Predict human antibody half-life across all six preclinical species in one hour.

The role of FcRn in antibody pharmacokinetics

The neonatal Fc receptor (FcRn) governs the serum half-life of immunoglobulin G (IgG) through a pH-dependent recycling mechanism. Following pinocytosis, IgG molecules are internalized into acidified endosomes (pH ~6.0), where FcRn binds with high affinity and rescues the antibody from lysosomal degradation. Upon fusion with the cell membrane at physiological pH (~7.4), the interaction reverses and intact IgG is returned to circulation.

For therapeutic antibody developers, FcRn affinity at pH 6.0 is a critical developability attribute, directly linked to dosing frequency, patient exposure, and the success of half-life-extending Fc engineering strategies, which introduce point mutations into the Fc region to tighten FcRn binding. Characterizing this interaction accurately and early in development directly informs lead selection and preclinical study design.

Why species selection matters for PK prediction

A central challenge in translational pharmacokinetics is that FcRn affinity differs substantially across preclinical species. The mouse-human gap can reach 5- to 10-fold for the same antibody, and rat FcRn binding is similarly attenuated. Together, these rodent-human discrepancies account for the systematic under-prediction of human half-life from rodent pharmacokinetic (PK) studies.

Allometric PK scaling, the standard practice of predicting human pharmacokinetics from animal data through body-size relationships, presumes consistent receptor biology across species. If the FcRn affinity of your molecule in the toxicology species differs substantially from its affinity in human, that presumption breaks and the human PK projection becomes unreliable.

Fc engineering for half-life extension requires ranking variants not only on human FcRn but across the preclinical species intended for PK and toxicology studies. Affinity gains observed on human FcRn are not always preserved to the same degree in mouse and rat. Identifying these discrepancies before in vivo studies prevents costly course-corrections.

FcRn affinity differences of 5- to 10-fold between mouse and human account for systematic under-prediction of human antibody half-life from murine PK studies. Characterizing the complete cross-species affinity profile early in development provides the data needed to calibrate allometric PK models and to select the most predictive tox species.

Demonstration of FcRn binding equivalence between a biosimilar and its reference is a key element of analytical comparability under ICH Q5E. The affinity differences that must be resolved are often less than twofold, at or below the practical noise floor of conventional SPR. Coherent mass detection plus 8 within-chip replicates is specifically designed for this analytical challenge.

Human, cynomolgus, marmoset, mouse, rat, and minipig FcRn profiled under identical assay conditions in the same injection series, eliminating the inter-assay variability of sequential chip runs.

Reported K_D, k_on, and k_off are the mean of 8 independent molograms per species, with confidence intervals derived from global fitting of all 64 sensorgrams simultaneously.

The pH 6.0 binding run and pH 7.4 specificity run are performed sequentially on the same chip, with no regeneration step required between them.

All six FcRn species are immobilized via DDI on the Oligo|PEG surface prior to shipment. No in-house coupling chemistry, no surface optimization, no batch-to-batch ligand variability.

Coherent mass density is not a proxy for binding. It is a direct physical readout of the mass that binds coherently to the mologram pattern, feeding directly into 1:1 Langmuir kinetic analysis without refractive-index conversion.

An IgG-binding-deficient FcRn variant occupies one position on every chip. Authentic FcRn-mediated signals on positions 1–6 should produce no response on this channel: a built-in assay integrity check on every run.