Complement activation determines the therapeutic activity of rituximab in vivo.
Rituximab is an anti-CD20 chimeric mAb effective for the treatment of B-NHL. It can lyse lymphoma cells in vitro through both C- and Ab-dependent cellular cytotoxicity. The mechanism of action of rituximab in vivo is however still unclear. We have set up a new in vivo model in nonimmunodeficient mice by stable transduction of the human CD20 cDNA in the murine lymphoma line EL4. Animals injected i.v. with the EL4-CD20(+) lymphoma cells died within 30 days with evident liver, spleen, and bone marrow involvement, confirmed by immunohistochemistry and PCR analysis. A single injection of rituximab or the murine anti-CD20 Ab 1F5, given i.p. 1 day after the tumor, cured 100% of the animals. Indeed, at week 4 after tumor cell inoculation, CD20(+) cells were undetectable in all organs analyzed in rituximab-treated animals, as determined by immunohistochemistry and PCR. Rituximab had no direct effect on tumor growth in vitro. Depletion of either NK cells or neutrophils or both in tumor-injected animals did not affect the therapeutic activity of the drug. Similarly, rituximab was able to eradicate tumor cells in athymic nude mice, suggesting that its activity is T cell independent. In contrast, the protective activity of rituximab or the 1F5 Ab was completely abolished in syngeneic knockout animals lacking C1q, the first component of the classical pathway of C (C1qa(-/-)). These data demonstrate that C activation is fundamental for rituximab therapeutic activity in vivo.
Di Gaetano
Nicola
N
Department of Immunology and Cell Biology, Istituto Ricerche Farmacologiche Mario Negri, Milan, Italy.
Cittera
Elena
E
Nota
Rachele
R
Vecchi
Annunciata
A
Grieco
Valeria
V
Scanziani
Eugenio
E
Botto
Marina
M
Introna
Martino
M
Golay
Josée
J
D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage* / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D000920:Antibody-Dependent Cell Cytotoxicity / Q000235:genetics / Q000276:immunology*; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000627:therapeutic use*; D002455:Cell Division / Q000235:genetics / Q000276:immunology; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D015922:Complement C1q / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D003171:Complement Pathway, Classical / Q000235:genetics / Q000276:immunology*; D006801:Humans; D008212:Lymphocyte Depletion; D008223:Lymphoma / Q000276:immunology* / Q000473:pathology / Q000517:prevention & control / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008819:Mice, Nude; D009362:Neoplasm Metastasis / Q000276:immunology / Q000517:prevention & control / Q000628:therapy; D009368:Neoplasm Transplantation; D009504:Neutrophils / Q000473:pathology; D000069283:Rituximab; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D000970:Antineoplastic Agents; D000069283:Rituximab; D015922:Complement C1q