T-cell tumor necrosis factor-alpha receptor binding in myasthenic patients

Targeting Regulatory T Cells by Addressing Tumor Necrosis Factor and Its Receptors in Allogeneic Hematopoietic Cell Transplantation and Cancer

An intricate network of molecular and cellular actors orchestrates the delicate balance between effector immune responses and immune tolerance. The pleiotropic cytokine tumor necrosis factor-alpha (TNF) proves as a pivotal protagonist promoting but also suppressing immune responses. These opposite actions are accomplished through specialist cell types responding to TNF via TNF receptors TNFR1 and TNFR2. Recent findings highlight the importance of TNFR2 as a key regulator of activated natural FoxP3⁺ regulatory T cells (Tregs) in inflammatory conditions, such as acute graft-vs.-host disease (GvHD) and the tumor microenvironment. Here we review recent advances in our understanding of TNFR2 signaling in T cells and discuss how these can reconcile seemingly conflicting observations when manipulating TNF and TNFRs. As TNFR2 emerges as a new and attractive target we furthermore pinpoint strategies and potential pitfalls for therapeutic targeting of TNFR2 for cancer treatment and immune tolerance after allogeneic hematopoietic cell transplantation.

Advances in autoimmune myasthenia gravis management

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder with no cure and conventional treatments limited by significant adverse effects and variable benefit. In the last decade, therapeutic development has expanded based on improved understanding of autoimmunity and financial incentives for drug development in rare disease. Clinical subtypes exist based on age, gender, thymic pathology, autoantibody profile, and other poorly defined factors, such as genetics, complicate development of specific therapies. Areas covered: Clinical presentation and pathology vary considerably among patients with some having weakness limited to the ocular muscles and others having profound generalized weakness leading to respiratory insufficiency. MG is an antibody-mediated disorder dependent on autoreactive B cells which require T-cell support. Treatments focus on elimination of circulating autoantibodies or inhibition of effector mechanisms by a broad spectrum of approaches from plasmapheresis to B-cell elimination to complement inhibition. Expert commentary: Standard therapies and those under development are disease modifying and not curative. As a rare disease, clinical trials are challenged in patient recruitment. The great interest in development of treatments specific for MG is welcome, but decisions will need to be made to focus on those that offer significant benefits to patients.

Etanercept treatment in myasthenia gravis

Etanercept is a tumor necrosis factor (TNF) blocking agent that has been shown to suppress ongoing experimental autoimmune myasthenia gravis (EAMG). This subcutaneously administered TNF blocking agent has also been shown to be safe and effective in several rheumatological diseases including rheumatoid arthritis, psoriasis, and ankylosing spondylitis. A prospective clinical pilot trial of etanercept in corticosteroid-dependent autoimmune myasthenia gravis (MG) patients supports further study into etanercept as a treatment for MG.

Therapeutic options in autoimmune myasthenia gravis

Autoimmune myasthenia gravis (MG) is associated with circulating antibodies to AChR, modification of the synaptic cleft, and destruction of the postsynaptic neuromuscular membrane. The hallmark is fluctuating muscular weakness and fatigability of muscles on sustained repeated activity. Various drugs and invasive procedures have been used in the treatment of MG including acetylcholinesterase inhibitors, corticosteroids, azathioprine, cyclosporine, cyclophosphamide, mycophenolate mofetil, tacrolimus, etanercept, intravenous immunoglobulin, plasma exchange and thymectomy. We review the role of each of these drugs and invasive procedures in MG. Although current treatment is highly successful and mortality is almost nil, further trials are required to identify the most suitable treatments for different subgroups of MG patients. In addition, safer and more potent drugs are required as most current drugs have major side effects due to immunosuppression. Therefore, the goal of novel therapies should be increased specificity of the immune-directed agents.

Tumor necrosis factor receptor p55 and p75 deficiency protects mice from developing experimental autoimmune myasthenia gravis

The precise pathogenic role of proinflammatory cytokines belonging to the tumor necrosis factor (TNF) family has not been investigated yet in antibody-mediated myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG). In this study we report that TNF receptor p55(-/-) p75(-/-) mice were resistant to the development of clinical EAMG induced by acetylcholine receptor (AChR) immunizations. The resistance was associated with reduced serum levels of IgG, IgG(1), IgG(2a), and IgG(2b) anti-AChR antibody isotypes. However, IgM anti-AChR antibodies were not reduced, suggesting defective anti-AChR IgG class switching in TNF receptor p55(-/-) p75(-/-) mice. We thus demonstrate the genetic evidence for the role of TNF receptor p55 and p75 in EAMG pathogenesis, and their requirement for the generation of anti-AChR IgG antibodies.

Tumor necrosis factor receptor-1 is critically involved in the development of experimental autoimmune myasthenia gravis

Tumor necrosis factor receptor-1 (TNFR1, CD120a) has been implicated in the pathogenesis of several experimental models of T cell-mediated autoimmune disorders, but its role in antibody-mediated autoimmune diseases has not been addressed. Experimental autoimmune myasthenia gravis (EAMG), an autoantibody-mediated T cell-dependent neuromuscular disorder, represents an animal model for myasthenia gravis in human. To investigate the role of TNFR1 in the pathogenesis of EAMG, TNFR1(-/-) and wild-type mice were immunized with TORPEDO: acetylcholine receptor (AChR) in complete Freund's adjuvant. TNFR1(-/-) mice failed to develop EAMG. Lymphoid cells from TNFR1(-/-) mice produced low amounts of T(h)1 (IFN-gamma, IL-2 and IL-12)-type cytokines, but elevated levels of T(h)2 (IL-4 and IL-10)-type cytokines compared with lymphoid cells of wild-type mice. Accordingly, the levels of anti-AChR IgG2 antibodies were severely reduced and the level of anti-AChR IgG1 antibodies were moderately reduced. Co-injection of recombinant mouse IL-12 with AChR in adjuvant restored T cell responses to AChR and promoted development of EAMG in TNFR1(-/-) mice. These results demonstrate that the TNF/TNFR1 system is required for the development of EAMG. The lack of a functional TNF/TNFR1 system can, at least in part, be substituted by IL-12 at the stage of initial priming with AChR and adjuvant.