M281: A Therapeutic Anti-FcRn Blocking Antibody for Rapid Clearance of IgG and IgG Autoantibodies in Immune Cytopenias and Other Auto/Allo-Immune Disease
Authors: Ling Leona E , Roy Sucharita , Daly Thomas , Cochran Edward , Tyler Steven , Markowitz Lynn , Bulik Dorota , Choudhury Amit , Meador James , Parge Viraj , Mekala Divya , Sipsey Sandra , Gurnani Srishti , Duffner Jay , Lee Stan , Washburn Nathaniel , Meccariello Robin , Schaeck John , Wang Jing , Schultes Birgit , Hillson Jan L. , Avery William , Kaundinya Ganesh V. , Manning Anthony M. 
Published: October 2019

Abstract
Introduction
IgG antibodies are the primary pathogenic agent in a number of auto- or allo-immune diseases. Efficacious therapies which decrease systemic levels of pathogenic antibodies include treatment with IVIG therapeutic plasmapheresis or immunoabsorption. Here, a novel strategy was evaluated to induce IgG clearance in diseases driven by IgG autoantibodies by blockade of FcRn-mediated IgG recycling.
Methods
M281 was developed as a high affinity, effectorless IgG1anti-FcRn monoclonal antibody. M281 effect on IgG recycling was evaluated in human umbilical vein endothelial cells in vitro. In vivo studies in transgenic human FCGRT/mouse FCGRT null mice and cynomolgus monkey were performed to characterize the pharmacokinetics, biodistribution, target occupancy, specificity of M281 and its efficacy in mouse models of thrombocytopenia and arthritis.
Results
M281 demonstrates specific dose-dependent, albumin-sparing IgG clearance in human FCGRT transgenic/mouse FCGRT null mice and in cynomolgus monkeys. M281 inhibits IgG recycling in endothelial cells in vitro and IgG clearance in vivo. Pharmacokinetics, target occupancy, pharmacodynamics and biodistribution indicate typical recombinant antibody biodistribution with rapid, dose dependent target inhibition and systemic clearance. M281 also demonstrated efficacy in mouse idiopathic thrombocytopenia purpura and collagen antibody-induced arthritis models of disease.
Conclusions
These findings support the evaluation of M281 as a strategy for the rapid and reversible suppression of pathogenic autoantibodies or alloantibodies in the setting of immune cytopenias, acquired inhibitors, thrombotic states and other disorders.

Disclosures
Ling: Momenta Pharmaceuticals: Employment, Equity Ownership. Roy:Momenta Pharmaceuticals: Employment, Equity Ownership. Daly:Momenta Pharmaceuticals: Employment, Equity Ownership. Cochran:Momenta Pharmaceuticals: Employment, Equity Ownership. Tyler:Momenta Pharmaceuticals: Employment, Equity Ownership. Markowitz:Momenta Pharmaceuticals: Employment, Equity Ownership. Bulik:Momenta Pharmaceuticals: Employment, Equity Ownership. Choudhury:Momenta Pharmaceuticals: Employment, Equity Ownership. Meador:Momenta Pharmaceuticals: Employment, Equity Ownership. Parge:Momenta Pharmaceuticals: Employment. Mekala:Momenta Pharmaceuticals: Employment, Equity Ownership. Sipsey:Momenta Pharmaceuticals: Employment, Equity Ownership. Gurnani:Momenta Pharmaceuticals: Employment, Equity Ownership. Duffner:Momenta Pharmaceuticals: Employment, Equity Ownership. Lee:Momenta Pharmaceuticals: Employment, Equity Ownership. Washburn:Momenta Pharmaceuticals: Employment, Equity Ownership. Meccariello:Momenta Pharmaceuticals: Employment, Equity Ownership. Schaeck:Momenta Pharmaceuticals: Employment, Equity Ownership. Wang:Momenta Pharmaceuticals: Employment, Equity Ownership. Schultes:Momenta Pharmaceuticals: Employment, Equity Ownership. Hillson:Momenta Pharmaceuticals: Employment, Equity Ownership. Avery:Momenta Pharmaceuticals: Employment, Equity Ownership. Kaundinya:Momenta Pharmaceuticals: Employment, Equity Ownership. Manning:Momenta Pharmaceuticals: Employment, Equity Ownership.