Objective:

Background:

FcRn recycles immunoglobulin G (IgG) in cells and is responsible for the long half-life of IgG relative to other plasma proteins but also recycles pathogenic IgG autoantibodies. Several anti-FcRn therapeutic agents have been approved for use in patients with generalized myasthenia gravis (gMG), including rozanolixizumab, a high-affinity monoclonal antibody (mAb) that directly blocks the IgG binding site on FcRn.

Design/Methods:

Using high-content imaging methods in human umbilical vein endothelial cells, the cellular uptake, endosomal trafficking and recycling of fluorescently-labelled rozanolixizumab and MST-HN IgG Fc (an analog of efgartigimod) were compared.

Results:

A time- and concentration-dependent uptake of rozanolixizumab into intracellular compartments was observed: uptake was rapid, not pH-dependent and competed out with unlabeled inhibitor, supporting a receptor-mediated mechanism. Conversely, uptake of MST-HN IgG Fc was slower and required higher concentrations to detect uptake which was pH-dependent, not competed out with unlabeled inhibitor, and occurred with similar potency in cells that did not express FcRn, suggesting a receptor-independent mechanism such as passive fluid phase pinocytosis. Using Rab proteins associated with different endosomal compartments, we showed that the two FcRn inhibitors appeared to traffic through recycling compartments in a similar manner and their return to the cell surface occurred with similar kinetics. PKPD model simulations demonstrated that efgartigimod requires 3.8-fold more moles compared to rozanolixizumab to keep the FcRn receptor occupied and achieve clinically relevant IgG decreases.

Conclusions: