Background Antibody effector functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) are mediated through the interaction of the antibody Fc region with Fc gamma receptors present on immune cells. Several approaches have been used to modulate antibody Fc-Fc gamma receptor interactions with the goal of driving an effective antitumor immune response. One such approach is removal of fucose on the antibody core glycan to increase binding to Fc gamma receptor IIIa (CD16a) and drive increased ADCC and immune agonism. However, robust antibody Fc engagement and immune cell binding of non-fucosylated antibodies in the periphery can lead to unwanted induction of systemic cytokine release and other dose-limiting infusion-related reactions. Identifying a balance between effective engagement of Fc gamma receptors that can induce antitumor activity without incurring systemic immune activation is an ongoing challenge in the field of antibody and immuno-oncology therapeutics.
Methods A method for the reversible modulation of antibody Fc interactions was designed and applied to a series of non-fucosylated antibodies. This methodology utilizes chemical conjugation of polyethylene glycol (PEG) linkers to the interchain disulfides of an antibody to initially impair binding to Fc gamma receptors on peripheral cells upon administration but allow for restoration of antibody effector function through de-conjugation over time. Impacts of PEGylation on Fc gamma receptor binding, signaling, and restoration of function were assessed in vitro and in vivo.
Results In vitro binding and signaling assays with various loaded conjugates were used to identify a preferred linker format that reduces binding and activity of non-fucosylated antibodies to the level of fucosylated parent antibodies. Plasma stability experiments demonstrated that the preferred linker technology can partially de-conjugate over time, allowing for restoration of Fc binding and function in a time-dependent manner. The lead technology was applied to an agonist CD40 antibody, which resulted in significant reductions in cytokine production in human CD40 mice and non-human primates, while demonstrating retained efficacy and improved pharmacokinetics compared to the parent antibody.
Conclusions A simple, modular approach using chemical conjugation can reversibly attenuate Fc gamma receptor binding and antibody-driven acute systemic immune activation. This approach can be rapidly applied to antibodies that suffer from systemic immune activation that occurs due to peripheral Fc binding immediately upon infusion. As a proof of concept, the technology was applied to an agonist CD40 antibody and resulted in significantly decreased pro-inflammatory cytokine production despite higher plasma concentrations and the same antitumor activity to the parent antibody.
Acknowledgements We would like to thank Bianka Haro and Jamie Mitchell for conjugation support.
Ethics Approval All animals studies were were conducted in accordance with protocols reviewed and approved by the Institutional Animal Care and Use Committee at Seagen.
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