Co-engaging CD47 and CD19 with a bispecific antibody abrogates B-cell receptor/CD19 association leading to impaired B-cell proliferation

Abstract

CD19 is a B cell-specific receptor that regulates the threshold of B cell receptor (BCR)-mediated cell proliferation. A CD47xCD19 bispecific antibody (biAb) was generated to target and deplete B cells via multiple antibody-mediated mechanisms. Interestingly, the biAb, constructed of a CD19 binding arm and a CD47 binding arm, inhibited BCR-mediated B-cell proliferation with an effect even more potent than a CD19 monoclonal antibody (mAb). The inhibitory effect of the biAb was not attributable to CD47 binding because a monovalent or bivalent anti-CD47 mAb had no effect on B cell proliferation. Fluorescence resonance energy transfer analysis demonstrated that co-engaging CD19 and CD47 prevented CD19 clustering and its migration to BCR clusters, while only engaging CD19 (with a mAb) showed no impact on either CD19 clustering or migration. The lack of association between CD19 and the BCR resulted in decreased phosphorylation of CD19 upon BCR activation. Furthermore, the biAb differentially modulated BCR-induced gene expression compared to a CD19 mAb. Taken together, this unexpected role of CD47xCD19 co-ligation in inhibiting B cell proliferation illuminates a novel approach in which two B cell surface molecules can be tethered, to one another in order, which may provide a therapeutic benefit in settings of autoimmunity and B cell malignancies.

Design and Efficacy of a Monovalent Bispecific PD-1/CTLA4 Antibody That Enhances CTLA4 Blockade on PD-1+ Activated T Cells

“…MEDI5752 leverages cross-arm avidity binding (where one of the fragment antigen binding (Fab) domains acts as an anchor for the other) to take advantage of both the more stable surface expression of PD-1, and the elevated cell surface density of PD-1 vs. CTLA-4. Our data demonstrate enhanced saturation of CTLA-4 with the PD-1/CTLA-4 bispecific when compared to equimolar concentrations of a conventional mAb targeting CTLA-4 and is consistent with recently reported data demonstrating the capacity of bispecific antibodies to promote improved target selectivity by cross-arm avidity binding to two antigens on the surface of the same cell(52)(53)(54)(55)(56)(57)(58). Moreover, we found that tethering PD-1 to CTLA-4 also lead to the internalization and subsequent degradation of PD-1, providing a novel mechanism of action which is distinct from other mAbs targeting this axis.…”

Bispecific antibodies targeting dual tumor-associated antigens in cancer therapy

“…BsAb TG-1801 could potentially overcome the limitation of CD47 monospecific targeting therapy by specifically blocking the 'do not eat me' signal only on B-cells. This is achieved by combining a low-affinity CD47 arm with a high-affinity CD19 arm, thereby reducing the risk of unwanted CD47 blockade in healthy cells (Buatois et al 2018 ; Hatterer et al 2019 ). Similarly, IMM0306, a CD20 x CD47 BsAb developed by ImmuneOnco has achieved remarkable therapeutic effects in various tumor models and showed no binding to human erythrocytes in pre-clinical study (Yu et al 2020 ).…”

Harnessing and Enhancing Macrophage Phagocytosis for Cancer Therapy

“…Another notable example of a bispecific engager was noted in NI-1701, a CD47/CD19 bispecific antibody constructed with the IgG1 isotype to elicit an ADCP response. This bispecific antibody demonstrated potent in vitro and in vivo activity across a plethora of B cell malignancy models, which rely on the co-engagement of CD47 and CD19 on B cells simultaneously to induce potent ADCP of target cells ( 86 , 87 ).…”