Designing antigens for the prevention and treatment of autoimmune diseases

Impact of Siglecs on autoimmune diseases

Autoimmune diseases affect tens of millions of people just in the United States alone. Most of the available treatment options are aimed at reducing symptoms but do not lead to cures. Individuals affected with autoimmune diseases suffer from the imbalance between tolerogenic and immunogenic functions of their immune system. Often pathogenesis is mediated by autoreactive B and T cells that escape central tolerance and react against self-antigens attacking healthy tissues in the body. In recent years Siglecs, sialic-acid-binding immunoglobulin (Ig)-like lectins, have gained attention as immune checkpoints for therapeutic interventions to dampen excessive immune responses and to restore immune tolerance in autoimmune diseases. Many Siglecs function as inhibitory receptors suppressing activation signals in various immune cells through binding to sialic acid ligands as signatures of self. In this review, we highlight potential of Siglecs in suppressing immune responses causing autoimmune diseases. In particular, we cover the roles of CD22 and Siglec-G/Siglec-10 in regulating autoreactive B cell responses. We discuss several functions of Siglec-10 in the immune modulation of other immune cells, and the potential of therapeutic strategies for restoring immune tolerance by targeting Siglecs and expanding regulatory T cells. Finally, we briefly review efforts evaluating Siglec-based biomarkers to monitor autoimmune diseases.

The impact of nanocarriers in the induction of antigen-specific immunotolerance in autoimmune diseases

Immunotolerance induction in an antigen-specific manner is the long-term goal of immunotherapy to treat autoimmune diseases. Nanocarriers (NCs) can be designed as a new generation of delivery systems to modulate the immune responses through targeted delivery of antigens and immunomodulators to antigen presenting cells (APCs). In this manuscript, several formulation factors in the preparation of NCs which affect their uptake using APCs and generation of tolerance have been reviewed. The physicochemical properties and composition of NCs have been shown to play essential roles in achieving the desired immunological outcome. Also, targeting of dendritic cells and macrophages as APCs and direct targeting of the autoreactive lymphocytes have been presented as two main ways for induction of antigen-specific tolerance by these tolerogenic nanocarriers (tNCs). These particles herald a promising approach to treat or even prevent unwanted immune reactions in humans specifically.

Induction of Tolerance to Therapeutic Proteins With Antigen-Processing Independent T Cell Epitopes: Controlling Immune Responses to Biologics

The immune response to exogenous proteins can overcome the therapeutic benefits of immunotherapies and hamper the treatment of protein replacement therapies. One clear example of this is haemophilia A resulting from deleterious mutations in the FVIII gene. Replacement with serum derived or recombinant FVIII protein can cause anti-drug antibodies in 20-50% of individuals treated. The resulting inhibitor antibodies override the benefit of treatment and, at best, make life unpredictable for those treated. The only way to overcome the inhibitor issue is to reinstate immunological tolerance to the administered protein. Here we compare the various approaches that have been tested and focus on the use of antigen-processing independent T cell epitopes (apitopes) for tolerance induction. Apitopes are readily designed from any protein whether this is derived from a clotting factor, enzyme replacement therapy, gene therapy or therapeutic antibody.

Peptide allergen-specific immunotherapy for allergic airway diseases-State of the art

Allergen-specific immunotherapy (AIT) is the only means of altering the natural immunological course of allergic diseases and achieving long-term remission. Pharmacological measures are able to suppress the immune response and/or ameliorate the symptoms but there is a risk of relapse soon after these measures are withdrawn. Current AIT approaches depend on the administration of intact allergens, often comprising crude extracts of the allergen. We propose that the challenges arising from current approaches, including the risk of serious side-effects, burdensome duration of treatment, poor compliance and high cost, are overcome by application of peptides based on CD4⁺ T cell epitopes rather than whole allergens. Here we describe evolving approaches, summarize clinical trials involving peptide AIT in allergic rhinitis and asthma, discuss the putative mechanisms involved in their action, address gaps in evidence and propose future directions for research and clinical development.

Manipulating antigen presentation for antigen-specific immunotherapy of autoimmune diseases

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Specific immunotherapy is the ‘holy grail’ for treatment of autoimmunity.

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Antigens are delivered by either direct or indirect presentation mechanisms.

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Liver APC and steady state DC mediate distinct forms of immune regulation.

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Tr1 cell induction involves epigenetic modification of tolerance associated genes.

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Trials reveal that antigen-specific immunotherapy can control autoimmune diseases.

Current treatments for autoimmune diseases do not address the immune pathology underlying their initiation and progression and too often rely on non-specific immunosuppressive drugs for control of symptoms. Antigen-specific immunotherapy aims to induce tolerance selectively among the cells causing the disease while leaving the rest of the adaptive immune system capable of protecting against infectious diseases and cancers. Here we describe how novel approaches for antigen-specific immunotherapy are designed to manipulate antigen presentation and promote tolerance to specific self-antigens. This analysis points to liver antigen presenting cells, targeted by carrier particles, and steady-state dendritic cells, to which antigen-processing independent T-cell epitopes (apitopes) bind directly, as the principal targets for antigen-specific immunotherapy. Delivery of antigens to these cells holds great promise for effective control of this rapidly expanding group of diseases.

The Mechanism of Action of Antigen Processing Independent T Cell Epitopes Designed for Immunotherapy of Autoimmune Diseases

Immunotherapy with antigen-processing independent T cell epitopes (apitopes) targeting autoreactive CD4⁺ T cells has translated to the clinic and been shown to modulate progression of both Graves’ disease and multiple sclerosis. The model apitope (Ac1-9[4Y]) renders antigen-specific T cells anergic while repeated administration induces both Tr1 and Foxp3⁺ regulatory cells. Here we address why CD4⁺ T cell epitopes should be designed as apitopes to induce tolerance and define the antigen presenting cells that they target in vivo. Furthermore, we reveal the impact of treatment with apitopes on CD4⁺ T cell signaling, the generation of IL-10-secreting regulatory cells and the systemic migration of these cells. Taken together these findings reveal how apitopes induce tolerance and thereby mediate antigen-specific immunotherapy of autoimmune diseases.

A century later, still fighting back: antigen-specific immunotherapies for type 1 diabetes

Type 1 diabetes (T1D) is a chronic metabolic disease caused by the autoimmune destruction of insulin-producing β-cells. Ever since the 1920s, the fate of patients suffering from T1D was dramatically improved owing to the isolation and production of insulin, and the scientific field has largely progressed as a result of the evidence gathered about its underpinnings and mechanisms. The last years have seen this knowledge transformed into actual antigen-specific immunotherapies with potential to restore selectively the breach of tolerance to β-cell autoantigens and halt the autoimmune aggression. However, so far, the results of both prevention and reversion trials in T1D have been rather discouraging, so there is still an urgent need to optimize those immunotherapies and their associated factors, for example, posology and administration patterns, route and timing. In this review, we look back on what has been achieved in the last century and identify the main autoantigens driving the autoimmune attack in T1D. Then, we take a deep dive into the numerous antigen-specific immunotherapies trialed and the ones still at a preclinical phase, ranging from peptides, proteins and agent combinations to gene transfer, nanoparticles, cell-based strategies and novel approaches exploiting naturally occurring tolerogenic processes. Finally, we provide insight into the several features to be considered in a T1D clinical trial, the ideal time point for intervention and the biomarkers needed for monitoring the successful regulatory effect of the antigen-specific immunotherapy. Although further research and optimization remain imperative, the development of a therapeutic armamentarium against T1D autoimmunity is certainly advancing with a confident step.

Antigen-Specific Immunotherapy for Treatment of Autoimmune Liver Diseases

The liver is a critical organ in controlling immune tolerance. In particular, it is now clear that targeting antigens for presentation by antigen presenting cells in the liver can induce immune tolerance to either autoantigens from the liver itself or tissues outside of the liver. Here we review immune mechanisms active within the liver that contribute both to the control of infectious diseases and tolerance to self-antigens. Despite its extraordinary capacity for tolerance induction, the liver remains a target organ for autoimmune diseases. In this review, we compare and contrast known autoimmune diseases of the liver. Currently patients tend to receive strong immunosuppressive treatments and, in many cases, these treatments are associated with deleterious side effects, including a significantly higher risk of infection and associated health complications. We propose that, in future, antigen-specific immunotherapies are adopted for treatment of liver autoimmune diseases in order to avoid such adverse effects. We describe various therapeutic approaches that either are in or close to the clinic, highlight their mechanism of action and assess their suitability for treatment of autoimmune liver diseases.

Murine models for studying treatment, prevention and pathogenesis of FNAIT

Maternal alloimmunization to paternally inherited antigens on fetal/neonatal platelets can cause fetal/neonatal alloimmune thrombocytopenia (FNAIT) after antibody-mediated removal of platelets from the fetal circulation. The complications vary from mild bleeding symptoms to severe intracranial hemorrhage and subsequent neurological impairment or death. Studies on in vivo mechanisms are challenging to measure directly in pregnant women, rendering murine models as valuable and attractive alternatives, despite some critical differences between mice and men affecting the translational value. Here we present and discuss, the different murine models that substantially have increased our knowledge and understanding of FNAIT pathogenesis - as well as pre-clinical evaluation of therapeutic and preventive strategies.

Immunotherapy With Apitopes Blocks the Immune Response to TSH Receptor in HLA-DR Transgenic Mice

We have combined major histocompatibility complex-binding assays with immunization and tolerance induction experiments in HLA-DR3 transgenic mice to design apitopes (antigen-processing independent epitopes) derived from thyrotropin receptor (TSHR) for treatment of patients with Graves' disease (GD). A challenge model was created by using an adenovirus-expressing part of the extracellular domain of the thyrotropin receptor (TSHR289). This model was used to test whether current drug treatments for GD would have an impact on effective antigen-specific immunotherapy using the apitope approach. Furthermore, selected peptides were assessed for their antigenicity using peripheral blood mononuclear cell samples from patients with GD. A mixture of two immunodominant apitopes was sufficient to suppress both the T-cell and antibody response to TSHR when administered in soluble form to HLA-DR transgenic mice. Tolerance induction was not disrupted by current drug treatments. These results demonstrate that antigen-specific immunotherapy with apitopes from TSHR is a suitable approach for treatment of GD.