Rituximab is a genetically engineered chimeric mouse/human monoclonal antibody that is a glycosylated immunoglobulin with sequences from the human IgG1 constant domain and the mouse light and heavy chain variable domains. The antibodies are produced by mammalian cell suspension culture (Chinese hamster ovary) and purified by affinity chromatography and ion exchange using specific virus inactivation and removal procedures. Rituximab specifically binds to the transmembrane antigen CD20, a non-glycosylated phosphoprotein located on pre-B lymphocytes and mature lymphocytes. This antigen is expressed on more than 95% of all B cells of non-Hodgkin lymphomas.