Mode of Nipocalimab Action and Pharmacology in Cells and Preclinical Models

Background: The neonatal Fc receptor (FcRn) is primarily an endosomal receptor responsible for maintaining the long half-life of immunoglobulin G (IgG), including IgG autoantibodies. FcRn drives IgG recycling, the process of binding to IgG and IgG autoantibodies internalized along with other serum proteins into cells and transporting the bound IgG to the cell surface for release back into circulation. FcRn-mediated IgG recycling thus rescues IgG and IgG autoantibodies from intracellular lysosomal degradation. Warm autoimmune hemolytic anemia (wAIHA) is a rare, life-threatening autoimmune disorder caused by hemolytic anti-erythrocyte IgG autoantibodies. Lowering anti-erythrocyte autoantibodies may decrease hemolysis and improve anemia. Nipocalimab is a high-affinity, fully human monoclonal antibody which selectively binds and blocks FcRn to decrease IgG autoantibodies. Nipocalimab was evaluated in healthy volunteers and in subjects with generalized myasthenia gravis (gMG) [Ling LE, et al. Clin Pharmacol Ther. 2019;105(4):1031-1039; Guptill J, et al. AAN 2021. Presentation 2157] and is currently being studied in over 10 autoantibody disorders including active primary or secondary wAIHA (NCT04119050). This study demonstrates the in vitro and in vivo pharmacology of nipocalimab confirming concentration dependent FcRn engagement, inhibition of IgG recycling, and increased clearance of IgG consistent with the pharmacodynamics (PD) of FcRn engagement and IgG clearance observed in Phase 1 and 2 studies. Methods: Primary human endothelial and villous trophoblast cells incubated in the presence of fluorescently-tagged IgG were treated with nipocalimab to assess its impact on IgG recycling by fluorescence microscopy and flow cytometry. After in vitro or in vivo nipocalimab administration, FcRn receptor occupancy (RO) was detected after cell fixation-permeablization with labeled nipocalimab. In vivo PD effects were assessed in human transgenic FcRn mice (Tg32, Jackson Labs) or cynomolgus monkeys due to nipocalimab's specificity for primate FcRn. RO was measured over time in circulating monocytes in both species. Endogenous serum IgG in monkeys and exogenous human IgG in human transgenic mice were used to assess nipocalimab effect on IgG in vivo. Results: Nipocalimab treatment of primary human target cells increased cellular IgG content by increasing lysosomal IgG consistent with inhibition of IgG recycling. Nipocalimab also demonstrated similar concentration-dependent inhibition of IgG recycling (IC50, 0.03 μg/mL) and FcRn saturation (EC50, 0.03 μg/mL) demonstrating a high degree of correlation between target engagement and PD effect. Saturation of FcRn binding by nipocalimab (full RO) occurred within 30’ to 2 hours at concentrations consistent with pharmacokinetic (PK) at full RO and the period of IgG lowering observed in clinical studies. In vivo, full RO also occurred rapidly within 2 hours of single i.v. infusions (dose ≥2 mg/kg) and was followed shortly by initiation of IgG lowering in both human FcRn transgenic mice and cynomolgus monkeys. PK and PD evaluation of single IV doses of nipocalimab in cynomolgus monkeys and human FcRn transgenic mice established consistent dose-, exposure-, and time-dependent relationships between PK, the PD effect on FcRn RO and the lowering of serum IgG concentrations. Duration of RO in peripheral blood monocytes in both preclinical species was dose-dependent, as was the duration of IgG clearance, suggesting a relationship between RO and maintenance of an increased IgG clearance rate. These pharmacological data demonstrate a high degree of correlation between nipocalimab-induced block in IgG recycling in in vitro cell models and in vivo PD effects (serum/plasma IgG lowering) seen in preclinical models. Conclusion: These in vitro and in vivo preclinical studies demonstrate the in vitro and in vivo mechanism of action for nipocalimab. Nipocalimab is under clinical investigation for multiple IgG-mediated autoantibody disorders, including wAIHA. The close mechanistic relationship between nipocalimab concentration, FcRn occupancy and inhibition of IgG recycling resulting in rapid, deep and sustained IgG lowering in vivo is consistent between preclinical and clinical studies.