Antigen-Specific Immunotherapy with Thyrotropin Receptor Peptides in Graves' Hyperthyroidism: A Phase I Study

Graves' disease: Clinical manifestations, immune pathogenesis (cytokines and chemokines) and therapy

Graves' disease (GD) is characterized by thyrotoxicosis, caused by the presence of circulating thyroid stimulating antibodies (TSAb), that are determinant also in the pathogenesis of its extrathyroidal manifestations [Graves' ophthalmopathy (GO), pretibial myxedema]. T helper (Th)1 immune response prevails in the immune-pathogenesis of GD and GO, during the active phase, when Th1 chemokines, and their (C-X-C)R3 receptor, play a key role. In GD, the existing treatments are not ideal for hyperthyroidism (long-term remission with anti-thyroid-drugs only in 50% of patients; while radioiodine and surgery cause hypothyroidism). In GD, antigen-specific therapy has been recently published, with the induction of T cell tolerance via an immunization by TSH-R peptides. In GO, rituximab and drugs targeting cytokines have been evaluated. Furthermore, teprotumumab (a human monoclonal anti-IGF-1R blocking antibody) showed to be very effective in GO patients. Further researches are necessary to identify novel effective therapies targeting GD, or GO.

Novel therapies for thyroid autoimmune diseases: An update

A Th1 immune-preponderance has been shown in the immunopathogenesis of autoimmune thyroiditis (AT), Graves' disease (GD) and Graves' Ophthalmopathy (GO), in which the Th1-chemokines (CXCL9, CXCL10, CXCL11), and their (C-X-C)R3 receptor, have a crucial role. Methimazole, and corticosteroids have been shown to modulate these chemokines; several efforts have been done to modulate the autoimmune reaction with other drugs, i.e. PPAR-γ, or -α ligands, or antibodies, or small molecules directed against CXCL10, or CXCR3. Antigen-specific therapy for GD, by inducing T cell tolerance through an immunization with TSH-R peptides, has been published. Drugs targeting cytokines [anti-TNFα (Etanercept), and anti-IL-6 (Tocilizumab)], and RTX (a chimeric monoclonal antibody vs. CD20) have been used in GO, with promising results. Teprotumumab (a human monoclonal anti-IGF-1R blocking antibody) has been investigated in a trial, showing it was very effective in GO patients. Still, more studies are needed for new therapies targeting autoimmune thyroid disorders.

Teprotumumab as a Novel Therapy for Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) has remained a vexing and poorly managed autoimmune component of Graves' disease where the tissues surrounding the eye and in the upper face become inflamed and undergo remodeling. This leads to substantial facial disfigurement while in its most severe forms, TAO can threaten eye sight. In this brief paper, I review some of the background investigation that has led to development of teprotumumab as the first and only US FDA approved medical therapy for TAO. This novel treatment was predicated on recognition that the insulin-like growth factor I receptor plays an important role in the pathogenesis of TAO. It is possible that a similar involvement of that receptor in other autoimmune disease may lead to additional indications for this and alternative insulin-like growth factor I receptor-inhibiting strategies.

Thyroid-associated ophthalmopathy: Emergence of teprotumumab as a promising medical therapy

Thyroid-associated ophthalmopathy (TAO) remains a vexing autoimmune component of Graves' disease that can diminish the quality of life as a consequence of its impact on visual function, physical appearance and emotional well-being. Because of its relative rarity and variable presentation, the development of highly effective and well-tolerated medical therapies for TAO has been slow relative to other autoimmune diseases. Contributing to the barriers of greater insight into TAO has been the historical absence of high-fidelity preclinical animal models. Despite these challenges, several agents, most developed for treatment of other diseases, have found their way into consideration for use in active TAO through repurposing. Among these, teprotumumab is a fully human inhibitory monoclonal antibody against the insulin-like growth factor I receptor. It has shown remarkable effectiveness in moderate to severe, active TAO in two completed multicenter, double masked, and placebo controlled clinical trials. The drug exhibits a favorable safety profile. Teprotumumab has recently been approved by the U.S. F.D.A, and may rapidly become the first line therapy for this disfiguring and potentially blinding condition.

Immunological Aspects of Graves' Ophthalmopathy

The body's autoimmune process is involved in the development of Graves' disease (GD), which is manifested by an overactive thyroid gland. In some patients, autoreactive inflammatory reactions contribute to the development of symptoms such as thyroid ophthalmopathy, and the subsequent signs and symptoms are derived from the expansion of orbital adipose tissue and edema of extraocular muscles within the orbit. The autoimmune process, production of antibodies against self-antigens such as TSH receptor (TSHR) and IGF-1 receptor (IGF-1R), inflammatory infiltration, and accumulation of glycosaminoglycans (GAG) lead to edematous-infiltrative changes in periocular tissues. As a consequence, edema exophthalmos develops. Orbital fibroblasts seem to play a crucial role in orbital inflammation, tissue expansion, remodeling, and fibrosis because of their proliferative activity as well as their capacity to differentiate into adipocytes and myofibroblasts and production of GAG. In this paper, based on the available medical literature, the immunological mechanism of GO pathogenesis has been summarized. Particular attention was paid to the role of orbital fibroblasts and putative autoantigens. A deeper understanding of the pathomechanism of the disease and the involvement of immunological processes may give rise to the introduction of new, effective, and safe methods of treatment or monitoring of the disease activity.

Will biological agents supplant systemic glucocorticoids as the first-line treatment for thyroid-associated ophthalmopathy?

In this article, the two authors present their opposing points of view concerning the likelihood that glucocorticoids will be replaced by newly developed biological agents in the treatment of active, moderate-to-severe thyroid-associated ophthalmopathy (TAO). TAO is a vexing, disfiguring and potentially blinding autoimmune manifestation of thyroid autoimmunity. One author expresses the opinion that steroids are nonspecific, frequently fail to improve the disease and can cause sometimes serious side effects. He suggests that glucocorticoids should be replaced as soon as possible by more specific and safer drugs, once they become available. The most promising of these are biological agents. The other author argues that glucocorticoids are proven effective and are unlikely to be replaced by biologicals. He reasons that while they may not uniformly result in optimal benefit, they have been proven effective in many reports. He remains open minded about alternative therapies such as biologicals but remains skeptical that they will replace steroids as the first-line therapy for active, moderate-to-severe TAO without head-to-head comparative clinical trials demonstrating superiority. Despite these very different points of view, both authors are optimistic about the availability of improved medical therapies for TAO, either as single agents or in combination. Further, both agree that better treatment options are needed to improve the care of our patients with active moderate-to-severe TAO.

A transgenic mouse that spontaneously develops pathogenic TSH receptor antibodies will facilitate study of antigen-specific immunotherapy for human Graves' disease

Graves' hyperthyroidism can be treated but not cured. Antigen-specific immunotherapy would accomplish this goal, for which purpose an animal model is an invaluable tool. Two types of animal models are available. First, pathogenic TSHR antibodies (TSHRAb) can be induced by injecting mice with fibroblasts co-expressing the human TSHR (hTSHR) and MHC class II, or in mammals using plasmid or adenovirus vectors encoding the hTSHR or its A-subunit. Second, a mouse model that spontaneously develops pathogenic TSHRAb resembling those in human disease was recently described. This outcome was accomplished by transgenic intrathyroidal expression of the hTSHR A-subunit in NOD.H2^h4 mice that are genetically predisposed to develop thyroiditis but, without the transgene, do not generate TSHRAb. Recently, novel approaches to antigen-specific immunotherapy have been tested, primarily in the induced model, by injecting TSHR A-subunit protein or cyclic TSHR peptides. T-cell tolerance has also been induced in "humanized" HLA-DR3 mice by injecting synthetic peptides predicted in silico to mimic naturally processed TSHR T-cell epitopes. Indeed, a phase 1 study based on the latter approach has been conducted in humans. In the spontaneous model (hTSHR/NOD.H2^h mice), injection of soluble or nanoparticle-bearing hTSHR A-subunits had the unwanted effect of exacerbating pathogenic TSHRAb levels. A promising avenue for tolerance induction, successful in other conditions and yet to be tested with the TSHR, involves encapsulating the antigen. In conclusion, these studies provide insight into the potential outcome of immunotherapeutic approaches and emphasize the importance of a spontaneous model to test future novel, antigen-specific immunotherapies for Graves' disease.