Biology subjects

Huijbers, M. G.

Publications and source records attributed to Huijbers, M. G..

8 recordsLinked to original sources

bioRxiv2026

IgG4 antibody repertoire diversity is stable over several years in health and autoimmune disease

Despite its relative anti-inflammatory nature, IgG4 is involved in a variety of pathological conditions such as autoimmune disease and cancer. To investigate whether the IgG4 repertoire presents any abnormalities in diseases where IgG4 autoantibodies predominate, we charted longitudinal IgG4 repertoires in health, in an IgG4-mediated autoimmune disease (AID; muscle-specific kinase myasthenia gravis (MuSK MG)), and in IgG1/IgG3 mediated AIDs (acetylcholine receptor (AChR) MG and Lambert-Eaton myasthenic syndrome (LEMS). In total, we assessed 218 samples of 69 donors using mass spectrometry-based antibody repertoire analysis, covering a timespan of up to eight years. Despite being superficially inconspicuous in clonal diversity and abundances, we detected a slightly elevated number of IgG4 clones in MuSK MG patients compared to healthy donors. Notably, this observation did not coincide with drastic repertoire changes during treatment, suggesting that a large portion of the IgG4 repertoire is not significantly affected by common MuSK MG treatment regimens. Comparing the IgG4 antibody repertoires of all donors, we found that they were exceptionally unique for each individual. Against what would be expected in the case of a constantly adapting antibody repertoire, a large portion of the IgG4 clones remained stable without any further maturation. This observation even extended to patients receiving B cell depleting or IgG modulating treatments. Our findings suggest that a dominating fraction of the IgG4 pool may be produced by long-lived plasma cells, which are unaffected by disease or medical interventions.

immunology↗

bioRxiv2026

Distinct transcriptional programs define human IgG4+ memory B cells

Human immunoglobulin G4 (IgG4) shapes both protective and pathogenic immunity, influencing conditions ranging from allergy and autoimmunity to cancer. However, subclass-specific targeting of memory B cells remains challenging due to limited knowledge of their phenotypic and functional heterogeneity. Here, we show that IgG4+ memory B cells are overrepresented in a niche of FCER2+BAFFR+ memory B cells, can be classified in several subtypes, have a distinct transcription factor profile and are the only memory B cell subset to express sterile IGHE transcripts. While IgG4+ B cells display a unique transcriptional profile, only BAFFR, IL5Rb and the B cell receptor were upregulated on protein level on IgG4+ cells. IgG4+ B cells have normal repertoire diversity, but a distinct germline V-gene usage, suggesting IgG4 responses are driven by specific antigens. By labeling autoreactive B cells, we confirmed that MuSK myasthenia gravis (an archetypal IgG4-mediatedautoimmune disease) patients have a normal memory B cell profile and that autoreactive IgG4+ memory B cells are extremely rare. These results highlight the unique features of IgG4+ B cells, provide insight on potential subclass-specific therapeutic targets and point towards an antigen-driven IgG4 response within a largely non-autoreactive memory B cell pool.

immunology↗

bioRxiv2026

MuSK antibodies differently affect the MuSK signaling cascade depending on valency and epitope specificity

Muscle-specific kinase (MuSK) is a pivotal player in forming and maintaining healthy neuromuscular junctions (NMJ). In MuSK myasthenia gravis (MG), autoantibodies targeting MuSK disrupt its function, impairing neuromuscular transmission and causing fatigable skeletal muscle weakness. MuSK autoantibodies predominantly belong to the IgG4 subclass, which bind in a monovalent fashion due to Fab-arm exchange, although autoantibodies of other subclasses also exist. Polyclonal autoreactive IgG from patients may therefore harbor a variety of monovalent and bivalent MuSK antibodies with potentially distinct effects on MuSK signaling. To further unravel the pathomechanisms underlying MuSK MG, we have investigated how MuSK antibody-binding affects MuSK functioning with a diverse panel of (patient-derived) monoclonal MuSK antibodies. Our findings reveal that the valency of antibody-binding influences binding kinetics to MuSK, inhibition of agrin-induced MuSK activation, Dok7 binding to MuSK and NMJ gene expression. Monovalent binding to the frizzled domain of MuSK did not inhibit agrin-induced MuSK activation, while monovalent binding to the Ig-like domain 1 does. Moreover, the kinetics of Dok7 degradation induced by bivalent MuSK antibodies appear to depend on binding-epitope of MuSK. Surprisingly, none of the clones tested (both bivalent and monovalent) increased MuSK internalization. Taken together, the cumulative pathogenic effect of polyclonal MuSK antibodies in individual MuSK MG patients thus likely depends on autoantibody titer, affinity and the unique composition of MuSK autoantibodies varying in epitope and valency. This research enriches our understanding of the intricate interactions between antibodies and MuSK in MuSK MG and offers potential insights into novel therapeutic strategies using MuSK antibodies.

immunology↗

bioRxiv2024

Patient-specific therapeutic benefit of MuSK agonist antibody ARGX-119 in MuSK myasthenia gravis passive transfer models

Muscle-specific kinase (MuSK) orchestrates establishment and maintenance of neuromuscular synapses, which enable muscle contraction. Autoantibodies targeting MuSK cause myasthenia gravis (MG), a disease characterized by fatigable skeletal muscle weakness which requires chronic immunosuppressive treatment and ventilatory support at some point in [~]30% of patients. MuSK autoantibodies are predominantly IgG4 and are bispecific, functionally monovalent antibodies due to Fab-arm exchange. Through monovalent binding, MuSK IgG4 autoantibodies act as antagonists on the MuSK signalling pathway, impairing neuromuscular synaptic function. In contrast, bivalent MuSK antibodies act as agonists of the MuSK signalling pathway. Since symptoms in MuSK MG are largely caused by antagonistic monovalent MuSK antibodies, we hypothesized that a bivalent MuSK agonist could rescue MuSK MG, bypassing the need for generalized immunosuppression. In this study, we investigated whether an agonist antibody targeting the Frizzled-like domain of MuSK, ARGX-119, can ameliorate disease in MuSK MG models induced by passive transfer of polyclonal IgG4 from unrelated patients. For each patient material we first established the minimal dose for a progressive MG phenotype based on muscle function tests. ARGX-119 significantly improved survival and muscle weakness in a mouse model induced by one patient material, but not by three others. Mechanistically, this patient-specific efficacy could not be explained by autoantibody epitope specificity, titer or competition for ARGX-119 binding, but rather correlated to the presence of MuSK activating antibodies in some patients. We further provide evidence that an in vitro assay may predict which patients potentially benefit from ARGX-119 and that this treatment, when effective in MuSK MG mice, follows a bell-shaped dose-effect curve. These results provide first proof of concept of a MuSK agonist in a clinically relevant model for MuSK MG. We anticipate this to be a starting point for investigating the therapeutic benefit of ARGX-119 in MuSK MG and other neuromuscular diseases hallmarked by neuromuscular synaptic dysfunction. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/606156v1_figu1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@15c08faorg.highwire.dtl.DTLVardef@1517281org.highwire.dtl.DTLVardef@3498c2org.highwire.dtl.DTLVardef@118e9af_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMuSK agonist ARGX-119 can rescue MuSK MG in a patient-specific manner C_LIO_LIMuSK agonism follows a bell-shaped efficacy curve in this MuSK MG mouse model C_LIO_LIVariation in ARGX-119 efficacy between patient models is not explained by competition for binding on MuSK, but rather appears related to an agonistic fraction of patient antibodies C_LIO_LIAn in vitro assay is potentially predictive for treatment efficacy of the MuSK agonist C_LI

neuroscience↗

bioRxiv2024

ARGX-119, a therapeutic agonist antibody targeting MuSK

ARGX-119 is a novel, humanized, agonist monoclonal SIMPLE Antibody specific for muscle-specific kinase (MuSK) that is being developed for treatment of patients with neuromuscular diseases. ARGX-119 is the first monoclonal antibody (mAb) that binds with high affinity to the Frizzled-like domain of human, non-human primate, rat and mouse MuSK, without off-target binding, making it suitable for clinical development. Within the Fc-region, ARGX-119 harbors L234A, L235A mutations to diminish potential immune-activating effector functions. Its mode-of-action is to activate MuSK without interfering with its natural ligand neural Agrin, and cluster acetylcholine receptors (AChRs) in a dose-dependent manner, thereby stabilizing neuromuscular function. In a mouse model for DOK7 congenital myasthenia (CM), ARGX-119 prevented early postnatal lethality and reversed disease relapse by restoring neuromuscular function and reducing muscle weakness and fatigability in a dose-dependent manner. Pharmacokinetic (PK) studies in non-human primates, rats and mice revealed non-linear PK behavior of ARGX-119, indicative of target-mediated-drug disposition (TMDD) and in vivo target engagement. Instability of neuromuscular synapses contributes to symptoms in many neuromuscular diseases for example congenital myasthenia (CM), amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). ARGX-119 is a novel, first-in-class MuSK agonist mAb in clinical development. Based on this proof-of-concept study, it has the potential to alleviate neuromuscular diseases hallmarked by impaired neuromuscular synaptic function. One sentence summaryARGX-119 is a novel first-in-class MuSK agonist monoclonal antibody in clinical development for treatment of neuromuscular diseases.

neuroscience↗

bioRxiv2023

Autoantibody subclass predominance is not driven by aberrant class switching or impaired B cell development

A subset of autoimmune diseases is characterized by predominant pathogenic IgG4 autoantibodies (IgG4-AIDs). Why IgG4 predominates in these disorders is unknown. We hypothesized that dysregulated B cell maturation or aberrant class switching causes overrepresentation of IgG4+ B cells and plasma cells. Therefore, we compared the B cell compartment of patients with muscle-specific kinase (MuSK) myasthenia gravis (MG), pemphigus, leucine-rich glioma inactivated (LGI1) encephalitis and contactin-associated protein-like 2 (CASPR2) encephalitis (four IgG4-AIDs) to patients with acetylcholine receptor (AChR) MG, Lambert-Eaton myasthenic syndrome (LEMS) (two IgG1-3-AIDs) and age-matched healthy donors, using flow cytometry. B cell subset relative abundance at all maturation stages was normal, except for a, possibly treatment-related, reduction in immature and naive CD5+ cells in IgG4-AIDs. IgG4+ B cell and plasma cell fractions were normal in IgG4-AID patients, however they had an (sub)class-independent 8-fold increase in circulating mature CD20-CD138+ plasma cells. No autoreactivity was found in this subset after sorting. In conclusion, patients with IgG4-AID do not show increased numbers of IgG4-expressing cells. These results argue against aberrant B cell development in these patients and rather suggest the autoantibody subclass predominance to be antigen-driven. The similarities between B cell subset numbers among these patients suggest that these IgG4-AIDs, despite displaying variable clinical phenotypes, share a similar underlying immune profile. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/546522v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@1444429org.highwire.dtl.DTLVardef@d70867org.highwire.dtl.DTLVardef@168a7c0org.highwire.dtl.DTLVardef@1dd4483_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2021

Timing and localization of myasthenia gravis-related gene expression

Myasthenia gravis (MG) is an acquired autoimmune disorder caused by autoantibodies binding acetylcholine receptors (AChR), muscle-specific kinase (MuSK), agrin or low-density lipoprotein receptor-related protein 4 (Lrp4). These autoantibodies inhibit neuromuscular transmission by blocking the function of these proteins, and thereby cause fluctuating skeletal muscle weakness. Several reports suggest that these autoantibodies might also affect the central nervous system (CNS) in MG patients. A comprehensive overview of the timing and localization of the expression of MG-related antigens in other organs is currently lacking. To investigate the spatio-temporal expression of MG-related genes outside skeletal muscle, we used in silico tools to assess public expression databases. Acetylcholine esterase, nicotinic AChR 1 subunit, agrin, collagen Q, Dok7, Lrp4, MuSK and rapsyn were included as MG-related genes because of their well-known involvement in either congenital or autoimmune MG. We investigated expression of MG-related genes in 1) all human tissues using GTEx data, 2) specific brain regions, 3) neurodevelopmental stages, and 4) cell types using datasets from the Allen Institute for Brain Sciences. MG-related genes show heterogenous spatio-temporal expression patterns in the human body as well as in the CNS. For each of these genes several (new) tissues, brain areas and cortical cell types with (relatively) high expression were identified suggesting a potential role for these genes outside skeletal muscle. The possible presence of MG-related antigens outside skeletal muscle suggests that autoimmune MG, congenital MG or treatments targeting the same proteins may affect MG-related protein function in other organs.

genetics↗

bioRxiv2020

Functional monovalency amplifies the pathogenicity of anti-MuSK IgG4 in myasthenia gravis

Human IgG4 usually displays anti-inflammatory activity, and observations of IgG4 autoantibodies causing severe autoimmune disorders are therefore poorly understood. In blood, IgG4 antibodies naturally engage in a stochastic process termed Fab-arm exchange in which unrelated IgG4s exchange half-molecules continuously. The resulting IgG4 antibodies are composed of two different binding sites, thereby acquiring monovalent binding and inability to cross-link for each antigen recognized. Here, we demonstrate this process amplifies autoantibody pathogenicity in a classic IgG4-mediated autoimmune disease: muscle-specific kinase (MuSK) myasthenia gravis (MG). In mice, monovalent anti-MuSK IgG4s caused rapid and severe myasthenic muscle weakness, whereas the same antibodies in their parental bivalent form were less potent or did not induce a phenotype. Mechanistically this could be explained by opposing effects on MuSK signaling. Isotype switching to IgG4 in an autoimmune response thereby may be a critical step in the development of disease. Our study establishes functional monovalency as a novel pathogenic mechanism in IgG4-mediated autoimmune disease and potentially other disorders. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=146 HEIGHT=200 SRC="FIGDIR/small/296293v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@45c221org.highwire.dtl.DTLVardef@1cc31cdorg.highwire.dtl.DTLVardef@d9b09borg.highwire.dtl.DTLVardef@1d9b681_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗