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Fc Binding by FcγRIIa Is Essential for Cellular Activation by the Anti-FcγRIIa mAbs 8.26 and 8.2

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posted on 10.12.2021, 02:11 by BD Wines, HM Trist, S Esparon, Rachael ImpeyRachael Impey, GA Mackay, RK Andrews, Tatiana Soares-da-CostaTatiana Soares-da-Costa, GA Pietersz, RI Baker, PM Hogarth
FcγR activity underpins the role of antibodies in both protective immunity and auto-immunity and importantly, the therapeutic activity of many monoclonal antibody therapies. Some monoclonal anti-FcγR antibodies activate their receptors, but the properties required for cell activation are not well defined. Here we examined activation of the most widely expressed human FcγR; FcγRIIa, by two non-blocking, mAbs, 8.26 and 8.2. Crosslinking of FcγRIIa by the mAb F(ab’)2 regions alone was insufficient for activation, indicating activation also required receptor engagement by the Fc region. Similarly, when mutant receptors were inactivated in the Fc binding site, so that intact mAb was only able to engage receptors via its two Fab regions, again activation did not occur. Mutation of FcγRIIa in the epitope recognized by the agonist mAbs, completely abrogated the activity of mAb 8.26, but mAb 8.2 activity was only partially inhibited indicating differences in receptor recognition by these mAbs. FcγRIIa inactivated in the Fc binding site was next co-expressed with the FcγRIIa mutated in the epitope recognized by the Fab so that each mAb 8.26 molecule can contribute only three interactions, each with separate receptors, one via the Fc and two via the Fab regions. When the Fab and Fc binding were thus segregated onto different receptor molecules receptor activation by intact mAb did not occur. Thus, receptor activation requires mAb 8.26 Fab and Fc interaction simultaneously with the same receptor molecules. Establishing the molecular nature of FcγR engagement required for cell activation may inform the optimal design of therapeutic mAbs.

Funding

This work was supported by the Australian NHRMC -Project Grant, to PH and BW (GNT1145303). Support to the Burnet Institute comes from the NHMRC Independent Research Institutes Infrastructure Support Scheme and a Victorian State Government Operational Infrastructure grant. TC holds an Australian Research Council fellowship (DE190100806).

History

Publication Date

25/10/2021

Journal

Frontiers in Immunology

Volume

12

Article Number

666813

Pagination

13p.

Publisher

Frontiers Media SA

ISSN

1664-3224

Rights Statement

© 2021 Wines, Trist, Esparon, Impey, Mackay, Andrews, Soares da Costa, Pietersz, Baker and Hogarth. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.