Involvement of neutrophils and natural killer cells in the anti-tumor activity of alemtuzumab in xenograft tumor models

Abstract

Alemtuzumab is a recombinant humanized IgG1 monoclonal antibody directed against CD52, an antigen expressed on the surface of normal and malignant B and T lymphocytes. Alemtuzumab is approved for the treatment of B-cell chronic lymphocytic leukemia (B-CLL), but the exact mechanism by which the antibody depletes malignant lymphocytes in vivo is not clearly defined. To address this issue, the anti-tumor activity of alemtuzumab was studied in disseminated and subcutaneous xenograft tumor models. The density of CD52 target antigen on the surface of tumor cells appeared to correlate with the anti-tumor activity of alemtuzumab. Deglycosylation of alemtuzumab resulted in a loss of cytotoxicity in vitro and was found to abolish anti-tumor activity in vivo. Individual inactivation of effector mechanisms in tumor-bearing mice indicated that the protective activity of alemtuzumab in vivo was primarily dependent on ADCC mediated by neutrophils and to a lesser extent NK cells. Increasing the number of circulating neutrophils by treatment with G-CSF enhanced the anti-tumor activity of the antibody, thus providing further evidence for the involvement of neutrophils as effector cells in the activity of alemtuzumab.

Keywords:

• Antibody based immunotherapy
• cell lines and animal models
• lymphoma and Hodgkin disease

Acknowledgements

The authors wish to thank Qun Zhou for the preparation of deglycosylated alemtuzumab, Tri-Hung Nguyen for generation of the CHO-CD52 cell line, and the Genzyme Department of Comparative Medicine for animal husbandry.

Declaration of interest: All authors are employees and shareholders of Genzyme Corporation, the manufacturer of alemtuzumab.