AChR Autoantibody Pathogenic Properties Are Heterogeneously Distributed and Undergo Temporal Changes Among Patients With Myasthenia Gravis

Acetylcholine receptor (AChR) autoantibodies contribute to myasthenia gravis (MG) pathogenesis through 3 mechanisms: complement activation, receptor internalization, and acetylcholine (ACh) binding site blocking. Recently approved therapies target these autoantibodies by inhibiting the complement pathway or blocking the neonatal Fc receptor, reducing IgG autoantibody levels. However, these approaches have limitations: complement inhibitors do not address complement-independent mechanisms, and FcRn blockers only target IgG. Understanding how different pathogenic mechanisms, isotypes, and IgG subclasses are represented in the AChR autoantibody repertoire could lead to more precise application of therapeutics. To address this, we used advanced live cell-based assays to study autoantibody heterogeneity in longitudinally collected patient samples. Serum samples (N = 210) from 50 AChR IgG+ generalized MG patients collected longitudinally over 2 years were evaluated using a set of cell-based assays to measure complement activation, receptor internalization, ACh binding site blocking, and the frequency of the IgM and IgA isotypes and IgG subclasses. In cross-sectional samples, IgA and IgM autoantibodies co-occurred with IgG in 10% and 12% of patients, respectively. In addition, 4% of patients had all 3 isotypes (IgA, IgM, and IgG) present simultaneously. AChR-IgG1 was found in 67.4%, followed by IgG3 (21.7%) and IgG2 (17.4%). Complement was active in 84.8%, followed by AChR internalization (63%) and blocking (30.4%). Complement and AChR internalization were simultaneously active in 45.6%, complement and blocking were active in 10.8%, and all 3 pathomechanisms were active in 17.4%. Blocking alone was active in only 2.1%; AChR internalization alone was not found. Autoantibody binding capacity was associated with the magnitude of complement activation and AChR internalization. Temporal fluctuations of autoantibody binding capacity and the associated pathogenic mechanisms were observed. Pathogenic mechanisms were not associated with disease severity in cross-sectional analyses. However, longitudinally, disease severity measures followed a similar trend to the AChR autoantibody repertoire and mediated pathogenic mechanisms in some individuals, but not others. These findings highlight subsets of patients with MG with autoantibodies that can mediate pathogenic mechanisms or include isotypes that some therapeutics may not effectively target. Consequently, we suggest incorporating comprehensive autoantibody profiling into future MG clinical trials to further investigate potential associations with treatment outcomes.