Treatment of experimental myasthenia gravis with total lymphoid irradiation

Standardization of the experimental autoimmune myasthenia gravis (EAMG) model by immunization of rats with Torpedo californica acetylcholine receptors--Recommendations for methods and experimental designs

Myasthenia gravis (MG) with antibodies against the acetylcholine receptor (AChR) is characterized by a chronic, fatigable weakness of voluntary muscles. The production of autoantibodies involves the dysregulation of T cells which provide the environment for the development of autoreactive B cells. The symptoms are caused by destruction of the postsynaptic membrane and degradation of the AChR by IgG autoantibodies, predominantly of the G1 and G3 subclasses. Active immunization of animals with AChR from mammalian muscles, AChR from Torpedo or Electrophorus electric organs, and recombinant or synthetic AChR fragments generates a chronic model of MG, termed experimental autoimmune myasthenia gravis (EAMG). This model covers cellular mechanisms involved in the immune response against the AChR, e.g. antigen presentation, T cell-help and regulation, B cell selection and differentiation into plasma cells. Our aim is to define standard operation procedures and recommendations for the rat EAMG model using purified AChR from the Torpedo californica electric organ, in order to facilitate more rapid translation of preclinical proof of concept or efficacy studies into clinical trials and, ultimately, clinical practice.

Immunotherapy in neuromuscular disorders: current and future strategies

Autoimmune mechanisms have recently been implicated in the pathogenesis of an increasing number of neuromuscular diseases. Many of these diseases can be treated with immunotherapeutic agents that are currently available--often with striking success. However, lack of specificity and adverse side effects impose limits on the effectiveness of these immunosuppressive treatments. This article reviews the basic principles of autoimmunity and immune tolerance, and outlines strategies that produce (a) generalized immunosuppression; (b) "selective" immunotherapy; and (c) "antigen-specific" immunotherapy. General immunosuppressive treatments, which are the ones most commonly used in current practice, down-regulate the immune system at multiple levels in "shotgun" fashion. The agents described here include: adrenal corticosteroids, azathioprine, cyclophosphamide, chlorambucil, methotrexate, total lymphoid irradiation, plasmapheresis, and intravenous immunoglobulin. "Selective" immunotherapeutic strategies are designed to interfere with mechanisms intrinsic to the immune system. Agents that are now being used clinically, or are in advanced stages of development include: cyclosporin A, which interferes with synthesis of the cytokine interleukin 2 (IL2); IL2 toxin, which binds to IL2 receptors on activated T cells, is endocytosed, and kills the cells; and CTLA4Ig, which blocks costimulatory molecules, thus preventing full activation of T cells. We have found that combinations of the selective agents may enhance their effectiveness. "Specific" strategies are designed to inactivate or suppress antigen-specific T cells. Oral administration of autoantigens has been shown to prevent experimental autoimmune diseases specifically, but the conditions required to suppress ongoing autoimmune diseases are capricious, and depend on many factors. Finally, we describe a method that is still in the experimental stage, which is designed to modify the individual's own antigen-presenting cells so that they will target and inactivate antigen-specific T cells, and thereby turn off the specific autoimmune response. Currently available immunosuppressive methods can now be used successfully to treat many autoimmune neuromuscular diseases, and the application of selective and specific immunotherapeutic strategies promises more precise and effective treatment in the future.

Trial of immunosuppression in amyotrophic lateral sclerosis using total lymphoid irradiation

Although the cause of amyotrophic lateral sclerosis (ALS) remains unknown, recent studies have suggested an autoimmune mechanism of pathogenesis. Previous trials of immunosuppressive treatment have yielded inconclusive results. Our study was designed to determine whether more powerful and prolonged immunosuppression, produced by total lymphoid irradiation (TLI), would alter the course of ALS. In a double-blind, randomized, placebo-controlled study, 30 patients with classic ALS were treated with TLI, and 31 were given sham radiation. Quantitative measurements of muscle strength, functional motor activity, and humoral and cellular immune status were followed for 2 years, or until death or respirator dependence. Motor function in the TLI-treated and control groups showed no significant differences throughout the study. Overall survival was not significantly different in the TLI-treated and control groups. TLI effectively suppressed cellular and humoral immune function throughout the 2-year study period. Analysis of the relationship between immunosuppression and motor functions showed no consistent effect of treatment. We conclude that powerful and prolonged immunosuppression produced by TLI did not benefit patients with ALS. This fails to support the concept of an autoimmune mechanism of pathogenesis of ALS.

Total lymphoid irradiation and antigen-specific tolerance: future therapy for experimental myasthenia gravis?

Total lymphoid irradiation (TLI) is effective in the immunosuppressive treatment of human and experimental autoimmune disorders, including experimental autoimmune myasthenia gravis (EAMG). Under certain circumstances. TLI may facilitate the induction of specific tolerance to antigens present during or shortly after the TLI treatment. This study was designed to determine whether TLI could induce or enhance tolerance to acetylcholine receptor (AChR), the antigen in myasthenia gravis, or to other antigens. We presented the antigens in various potentially tolerogenic forms to rats that were first pre-treated with TLI, or controls treated with sham irradiation. Injection of deaggregated human gamma globulin (HGG), a classical tolerogen, was most effective; it produced antigen-specific tolerance, which was significantly enhanced by pre-treatment with TLI. Injection of HGG coupled to rat peritoneal cells induced a moderate degree of specific tolerance; in this case, pre-treatment with TLI added only nonspecific suppression. In contrast, AChR, either in solubilized form with no adjuvant, or coupled to syngeneic rat peritoneal cells, failed to induce tolerance, and actually primed the immune system, when given alone or in conjunction with TLI. Subsequent challenge with AChR resulted in an enhanced (secondary) anti-AChR antibody response. These results show that the nature of the antigen itself may predispose to tolerance or to immune stimulation. AChR appears to be highly immunogenic. However, if a tolerogenic fragment or form of AChR can be identified, its use in combination with TLI may result in specific tolerance. If such specific tolerance can be induced during an ongoing autoimmune reaction to AChR, it would be an effective treatment for myasthenia gravis.

Induction of non-specific suppressor cells in normal Lewis rats by a novel azaspirane SK&F 105685

SK&F 105685 (N,N-Dimethyl-8,8-dipropyl-2-azaspiro[4,5]decane-2- propanamine dihydrochloride) is a novel azaspirane which has therapeutic activity in rat models of autoimmune disease. In this study, we have demonstrated that SK&F 105685 is a potent inducer of non-specific suppressor cells (SC). Oral administration of 15-30 mg/kg/day results in the generation of SC in the spleen, lymph nodes and bone marrow, but not the thymus of Lewis rats. Splenic SC suppress Con-A-induced proliferation in co-culture assays at effector-responder ratios of 1:1 to 1:64. SC are radiation resistant (2000 R), non-T, non-B cells, partially adherent to plastic surfaces and are enriched in a 1.07 g/ml fraction of a Percoll density gradient. Their activity is increased, rather than ablated, by indomethacin. No definitive changes in Ig+, OX-19+, OX-8+, W3/25+ or asialo GM1+ cells could be detected in the spleens of treated rats compared to control untreated animals. Elevated levels of both radiation-sensitive and radiation-resistant suppressor cells were found in the bone marrow of treated rats in addition to the radiosensitive SC normally present in this tissue.

Inhibition of animal models of autoimmune disease and the induction of non-specific suppressor cells by SK&F 105685 and related azaspiranes

SK&F 105685 (N,N-dimethyl-8,8-dipropyl-2-azaspiro[4.5]decane-2-propanamine+ ++ dihydrochloride), administered orally to adjuvant arthritic (AA) rats inhibited immune-mediated hindpaw inflammation with an ED50 of 20 mg/kg/day. Both prophylactic and therapeutic administration were effective in this model. In addition, SK&F 105685 inhibited skin wheal responses to purified protein derivative (PPD) of tuberculin in AA rats and the development of hindleg paralysis associated with experimental allergic encephalomyelitis (EAE). Spleens of normal rats treated with SK&F 105685 were found to contain a population(s) of suppressor cells (SC) which inhibited the response of normal cells to Concanavalin A (Con A) in co-culture assays. The association between SC induction and anti-arthritic activity was determined by evaluating a series of chemically related azaspiranes in the AA rat model and for SC induction in normal rats. A statistically significant correlation was demonstrated (r = 0.79, P less than 0.001), indicating that SC induction may be responsible for the therapeutic activity of these compounds.