Complement Activation Determines the Therapeutic Activity of Rituximab In Vivo

• Published in: The Journal of immunology (1950) Vol. 171; no. 3; pp. 1581 - 1587
• Main Authors: Di Gaetano, Nicola, Cittera, Elena, Nota, Rachele, Vecchi, Annunciata, Grieco, Valeria, Scanziani, Eugenio, Botto, Marina, Introna, Martino, Golay, Josee
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 01.08.2003
• Subjects: Animals; Antibodies, Monoclonal - administration & dosage; Antibodies, Monoclonal - therapeutic use; Antibodies, Monoclonal, Murine-Derived; Antibody-Dependent Cell Cytotoxicity - genetics; Antibody-Dependent Cell Cytotoxicity - immunology; Antineoplastic Agents - administration & dosage; Antineoplastic Agents - therapeutic use; Cell Division - genetics; Cell Division - immunology; Cell Survival - genetics; Cell Survival - immunology; Complement C1q - deficiency; Complement C1q - genetics; Complement C1q - physiology; Complement Pathway, Classical - genetics; Complement Pathway, Classical - immunology; Humans; Lymphocyte Depletion; Lymphoma - immunology; Lymphoma - pathology; Lymphoma - prevention & control; Lymphoma - therapy; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Nude; Neoplasm Metastasis - immunology; Neoplasm Metastasis - prevention & control; Neoplasm Metastasis - therapy; Neoplasm Transplantation; Neutrophils - pathology; Rituximab; Tumor Cells, Cultured
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.171.3.1581

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.