Efgartigimod improves muscle weakness in a mouse model for muscle-specific kinase myasthenia gravis.

Myasthenia gravis is hallmarked by fatigable muscle weakness resulting from neuromuscular synapse dysfunction caused by IgG autoantibodies. The variant with muscle-specific kinase (MuSK) autoantibodies is characterized by prominent cranial and bulbar weakness and a high frequency of respiratory crises. The majority of MuSK MG patients requires long-term immunosuppressive treatment, but the result of these treatments is considered less satisfactory than in MG with acetylcholine receptor antibodies. Emergency treatments are more frequently needed, and many patients develop permanent facial weakness and nasal speech. Therefore, new treatment options would be welcome. The neonatal Fc receptor protects IgG from lysosomal breakdown, thus prolonging IgG serum half-life. Neonatal Fc receptor antagonism lowers serum IgG levels and thus may act therapeutically in autoantibody-mediated disorders. In MuSK MG, IgG4 anti-MuSK titres closely correlate with disease severity. We therefore tested efgartigimod (ARGX-113), a new neonatal Fc receptor blocker, in a mouse model for MuSK myasthenia gravis. This model involves 11 daily injections of purified IgG4 from MuSK myasthenia gravis patients, resulting in overt myasthenic muscle weakness and, consequently, body weight loss. Daily treatment with 0.5 mg efgartigimod, starting at the fifth passive transfer day, reduced the human IgG4 titres about 8-fold, despite continued daily injection. In muscle strength and fatigability tests, efgartigimod-treated myasthenic mice outperformed control myasthenic mice. Electromyography in calf muscles at endpoint demonstrated less myasthenic decrement of compound muscle action potentials in efgartigimod-treated mice. These substantial in vivo improvements of efgartigimod-treated MuSK MG mice following a limited drug exposure period were paralleled by a tendency of recovery at neuromuscular synaptic level (in various muscles), as demonstrated by ex vivo functional studies. These synaptic improvements may well become more explicit upon longer drug exposure. In conclusion, our study shows that efgartigimod has clear therapeutic potential in MuSK myasthenia gravis and forms an exciting candidate drug for many autoantibody-mediated neurological and other disorders.

MuSK myasthenia gravis monoclonal antibodies: Valency dictates pathogenicity.

Objective: To isolate and characterize muscle-specific kinase (MuSK) monoclonal antibodies from patients with MuSK myasthenia gravis (MG) on a genetic and functional level. Methods: We generated recombinant MuSK antibodies from patient-derived clonal MuSK-specific B cells and produced monovalent Fab fragments from them. Both the antibodies and Fab fragments were tested for their effects on neural agrin-induced MuSK phosphorylation and acetylcholine receptor (AChR) clustering in myotube cultures. Results: The isolated MuSK monoclonal antibody sequences included IgG1, IgG3, and IgG4 that had undergone high levels of affinity maturation, consistent with antigenic selection. We confirmed their specificity for the MuSK Ig-like 1 domain and binding to neuromuscular junctions. Monovalent MuSK Fab, mimicking functionally monovalent MuSK MG patient Fab-arm exchanged serum IgG4, abolished agrin-induced MuSK phosphorylation and AChR clustering. Surprisingly, bivalent monospecific MuSK antibodies instead activated MuSK phosphorylation and partially induced AChR clustering, independent of agrin. Conclusions: Patient-derived MuSK antibodies can act either as MuSK agonist or MuSK antagonist, depending on the number of MuSK binding sites. Functional monovalency, induced by Fab-arm exchange in patient serum, makes MuSK IgG4 antibodies pathogenic.

Passive transfer models of myasthenia gravis with muscle-specific kinase antibodies.

Myasthenia gravis (MG) with antibodies to muscle-specific kinase (MuSK) is characterized by fluctuating fatigable weakness. In MuSK MG, involvement of bulbar muscles, neck, and shoulder and respiratory weakness are more prominent than in acetylcholine receptor (AChR) MG. MuSK autoantibodies are mainly of the IgG4 subclass, and as such are unable to activate complement, have low affinity for Fc receptors, and are functionally monovalent. Therefore, the pathogenicity of IgG4 MuSK autoantibodies was initially questioned. A broad collection of in vitro active immunization and passive transfer models has been developed that have shed light on the pathogenicity of MuSK autoantibodies. Passive transfer studies with purified IgG4 from MuSK MG patients confirmed that IgG4 is sufficient to reproduce clear clinical, electrophysiological, and histological signs of myasthenia. In vitro experiments revealed that MuSK IgG4 autoantibodies preferably bind the first Ig-like domain of MuSK, correlate with disease severity, and interfere with the association between MuSK and low-density lipoprotein receptor-related protein 4 and collagen Q. Some patients have additional IgG1 MuSK autoantibodies, but their role in the disease is unclear. Altogether, this provides a rationale for epitope-specific or IgG4-specific treatment strategies for MuSK MG and emphasizes the importance of the development of different experimental models.

A prospective, placebo controlled study on the humoral immune response to and safety of tetanus revaccination in myasthenia gravis.

OBJECTIVE: To investigate the humoral immune response to and safety of a tetanus revaccination in patients with myasthenia gravis or Lambert-Eaton myasthenic syndrome. METHODS: A tetanus revaccination was administered to 66 patients. Before and 4weeks after revaccination a blood sample and clinical outcome scores were obtained. Anti-tetanus IgG total, IgG1 and IgG4 titres were measured with an ELISA and disease-specific antibody titres (AChR, MuSK or VGCC) with a radio-immunoprecipitation assay. A historic healthy control group was used for comparing tetanus antibody titres with that of our patients. A placebo (saline) vaccination group was used to investigate the variability of clinical outcome scores with a 4weeks interval. RESULTS: In 60 of 65 patients, a significant increase of the anti-tetanus antibody response was measured. Thymectomy did not have an impact on this responsiveness. Patients with immunosuppressive medication had a significantly lower pre and post titre compared to healthy controls, but their response was still significant. The titres of disease-specific antibodies were unchanged 4weeks after revaccination. The clinical outcome scores showed no exacerbation of symptoms of the disease. CONCLUSION: A tetanus revaccination in patients with myasthenia gravis or Lambert-Eaton myasthenic syndrome is safe and induces a significant immune response, irrespectively of their immunosuppressive medication. We observed neither immunological nor clinical relevant exacerbations associated with the tetanus revaccination. CLINICAL TRIAL REGISTRY: The tetanus trial is listed on clinicaltrialsregister.eu under 2014-004344-35. The placebo AChR MG group was part of another clinical trial, investigating influenza vaccination in myasthenic patients. This trial is listed on clinicaltrialsregister.eu under 2016-003138-26.

Colony-stimulating factor (CSF) 1 receptor blockade reduces inflammation in human and murine models of rheumatoid arthritis.

BACKGROUND: CSF-1 or IL-34 stimulation of CSF1R promotes macrophage differentiation, activation and osteoclastogenesis, and pharmacological inhibition of CSF1R is beneficial in animal models of arthritis. The objective of this study was to determine the relative contributions of CSF-1 and IL-34 signaling to CSF1R in RA. METHODS: CSF-1 and IL-34 were detected by immunohistochemical and digital image analysis in synovial tissue from 15 biological-naïve rheumatoid arthritis (RA) , 15 psoriatic arthritis (PsA) and 7 osteoarthritis (OA) patients . Gene expression in CSF-1- and IL-34-differentiated human macrophages was assessed by FACS analysis and quantitative PCR. RA synovial explants were incubated with CSF-1, IL-34, control antibody (Ab), or neutralizing/blocking Abs targeting CSF-1, IL-34, or CSF1R. The effect of a CSF1R-blocking Ab was examined in murine collagen-induced arthritis (CIA). RESULTS: CSF-1 (also known as M-CSF) and IL-34 expression was similar in RA and PsA synovial tissue, but lower in controls (P < 0.05). CSF-1 expression was observed in the synovial sublining, and IL-34 in the sublining and the intimal lining layer. CSF-1 and IL-34 differentially regulated the expression of 17 of 336 inflammation-associated genes in macrophages, including chemokines, extra-cellular matrix components, and matrix metalloproteinases. Exogenous CSF-1 or IL-34, or their independent neutralization, had no effect on RA synovial explant IL-6 production. Anti-CSF1R Ab significantly reduced IL-6 and other inflammatory mediator production in RA synovial explants, and paw swelling and joint destruction in CIA. CONCLUSIONS: Simultaneous inhibition of CSF1R interactions with both CSF-1 and IL-34 suppresses inflammatory activation of RA synovial tissue and pathology in CIA, suggesting a novel therapeutic strategy for RA.

Inflammatory cytokines epigenetically regulate rheumatoid arthritis fibroblast-like synoviocyte activation by suppressing HDAC5 expression.

OBJECTIVES: Epigenetic modifications play an important role in the regulation of gene transcription and cellular function. Here, we examined if pro-inflammatory factors present in the inflamed joint of patients with rheumatoid arthritis (RA) could regulate histone deacetylase (HDAC) expression and function in fibroblast-like synoviocytes (FLS). METHODS: Protein acetylation in synovial tissue was assessed by immunohistochemistry. The mRNA levels of HDAC family members and inflammatory mediators in the synovial tissue and the changes in HDAC expression in RA FLS were measured by quantitative (q) PCR. FLS were either transfected with HDAC5 siRNA or transduced with adenoviral vector encoding wild-type HDAC5 and the effects of HDAC5 manipulation were examined by qPCR arrays, ELISA and ELISA-based assays. RESULTS: Synovial class I HDAC expression was associated with local expression of tumour necrosis factor (TNF) and matrix metalloproteinase-1, while class IIa HDAC5 expression was inversely associated with parameters of disease activity (erythrocyte sedimentation rate, C-reactive protein, Disease Activity Score in 28 Joints). Interleukin (IL)-1ß or TNF stimulation selectively suppressed HDAC5 expression in RA FLS, which was sufficient and required for optimal IFNB, CXCL9, CXCL10 and CXCL11 induction by IL-1ß, associated with increased nuclear accumulation of the transcription factor, interferon regulatory factor 1(IRF1). CONCLUSIONS: Inflammatory cytokines suppress RA FLS HDAC5 expression, promoting nuclear localisation of IRF1 and transcription of a subset of type I interferon response genes. Our results identify HDAC5 as a novel inflammatory mediator in RA, and suggest that strategies rescuing HDAC5 expression in vivo, or the development of HDAC inhibitors not affecting HDAC5 activity, may have therapeutic applications in RA treatment.

Btk inhibition suppresses agonist-induced human macrophage activation and inflammatory gene expression in RA synovial tissue explants.

OBJECTIVES: Bruton's tyrosine kinase (Btk) is required for B lymphocyte and myeloid cell contributions to pathology in murine models of arthritis. Here, we examined the potential contributions of synovial Btk expression and activation to inflammation in rheumatoid arthritis (RA). MATERIALS AND METHODS: Btk was detected by immunohistochemistry and digital image analysis in synovial tissue from biologically naive RA (n=16) and psoriatic arthritis (PsA) (n=12) patients. Cell populations expressing Btk were identified by immunofluorescent double labelling confocal microscopy, quantitative (q-) PCR and immunoblotting. The effects of a Btk-specific inhibitor, RN486, on gene expression in human macrophages and RA synovial tissue explants (n=8) were assessed by qPCR, ELISA and single-plex assays. RESULTS: Btk was expressed at equivalent levels in RA and PsA synovial tissue, restricted to B lymphocytes, monocytes, macrophages and mast cells. RN486 significantly inhibited macrophage IL-6 production induced by Fc receptor and CD40 ligation. RN486 also reduced mRNA expression of overlapping gene sets induced by IgG, CD40 ligand (CD40L) and RA synovial fluid, and significantly suppressed macrophage production of CD40L-induced IL-8, TNF, MMP-1 and MMP-10, LPS-induced MMP-1, MMP-7 and MMP-10 production, and spontaneous production of IL-6, PDGF, CXCL-9 and MMP-1 by RA synovial explants. CONCLUSIONS: Btk is expressed equivalently in RA and PsA synovial tissue, primarily in macrophages. Btk activity is needed to drive macrophage activation in response to multiple agonists relevant to inflammatory arthritis, and promotes RA synovial tissue cytokine and MMP production. Pharmacological targeting of Btk may be of therapeutic benefit in the treatment of RA and other inflammatory diseases.

Tie2 signaling cooperates with TNF to promote the pro-inflammatory activation of human macrophages independently of macrophage functional phenotype.

Angiopoietin (Ang) -1 and -2 and their receptor Tie2 play critical roles in regulating angiogenic processes during development, homeostasis, tumorigenesis, inflammation and tissue repair. Tie2 signaling is best characterized in endothelial cells, but a subset of human and murine circulating monocytes/macrophages essential to solid tumor formation express Tie2 and display immunosuppressive properties consistent with M2 macrophage polarization. However, we have recently shown that Tie2 is strongly activated in pro-inflammatory macrophages present in rheumatoid arthritis patient synovial tissue. Here we examined the relationship between Tie2 expression and function during human macrophage polarization. Tie2 expression was observed under all polarization conditions, but was highest in IFN-γ and IL-10 -differentiated macrophages. While TNF enhanced expression of a common restricted set of genes involved in angiogenesis and inflammation in GM-CSF, IFN-γ and IL-10 -differentiated macrophages, expression of multiple chemokines and cytokines, including CXCL3, CXCL5, CXCL8, IL6, and IL12B was further augmented in the presence of Ang-1 and Ang-2, via Tie2 activation of JAK/STAT signaling. Conditioned medium from macrophages stimulated with Ang-1 or Ang-2 in combination with TNF, sustained monocyte recruitment. Our findings suggest a general role for Tie2 in cooperatively promoting the inflammatory activation of macrophages, independently of polarization conditions.

µ-Opioid receptors in the nucleus accumbens shell region mediate the effects of amphetamine on inhibitory control but not impulsive choice.

Acute challenges with psychostimulants such as amphetamine affect impulsive behavior in both animals and humans. With regard to amphetamine, it is important to unravel how this drug affects impulsivity since it is not only a widely abused recreational drug but also regularly prescribed to ameliorate maladaptive impulsivity. Therefore, we studied the effects of amphetamine in two rat models of impulsivity, the five-choice serial reaction time task and the delayed-reward task, providing measures of inhibitory control and impulsive choice, respectively. We focused on the role of opioid receptor activation in amphetamine-induced impulsivity as there is ample evidence indicating an important role for endogenous opioids in several behavioral and neurochemical effects of amphetamine. Results showed that amphetamine-induced inhibitory control deficits were dose-dependently attenuated by the preferential µ-opioid receptor antagonist naloxone, but not by the selective δ-opioid receptor antagonist naltrindole or κ-opioid receptor antagonist nor-BNI (nor-binaltorphimine dihydrochloride). In contrast, naloxone did not affect amphetamine-induced improvements in impulsive decision making. Naloxone also completely prevented inhibitory control deficits induced by GBR 12909 [1-(2-[bis(4-fluorophenyl)methoxy] ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride], a selective dopamine transporter inhibitor. Intracranial infusions of naloxone, the selective µ-opioid receptor antagonist CTAP (H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)), morphine, and the selective µ-opioid receptor agonist DAMGO ([D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin acetate salt) revealed that µ-opioid receptor activation in the shell rather than the core subregion of the nucleus accumbens (NAc) modulates inhibitory control and subserves the effect of amphetamine thereon. Together, these results indicate an important role for NAc shell µ-opioid receptors in the regulation of inhibitory control, probably via an interaction between these receptors and the mesolimbic dopamine system.