Cellular recycling-driven in vivo half-life extension using recombinant albumin fusions tuned for neonatal Fc receptor (FcRn) engagement

Maja Thim Larsen, Helen Rawsthorne, Karen Kræmmer Schelde, Frederik Dagnæs-Hansen, Jason Cameron, Ken Howard

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review


Recombinant albumin-drug genetic fusions are an effective technology to prolong the serum half-life of therapeutics that has resulted in marketed products. Indirect evidence suggests albumin fusions’ long circulation is controlled by engagement with the cellular recycling neonatal Fc receptor (FcRn) in addition to reduced kidney filtration. In this work, we have used a panel of recombinant fusions, engineered with different human FcRn (hFcRn) affinity, including a novel high binding albumin variant (HBII), to directly define and importantly, control the intracellular mechanism as a half-life extension tuning method. mNeonGreen or mCherry fusion to the N-terminal of the recombinant human albumin (rHA) variants null-binder (rHA NB), wild-type (rHA WT), high-binder I (rHA HBI), and high-binder II (rHA HBII) did not generally interfere with hFcRn interaction determined by Biolayer Interferometry. Co-localisation of the albumins with endosomal, but not lysosomal, markers was shown by confocal microscopy for high, but not low, hFcRn binders in a human microvascular endothelial hFcRn overexpressing cell line (HMEC-1 FcRn) suggestive of endosomal compartmentalisation. Furthermore, a cellular recycling assay revealed increased recycling of albumin fusions for the high binding variants (mNeonGreen WT; ~1, mNeonGreen HBI; 5.26-fold higher, and mNeonGreen HBII; 5.77-fold higher) in the hFcRn overexpressing cell line. In vivo experiments demonstrated a direct in vitro recycling/in vivo half-life correlation with a longer circulation for the mCherry fusions engineered with high hFcRn affinity that was highest with the HBII variant of 30.1 h compared to 18.2 h for the mCherry WT. This work gives the first direct evidence for an FcRn-driven endosomal cellular recycling pathway for recombinant albumin fusions that correlates with half-life extension controlled by the affinity to hFcRn; promoting a versatile method to tune the pharmacokinetics of albumin fusion-based therapeutics not met by current technologies.

Original languageEnglish
JournalJournal of Controlled Release
Pages (from-to)132-141
Number of pages10
Publication statusPublished - 10 Oct 2018


  • Albumin
  • Albumin fusion
  • Half-life extension
  • Intracellular recycling
  • Neonatal Fc receptor
  • Pharmacokinetics


Dive into the research topics of 'Cellular recycling-driven in vivo half-life extension using recombinant albumin fusions tuned for neonatal Fc receptor (FcRn) engagement'. Together they form a unique fingerprint.

Cite this