Potent targeting of B cell lymphoma and plasma cell tumors by a tetravalent, Fc-engineered antibody directed against the glycoantigen CD75s.

Abstract

e14004 Background: Monoclonal antibodies are established treatment options for B cell-derived malignancies, but relapse is still the major challenge. Novel target structures may open alternative avenues to develop effective antibody therapies. Here, we characterized the novel tetravalent antibody ‘EBU-141 Tetra’ and identified the glycoantigen CD75s (α-2,6-sialylated lactosamines) as suitable target structure for antibody-based therapy. CD75s was detected on most B cell lymphomas, including Burkitt’s lymphoma, FL, DLBCL, MCL, CLL, and plasma cell tumors. Classical Hodgkin lymphomas were consistently negative while reactivity on individual cases of peripheral T cell lymphoma was seen. To evaluate CD75s as a target for antibody therapy, we generated a tetravalent, Fc-engineered chEBU-141 IgG1 antibody with enhanced avidity for CD75s and potent effector functions. Methods: ‘EBU-141 Tetra’ was produced by transient transfection and purified by affinity chromatography. Direct anti-tumor effects and Fc-mediated effector functions were investigated in cell proliferation assays, by fluorescence microscopy and in 51Cr release experiments using lymphoma and myeloma cell lines and patient-derived tumor cells. Peripheral blood mononuclear cells and monocyte-derived macrophages of healthy donors were used as human effector cells in the experiments. Results: ‘EBU-141 Tetra’ showed improved binding to CD75s on cell surface of mature B cell lymphoma as well as myeloma plasma cells compared to the conventional chimeric antibody chEBU-141 IgG1. The higher avidity for CD75s resulted in markedly improved ADCC activity of ‘EBU-141 Tetra’ against Daudi Burkitt’s lymphoma, U266 plasma cells and CLL patient-derived tumor cells with EC50 values in the low nanomolar range. In addition, ‘EBU-141 Tetra’ demonstrated efficient phagocytosis of Burkitt’s lymphoma and myeloma cell lines. Thus, the novel tetravalent, chimeric, Fc-engineered antibody ‘EBU-141 Tetra’ efficiently recruits immune effector cells for tumor cell lysis. Conclusions: Our findings further demonstrate that highly potent IgG-like antibodies against glycan-structures can be generated from mouse IgM antibodies and may open a new therapeutic window for therapy of patients with mature B cell lymphomas and multiple myeloma.