause immune responses in the body.
MEDI-551 is a humanized monoclonal antibody, a protein made in the laboratory for human use that acts against a specific antigen called CD19, which is attached to the surface of a B cell. These B cells are responsible for the production of autoantibodies against the aquaporin-4 (AQP4) channel protein in the central nervous system, which plays a major role in causing the nerve tissue injury seen in neuromyelitis optica (NMO) or neuromyelitis optica spectrum disorders (NMOSD). Human studies have shown that when MEDI 551 attaches to the surface of these B cells it starts a process that eliminates these cells. Reducing the number of these B cells may reduce the ability of the immune system to produce the autoantibodies that attack the healthy nerve tissues and may delay or prevent an NMO/NMOSD attack.