Competition for FcRn-mediated transport gives rise to short half-life of human IgG3 and offers therapeutic potential

Abstract

Human IgG3 displays the strongest effector functions of all IgG subclasses but has a short half-life for unresolved reasons. Here we show that IgG3 binds to IgG-salvage receptor (FcRn), but that FcRn-mediated transport and rescue of IgG3 is inhibited in the presence of IgG1 due to intracellular competition between IgG1 and IgG3. We reveal that this occurs because of a single amino acid difference at position 435, where IgG3 has an arginine instead of the histidine found in all other IgG subclasses. While the presence of R435 in IgG increases binding to FcRn at neutral pH, it decreases binding at acidic pH, affecting the rescue efficiency—but only in the presence of H435–IgG. Importantly, we show that in humans the half-life of the H435-containing IgG3 allotype is comparable to IgG1. H435–IgG3 also gave enhanced protection against a pneumococcal challenge in mice, demonstrating H435–IgG3 to be a candidate for monoclonal antibody therapies.

Evaluation of an Fcrn Affinity Chromatographic Method for Igg1-Type Antibodies and Evaluation of Igg Variants

“…Still, recent reports identified a competition between IgG subtypes in the early endosome to be responsible for the short serum half-life of IgG3 [6]. This is due to an arginine at position 435 in IgG3 instead of histidine as in other IgG subtypes.…”

“…It has been recognized recently that binding to FcRn at low pH and dissociation from FcRn at neutral pH appear to be critical for the reported long FcRn-dependent serum halflife of IgG-type antibodies [4][5][6]. Since both events are critical components of the FcRnIgG interaction, they should be included in a comprehensive analytical strategy as part of the candidate selection, quality control of therapeutic monoclonal antibodies (mAbs) or during quality by design studies [7][8][9].…”

Affinity of human IgG subclasses to mouse Fc gamma receptors

“…[37][38][39] Similarly, hIgG3 has been found highly efficient in protecting against pneumococcal infections in vivo, also through complement. 40,41 hIgG2 has a comparable binding pattern for the mouse Fc receptors as mIgG1, but with an estimated 5-to 50-fold lower affinity than mIgG1. This is in agreement with the results found by Overdijk et al, who showed hIgG2 to compete moderately with mIgG1 binding for mFcgRIIb and mFcgRIV.…”

Regulation of complement and modulation of its activity in monoclonal antibody therapy of cancer

“…97 The shorter serum half-life of IgG3 can be rescued by the introduction of the R435H mutation, resulting in a potent mAb for CDC. 98 IgG1/IgG3 chimera targeting CD20 showed stronger C1q binding, increased CDC capacity and more efficient B cell depletion in cynomolgus monkeys compared with the isotypematched parental mAbs. 99 Antibody amino-acid engineering influencing the binding of C1q to the Fc of an antibody can enhance complement activation.…”