The clinical need for clustered AChR cell-based assay testing of seronegative MG

Concordance between radioimmunoassay and fixed cell-based assay in subjects without myasthenia gravis: optimizing the diagnostic approach

BACKGROUND AND PURPOSE

Acetylcholine receptor antibody (AChR-Ab) detection is crucial in myasthenia gravis (MG) diagnosis and, currently, the radioimmunoassay (RIA) is the gold standard. However, RIA may detect AChR-Ab against nonpathogenic intracellular epitopes. In this study, we performed fixed cell-based assay (F-CBA) in RIA-AChR-Ab positive subjects without MG symptoms, to assess whether F-CBA could show a higher specificity compared to RIA in detecting pathogenic Abs.

METHODS

We reviewed medical records of patients referred to our MG outpatient clinic because of RIA-AChR-Ab detection. MG diagnosis was based on clinical examination, electrophysiology and Ab detection. AChR-Abs were tested by RIA in the whole cohort. Serum samples from RIA-positive asymptomatic subjects were retested by F-CBA.

RESULTS

Of 605 subjects who tested RIA-AChR-Ab positive, MG diagnosis was confirmed in 599. Six subjects were RIA-AChR-Ab positive although they had never had MG symptoms; in four of these subjects AChR-Abs were not detected by F-CBA, whereas the remaining two (both non-MG thymoma cases) were positive also by F-CBA.

CONCLUSIONS

RIA false positivity for AChR-Ab is very rare. Previous literature has demonstrated that F-CBA has higher sensitivity than RIA for MG, especially in ocular cases. Our preliminary results show that, in rare instances, F-CBA may be more specific than RIA for MG diagnosis.

Long-term safety, tolerability, and efficacy of efgartigimod (ADAPT+): interim results from a phase 3 open-label extension study in participants with generalized myasthenia gravis

Objective

ADAPT+ assessed the long-term safety, tolerability, and efficacy of efgartigimod in adult participants with generalized myasthenia gravis (gMG).

Methods

ADAPT+ was an open-label, single-arm, multicenter, up to 3-year extension of the pivotal phase 3 ADAPT study. Efgartigimod was administered in treatment cycles of 4 intravenous infusions (one 10 mg/kg infusion per week). Initiation of subsequent treatment cycles was individualized based on clinical evaluation. Safety endpoints included incidence and severity of adverse events. Efficacy endpoints assessed disease severity using Myasthenia Gravis-Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores.

Results

As of January 2022, 151 participants had rolled over to ADAPT+ and 145 had received ≥1 dose of efgartigimod, of whom, 111 (76.6%) were AChR-Ab+ and 34 (23.4%) were AChR-Ab-. Mean study duration (treatment plus follow-up) was 548 days, and participants received up to 17 treatment cycles, corresponding to 217.6 participant-years of exposure. In the overall population, 123 (84.8%) participants reported ≥1 treatment-emergent adverse event; most frequent were headache (36 [24.8%]), COVID-19 (22 [15.2%]), and nasopharyngitis (20 [13.8%]). Clinically meaningful improvement (CMI) in mean MG-ADL and QMG scores was seen as early as 1 week following the first infusion across multiple cycles in AChR-Ab+ and AChR-Ab- participants. Maximal MG-ADL and QMG improvements aligned with onset and magnitude of total IgG and AChR-Ab reductions. For AChR-Ab+ participants at any time point in each of the first 10 treatment cycles, more than 90% had a maximum reduction of ≥2 points (CMI) in MG-ADL total score; across the 7 cycles in which QMG was measured, 69.4% to 91.3% of participants demonstrated a maximum reduction of ≥3 points (CMI) in QMG total score. Many participants demonstrated improvements well beyond CMI thresholds. In AChR-Ab+ participants with ≥1 year of combined follow-up between ADAPT and ADAPT+, mean number of annualized cycles was 4.7 per year (median [range] 5.0 [0.5-7.6]).

Conclusion

Results of ADAPT+ corroborate the substantial clinical improvements seen with efgartigimod in ADAPT and support its long-term safety, tolerability, and efficacy, as well as an individualized dosing regimen for treatment of gMG.

Clinical trial registration

https://classic.clinicaltrials.gov/ct2/show/NCT03770403, NCT03770403.

Remission of severe myasthenia gravis after autologous stem cell transplantation

OBJECTIVE

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.

METHODS

As part of a pilot study of HDIT/HCT for patients with treatment-resistant autoimmune neurological disorders, a patient with severe refractory MG underwent treatment. After mobilization of hematopoietic stem cells with rituximab, prednisone, and G-CSF, the patient had HDIT consisting of carmustine, etoposide, cytarabine, melphalan, and rabbit antithymocyte globulin, followed by autologous HCT. The effect of treatment on the autoantibody to the acetylcholine receptor (AChR) was assessed.

RESULTS

The patient had been diagnosed with AChR antibody-positive MG 14 years before HDIT/HCT and had failed thymectomy, therapeutic plasma exchange, and multiple immunomodulatory agents. The Myasthenia Gravis Foundation of America (MGFA) clinical classification was IVb before HDIT/HCT. She tolerated HDIT/HCT well and started to improve clinically within days of treatment. At both 1 and 2 years after HDIT/HCT, patients remained symptom-free. After HDIT/HCT, AChR-binding autoantibodies persisted, and the relative frequency of immune cell subtypes shifted.

INTERPRETATION

HDIT/HCT induced a complete response of disease activity in a patient with severe refractory MG. This response may suggest that a cell-mediated etiology may be a significant contributing factor in refractory MG cases. A phase 2 clinical trial is warranted to establish if HDIT/HCT can be an effective therapy for severe refractory MG and to gain a further understanding of disease pathogenesis.

A multicentre, prospective, double-blind study comparing the accuracy of autoantibody diagnostic assays in myasthenia gravis: the SCREAM study

BACKGROUND

Laboratory determination of autoantibodies against acetylcholine receptor (AChR), muscle-specific kinase (MuSK) and other autoantigens have been integrated into the diagnosis of myasthenia gravis (MG). However, evidence supporting the selection of methodologies is lacking.

METHODS

In this prospective, multicentre cohort study, we recruited patients with suspected MG to evaluate the diagnostic accuracy of cell-based assay (CBA), radioimmunoprecipitation assay (RIPA) and enzyme-linked immunosorbent assay (ELISA) in detecting AChR and MuSK autoantibodies. This study is registered with www.clinicaltrials.gov, number NCT05219097.

FINDINGS

2272 eligible participants were recruited, including 2043 MG, 229 non-MG subjects. AChR antibodies were detected in 1478, 1310, and 1280 out of a total of 2043 MG patients by CBA, RIPA, and ELISA, respectively; sensitivity, 72.3% (95% CI, 70.3-74.3), 64.1% (95% CI, 62.0-66.2), 62.7% (95% CI, 60.5-64.8); specificity, 97.8% (95% CI, 95.0-99.3), 97.8% (95% CI, 95.0-99.3), 94.8% (95% CI, 91.9-97.7). MuSK antibodies were found in 59, 50, and 54 from 2043 MG patients by CBA, RIPA and ELISA, respectively; sensitivity, 2.9% (95% CI, 2.2-3.7), 2.4% (95% CI, 1.8-3.2), 2.6% (95% CI, 2.0-3.4); specificity, 100% (95% CI, 98.4-100), 100% (95% CI, 98.4-100), and 99.1% (95% CI, 96.9-99.9). The area under the curve of AChR antibodies tested by CBA was 0.858, and there were statistical differences with RIPA (0.843; p = 0.03) and ELISA (0.809; p < 0.0001).

INTERPRETATION

CBA has a higher diagnostic accuracy compared to RIPA or ELISA in detecting AChR and MuSK autoantibodies for MG diagnosis.

FUNDING

New Terrain Biotechnology, Inc., Tianjin, China.

Individual myasthenia gravis autoantibody clones can efficiently mediate multiple mechanisms of pathology

Serum autoantibodies targeting the nicotinic acetylcholine receptor (AChR) in patients with autoimmune myasthenia gravis (MG) can mediate pathology via three distinct molecular mechanisms: complement activation, receptor blockade, and antigenic modulation. However, it is unclear whether multi-pathogenicity is mediated by individual or multiple autoantibody clones. Using an unbiased B cell culture screening approach, we generated a library of 11 human-derived AChR-specific recombinant monoclonal autoantibodies (mAb) and assessed their binding properties and pathogenic profiles using specialized cell-based assays. Five mAbs activated complement, three blocked α-bungarotoxin binding to the receptor, and seven induced antigenic modulation. Furthermore, two clonally related mAbs derived from one patient were each highly efficient at more than one of these mechanisms, demonstrating that pathogenic mechanisms are not mutually exclusive at the monoclonal level. Using novel Jurkat cell lines that individually express each monomeric AChR subunit (α2βδε), these two mAbs with multi-pathogenic capacity were determined to exclusively bind the α-subunit of AChR, demonstrating an association between mAb specificity and pathogenic capacity. These findings provide new insight into the immunopathology of MG, demonstrating that single autoreactive clones can efficiently mediate multiple modes of pathology. Current therapeutic approaches targeting only one autoantibody-mediated pathogenic mechanism may be evaded by autoantibodies with multifaceted capacity.

Clinicoserological insights into patients with immune checkpoint inhibitor-induced myasthenia gravis

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.

Comparison of Fixed and Live Cell-Based Assay for the Detection of AChR and MuSK Antibodies in Myasthenia Gravis

BACKGROUND AND OBJECTIVES

Live cell-based assay (CBA) can detect acetylcholine receptors (AChRs) or muscle-specific tyrosine kinase (MuSK) antibodies (Abs) in a proportion of patients with radioimmunoassay (RIA)-double seronegative myasthenia gravis (dSN-MG). A commercial fixed CBA for AChR and MuSK Abs has recently become available; however, comparative studies on fixed and live CBAs are lacking. In this study, we compared the performance of fixed and live CBAs in patients with RIA-dSN MG and assessed their sensitivity in RIA-positive MG samples and their specificity.

METHODS

AChR and MuSK Abs were tested in 292 serum samples from 2 Italian MG referral centers by live and fixed CBAs: 192 from patients with MG and 100 from controls. All samples had been previously assessed by RIA: 66 were AChR positive, 40 MuSK positive, and 86 dSN. All controls were negative. Two independent raters assessed the CBA results. Fixed and live CBAs were compared with the McNemar test; interrater and interlaboratory agreement were assessed with Cohen's kappa or interclass correlation coefficient (ICC), as appropriate.

RESULTS

In 86 RIA-dSN samples, fixed CBA detected Abs in 10 cases (11.6%, 95% CI 5.7-20.3), whereas live CBA detected Abs in 16 (18.6%, 95% CI 11.0-28.5) (p = 0.0143). Of these sera, those positive by fixed CBA were also positive by live CBA. In addition, live CBA could detect MuSK Abs in 4 and AChR Abs in 2 samples that were negative by fixed CBA, providing an 8% (95% CI 2.9-16.6) further increase in the Ab detection rate. These results were confirmed by flow cytometry. In the RIA-positive cohort, the sensitivity for AChR Abs was 98.5% (95% CI 91.9%-99.9%) for fixed CBA and 100% (95% CI 94.6-100) for live CBA (p = 0.1573). For both assays, the sensitivity for MuSK Abs was 100% (95% CI 91.2-100), and the specificity was 100% (95% CI 96.4-100). Interrater agreement was almost perfect for live and fixed CBAs (Cohen's kappa 0.972 and 0.978, respectively), alike interlaboratory agreement. Interrater agreement for the CBA score ranged from good to excellent (ICC: 0.832-0.973).

DISCUSSION

Fixed CBA represents a valuable alternative to RIA for AChR and MuSK Ab detection in patients with MG and could be considered as a first-step diagnostic test. Live CBA can be useful in the serologic evaluation of RIA- and fixed CBA-negative samples.

Novel pathophysiological insights in autoimmune myasthenia gravis

PURPOSE OF REVIEW

This review summarizes recent insights into the immunopathogenesis of autoimmune myasthenia gravis (MG). Mechanistic understanding is presented according to MG disease subtypes and by leveraging the knowledge gained through the use of immunomodulating biological therapeutics.

RECENT FINDINGS

The past two years of research on MG have led to a more accurate definition of the mechanisms through which muscle-specific tyrosine kinase (MuSK) autoantibodies induce pathology. Novel insights have also emerged from the collection of stronger evidence on the pathogenic capacity of low-density lipoprotein receptor-related protein 4 autoantibodies. Clinical observations have revealed a new MG phenotype triggered by cancer immunotherapy, but the underlying immunobiology remains undetermined. From a therapeutic perspective, MG patients can now benefit from a wider spectrum of treatment options. Such therapies have uncovered profound differences in clinical responses between and within the acetylcholine receptor and MuSK MG subtypes. Diverse mechanisms of immunopathology between the two subtypes, as well as qualitative nuances in the autoantibody repertoire of each patient, likely underpin the variability in therapeutic outcomes. Although predictive biomarkers of clinical response are lacking, these observations have ignited the development of assays that might assist clinicians in the choice of specific therapeutic strategies.

SUMMARY

Recent advances in the understanding of autoantibody functionalities are bringing neuroimmunologists closer to a more detailed appreciation of the mechanisms that govern MG pathology. Future investigations on the immunological heterogeneity among MG patients will be key to developing effective, individually tailored therapies.

Optimization of peripheral blood volume for in silico reconstitution of the human B cell receptor repertoire

B cells recognize antigens via membrane‐expressed B‐cell receptors (BCR) and antibodies. Similar human BCR sequences are frequently found at a significantly higher frequency than that theoretically calculated. Patients infected with SARS‐CoV2 and HIV or with autoimmune diseases share very similar BCRs. Therefore, in silico reconstitution of BCR repertoires and identification of stereotypical BCR sequences related to human pathology have diagnostic potential. Furthermore, monitoring changes of clinically significant BCR sequences and isotype conversion has prognostic potential. For BCR repertoire analysis, peripheral blood (PB) is the most convenient source. However, the optimal human PB volume for in silico reconstitution of the BCR repertoire has not been studied in detail. Here, we sampled 5, 10, and 20 mL PB from the left arm and 40 mL PB from the right arm of two volunteers, reconstituted in silico PB BCR repertoires, and compared their composition. In both volunteers, PB sampling over 20 mL resulted in slight increases in functional unique sequences (FUSs) or almost no increase in repertoire diversity. All FUSs with a frequency above 0.08% or 0.03% in the 40 mL PB BCR repertoire were detected even in the 5 mL PB BCR repertoire from each volunteer. FUSs with a higher frequency were more likely to be found in BCR repertoires from reduced PB volume, and those coexisting in two repertoires showed a statistically significant correlation in frequency irrespective of sampled anatomical site. The correlation was more significant in higher‐frequency FUSs. These observations support the potential of BCR repertoire analysis for diagnosis.