Extended plasma half-life of albumin-binding domain fused human IgA upon pH-dependent albumin engagement of human FcRn in vitro and in vivo

MAbs. 2021 Jan-Dec;13(1):1893888. doi: 10.1080/19420862.2021.1893888.


Albumin has a serum half-life of 3 weeks in humans. This feature can be used to improve the pharmacokinetics of shorter-lived biologics. For instance, an albumin-binding domain (ABD) can be used to recruit albumin. A prerequisite for such design is that the ABD-albumin interaction does not interfere with pH-dependent binding of albumin to the human neonatal Fc receptor (FcRn), as FcRn acts as the principal regulator of the half-life of albumin. Thus, there is a need to know how ABDs act in the context of fusion partners and human FcRn. Here, we studied the binding and transport properties of human immunoglobulin A1 (IgA1), fused to a Streptococcus protein G-derived engineered ABD, in in vitro and in vivo systems harboring human FcRn. IgA has great potential as a therapeutic protein, but its short half-life is a major drawback. We demonstrate that ABD-fused IgA1 binds human FcRn pH-dependently and is rescued from cellular degradation in a receptor-specific manner in the presence of albumin. This occurs when ABD is fused to either the light or the heavy chain. In human FcRn transgenic mice, IgA1-ABD in complex with human albumin, gave 4-6-fold extended half-life compared to unmodified IgA1, where the light chain fusion showed the longest half-life. When the heavy chain-fused protein was pre-incubated with an engineered human albumin with improved FcRn binding, cellular rescue and half-life was further enhanced. Our study reveals how an ABD, which does not interfere with albumin binding to human FcRn, may be used to extend the half-life of IgA.Abbreviations: ABD - Albumin binding domain, ADA - anti-drug-antibodies, ADCC - Antibody-dependent cellular cytotoxicity, ELISA - Enzyme-linked Immunosorbent assay, FcαRI - Fcα receptor, FcγR - Fcγ receptor, FcRn - The neonatal Fc receptor, GST - Glutathione S-transferase, HC - Heavy chain, HERA - Human endothelial cell-based recycling assay, Her2 - Human epidermal growth factor 2, HMEC - Human microvascular endothelial cells, IgG - Immunoglobulin G, IgA - Immunoglobulin A, LC - Light chain, QMP - E505Q/T527M/K573P, WT - Wild type.

Keywords: Immunoglobulin A (IgA); albumin-binding-domain (ABD); half-life; human FcRn transgenic mice; human serum albumin (HSA); the neonatal Fc receptor (FcRn).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibody Specificity
  • Bacterial Proteins / genetics
  • Bacterial Proteins / immunology
  • Bacterial Proteins / metabolism*
  • HEK293 Cells
  • Half-Life
  • Histocompatibility Antigens Class I / genetics
  • Histocompatibility Antigens Class I / immunology
  • Histocompatibility Antigens Class I / metabolism*
  • Humans
  • Immunoglobulin A / genetics
  • Immunoglobulin A / immunology
  • Immunoglobulin A / metabolism*
  • Mice, Transgenic
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Stability
  • Proteolysis
  • Receptors, Fc / genetics
  • Receptors, Fc / immunology
  • Receptors, Fc / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • Serum Albumin, Human / genetics
  • Serum Albumin, Human / immunology
  • Serum Albumin, Human / metabolism*


  • ALB protein, human
  • Bacterial Proteins
  • Histocompatibility Antigens Class I
  • IgG Fc-binding protein, Streptococcus
  • Immunoglobulin A
  • Receptors, Fc
  • Recombinant Fusion Proteins
  • Fc receptor, neonatal
  • Serum Albumin, Human

Grants and funding

This work was supported by the Horizon 2020 Framework Programme [825821]; KWF Kankerbestrijding [7650]; Norges Forskningsråd [230526]; Norges Forskningsråd [179573]; Norges Forskningsråd [300740]; South-Eastern Norway Regional Health Authority [40018]; Research Council of Norway [179573, 230526, 287927]; South-Eastern Norway Regional Health Authority [40018].