Therapeutic apheresis in myasthenia gravis

Use of Therapeutic Apheresis methods in Neurology patients

The therapeutic apheresis consists of a continuously improving therapeutic method for diseases with high mortality and morbidity, especially in cases with poor outcome by using current medications. Neurology is one the most famous and at the same most interesting era of apheresis intervention in clinical practice.

Transcriptional landscape of myasthenia gravis revealed by weighted gene coexpression network analysis

Background: As one of the most common autoimmune diseases, myasthenia gravis (MG) severely affects the quality of life of patients. Therefore, exploring the role of dysregulated genes between MG and healthy controls in the diagnosis of MG is beneficial to reveal new and promising diagnostic biomarkers and clinical therapeutic targets.

Methods: The GSE85452 dataset was downloaded from the Gene Expression Omnibus (GEO) database and differential gene expression analysis was performed on MG and healthy control samples to identify differentially expressed genes (DEGs). The functions and pathways involved in DEGs were also explored by functional enrichment analysis. Significantly associated modular genes were identified by weighted gene co-expression network analysis (WGCNA), and MG dysregulated gene co-expression modular-based diagnostic models were constructed by gene set variance analysis (GSVA) and least absolute shrinkage and selection operator (LASSO). In addition, the effect of model genes on tumor immune infiltrating cells was assessed by CIBERSORT. Finally, the upstream regulators of MG dysregulated gene co-expression module were obtained by Pivot analysis.

Results: The green module with high diagnostic performance was identified by GSVA and WGCNA. The LASSO model obtained NAPB, C5orf25 and ERICH1 genes had excellent diagnostic performance for MG. Immune cell infiltration results showed a significant negative correlation between green module scores and infiltration abundance of Macrophages M2 cells.

Conclusion: In this study, a diagnostic model based on the co-expression module of MG dysregulated genes was constructed, which has good diagnostic performance and contributes to the diagnosis of MG.

Application of Extracorporeal Apheresis in Treatment of COVID-19: a Rapid Review

Spread of a novel coronavirus infection in 2019 caused by SARS-CoV-2 virus has become a real threat to public health all around the world. The new pandemic required the mobilization of all resources for effective treatment of COVID-19 patients. Extracorporeal apheresis methods were suggested as an addition to the therapy of severe COVID-19 patients, especially when there is a threat of cytokine storm. Cytokine storm has a complex and not fully understood mechanism, and it can result in the multiple organ failure syndrome, associated with high mortality. The main cytokines that play the key role in the cytokine storm are IL-6, IL-10, and TNF-alpha. Removal of the target pro-inflammatory cytokines from the bloodstream can be beneficial in reducing the risk of complications as well as the mortality rate. We describe and compare different methods of extracorporeal apheresis: hemoadsorption, selective plasma filtration, and plasma exchange therapy in the context of their potential use in COVID-19 treatment.

Current and Upcoming Treatment Modalities in Myasthenia Gravis

ABSTRACT

Myasthenia gravis (MG) is one of the extensively studied autoimmune disorder. There has been a dramatic increase in research to further understand molecular pathogenesis of MG and clinical trials for new drugs in MG treatment in the past decade. This review article is to consolidate the available information in simple terms with students, residents, and fellows as target audience for easy learning and help application of this knowledge to clinical practice.

Emerging New Approaches in Desensitization: Targeted Therapies for HLA Sensitization

There is an urgent need for therapeutic interventions for desensitization and antibody-mediated rejection (AMR) in sensitized patients with preformed or de novo donor-specific HLA antibodies (DSA). The risk of AMR and allograft loss in sensitized patients is increased due to preformed DSA detected at time of transplant or the reactivation of HLA memory after transplantation, causing acute and chronic AMR. Alternatively, de novo DSA that develops post-transplant due to inadequate immunosuppression and again may lead to acute and chronic AMR or even allograft loss. Circulating antibody, the final product of the humoral immune response, has been the primary target of desensitization and AMR treatment. However, in many cases these protocols fail to achieve efficient removal of all DSA and long-term outcomes of patients with persistent DSA are far worse when compared to non-sensitized patients. We believe that targeting multiple components of humoral immunity will lead to improved outcomes for such patients. In this review, we will briefly discuss conventional desensitization methods targeting antibody or B cell removal and then present a mechanistically designed desensitization regimen targeting plasma cells and the humoral response.

Use of Cellular and Plasma Apheresis in the Critically Ill Patient: Part II: Clinical Indications and Applications

Apheresis is the process of separating the blood and removing or manipulating a cellular or plasma component for therapeutic benefit. Such procedures may be indicated in the critical care setting as primary or adjunctive therapy for certain hematologic, neurologic, renal, and autoimmune/rheumatologic disorders. In part I of this series, the technical aspects of apheresis were described and the physiologic rationale and clinical considerations were discussed. This review highlights the pathophysiologic basis, specific clinical indications, and treatment parameters for disorders that more commonly require management in the intensive care unit. The choice of plasma or cellular apheresis in these cases is guided by wellaccepted, evidence-based clinical treatment guidelines. For some disorders, such as liver failure, severe sepsis, and multiple-organ dysfunction syndrome, apheresis treatment approaches remain experimental. Ongoing studies are investigating the potential utility of conventional plasma exchange, ex vivo plasma manipulation, and newer technologies for these and other disorders in severely ill patients.

Current Treatment, Emerging Translational Therapies, and New Therapeutic Targets for Autoimmune Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease associated with the production of autoantibodies against 1) the skeletal muscle acetylcholine receptor; 2) muscle-specific kinase, a receptor tyrosine kinase critical for the maintenance of neuromuscular synapses; 3) low-density lipoprotein receptor-related protein 4, an important molecular binding partner for muscle-specific kinase; and 4) other muscle endplate proteins. In addition to the profile of autoantibodies, MG may be classified according the location of the affected muscles (ocular vs generalized), the age of symptom onset, and the nature of thymic pathology. Immunopathologic events leading to the production of autoantibodies differ in the various disease subtypes. Advances in our knowledge of the immunopathogenesis of the subtypes of MG will allow for directed utilization of the ever-growing repertoire of therapeutic agents that target distinct nodes in the immune pathway relevant to the initiation and maintenance of autoimmune disease. In this review, we examine the pathogenesis of MG subtypes, current treatment options, and emerging new treatments and therapeutic targets.

Direct proof of the in vivo pathogenic role of the AChR autoantibodies from myasthenia gravis patients

Several studies have suggested that the autoantibodies (autoAbs) against muscle acetylcholine receptor (AChR) of myasthenia gravis (MG) patients are the main pathogenic factor in MG; however, this belief has not yet been confirmed with direct observations. Although animals immunized with AChR or injected with anti-AChR monoclonal Abs, or with crude human MG Ig fractions exhibit MG symptoms, the pathogenic role of isolated anti-AChR autoAbs, and, more importantly, the absence of pathogenic factor(s) in the autoAb-depleted MG sera has not yet been shown by in vivo studies. Using recombinant extracellular domains of the human AChR α and β subunits, we have isolated autoAbs from the sera of four MG patients. The ability of these isolated anti-subunit Abs and of the Ab-depleted sera to passively transfer experimental autoimmune MG in Lewis rats was investigated. We found that the isolated anti-subunit Abs were at least as efficient as the corresponding whole sera or whole Ig in causing experimental MG. Abs to both α- and β-subunit were pathogenic although the anti-α-subunit were much more efficient than the anti-β-subunit ones. Interestingly, the autoAb-depleted sera were free of pathogenic activity. The later suggests that the myasthenogenic potency of the studied anti-AChR MG sera is totally due to their anti-AChR autoAbs, and therefore selective elimination of the anti-AChR autoAbs from MG patients may be an efficient therapy for MG.

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.

Scale up and safety parameters of antigen specific immunoadsorption of human anti-acetylcholine receptor antibodies

Myasthenia gravis is an autoimmune disease usually caused by autoantibodies against the muscle nicotinic acetylcholine receptor (nAChR). Current treatments are not specific, and thus often cause side effects. Here, we elaborate on our previous findings on antigen specific immunoadsorption towards scaling up the method as well as testing whole blood apheresis. The average percent of plasma or whole blood immunoadsorption was up to 79.5%±2.9. Moreover, neither pyrogens were co-administered nor did complement activation occur after immunoadsorption. Thus, antigen-specific apheresis of anti-AChR autoantibodies seems a safe and effective treatment for myasthenia gravis that can be scaled up for clinical testing.

Current topics in therapeutic plasmapheresis

Therapeutic plasmapheresis has been used for intractable diseases that cannot be cured by conventional drug therapy. Currently, the use of therapeutic plasmapheresis has been approved for 27 diseases by Japan's National Health Insurance system and is mainly categorized into three modalities: plasma exchange (PE), double-filtration plasmapheresis (DFPP), and plasma adsorption (PA). Plasma separators and/or fractionators are essential for the therapy. PE is performed for two purposes: removal of pathogenic antigens or substances in the plasma fraction and supplementation of essential factors, such as albumin and coagulation factors. PE can be used for thrombotic microangiopathy and acute hepatic failure. DFPP can be performed for selective removal of macromolecules while avoiding the use of substitution fluid (i.e., albumin or fresh frozen plasma). DFPP has now been used for conditions involving relatively larger plasma molecules, including hyperviscosity syndrome and ABO-incompatible kidney transplantation. PA can specifically remove pathogenic agents, such as low-density lipoprotein or autoantibodies, in the IgG fractions by the adsorption column and does not require substitution fluids. PA has now been used for a wide variety of neurological diseases, including chronic inflammatory demyelinating polyneuropathy. This review describes the characteristics of each modality, seeking to improve the efficacy and specificity of removal of the target substance.

A case of Castleman's disease with myasthenia gravis

A rare case of Castleman's disease with myasthenia gravis is reported. A 55-year-old woman with bilateral ptosis, speech impairment, and severe dyspnea had been previously diagnosed with myasthenia gravis. Computed tomography showed a 5 cm × 3 cm paratracheal mass in the mediastinum, thought to be an ectopic thymoma. Two days after surgical resection, the patient suddenly developed dyspnea. Postoperative myasthenic crisis was diagnosed, and plasmapheresis was performed. Her general condition improved, and her subsequent course was uneventful. The final pathological diagnosis was mediastinal solitary Castleman's disease, hyaline vascular type. Castleman's disease with myasthenia gravis is especially rare. One of the serious complications is postoperative myasthenic crisis. For patients with myasthenia gravis, the rate of postoperative myasthenic crisis seems significantly higher in Castleman's disease patients than in patients with thymic epithelial tumors. Castleman's disease with myasthenia gravis is discussed along with a review of the literature.

Ocular myasthenia gravis

PURPOSE OF REVIEW

To review ocular myasthenia gravis (OMG), a localized form of myasthenia gravis clinically involving only the extraocular, levator palpebrae superioris, and orbicularis oculi muscles.

RECENT FINDINGS

Ocular manifestations can masquerade as a variety of ocular motility disorders, including central nervous system disorders and peripheral cranial nerve palsies. While sparing the pupils, the diagnosis and management can be challenging.

SUMMARY

Because several diagnostic and treatment options are available for OMG, clinicians must decide the sequence and combination based on the level of disease activity and patient disability.

Myasthenia gravis: a review

Acquired myasthenia gravis is a relatively uncommon disorder, with prevalence rates that have increased to about 20 per 100,000 in the US population. This autoimmune disease is characterized by muscle weakness that fluctuates, worsening with exertion, and improving with rest. In about two-thirds of the patients, the involvement of extrinsic ocular muscle presents as the initial symptom, usually progressing to involve other bulbar muscles and limb musculature, resulting in generalized myasthenia gravis. Although the cause of the disorder is unknown, the role of circulating antibodies directed against the nicotinic acetylcholine receptor in its pathogenesis is well established. As this disorder is highly treatable, prompt recognition is crucial. During the past decade, significant progress has been made in our understanding of the disease, leading to new treatment modalities and a significant reduction in morbidity and mortality.

Immunotherapies in neurologic disorders

Therapy for autoimmune demyelinating disorders has evolved rapidly over the past 10 years to include traditional immunosuppressants as well as novel biologicals. Antibody-mediated neuromuscular disorders are treated with therapies that acutely modulate pathogenic antibodies or chronically inhibit the humoral immune response. In other inflammatory autoimmune disorders of the peripheral and central nervous system, corticosteroids, often combined with conventional immunosuppression, and immunomodulatory treatments are used. Because autoimmune neurologic disorders are so diverse, evidence from randomized controlled trials is limited for most of the immunotherapies used in neurology. This review provides an overview of the immunotherapies currently used for neurologic disorders.

Treatment of myasthenia gravis based on its immunopathogenesis

The prognosis of myasthenia gravis (MG) has improved dramatically due to advances in critical-care medicine and symptomatic treatments. Its immunopathogenesis is fundamentally a T-cell-dependent autoimmune process resulting from loss of tolerance toward self-antigens in the thymus. Thymectomy is based on this immunological background. For MG patients who are inadequately controlled with sufficient symptomatic treatment or fail to achieve remission after thymectomy, remission is usually achieved through the addition of other immunotherapies. These immunotherapies can be classified into two groups: rapid induction and long-term maintenance. Rapid induction therapy includes intravenous immunoglobulin (IVIg) and plasma exchange (PE). These produce improvement within a few days after initiation, and so are useful for acute exacerbation including myasthenic crisis or in the perioperative period. High-dose prednisone has been more universally preferred for remission induction, but it acts more slowly than IVIg and PE, commonly only after a delay of several weeks. Slow tapering of steroids after a high-dose pulse offers a method of maintaining the state of remission. However, because of significant side effects, other immunosuppressants (ISs) are frequently added as "steroid-sparing agents". The currently available ISs exert their immunosuppressive effects by three mechanisms: 1) blocking the synthesis of DNA and RNA, 2) inhibiting T-cell activation and 3) depleting the B-cell population. In addition, newer drugs including antisense molecule, tumor necrosis factor alpha receptor blocker and complement inhibitors are currently under investigation to confirm their effectiveness. Until now, the treatment of MG has been based primarily on experience rather than gold-standard evidence from randomized controlled trials. It is hoped that well-organized studies and newer experimental trials will lead to improved treatments.

Therapeutic Apheresis of Immune Diseases in Nephrology Department

OBJECTIVE

The clinical efficacy of therapeutic apheresis is still controversial. We undertook a retrospective review of apheresis treatment to ascertain its safety and efficacy.

METHODS

We reviewed 31 patients (13 male, 18 female). Plasmapheresis was performed on 7 patients with hematologic disorders, 5 patients with neurologic disorders, 6 patients with systemic diseases, and 3 patients with Lyell syndrome. Immunoadsorption onto protein A sepharose was evaluated as rescue therapy in 7 patients. Low-density lipoprotein (LDL) apheresis was performed on 3 patients.

RESULTS

There were five mortalities due to serious complications of their primary disease. Most complications were mild such as hypotension and hypocalcemia. Two patients who received LDL apheresis had severe anaphylactic reactions. Apheresis was effective in the remaining 24 patients.

CONCLUSIONS

The therapeutic apheresis consists of a continuously improving therapeutic method for diseases with high mortality and morbidity, especially in cases with poor outcome by using current medications.

Autoimmune myasthenia gravis: emerging clinical and biological heterogeneity

Acquired myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction in which patients experience fluctuating skeletal muscle weakness that often affects selected muscle groups preferentially. The target of the autoimmune attack in most cases is the skeletal muscle acetylcholine receptor (AChR), but in others, non-AChR components of the neuromuscular junction, such as the muscle-specific receptor tyrosine kinase, are targeted. The pathophysiological result is muscle endplate dysfunction and consequent fatigable muscle weakness. Clinical presentations vary substantially, both for anti-AChR positive and negative MG, and accurate diagnosis and selection of effective treatment depends on recognition of less typical as well as classic disease phenotypes. Accumulating evidence suggests that clinical MG subgroups might respond differently to treatment. In this Review, we provide current information about the epidemiology, immunopathogenesis, clinical presentations, diagnosis, and treatment of MG, including emerging therapeutic strategies.

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.

Complications of therapeutic plasma exchange: A prospective study of 1,727 procedures

The type and number of complications was prospectively examined in 1,727 successive TPE treatments in 174 patients over 66 months at a single center. Most treatments were prescribed for thrombotic thrombocytopenic purpura (TTP; 42%), recurrent focal segmental glomerulosclerosis (FSGS; 22%), or myasthenia gravis (MG; 13%). About 57% of treatments used albumin-saline as the replacement solution and 43% used fresh-frozen plasma (FFP), almost all for TTP. There were 889 complications; 614 treatments (36% of the total) involved a complication. Most complications were minor; there were no deaths. Three treatments (0.2%) were discontinued due to a complication, and 2 (0.1%) required transfer to a higher acuity hospital bed. The most common complications were fever (7.7% of treatments), urticaria (7.4%), and hypocalcemic symptoms (7.3%). 42% of treatments with FFP involved a complication, compared to 30% of treatments using albumin-saline (P < 0.0001). The most common complications with FFP were urticaria (17%) and pruritus (13%); these occurred more commonly than in patients receiving albumin-saline. The most common complications with albumin-saline replacement were hypocalcemic symptoms (8.2%) and mild hypotension (8.1%). Mild and severe hypotension was significantly (P < 0.0001) more common with albumin-saline replacement. TPE is associated with a number of minor complications. Complications occur more commonly with FFP replacement compared to albumin-saline replacement. Pruritus and urticaria occur more commonly with FFP, and hypotension occurs more commonly with albumin-saline.

Recent advances in the understanding and therapy of myasthenia gravis

Myasthenia gravis (MG) is a T-cell dependent autoimmune disease mediated by autoantibodies, which mainly target muscle nicotinic acetylcholine receptors (AChR) and cause loss of functional AChRs in the neuromuscular junction. Both MG and its major autoantigen are studied extensively, yet the etiology of the disease remains unclear, although it is known to be associated with the thymus. A genetic predisposition, combined with several unidentified environmental stimuli, likely creates a favorable milieu in which the disease can appear. Current research focusses on elucidating the cellular and molecular pathways of immune dysregulation, which underly MG outburst and progression. Considerable progress has been made concerning the involvement of the thymus, the identification of impaired mechanisms of immune control and the B–T-cell interaction in MG pathogenesis, while the role of chemokines arises as an intriguing new puzzle. Recent findings fueled the development of novel therapeutic approaches with some encouraging, although preliminary, results. This review summarizes recent achievements in the fields of both basic research and therapeutics.

Long-term Effects of a Multimodal Approach Including Immunoadsorption for the Treatment of Myasthenic Crisis

A multimodal treatment protocol with immunoadsorption (IA) as the central element was used in the treatment of myasthenic crisis (MC). Fifteen patients with MC were treated in repeated, uninterrupted 7-day cycles until mobilization with: (i) large-volume IA using an antihuman-IgG adsorber, days 1-5; (ii) intravenous immunoglobulin substitution (0.3-0.5 g/kg body weight [BW]/day), days 5-7; and (iii) immunosuppression with cyclophosphamide (1-2 mg/kg BW/day) and prednisolone (0.5-1 mg/kg BW/day), until remission. Patients required a median of 8 days of mechanical ventilation, 12 days in the intensive care unit, and 35 days of hospitalization. Functional improvement compared to their precrisis condition was attained by 14 of 15 patients. MG severity score improved by a mean of 10 points, quality of life score by 9.8 points, and Karnofsky index by 29 points in 14 of 15 patients. Improvements remained stable and no further crises occurred during long-term follow-up, which averaged 4.4 years. No fatalities due to MC occurred. The results demonstrate that our protocol is a potent therapeutic approach in the treatment of MC.

Treatment review and update for myasthenia gravis

Myasthenia gravis (MG) is the best understood autoimmune disease, with well-characterized humoral and cellular effector mechanisms. It is not surprising, therefore, that immunotherapies play a key role in the management of MG. Significant progress has been made over the last few decades in the treatment of patients with MG, and the number of effective avenues of therapy continue to increase. In this review, we provide an update on management options in MG, highlighting recent literature on both traditional and more novel approaches.

Plasmapheresis as effective treatment for thyrotoxic storm after sleeve pneumonectomy

Thyrotoxicosis is a life-threatening disorder when encountered after a major surgical procedure. Plasma exchange is an occasionally reported alternative treatment to thyroidectomy, iodine ablative therapy, or the administration of thyreostatic drugs. We used plasmapheresis as a lifesaving treatment in a patient with thyrotoxicosis, as encountered after a left-sleeve pneumonectomy, in whom many classic therapies either failed or were not retained.

Construction of a functional S-layer fusion protein comprising an immunoglobulin G-binding domain for development of specific adsorbents for extracorporeal blood purification

The chimeric gene encoding a C-terminally-truncated form of the S-layer protein SbpA from Bacillus sphaericus CCM 2177 and two copies of the Fc-binding Z-domain was constructed, cloned, and heterologously expressed in Escherichia coli HMS174(DE3). The Z-domain is a synthetic analogue of the B-domain of protein A, capable of binding the Fc part of immunoglobulin G (IgG). The S-layer fusion protein rSbpA(31-1068)/ZZ retained the specific properties of the S-layer protein moiety to self-assemble in suspension and to recrystallize on supports precoated with secondary cell wall polymer (SCWP), which is the natural anchoring molecule for the S-layer protein in the bacterial cell wall. Due to the construction principle of the S-layer fusion protein, the ZZ-domains remained exposed on the outermost surface of the protein lattice. The binding capacity of the native or cross-linked monolayer for human IgG was determined by surface plasmon resonance measurements. For batch adsorption experiments, 3-microm-diameter, biocompatible cellulose-based, SCWP-coated microbeads were used for recrystallization of the S-layer fusion protein. In the case of the native monolayer, the binding capacity for human IgG was 5.1 ng/mm(2), whereas after cross-linking with dimethyl pimelimidate, 4.4 ng of IgG/mm(2) was bound. This corresponded to 78 and 65% of the theoretical saturation capacity of a planar surface for IgGs aligned in the upright position, respectively. Compared to commercial particles used as immunoadsorbents to remove autoantibodies from sera of patients suffering from an autoimmune disease, the IgG binding capacity of the S-layer fusion protein-coated microbeads was at least 20 times higher. For that reason, this novel type of microbeads should find application in the microsphere-based detoxification system.

Future Therapeutic Strategies in Autoimmune Myasthenia Gravis

Antibodies against muscle acetylcholine receptor (AChR) undoubtedly play a critical role in the pathology of most myasthenia gravis (MG) cases. Selective elimination of the majority of these antibodies should result in a considerable improvement of the MG symptoms. Such a specific elimination could be achieved by AChR-based immunoadsorbents. However, sufficient quantities of native human AChR are not available while bacterially expressed recombinant domains of the AChR are unable to bind satisfactorily MG antibodies. We have undertaken the production of the extracellular domains of human AChR subunits in eukaryotic systems, in native-like conformation, for their use as potent immunoadsorbents. The N-terminal extracellular domain (amino acids 1-210; alpha(1-210)) of the alpha(1) subunit of the human muscle AChR was expressed in the yeast Pichia pastoris. The polypeptide was water-soluble, glycosylated, and in monomer form. The alpha(1-210) bound 125I-alpha-bungarotoxin (125I-alpha-BTX) with a high affinity (Kd = 5.1 +/- 2.4 nM), and this binding was blocked by unlabeled d-tubocurarine and gallamine. Several conformation-dependent anti-AChR antibodies were able to bind alpha(1-210) as did antibodies from a large proportion of MG patients. The purified protein was subsequently immobilized on Sepharose-CNBr and was used to immunoadsorb anti-AChR antibodies from 64 MG sera. It eliminated more than 50% (50-94%) of the anti-AChR antibodies in 20% of the sera, whereas from another 30% of the sera it eliminated 20-60% of their anti-AChR antibodies. Work is in progress for the expression of the extracellular domain of all other muscle AChR subunits. It is expected that their combined use may eliminate the great majority of the anti-AChR antibodies from most MG patients.

Plasmaperfusion on triptophan columns can improve the clinical outcome of patients affected with myasthenia gravis

Myasthenia Gravis (MG) is a neuromuscular disease often associated with thymic pathology due to neuromuscular transmission impairment by circulating antibodies directed against the cholinergic postsynaptic receptor on the neuromuscular junction (Anti-AchR-Ab). The treatment of MG includes cholinesterase inhibitors, steroids and thymectomy. Plasmapheresis can remove Anti-AchR-Ab but more recently plasma-perfusion (PP), a more specific apheresis for selective removal of noxious plasma components, has been developed.

AIM OF THE STUDY

To study the effect of PP treatment, performed by using specific immunocolumns for Anti-AchR-Ab, on the clinical outcome of MG patients non-responder to steroid therapy or thymectomy.

MATERIALS AND METHODS

We treated 8 patients suffering from severe MG by a cycle of 6 sessions of PP. We used columns containing triptophan as a specific ligand for Anti-AchR-Ab. In order to evaluate the effectiveness of treatment we used functional tests (muscular tests, respiratory function, electromyography) and laboratory tests (Anti-AchR-Ab; immunoglobulins, complement fractions, immunocomplexes).

RESULTS

After one to three PP sessions, early clinical improvement in bulbar and respiratory symptoms were found in all patients and EMG showed improvement of neuromuscular transmission. Serum concentration of immunological markers decreased progressively and significantly during the treatment. Clinical improvements were progressive despite the tendency for Anti-AchR-Ab to reach initial values between one session and another. We observed no side effects due to the type of immunocolumns used.

CONCLUSIONS

Triptophan columns appear to be able to remove large quantities of Anti-AchR-Ab and immunological markers from plasma. Our experience shows that PP performed using triptophan columns in patients suffering from severe MG provides good clinical results, improving patients' outcome, without any risk linked to the procedure.