pH-dependent Binding Engineering Reveals an FcRn Affinity Threshold That Governs IgG Recycling

Abstract

Background: FcRn controls the serum persistence of antibodies. Results: A panel of novel Fc mutations reveals sites controlling pH dependence and FcRn affinity. Conclusion: FcRn affinity thresholds determine IgG recycling efficiency. Significance: Knowledge of the relationship between FcRn binding and serum persistence can aid in designing better therapeutic antibodies.

Extending human IgG half-life using structure-guided design

“…Motavizumab containing the Fc modifications DF215 and DF228 had a half-life of 15.1 and 18.8 days, respectively, indicating a greater than 3.9-fold increase in half-life with incorporation of the DF228 design (reported fold increase in t 1/2 with YTE mutation on motavizumab are 2, 3.5 and 3.7 – fold). 10,44 Taken together these data demonstrate a significant increase in antibody persistence in the sera of animals known to be reliable models of human antibody half-life, strongly suggesting that these designs will indeed increase the time a biologic will remain at therapeutic concentrations in vivo .…”

“…Incorporation of Fc modifications DF215 and DF228 significantly lowered the clearance rate (77 % and 83 %, respectively). The fitted parameters indicated a β-phase elimination half-life of 4.8 days for motavizumab in cynomolgus monkeys (t 1/2 values reported in the literature for motavizumab are 5.7 ± 1.4 days, 6.1 ± 1.2 days, 10 and 5.8 days 44 ) (Table 5). Motavizumab containing the Fc modifications DF215 and DF228 had a half-life of 15.1 and 18.8 days, respectively, indicating a greater than 3.9-fold increase in half-life with incorporation of the DF228 design (reported fold increase in t 1/2 with YTE mutation on motavizumab are 2, 3.5 and 3.7 – fold).…”

A novel in vitro assay to predict neonatal Fc receptor-mediated human IgG half-life

“…49 Furthermore, other literature reports stress the importance of assessing dissociation characteristics at physiological pH to more accurately predict half-life. 25,37,55,63 It is likely that both the rates of association in the endosome and extracellular dissociation of the mAb-FcRn complex are critical for recycling. Our results support the use of on/off rates rather than equilibrium binding while considering the association and dissociation at relevant pH to accurately predict in vivo half-life.…”

“…For example, several studies have attempted to measure the mAbFcRn interaction in vitro and draw a correlation to in vivo halflife, but the results have been largely mixed. 24,25,37,50,52,55,56,[61][62][63][64] This creates a dependency on the available transgenic FcRn mice for an accurate model of preclinical PK assessment, 22,64,65 which is lower throughput and more costly when compared to in vitro assays. Thus, a better assay is needed to support the fast-paced mAb discovery platforms currently in use.…”

“…[43][44][45][46][47] More recently, mutations in these residues have exemplified the complex binding relationship of FcRn and IgG that modulates in vivo half-life, while highlighting the importance of both association at acidic pH (6.0) and dissociation at physiological pH (7.4). 11,18,23,37,38,[48][49][50][51][52][53][54][55] Independent of the direct mAb-FcRn contact within the IgG constant region (Fc), additional studies have determined the antigen binding fragment (Fab) can have a significant effect on the mAb-FcRn interaction and in vivo half-life. 25,56,57 This phenomenon explains why circulating IgGs with identical Fc regions can vary 2-3 fold in serum half-life even when the same antigen is targeted.…”