Half-life is an essential pharmacokinetic attribute of therapeutic antibodies and thus, tools to accurately predict their clearance can advance development of novel therapies. An important determinant of the serum half-life of immunoglobulins is binding to neonatal Fc receptor (FcRn). In vivo, FcRn binds IgG at an acidic pH (<6.5) and then releases it at neutral or physiological pH to unidirectionally ferry it across epithelial cells from the lumen-facing surface to interstitial space or the bloodstream while avoiding lysosomal degradation.1 A simple and robust device to characterize FcRn binding to antibodies that overcomes limitations of technologies like surface plasmon resonance (SPR) immunoassays constitutes a versatile method to standardize and speed up half-life analyses.
SPR immunoassay format limits resolution of antibody complexity and heterogeneity
The interaction of an antibody with FcRn is complex. Binding takes place at the Fc region of both antibody heavy chains, plus FcRn can dimerize, giving rise to complexes with 4 FcRn molecules binding 3 antibodies or any permutation of that construct (Figure 1). Given their planar nature, SPR immunoassays simply cannot capture the three-dimensionality of this interaction. Any adjustments to the format of the immunoassay – immobilizing the antibody instead of FcRn or increasing the density of the immobilized reagent – cannot compensate for this spatial limitation and thus, SPR assays cannot reflect the full heterogeneity of the FcRn-mAb interaction.