Rituximab (Rituxan) is a humanized monoclonal antibody that is approved by the U.S. Food and Drug Administration for the trea™ent of patients with certain autoimmune diseases and types of cancer, such as non-Hodgkin's lymphoma, chronic lymphocytic leukemia, rheumatoid arthritis, idiopathic thrombocytopenic purpura, and pemphigus vulgaris. Rituximab is a chimeric monoclonal antibody against the protein CD20, which is primarily found on the surface of immune system B cells. When it binds to this protein it triggers cell death.