Special regulatory T-cell review: T-cell dependent suppression revisited

Site-directed Fragnomics and MD Simulations Approaches to Identify Interleukin-2 Inhibitors

INTRODUCTION

The aberrant expression of Interleukin-2 (IL2), the chief regulator of immunity, is associated with many auto-immune diseases. At present, there is no FDA approved drug targeting IL2, which puts forth the need for small molecular inhibitors to block IL2 and its receptor interaction.

METHODOLOGY

Herein, we used the contemporary fragnomics approach to design novel drug-like inhibitors targeting IL2. Briefly, the RECAP (Retrosynthetic Combinatorial Analysis Procedure) package implemented in MOE (Molecular Operating Environment check) software suite was utilised to obtain fragments fulfilling the 'rule of three' criteria for fragments. The binding site of IL2 was divided into three smaller grooves, and the fragments were docked to screen their affinity for a particular site, followed by site-directed RECAP synthesis.

RESULTS

A focused library of 10,000 compounds was prepared by re-combining the fragments according to their affinity for a particular site as observed in docking. Docking and subsequent analysis of newly synthesised compounds identified 40 privileged leads, presenting hydrogen bonding with basic residues of the pocket. A QSAR model was implied to predict the IC50 of the compounds and to analyse the electrostatic and hydrophobic contour maps. The resulting hits were found to be modest IL2 inhibitors with predicted inhibitory activity in the range of 5.17-4.40 nM. Further Dynamic simulation studies were carried out to determine the stability of the inhibitor-IL2 complex.

CONCLUSION

Our findings underline the potential of the novel compounds as valuable pharmacological agents in diseases characterised by IL2 overexpression.

Regulatory T cell-deficient scurfy mice develop systemic autoimmune features resembling lupus-like disease

Introduction

Scurfy mice are deficient in regulatory T cells (Tregs), develop a severe, generalized autoimmune disorder that can affect almost every organ and die at an early age. Some of these manifestations resemble those found in systemic lupus erythematosus (SLE). In addition, active SLE is associated with low Treg numbers and reduced Treg function, but direct evidence for a central role of Treg malfunction in the pathophysiology of lupus-like manifestations is still missing. In the present study, we characterize the multiorgan pathology, autoantibody profile and blood count abnormalities in scurfy mice and show their close resemblances to lupus-like disease.

Methods

Scurfy mice have dysfunctional Tregs due to a genetic defect in the transcription factor Forkhead box protein 3 (Foxp3). We analyzed skin, joints, lung and kidneys of scurfy mice and wild-type (WT) controls by conventional histology and immunofluorescence (IF) performed hematological workups and tested for autoantibodies by IF, immunoblotting and enzyme-linked immunosorbent assay. We also analyzed the intestines, liver, spleen and heart, but did not analyze all organs known to be affected in scurfy mice (such as the testicle, the accessory reproductive structures, the pancreas or the eyes). We transferred CD4⁺ T cells of scurfy or WT mice into T cell-deficient B6/nude mice.

Results

We confirm previous reports that scurfy mice spontaneously develop severe pneumonitis and hematological abnormalities similar to those in SLE. We show that scurfy mice (but not controls) exhibited additional features of SLE: severe interface dermatitis, arthritis, mesangioproliferative glomerulonephritis and high titers of anti-nuclear antibodies, anti-double-stranded DNA antibodies, anti-histone antibodies and anti-Smith antibodies. Transfer of scurfy CD4⁺ T cells (but not of WT cells) induced autoantibodies and inflammation of lung, skin and kidneys in T cell-deficient B6/nude mice.

Conclusion

Our observations support the hypothesis that lupus-like autoimmune features develop in the absence of functional Tregs.

Do Natural T Regulatory Cells become Activated to Antigen Specific T Regulatory Cells in Transplantation and in Autoimmunity?

Antigen specific T regulatory cells (T_reg) are often CD4⁺CD25⁺FoxP3⁺ T cells, with a phenotype similar to natural T_reg (nT_reg). It is assumed that nT_reg cannot develop into an antigen specific T_reg as repeated culture with IL-2 and a specific antigen does not increase the capacity or potency of nT_reg to promote immune tolerance or suppress in vitro. This has led to an assumption that antigen specific T_reg mainly develop from CD4⁺CD25⁻FoxP3⁻ T cells, by activation with antigen and TGF-β in the absence of inflammatory cytokines such as IL-6 and IL-1β. Our studies on antigen specific CD4⁺CD25⁺ T cells from animals with tolerance to an allograft, identified that the antigen specific and T_reg are dividing, and need continuous stimulation with specific antigen T cell derived cytokines. We identified that a variety of cytokines, especially IL-5 and IFN-γ but not IL-2 or IL-4 promoted survival of antigen specific CD4⁺CD25⁺FoxP3⁺ T_reg. To examine if nT_reg could be activated to antigen specific T_reg, we activated nT_reg in culture with either IL-2 or IL-4. Within 3 days, antigen specific T_reg are activated and there is induction of new cytokine receptors on these cells. Specifically nT_reg activated by IL-2 and antigen express the interferon-γ receptor (IFNGR) and IL-12p70 (IL-12Rβ2) receptor but not the IL-5 receptor (IL-5Rα). These cells were responsive to IFN-γ or IL-12p70. nT_reg activated by IL-4 and alloantigen express IL-5Rα not IFNGR or IL-12p70Rβ2 and become responsive to IL-5. These early activated antigen specific T_reg, were respectively named Ts1 and Ts2 cells, as they depend on Th1 or Th2 responses. Further culture of Ts1 cells with IL-12p70 induced Th1-like T_reg, expressing IFN-γ, and T-bet as well as FoxP3. Our studies suggest that activation of nT_reg with Th1 or Th2 responses induced separate lineages of antigen specific T_reg, that are dependent on late Th1 and Th2 cytokines, not the early cytokines IL-2 and IL-4.

T regulatory cells in B-cell malignancy - tumour support or kiss of death?

It is well established that T regulatory (Treg) cells counteract tumour immunity. However, conflicting results describing the role of Treg cells in haematological tumours warrant further investigations to clarify the interactions between Treg cells and the tumour. B-cell malignancy derives from different stages of B-cell development and differentiation in which T cells play a profound role. The transformed B cell may still be in need of T-cell help to thrive but simultaneously they may be recognized and destroyed by cytotoxic lymphocytes. Recent reports demonstrate that Treg cells can suppress and even kill B cells as part of their normal function to rescue the body from autoimmunity. An emerging body of evidence points out that Treg cells not only inhibit tumour-specific T cells but may also have a role in suppressing the progression of the B-cell tumour. In this review, we discuss the origin and function of Treg cells and their role in patients with B-cell tumours.

Emerging cellular networks for regulation of T follicular helper cells

The cellular networks that regulate humoral immune responses have been a focus of research over the past three decades. Studies have shown that inhibition of immune responses can be attributed to both suppressor T cells and B cells. More recently, T follicular helper (Tfh) cells have been identified as a target of immune regulation. Tfh cells are a subset of highly activated T helper cells specialized for providing cognate help to B cells during germinal center reactions. In this review, we describe emerging evidence for cellular networks that alter Tfh cell phenotype and function and regulate antibody production during the germinal center reaction. We discuss how these new findings influence our understanding of Tfh cells.

Immunologic similarities between selected autoimmune diseases and peanut allergy: possible new therapeutic approaches

Food allergies are an important medical problem in Westernized countries. Allergy to peanuts is a dramatic example of a food allergy that tends to be particularly severe and long-lived. This article examines food allergy-specifically peanut allergy-from the perspective that tolerance to foods is a normal state, just as tolerance to self-proteins is a normal state. From this vantage point, loss of tolerance to foods in food-allergic individuals can be viewed as parallel to the loss of tolerance to self-proteins in those with autoimmune diseases. Although our knowledge base is far from satisfactory, there are important similarities in the immunologic abnormalities that are characteristic of both peanut allergy and several autoimmune diseases. Delineation of these similarities may open the door to new therapeutic approaches for the treatment of severe food allergies.

Novel highly sensitive IL-10-beta-lactamase reporter mouse reveals cells of the innate immune system as a substantial source of IL-10 in vivo

In this study, we report on a novel, highly sensitive IL-10 reporter mouse based on the reporter enzyme β-lactamase and the fluorescence resonance energy transfer substrate coumarin-cephalosporin-fluorescein (4). In contrast to an IL-10 reporter mouse model that we generated by using enhanced GFP as reporter and allowed tracking IL-10 expression only in T cells, the IL-10-β-lactamase reporter (ITIB) mouse enables us to easily analyze and quantify IL-10 production at the single-cell level in all myeloid and lymphoid cell types. Furthermore, the ITIB mouse allows studying of the kinetics of IL-10 expression on a single-cell basis and provides a valuable tool for in vivo screening of cell type-specific IL-10-modulating drugs. Remarkably, the ITIB mouse revealed that, although a significant portion of each myeloid and lymphoid cell type produces IL-10, macrophages represent the major IL-10 producer population in several organs of naive mice. Moreover, using the examples of bacterial infection and transplantable skin melanoma models, we demonstrate the exceptional applicability of the ITIB mouse for the identification of IL-10-producing cells during immune responses in vivo. In this study, we identified tumor-infiltrating F4/80(+) macrophages as the major source for IL-10 in B16-F10 melanoma in vivo. During systemic infection with Yersinia enterocolitica, although the proportion of IL-10(+) cells increased in each myeloid and lymphoid cell type population, infiltrating CD11b(+)Ly6G(+) neutrophils represent a majority among IL-10-producing cells at the site of infection. We conclude that cells of the innate immune system that are involved in immune homeostasis or immune responses are substantial sources of IL-10.

The hygiene hypothesis revisited: role of materno-fetal interactions

For 20 years, the hygiene hypothesis has dominated attempts to explain the increasing prevalence of allergic disease. A causal link between maternal innate immune response during pregnancy and disease protection in the offspring was recently demonstrated. Central to this was a systemically diffused signal that downregulated Toll-like receptor expression in placental tissues. Herein we develop the hypothesis that maternal systemic regulatory mechanisms operational during pregnancy could impact allergic disease risk of the offspring, depending on the type of inflammatory response from which they originate. Classic microbial-derived, mild, subacute inflammation provides a protective signal, whereas allergic inflammation provides a negative one. Mild, subacute inflammation of pregnant women leads to systemically diffused signals manifest in the gestation-associated tissues and by the fetus and newborn as a dampened inflammatory response. The converse is true if the mother has allergic inflammation during pregnancy. In both cases, these impact on development of the airways and of balanced immune function at birth and in early postnatal life. Thus, we seem to be at the dawn of a new incarnation of the hygiene hypothesis in which the pregnant woman's inflammatory response is crucial to determining the child's likelihood of developing allergic disease.

Pathogenetic aspects of systemic lupus erythematosus with an emphasis on regulatory T cells

The development of autoimmune diseases is characterized by the breakdown of mechanism(s) that are responsible for maintaining immunological tolerance against self-structures in the periphery. Several aberrations of immune cells have been described so far. Most recently quantitative and/or qualitative defects of T cells with the capacity to suppress or regulate the proliferation of effector T cells in vitro - subsequently termed regulatory T cells (Treg) - have been suggested to substantially contribute to the imbalance of peripheral tolerance and trigger the outbreak of autoimmune reactions. The aim of this article is to summarize current knowledge about pathomechanisms that are involved in the development of autoimmunity with a special emphasis on the role of Treg in patients with systemic lupus erythematosus (SLE).

Oral tolerance: can we make it work?

Mucosal tolerance remains an attractive approach for the treatment of autoimmune and inflammatory diseases. The agents used in these treatments lack toxicity, can be easily administered, and enable the promotion of antigen-specific immune responses. The limited success of clinical trials over the past 2 decades has led to the fear that the beneficial effect observed in animal models cannot be repeated in humans. Successful application of mucosal tolerance for the treatment of human diseases will depend on strategies that target the correct cells in the gut-liver axis, improve antigen presentation, alter the administered dose and formulations, utilize potent mucosal adjuvants, develop immune biomarkers enabling follow-up of the effect, utilize combination therapies with other immune modulatory agents, and target the right patient populations. Here, we discuss 12 of the major questions related to oral tolerance and its clinical application to humans with immune-mediated disorders.

Murine CD8+ regulatory T lymphocytes: the new era

Regulatory T lymphocytes unequivocally play a major role in the maintenance of immunologic homeostasis. The first descriptions of regulatory T lymphocytes concerned CD8(+) cells, but this field was brought into discredit when some of its central tenets turned out to be erroneous. CD4(+) regulatory T cells took over and, with the help of newly developed molecular tools, rapidly were phenotypically and functionally characterized. We now know that these cells control a large variety of immune responses. However some observations of in vitro or in vivo immune regulation could not be explained with CD4(+) regulatory T cell activity and depended on the action of a variety of CD8(+) T cell populations. In recent years, substantial progress has been made in the phenotypic and functional characterization of CD8(+) regulatory T cells. These cells play a role in the control of intestinal immunity, immunopathology, and autoimmunity, as well as in immune privilege of the eye, in oral tolerance, and in prevention of graft-versus-host disease and graft-rejection. The suppressor effector mechanisms used by these cells are in part shared with CD4(+) regulatory T cells and in part unique to this population. We here review the current literature on naturally occurring and experimentally induced murine CD8(+) regulatory T-cell populations.