title: Rituximab (anti-CD20) therapy of B-cell lymphomas: direct complement killing is superior to cellular effector mechanisms.
abstract: Rituximab (IDEC-C2B8, Mabthera(R)) is a chimeric (human-mouse) monoclonal antibody (MoAb) against the B-cell specific CD20-antigen. It has been used for the clinical treatment of non-Hodgkin's lymphomas, but variable clinical results suggest that some lymphoma cells remain resistant. In the present study we have evaluated the relative efficiencies of humoral and cell-mediated effector mechanisms complement-dependent cytotoxicity (CDC), antibody-(ADCC), complement-(CDCC) dependent cellular cytotoxicity and apoptosis on lymphoma cell killing by rituximab. Rituximab activated the cytolytic complement (C) cascade and induced a strong CDC, but the rituximab-triggered ADCC and CDCC were relatively ineffective. The CDC was strongly enhanced by antibodies against the C inhibitor CD59 (protectin). Neutralization of CD55 (DAF) and CD46 (MCP) had a similar but weaker effect. Rituximab also induced apoptosis but in a cell line-dependent fashion. The results strongly emphasize the role of direct CDC as the major, fast and efficient effector mechanism of rituximab. In the immunotherapeutic treatment of B-cell lymphomas, it is important to consider the role of C-regulatory proteins as an escape mechanism of the malignant cells. Our results suggest that the effect of rituximab therapy could be enhanced by combining it with neutralization of CD59.
authors.affiliation: Department of Bacteriology and Immunology, University and University Central Hospital of Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Harjunpää
authors.forename: S
authors.initials: S
authors.lastname: Junnikkala
authors.forename: S
authors.initials: S
authors.lastname: Meri
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D000920:Antibody-Dependent Cell Cytotoxicity; D015703:Antigens, CD / Q000096:biosynthesis; D018951:Antigens, CD20 / Q000276:immunology*; D000970:Antineoplastic Agents / Q000627:therapeutic use; D017209:Apoptosis / Q000276:immunology; D018958:CD55 Antigens / Q000096:biosynthesis; D018957:CD59 Antigens / Q000096:biosynthesis; D003169:Complement Inactivator Proteins / Q000096:biosynthesis; D003165:Complement System Proteins / Q000276:immunology* / Q000378:metabolism; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D006801:Humans; D016393:Lymphoma, B-Cell / Q000628:therapy*; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D000069283:Rituximab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D015703:Antigens, CD; D018951:Antigens, CD20; D000970:Antineoplastic Agents; C497857:CD46 protein, human; D018958:CD55 Antigens; D018957:CD59 Antigens; D003169:Complement Inactivator Proteins; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D000069283:Rituximab; D003165:Complement System Proteins