Plasmapheresis in myasthenia gravis. A survey

Myasthenia Gravis: A Systematic Review

Myasthenia gravis (MG), a rare disease, is the most common neuromuscular junction problem. It's the quintessential autoimmune disease with ocular, bulbar, respiratory, axial, and limb muscles exhibiting a typical fatigable weakening due to the development of antibodies against the acetylcholine receptor (AChR). Infections, stress, surgeries, thymus gland anomalies, and pharmaceutical side effects can also cause it. Ocular symptoms are initially experienced by most of the sufferers. The majority of the sufferers will go through at least one episode of symptom exacerbation during their illness. The immune system in MG interferes with nerve-muscle communication, causing muscles to become weak and tired quickly. The actual cause is not yet known, but a problem in the thymus gland may be the cause. In a person suffering from this disease, the size of the thymus becomes larger than normal, which is also called thymic hyperplasia. It is more common for women to have early-onset MG (EOMG) than for males to have late-onset MG (LOMG). Merely clinical evidence, encompassing the patients' medical history and physical indications of fluctuating muscle weakness in a specific region, is utilized to diagnose MG. Complementary diagnostic procedures and lab techniques aid in confirming the synaptic dysfunction and characterizing its kind and degree. Early diagnosis and the availability of effective treatments have reduced the burden of severe impairment and high mortality previously associated with MG. Current immunomodulation-based therapies come with side effects brought on by persistent immune suppression. Improved knowledge of this relatively uncommon but curable condition is required among primary carers. The objective of this review is to provide information about MG and to help people recognize its symptoms and start treatment without panic so that the progression of this disease can be stopped and complications can be avoided.

Therapeutic Plasma Exchange in Myasthenia Gravis: A Systematic Literature Review and Meta-Analysis of Comparative Evidence

Background: Patients with Myasthenia Gravis (MG) can be treated acutely with therapeutic plasma exchange (TPE) or intravenous immune globulin (IVIG). To date, there is no definitive understanding of which of the two treatments is more effective and safer. The purpose of this study was to systematically review the literature on the comparative efficacy and safety of TPE to other available treatments for MG. Methods: A systematic literature search for studies published between 1997 and 2017 was performed per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using two database sources, MEDLINE (through the PubMed database) and Cochrane Library. Results: The search strategy resulted in 535 articles whose abstracts were reviewed. Among these, 165 full texts articles were reviewed for eligibility and 101 articles were excluded. Of the 165 articles, 64 articles were included for a systematic literature and 11 articles for a meta-analysis. Conclusions: This systematic literature review and meta-analysis of treatment options showed that there was a higher response rate with TPE than IVIG in acute MG patients and patients undergoing thymectomy. There was no difference in mortality between the two treatment options. Our findings highlight the need for additional randomized clinical trials in these patients with MG.

Antigen-specific immunoadsorption of MuSK autoantibodies as a treatment of MuSK-induced experimental autoimmune myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease affecting the neuromuscular junction. Approximately 9% of MG patients have autoantibodies targeting the muscle specific kinase (MuSK), and are challenging therapeutically, since they often present with more severe symptoms. A useful therapy is plasmapheresis, but it is highly non-specific. Antigen-specific immunoadsorption would only remove the pathogenic autoantibodies, minimizing the possible side effects and maximizing the benefit. We used rats with human MuSK-induced experimental autoimmune MG to perform antigen-specific immunoadsorptions, and found it very effective, resulting in a dramatic autoantibody titer decrease, while immunoadsorbed, but not mock-treated, animals showed an significant improvement of their clinical symptoms. Overall, the procedure was efficient, supporting its application for MG treatment.

Randomized phase 2 study of FcRn antagonist efgartigimod in generalized myasthenia gravis

OBJECTIVE

To investigate safety and explore efficacy of efgartigimod (ARGX-113), an anti-neonatal Fc receptor immunoglobulin G1 Fc fragment, in patients with generalized myasthenia gravis (gMG) with a history of anti-acetylcholine receptor (AChR) autoantibodies, who were on stable standard-of-care myasthenia gravis (MG) treatment.

METHODS

A phase 2, exploratory, randomized, double-blind, placebo-controlled, 15-center study is described. Eligible patients were randomly assigned (1:1) to receive 4 doses over a 3-week period of either 10 mg/kg IV efgartigimod or matched placebo combined with their standard-of-care therapy. Primary endpoints were safety and tolerability. Secondary endpoints included efficacy (change from baseline to week 11 of Myasthenia Gravis Activities of Daily Living, Quantitative Myasthenia Gravis, and Myasthenia Gravis Composite disease severity scores, and of the revised 15-item Myasthenia Gravis Quality of Life scale), pharmacokinetics, pharmacodynamics, and immunogenicity.

RESULTS

Of the 35 screened patients, 24 were enrolled and randomized: 12 received efgartigimod and 12 placebo. Efgartigimod was well-tolerated in all patients, with no serious or severe adverse events reported, no relevant changes in vital signs or ECG findings observed, and no difference in adverse events between efgartigimod and placebo treatment. All patients treated with efgartigimod showed a rapid decrease in total immunoglobulin G (IgG) and anti-AChR autoantibody levels, and assessment using all 4 efficacy scales consistently demonstrated that 75% showed a rapid and long-lasting disease improvement.

CONCLUSIONS

Efgartigimod was safe and well-tolerated. The correlation between reduction of levels of pathogenic IgG autoantibodies and disease improvement suggests that reducing pathogenic autoantibodies with efgartigimod may offer an innovative approach to treat MG.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that efgartigimod is safe and well-tolerated in patients with gMG.

Expression of extracellular domains of muscle specific kinase (MuSK) and use as immunoadsorbents for the development of an antigen-specific therapy

Antibodies against MuSK seem to be the pathogenic factor in approximately 5-8% of myasthenia gravis (MG) patients. We aim to develop an antigen-specific therapy in which only MuSK antibodies will be removed from patients' plasma using MuSK extracellular domain (MuSK-ECD) as immunoadsorbent. We showed that two different immunoadsorbents, very efficiently and selectively depleted the MuSK antibodies from all tested sera, were stable during the procedure and were reusable. Furthermore, animal experiments showed that the treatment has no toxic effects to the animals. We conclude that the MuSK-ECD-mediated immunoadsorption can be used as an efficient antigen-specific therapy for MuSK-MG.

Antigen-specific apheresis of pathogenic autoantibodies from myasthenia gravis sera

Myasthenia gravis (MG) is usually caused by autoantibodies against muscle nicotinic acetylcholine receptor (AChR), which is composed of five subunits (alpha(2)betagammadelta or alpha(2)betaepsilondelta). Current treatments, including plasmapheresis, are nonspecific, causing several side effects. We aim to develop an antigen-specific alternative to plasmapheresis, since the latter removes indispensable plasma components in addition to anti-AChR antibodies. We are developing a method for the selective depletion of the anti-AChR autoantibodies from patients' plasma through the construction of "immunoadsorbent" columns carrying AChR domains. We have expressed the extracellular domains (ECDs, amino acids approximately 1-210/220) of all human muscle AChR subunits in Pichia pastoris and, in preliminary experiments, in E. coli. The ECDs were immobilized (individually or mixed) on Sepharose beads, producing Sepharose-ECD columns, which were tested for their immunoadsorbing capacity on MG sera and shown to specifically eliminate major autoantibody fractions from several MG sera. The immobilized ECDs remained stable and did not dissociate from their matrix after incubation with serum, whereas the procedure was neither toxic nor immunogenic in two experimental rabbits. Testing the intact or antibody-depleted MG sera and the affinity purified autoantibodies showed that both the intact sera and the purified autoantibodies, but not the antibody-depleted sera, could induce AChR loss in cell cultures and experimental MG in rats. This preliminary study suggests that the myasthenic potency of MG sera is entirely due to their anti-AChR antibodies and therefore their depletion should be of therapeutic value. We conclude that ECD-mediated immunoadsorption can be used as an efficient, antigen-specific therapy for MG.

Extracellular domains of the β, γ and ε subunits of the human acetylcholine receptor as immunoadsorbents for myasthenic autoantibodies: A combination of immunoadsorbents results in increased efficiency

Myasthenia gravis (MG) is usually caused by autoantibodies against the human muscle acetylcholine receptor (AChR). Plasmapheresis offers a therapeutic option, but, as well as removing the pathogenic anti-AChR autoantibodies, it non-specifically removes indispensable immunoglobulins. An attractive alternative to plasmapheresis would be the extracorporeal specific removal of the autoantibodies using AChR-based immunoadsorbents. Previously, we used the N-terminal extracellular domain (ECD) of the AChR alpha subunit to immunoadsorb anti-alpha subunit autoantibodies from MG sera. In this study, we immobilised the beta -, gamma- and epsilon-AChR ECDs on Sepharose and tested them as immunoadsorbents on 50 MG sera. A given ECD removed a different percentage of autoantibodies from different sera and different ECDs removed different percentages from the same serum; on average, the beta-, gamma- and epsilon-ECDs removed 22%, 20% and 15.5% of the autoantibodies, respectively. Immunoadsorption was completed in 3 min, 1 mug of ECD removed approximately 2 pmol of autoantibodies, and the immunoadsorbent could be recycled approximately 4 times. The combined use of two (alpha+gamma) or four (alpha+beta+gamma+epsilon) ECDs in a single immunoadsorbent resulted in much higher (often additive) immunoadsorption. These results show that MG sera have autoantibodies against several AChR subunits, and suggest that the combined use of all AChR ECDs could provide the basis for a novel, antigen-specific therapy for MG.

Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets

Myasthenia gravis (MG) is a well-recognised disorder of neuromuscular transmission that can be diagnosed by the presence of antibodies to the acetylcholine receptor (AChR). However, some patients (about 15%) with generalised MG do not have detectable AChR antibodies. There is some evidence, however, that this "seronegative" MG is an antibody-mediated disorder. Plasma from patients with the disorder seems to contain various distinct humoral factors: IgG antibodies that reversibly inhibit AChR function; a non-IgG (possibly IgM) factor that indirectly inhibits AChR function; and an IgG antibody against the muscle-specific kinase (MuSK). The presence of antibodies against MuSK appears to define a subgroup of patients with seronegative MG who have predominantly localised, in many cases bulbar, muscle weaknesses (face, tongue, pharynx, etc) and reduced response to conventional immunosuppressive treatments. Moreover, muscle wasting may be present, which prevents complete response to these therapies.

Sensitivity to vecuronium in seropositive and seronegative patients with myasthenia gravis

Patients with myasthenia gravis (MG) are hypersensitive to nondepolarizing neuromuscular blocking drugs. Although antibodies to the acetylcholine receptor (AChR) often are observed in MG patients, 10% to 30% of patients do not show an anti-AChR antibody. Little is known about differences in sensitivity to nondepolarizing neuromuscular blocking drugs between MG patients with and without anti-AChR antibody. Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative MG patients and in non-MG patients (n = 8 each). During anesthesia with sevoflurane (2.5%) and nitrous oxide (60%) in oxygen, neuromuscular transmission was monitored by measuring the twitch tension of the adductor pollicis muscle with supramaximal stimulation. After baseline measurements, 10 microg/kg IV dose increments of vecuronium were administered sequentially until blockade exceeded 90%. The degree of blockade and onset time after the initial 10 microg/kg of vecuronium were assessed, and doses required to exceed 90% blockade were recorded. In addition, effective doses of 50% and 95% for vecuronium were calculated from a single data point. Both types of MG patients showed increased sensitivity to vecuronium compared with non-MG patients.

IMPLICATIONS

Hypothesizing that seronegative patients are as sensitive to vecuronium as seropositive patients, we assessed sensitivity in seropositive and seronegative myasthenia gravis (MG) patients and in non-MG patients. They were, indeed, both equally sensitive to vecuronium.

The six year experience of plasmapheresis in patients with myasthenia gravis

Plasmapheresis (PP) effectively removes autoantibodies in various autoimmune diseases. The use of PP in the treatment of myasthenia gravis (MG) has been widely accepted since the 1970s. The treatment protocol, however, has not been standardized. For the last 6 years, we collected a total of 94 MG patients, 38 males and 56 females aged 14-80 years, who received 175 courses of PP treatment for a total of 823 sessions. The methods we used were double filtration plasmapheresis (DF), immunoadsorption plasmapheresis (IA), and plasma exchange (PE). There were 167 courses of DF, 6 courses of IA, and 2 courses of PE. Each course of treatment consists of 4 to 5 sessions of apheresis. The processed volume of plasma is 1 calculated plasma volume. All patients tolerated PP well although 2.3% of them experienced hypotension. Our experiences are summarized as follows. Both DF and IA effectively ameliorate symptoms and signs of MG. IA removes acetylcholine receptor antibody more effectively than DF does, but clinical effects between these 2 methods are similar. A daily schedule seems more effective than an alternate daily schedule. The optimal number of PP sessions for each course is 4. The factors correlating with better clinical response are high MG score, nonthymoma patients, younger age at onset, and higher removal rate for immunoglobulin G.

Therapeutic apheresis in myasthenia gravis

Plasma exchange (PE) is an easily applicable technique for rapid and massive removal of antibodies, and its beneficial role is well established in the management of myasthenia gravis (MG), an antibody-mediated disorder of the neuromuscular junction. PE is useful in myasthenic crisis, in most severe forms of MG before thymectomy, in the early postoperative period, and in cases of symptom worsening during tapering or initiation of immunosuppressive therapy. Clinical efficacy varies from 55% to 100%, and improvement rarely persists for more than 4-10 weeks; thus immunosuppressive therapy has to be associated. New apheretic techniques (double filtration plasmapheresis, immunoadsorption systems with staphylococcal protein A columns or thryptophan-polyvinyl alcohol gel columns) that allow the selective removal of IgG and anti-AChR antibody were recently used in the management of MG with positive effects. Whether their therapeutic effect and cost effect prove more favorable than those obtained by PE still must be demonstrated.