An IgG1-like bispecific antibody targeting CD52 and CD20 for the treatment of B-cell malignancies

Bispecific antibodies (biAb) targeting two different antigens or two distinct epitopes on the same antigen have demonstrated broad therapeutic utility. CD52 and CD20 are co-expressed on the cell surface of malignant B cells in B-cell non-Hodgkin lymphoma (B-NI-IL) and chronic lymphocytic leukemia (CLL) and increased expression of both antigens is detected on dividing or recently divided cells (proliferative fraction) in CLL. The CD52-targeting monoclonal antibody (mAb) alemtuzumab (atz) not only depletes malignant B cells but also healthy CD52(+) B and T lymphocytes and monocytes, causing severe immunosuppression. Loss of CD20 can occur in CLL after treatment with rituximab (rtx) and other CD20-targeting mAbs. To broaden the benefit of atz and rtx, we engineered an IgG1-like biAb, atz x rtx scFv Fc. The Fc fragment of the biAb facilitates purification by Protein A affinity chromatography and supports a longer circulatory half-life. While atz x rtx scFv-Fc retained both antigen binding specificities, it showed superior binding to CD52(+) CD20(+) B cells compared to CD52(+)CD20(-) T cells. Moreover, atz x rtr scFv-Fc mediated potent complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) in vitro and exhibited B-cell depleting but T-cell sparing activities in vivo in a CLL patient-derived xenograft model. B-cell depletion was more pronounced for cells of the proliferative fraction.