Immunoadsorption in myasthenia gravis based on specific ligands mimicking the immunogenic sites of the acetylcholine receptor

Immunoadsorption versus plasma exchange versus combination for treatment of myasthenic deterioration

OBJECTIVES

The goal of this study was to analyze safety and assess the efficacy of standard plasma exchange (PE) compared with immunoadsorption (IA) alone, or an alternating combination of both in deteriorating myasthenia gravis (MG).

METHODS

A total of 72 patients with MG who had received PE procedures for treatment of severe deterioration were retrospectively analyzed. They received either five cycles of PE (1-1.5 plasma volumes), or five cycles of IA in line with plasma separation, or a sequential alternating procedure of one cycle of PE followed by two cycles of IA, which was repeated once or more if needed.

RESULTS

A total of 19 patients received PE, 24 patients IA, and 29 the alternating combination therapy. All groups were equally distributed by sex and mean MG score before treatment. The number of treatment cycles and days on therapy did not differ between the groups. Mean MG scores at discharge were 3.0 (PE), 1.8 (IA) and 1.6 (combination) (p = 0.028 for combination versus PE). Inpatient time was 30.7 days (PE), 22.3 days (IA) and 20.0 days in combination therapy (p < 0.05 for combination versus PE). Side effects such as allergic reactions or hypocoagulability were significantly more frequent in the PE group (37% in PE versus 4% in IA and 3.6% in the alternating combination, p < 0.05).

CONCLUSION

Semiselective IA in combination with PE, and to a lesser extent IA alone, was associated with a shorter hospital stay and more pronounced reduction of the MG score than PE.

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 and emerging treatments for the management of myasthenia gravis

Myasthenia gravis is an autoimmune neuromuscular disorder. There are several treatment options, including symptomatic treatment (acetylcholinesterase inhibitors), short-term immunosuppression (corticosteroids), long-term immunosuppression (azathioprine, cyclosporine, cyclophosphamide, methotrexate, mycophenolate mofetil, rituximab, tacrolimus), rapid acting short-term immunomodulation (intravenous immunoglobulin, plasma exchange), and long-term immunomodulation (thymectomy). This review explores in detail these different treatment options. Potential future treatments are also discussed.

Antigen-specific immunoadsorption of anti-acetylcholine receptor antibodies from sera of patients with myastenia gravis

BACKGROUND

The binding of anti-acetylcholine receptor antibodies (AChRAb) to the main immunogenic region (MIR) of AChR alpha-subunit in the neuromuscular junction is the major pathogenesis of myasthenia gravis (MG).

METHODS

A synthetic peptide of 10 amino acids corresponding to the MIR of human AChR was coupled with cellulose beads to make an antigen-specific immunoadsorbent (hMIR10-CB).

RESULTS

The hMIR10-CB could remove AChRAb in MG sera by 40.3+/-2.3%, compared to a tryptophan nonspecific adsorbent Trp-CB by only 22.4+/-1.5% as determined in ELISA, and also showed good blood compatibility for blood cells, plasma ions and plasma proteins as checked in whole blood perfusion in rabbits.

CONCLUSIONS

The antigen-specific immunoadsorbent hMIR10-CB can serve as a potential candidate in the immunoadsorption treatment of MG.

[Recent advance in research for myasthenia gravis, in relation to various antibodies affecting synaptic structure and function]

Autoantibodies impair acetylcholine receptor (AChR) in myasthenia gravis (MG) and P/Q-type voltage-gated calcium channel (VGCC) in Lambert-Eaton myasthenic syndrome (LEMS). (1) Some of MG and LEMS patients are "seronegative" for respective antibodies or modified by antibodies that recognize other proteins than AChR and VGCC such as MuSK, AChR allosteric site, membrane Na+ channel and ryanodine receptor-1 (RyR1) in MG, and synaptotagmin-1 in LEMS. (2) Autoimmune responses affect the proteins participating in the mechanisms to compensate for synaptic disorders on the basis of presynaptic Ca2+ homeostasis provided by VGCC and non-VGCC (receptor-operated TRPCs): they act as enhancers of Ca(2+) -mediated ACh release via phospholipase C signaling pathways including M1-type presynaptic muscarinic AChR, neurotrophin receptor (TrkB), and fast-mode of synaptic vesicle recycling. (3) The pathophysiology contributive to contractile fatigue in MG includes RyR1 and also TRPC3. The TRPC3 also forms a complex with STIM1 and Orail to make up for Ca2+ after sarcoplasmic Ca2+ release. The prevalent detection of anti-TRPC3 antibodies in MG with thymoma could affect muscle contractile machineries in addition to anti-RyR1-induced affection. (4) When one faces "seronegative" MG, one should be cautious to conformation-specific antibodies and also congenital myasthenic syndromes.

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.

Towards antigen-specific apheresis of pathogenic autoantibodies as a further step in the treatment of myasthenia gravis by plasmapheresis

Myasthenia gravis (MG), a prototypic antibody-mediated autoimmune disease, presents an excellent target for scientific research aimed at a better understanding of the disease itself and the source that triggers an autoimmune reaction in an organism. MG is a neuromuscular disease caused mainly by an autoimmune response against the nicotinic acetylcholine receptor (AChR) which interferes with neuromuscular transmission. This review focuses on our studies on the extracellular domains of human muscle AChR subunits in an effort to develop an approach for the specific therapeutic apheresis of autoantibodies from patients' sera using the immobilized subunits as immunoadsorbents. The ability of the anti-AChR antibodies isolated by this technique, but not of the depleted sera, to induce disease is also described. This review is dedicated to the late Prof. John Newsom-Davis, who was the first to introduce the use of plasmapheresis 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.

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.

Immunoadsorption against two distinct epitopes on human type XVII collagen abolishes dermal-epidermal separation induced in vitro by autoantibodies from pemphigoid gestationis patients

Pemphigoid gestationis (PG) is a subepidermal autoimmune blistering disease characterized by self-reactive T and B cells specific for the transmembrane hemidesmosomal protein type XVII collagen/BP180. Major T and B cell epitopes are located within the immunodominant 16th non-collagenous domain A (NC16A) of type XVII collagen. The aim of the present study was to map the pathogenically relevant epitopes targeted by blister-inducing patients' autoantibodies. For this purpose, we used an in vitro model of autoantibody-induced leukocyte-dependent dermal-epidermal separation. Pre-adsorption against a recombinant form of the NC16A region abolished the blister-inducing potential of autoantibodies from all PG patients. Using overlapping synthetic peptides, we demonstrated that PG autoantibodies bind to two defined epitopes within the NC16A region (aa 500-514 and aa 511-523). Importantly, pre-adsorption using an affinity matrix containing these epitopes completely abolished dermal-epidermal separation induced by PG autoantibodies. This study identifies the epitopes relevant for blister induction in PG and should facilitate the development of an antigen-specific immunoadsorption therapy for this disease.

Quo vadis haemapheresis. Current developments in haemapheresis

The techniques of haemapheresis originated in the development of centrifugal devices separating cells from plasma and later on plasma from cells. Subsequently membrane filtration was developed allowing for plasma-cell separation. The unspecificity of therapeutic plasma exchange led to the development of secondary plasma separation technologies being specific, semi-selective or selective such as adsorption, filtration or precipitation. In contrast on-line differential separation of cells is still under development. Whereas erythrocytapheresis, granulocytapheresis, lymphocytapheresis and stem cell apheresis are technically advanced, monocytapheresis may need further improvement. Also, indications such as erythrocytapheresis for the treatment of polycythaemia vera or photopheresis though being clinically effective and of considerable importance for an appropriate disease control are to some extent under debate as being either too costly or without sufficient understanding of the mechanism. Other forms of cell therapy are under development. Rheohaemapheresis as the most advanced technology of extracorporeal haemorheotherapy is a rapidly developing approach contributing to the treatment of microcirculatory diseases and tissue repair. Whereas the control of a considerable number of (auto-) antibody mediated diseases is beyond discussion, the indication of apheresis therapy for immune complex mediated diseases is quite often still under debate. Detoxification for artificial liver support advanced considerably during the last years, whereas conclusions on the efficacy of septicaemia treatment are debatable indeed. LDL-apheresis initiated in 1981 as immune apheresis is well established since 24 years, other semi-selective or unspecific procedures, allowing for the elimination of LDL-cholesterol among other plasma components are also being used. Correspondingly Lp(a) apheresis is available as a specific, highly efficient elimination procedure superior to techniques which also eliminate Lp(a). Quality control systems, more economical technologies as for instance by increasing automation, influencing the over-interpretation of evidence based medicine especially in patients with rare diseases without treatment alternative, more insight into the need of controlled clinical trials or alternatively improved diagnostic procedures are among others tools ways to expand the application of haemapheresis so far applied in cardiology, dermatology, haematology, immunology, nephrology, neurology, ophthalmology, otology, paediatrics, rheumatology, surgery and transfusion medicine.

Preparation of an immunoadsorbent coupled with a recombinant antigen to remove anti-acetylcholine receptor antibodies in abnormal serum

An immunoadsorbent that removes anti-acetylcholine receptor antibodies (AChRAb) in abnormal serum of myasthenia gravis (MG) patient was efficiently prepared by an expression product, the functional fragment of AChR(alpha205) fused with maltose binding protein (MBP). The ligand can then covalently bind to amylose resin through MBP fusion protein. It was shown from the result of this study with anti-AChR mice sera that the removal rate of AChRAb on this immunoadsorbent reached 87+/-10% (mean value of 10 mice) and the maximally binding capacity of AChRAb was approximately 260 microg/g immunoadsorbent (wet weight). Moreover, the immunoadsorption test of sera in two MG patients indicated that about 90% and 96% of abnormal AChRAb could be eliminated, while other serum components such as albumin, IgG, IgM and IgA only dropped 18%, 35%, 22%, 15% and 24%, 27%, 15%, 12%, respectively, for two MG patient sera. It is anticipated from this study that the immunoadsorbent reported here could, with further development, find its clinical application for removal of AChRAb from patient serum.

Removal of Pathogenic Autoantibodies by Immunoadsorption

Autoimmune diseases result from disrupted tolerance to self-antigens and subsequent damage to tissues and organs. In several diseases, specific autoantibodies have been either proved or suspected to play a role in this process. Consequently, several strategies have been devised in an attempt to discard the destructive immunoglobulins. Currently, both nonselective and epitope-specific methods are applied in several diseases. In this review, we provide a summary of the available data on elimination of pathogenic autoantibodies and discuss the advantages and pitfalls of the different approaches.

Specific immunoadsorption of the autoantibodies from myasthenic patients using the extracellular domain of the human muscle acetylcholine receptor α-subunit. Development of an antigen-specific therapeutic strategy

Antibodies against the acetylcholine receptor (AChR) are the main pathogenic factor in myasthenia gravis (MG). Clinical improvement correlates well with a reduction in levels of circulating anti-AChR antibodies, and plasmapheresis is an efficient short-term MG treatment. The Sepharose-immobilized N-terminal extracellular domain of human muscle AChR alpha-subunit was used to immunoadsorb anti-AChR autoantibodies from 50 MG patients sera. The immunoadsorbents removed 60-94% of the anti-AChR antibodies in 10 sera and a mean of 35% from all samples combined. Immunoadsorption was fast, efficient, and the columns could be used repeatedly without any release or proteolysis of the polypeptide, suggesting the feasibility of antigen-specific MG immunoadsorption therapy.

New trends in specific immunoadsorption

Plasma exchange is widely accepted to remove pathogenic substances from patients' blood that cannot be eliminated otherwise like cholesterol in severe forms of familial hypercholesterolaemia or immunoglobulins and circulating immune complexes (CIC) in many autoimmune disorders. But dilution of other plasma proteins, as well as side effects and costs of substitution fluids, limit its efficiency. In immunoadsorption, the pathogen is bound specifically, generally no substitution fluids are needed and plasma can be conducted over the immunoadsorption columns as often as needed to achieve any reduction that one aims at, in some instances below the detection limit (e.g. HLA-antibodies in transplantations). The frequency of aphaereses is determined by the speed of the patients' improvement and the rebound of the eliminated substance, which can in some disorders be slowed down or stopped by concomitant immunosuppression. Generally, immunoadsorption is used in patients, where less expensive and demanding treatment options have failed, like severe hypercholesterolaemia, autoimmune disorders or hyperviscosity syndromes.

Adsorption column for myasthenia gravis treatment: Medisorba MG-50

Adsorption column Medisorba MG-50 (Kuraray Medical Inc.) for the treatment of myasthenia gravis (MG) is introduced. The adsorbent in this column is composed of cellulose beads as carrier material and covalent-bound synthetic peptide as a ligand that has a specific affinity to the pathogenic anti-acetylcholine receptor antibody of MG. The amino acid sequence of the peptide is modified from the segment of alpha 183-200 of the torpedo acetylcholine receptor (AChR) protein, and the segment is the acetylcholine binding site on AChR and the target site of anti-AChR antibody. The adsorbent showed specific adsorption characteristics to the anti-ACHR antibody (blocking antibody) in vitro. Clinically, MG-50 is used in plasma-perfusion therapy, and it is recognized that MG-50 specifically reduces blocking antibody titer and improves MG symptoms. MG-50 is approved in Japan.