Pathogenic muscle-specific tyrosine kinase (MuSK)-specific IgG4 autoantibodies in autoimmune myasthenia gravis (MG) are functionally monovalent as a result of Fab-arm exchange. The development of these unique autoantibodies is not well understood. We examined MG patient-derived monoclonal autoantibodies (mAbs), their corresponding germline-encoded unmutated common ancestors (UCAs), and monovalent antigen-binding fragments (Fabs) to investigate how affinity maturation contributes to binding and immunopathology. Mature mAbs, UCA mAbs, and mature monovalent Fabs bound to MuSK and demonstrated pathogenic capacity. However, monovalent UCA Fabs bound to MuSK but did not have measurable pathogenic capacity. Affinity of the UCA Fabs for MuSK was 100-fold lower than the subnanomolar affinity of the mature Fabs. Crystal structures of two Fabs revealed how mutations acquired during affinity maturation may contribute to increased MuSK-binding affinity. These findings indicate that the autoantigen drives autoimmunity in MuSK MG through the accumulation of somatic mutations such that monovalent IgG4 Fab-arm-exchanged autoantibodies reach a high-affinity threshold required for pathogenic capacity.

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

To compare the immunopathology of immune checkpoint inhibitor-induced myasthenia gravis (ICI-MG) and idiopathic MG, we profiled the respective AChR autoantibody pathogenic properties. Of three ICI-MG patients with AChR autoantibodies, only one showed complement activation and modulation/blocking potency, resembling idiopathic MG. In contrast, AChR autoantibody-mediated effector functions were not detected in the other two patients, questioning the role of their AChR autoantibodies as key mediators of pathology. The contrasting properties of AChR autoantibodies in these cases challenge the accuracy of serological testing in establishing definite ICI-MG diagnoses and underscore the importance of a thorough clinical assessment when evaluating ICI-related adverse events.

Myasthenia gravis (MG) is an autoimmune condition in which neurotransmission is impaired by binding of autoantibodies to acetylcholine receptors (AChR) or, in a minority of patients, to muscle specific kinase (MuSK). There are differences in the dominant IgG subclass, pathogenic mechanisms, and treatment responses between the two MG subtypes (AChR or MuSK). The antibodies are thought to be T-cell dependent, but the mechanisms underlying their production are not well understood. One aspect not previously described is whether defects in central and peripheral tolerance checkpoints, which allow autoreactive B cells to accumulate in the naive repertoire, are found in both or either form of MG.

Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by muscle weakness and caused by pathogenic autoantibodies that bind to membrane proteins at the neuromuscular junction. Most patients have autoantibodies against the acetylcholine receptor (AChR), but a subset of patients have autoantibodies against muscle-specific tyrosine kinase (MuSK) instead. MuSK is an essential component of the pathway responsible for synaptic differentiation, which is activated by nerve-released agrin. Through binding MuSK, serum-derived autoantibodies inhibit agrin-induced MuSK autophosphorylation, impair clustering of AChRs, and block neuromuscular transmission. We sought to establish individual MuSK autoantibody clones so that the autoimmune mechanisms could be better understood. We isolated MuSK autoantibody-expressing B cells from 6 MuSK MG patients using a fluorescently tagged MuSK antigen multimer, then generated a panel of human monoclonal autoantibodies (mAbs) from these cells. Here we focused on 3 highly specific mAbs that bound quantitatively to MuSK in solution, to MuSK-expressing HEK cells, and at mouse neuromuscular junctions, where they colocalized with AChRs. These 3 IgG isotype mAbs (2 IgG4 and 1 IgG3 subclass) recognized the Ig-like domain 2 of MuSK. The mAbs inhibited AChR clustering, but intriguingly, they enhanced rather than inhibited MuSK phosphorylation, which suggests an alternative mechanism for inhibiting AChR clustering.

Myasthenia gravis (MG) is an autoantibody-mediated neuromuscular junction disorder involving the acetylcholine receptors on the motor endplate. The safety and response to high-dose chemotherapy (HDIT) and autologous hematopoietic cell transplantation (HCT) were assessed in a patient with severe refractory MG.

To assess the safety, tolerability, and key pharmacodynamic effects of subcutaneous batoclimab, a fully human anti-neonatal Fc receptor monoclonal antibody, in patients with generalized myasthenia gravis and anti-acetylcholine receptor antibodies.

Trial eligibility in myasthenia gravis (MG) remains largely dependent on a positive autoantibody serostatus. This significantly hinders seronegative MG (SNMG) patients from receiving potentially beneficial new treatments. In a subset of SNMG patients, acetylcholine receptor (AChR) autoantibodies are detectable by a clustered AChR cell-based assay (CBA). Of 99 SNMG patients from two academic U.S. centers, 18 (18.2%) tested positive by this assay. Autoantibody positivity was further validated in 17/18 patients. In a complementary experiment, circulating AChR-specific B cells were identified in a CBA-positive SNMG patient. These findings corroborate the clinical need for clustered AChR CBA testing when evaluating SNMG patients.

Myasthenia gravis (MG) is an autoantibody-mediated autoimmune disorder of the neuromuscular junction. A small subset of patients (<10%) with MG, have autoantibodies targeting muscle-specific tyrosine kinase (MuSK). MuSK MG patients respond well to CD20-mediated B cell depletion therapy (BCDT); most achieve complete stable remission. However, relapse often occurs. To further understand the immunomechanisms underlying relapse, we studied autoantibody-producing B cells over the course of BCDT. We developed a fluorescently labeled antigen to enrich for MuSK-specific B cells, which was validated with a novel Nalm6 cell line engineered to express a human MuSK-specific B cell receptor. B cells (≅ 2.6 million) from 12 different samples collected from nine MuSK MG patients were screened for MuSK specificity. We successfully isolated two MuSK-specific IgG4 subclass-expressing plasmablasts from two of these patients, who were experiencing a relapse after a BCDT-induced remission. Human recombinant MuSK mAbs were then generated to validate binding specificity and characterize their molecular properties. Both mAbs were strong MuSK binders, they recognized the Ig1-like domain of MuSK, and showed pathogenic capacity when tested in an acetylcholine receptor (AChR) clustering assay. The presence of persistent clonal relatives of these MuSK-specific B cell clones was investigated through B cell receptor repertoire tracing of 63,977 unique clones derived from longitudinal samples collected from these two patients. Clonal variants were detected at multiple timepoints spanning more than five years and reemerged after BCDT-mediated remission, predating disease relapse by several months. These findings demonstrate that a reservoir of rare pathogenic MuSK autoantibody-expressing B cell clones survive BCDT and reemerge into circulation prior to manifestation of clinical relapse. Overall, this study provides both a mechanistic understanding of MuSK MG relapse and a valuable candidate biomarker for relapse prediction.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is an inflammatory demyelinating CNS condition characterized by the presence of MOG autoantibodies. We sought to investigate whether human MOG autoantibodies are capable of mediating damage to MOG-expressing cells through multiple mechanisms. We developed high-throughput assays to measure complement activity (CA), complement-dependent cytotoxicity (CDC), antibody-dependent cellular phagocytosis (ADCP), and antibody-dependent cellular cytotoxicity (ADCC) of live MOG-expressing cells. MOGAD patient sera effectively mediate all of these effector functions. Our collective analyses reveal that (a) cytotoxicity is not incumbent on MOG autoantibody quantity alone; (b) engagement of effector functions by MOGAD patient serum is bimodal, with some sera exhibiting cytotoxic capacity while others did not; (c) the magnitude of CDC and ADCP is elevated closer to relapse, while MOG-IgG binding is not; and (d) all IgG subclasses can damage MOG-expressing cells. Histopathology from a representative MOGAD case revealed congruence between lesion histology and serum CDC and ADCP, and we identified NK cells, mediators of ADCC, in the cerebrospinal fluid of relapsing patients with MOGAD. Thus, MOGAD-derived autoantibodies are cytotoxic to MOG-expressing cells through multiple mechanisms, and assays quantifying CDC and ADCP may prove to be effective tools for predicting risk of future relapses.

The aim of this study was to test whether autoantibodies against neurologic surface Ags are found in nonneurologic autoimmune diseases, indicating a broader loss of tolerance. Patient and matched healthy donor (HD) sera were derived from four large cohorts: 1) rheumatoid arthritis (RA) (n = 194, HD n = 64), 2) type 1 diabetes (T1D) (n = 200, HD n = 200), 3) systemic lupus erythematosus (SLE) (n = 200, HD n = 67; neuro-SLE n = 49, HD n = 33), and 4) a control cohort of neurologic autoimmunity (relapsing-remitting multiple sclerosis [MS] n = 110, HD n = 110; primary progressive MS n = 9; secondary progressive MS n = 10; neuromyelitis optica spectrum disorders n = 15; and other neurologic disorders n = 26). Screening of 1287 unique serum samples against four neurologic surface Ags (myelin oligodendrocyte glycoprotein, aquaporin 4, acetylcholine receptor, and muscle-specific kinase) was performed with live cell-based immunofluorescence assays using flow cytometry. Positive samples identified in the screening were further validated using autoantibody titer quantification by serial dilutions or radioimmunoassay. Autoantibodies against neurologic surface Ags were not observed in RA and T1D patients, whereas SLE patients harbored such autoantibodies in rare cases (2/200, 1%). Within the CNS autoimmunity control cohort, autoantibodies against aquaporin 4 and high-titer Abs against myelin oligodendrocyte glycoprotein were, as expected, specific for neuromyelitis optica spectrum disorders. We conclude that neurologic autoantibodies do not cross disease barriers in RA and T1D. The finding of mildly increased neurologic autoantibodies in SLE may be consistent with a broader loss of B cell tolerance in this form of systemic autoimmunity.

The COVID-19 pandemic mandated rapid transition from face-to-face encounters to teleneurology visits. While teleneurology is regularly used in acute stroke care, its application in other branches of neurology was limited. Here we review how the recent pandemic has created a paradigm shift in caring for patients with chronic neurological disorders and how academic institutions have responded to the present need.

In the phase III eculizumab for refractory generalized myasthenia gravis REGAIN study [ClinicalTrials.gov identifier: NCT01997229] and its open-label extension (OLE) [ClinicalTrials.gov identifier: NCT02301624], patients with treatment-refractory antiacetylcholine receptor antibody-positive generalized myasthenia gravis had clinically meaningful improvements with eculizumab versus placebo. This subgroup analysis evaluated data from patients with a recent history of chronic intravenous immunoglobulin (IVIg) use before study entry.

Introduction: Chronic, broad-spectrum immunosuppressive therapy (IST) can be associated with side effects in many people with generalized myasthenia gravis (gMG), and treatment guidelines recommend that the IST dose be tapered once patients achieve a stable treatment response. We therefore examined IST use in eculizumab-treated patients with refractory gMG. Methods: The REGAIN open-label extension (OLE) enrolled 117 adults with refractory anti-acetylcholine receptor antibody-positive gMG who had completed the 6-month, randomized, double-blind, placebo-controlled REGAIN study of eculizumab. Eligible patients had received ≥2 ISTs for ≥1 year or ≥1 IST with intravenous immunoglobulin or plasma exchange ≥4 times in 1 year, without symptom control. During REGAIN, changes in concomitant MG therapies were not permitted; during the OLE, they were permitted at the investigators' discretion. Participants received eculizumab 1,200 mg every 2 weeks for up to 4 years; concomitant prednisone and related corticosteroids (PRED), azathioprine (AZA), and mycophenolate mofetil (MMF) use was recorded. Changes in MG Activities of Daily Living and Quantitative MG total scores, MG exacerbations, and adverse events were also recorded. Results: At last OLE assessment, 88.0% (103/117) of participants were using ≥1 IST vs. 98.3% (115/117) at OLE baseline. During the OLE, 76.9% (90/117) of patients experienced a total of 719 IST changes. Almost half of participants [48.7% (57/117)] stopped or decreased ≥1 IST owing to MG symptom improvement, representing 38.9% (280/719) of all changes. In patients who decreased and/or stopped ≥1 IST, mean daily doses of PRED, AZA, and MMF decreased between OLE baseline and last assessment by 60.8% [standard deviation (SD), 28.07; P < 0.0001], 89.1% (SD, 25.77; P < 0.0001), and 56.0% (SD, 32.99; P < 0.0001), respectively. Improved clinical outcomes were observed with eculizumab regardless of IST changes during the OLE, and eculizumab's safety profile was similar in patients who used PRED, AZA, and MMF. Conclusions: Use of ISTs by patients with previously refractory gMG decreased during eculizumab treatment in the REGAIN OLE. Clinical improvements with eculizumab were maintained by patients in all groups, including those who decreased and/or stopped concomitant ISTs. Trial registration: www.clinicaltrials.gov: NCT01997229, NCT02301624.

Many patients with generalized myasthenia gravis (gMG) have substantial clinical disability, persistent disease burden, and adverse effects attributable to chronic immunosuppression. Therefore, there is a significant need for targeted, well-tolerated therapies with the potential to improve disease control and enhance quality of life.

Inclusion body myositis (IBM) is an autoimmune and degenerative disorder of skeletal muscle. The B cell infiltrates in IBM muscle tissue are predominantly fully differentiated Ab-secreting plasma cells, with scarce naive or memory B cells. The role of this infiltrate in the disease pathology is not well understood. To better define the humoral response in IBM, we used adaptive immune receptor repertoire sequencing, of human-derived specimens, to generate large BCR repertoire libraries from IBM muscle biopsies and compared them to those generated from dermatomyositis, polymyositis, and circulating CD27+ memory B cells, derived from healthy controls and Ab-secreting cells collected following vaccination. The repertoire properties of the IBM infiltrate included the following: clones that equaled or exceeded the highly clonal vaccine-associated Ab-secreting cell repertoire in size; reduced somatic mutation selection pressure in the CDRs and framework regions; and usage of class-switched IgG and IgA isotypes, with a minor population of IgM-expressing cells. The IBM IgM-expressing population revealed unique features, including an elevated somatic mutation frequency and distinct CDR3 physicochemical properties. These findings demonstrate that some of IBM muscle BCR repertoire characteristics are distinct from dermatomyositis and polymyositis and circulating Ag-experienced subsets, suggesting that it may form through selection by disease-specific Ags.

Myasthenia gravis (MG) is an autoimmune disease characterized by dysfunction at the neuromuscular junction. Treatment frequently includes corticosteroids (CSs) and IV immunoglobulin (IVIG). This study was conducted to determine whether immune globulin (human), 10% caprylate/chromatography purified (IGIV-C) could facilitate CS dose reduction in CS-dependent patients with MG.

Autoantibodies targeting the acetylcholine receptor (AChR), found in patients with myasthenia gravis (MG), mediate pathology through 3 mechanisms: complement-directed tissue damage, blocking of the acetylcholine binding site, and internalization of the AChR. Clinical assays, used to diagnose and monitor patients, measure only autoantibody binding. Consequently, they are limited in providing association with disease burden, understanding of mechanistic heterogeneity, and monitoring therapeutic response. The objective of this study was to develop a cell-based assay that measures AChR autoantibody-mediated complement membrane attack complex (MAC) formation.

The prevalence and burden of autoimmune and autoantibody mediated disease is increasing worldwide, yet most disease etiologies remain unclear. Despite numerous new targeted immunomodulatory therapies, comprehensive approaches to apply and evaluate the effects of these treatments longitudinally are lacking. Here, we leverage advances in programmable-phage immunoprecipitation (PhIP-Seq) methodology to explore the modulation, or lack thereof, of proteome-wide autoantibody profiles in both health and disease. We demonstrate that each individual, regardless of disease state, possesses a distinct set of autoreactivities constituting a unique immunological fingerprint, or "autoreactome", that is remarkably stable over years. In addition to uncovering important new biology, the autoreactome can be used to better evaluate the relative effectiveness of various therapies in altering autoantibody repertoires. We find that therapies targeting B-Cell Maturation Antigen (BCMA) profoundly alter an individual's autoreactome, while anti-CD19 and CD-20 therapies have minimal effects, strongly suggesting a rationale for BCMA or other plasma cell targeted therapies in autoantibody mediated diseases.