Enhanced Complement-Dependent Cytotoxicity of DuoHexaBody-CD37: A Promising Approach for B-Cell Malignancies

CD37 is a plasma membrane protein frequently present on B-cells, making it a potential target for treating B-cell malignancies. However, CD37-targeting antibodies that are being developed for clinical use are not very effective at inducing CDC, a crucial immune response for eliminating cancer cells. DuoHexaBody-CD37 is a newly developed humanized IgG1 bispecific antibody that targets two separate CD37 epitopes and has been enhanced with a mutation (E430G) to improve hexamer formation, leading to more efficient C1q binding and complement activation.

This hexamerization-enhancing mutation was incorporated into two humanized CD37 monoclonal antibodies (mAbs) that bind to non-overlapping CD37 epitopes. Various formats and combinations of these antibodies were tested for their ability to induce CDC and ADCC. The bispecific hexamerization-enhanced antibody, DuoHexaBody-CD37, demonstrated superior CDC activity compared to the individual mAbs or their combination, both in vitro across different B-cell lines and ex vivo using tumor samples from chronic lymphocytic leukemia (CLL) patients.

In a CDC assay with tumor cells from a relapsed/refractory CLL patient who had prior treatment with rituximab, ibrutinib, and idelalisib, DuoHexaBody-CD37 induced nearly complete lysis, significantly outperforming the individual antibodies and their combination. DuoHexaBody-CD37 also induced potent ADCC against Daudi cells, as assessed using peripheral blood mononuclear cells from healthy human donors.

In whole blood assays, DuoHexaBody-CD37 showed efficient B-cell binding and potent depletion of the B-cell population. Additionally, it induced significant inhibition of tumor growth in vivo in mouse xenograft models of Burkitt's lymphoma and CLL at low doses.

In conclusion, DuoHexaBody-CD37, which combines the DuoBody and HexaBody platforms for the first time, has shown highly potent CDC and efficient ADCC in preclinical models. These results suggest that DuoHexaBody-CD37 could be a potential therapeutic monoclonal antibody for treating human B-cell malignancies.