Induction of rapid T cell activation and tolerance by systemic presentation of an orally administered antigen

Oral tolerance to prevent anti-drug antibody formation in protein replacement therapies

Protein based therapeutics have successfully improved the quality of life for patients of monogenic disorders like hemophilia, Pompe and Fabry disease. However, a significant proportion of patients develop immune responses towards intravenously infused therapeutic protein, which can complicate or neutralize treatment and compromise patient safety. Strategies aimed at circumventing immune responses following therapeutic protein infusion can greatly improve therapeutic efficacy. In recent years, antigen-based oral tolerance induction has shown promising results in the prevention and treatment of autoimmune diseases, food allergies and can prevent anti-drug antibody formation to protein replacement therapies. Oral tolerance exploits regulatory mechanisms that are initiated in the gut associated lymphoid tissue (GALT) to promote active suppression of orally ingested antigen. In this review, we outline general perceptions and current knowledge about the mechanisms of oral tolerance, including tissue specific sites of tolerance induction and the cells involved, with emphasis on antigen presenting cells and regulatory T cells. We define several factors, such as cytokines and metabolites that impact the stability and expansion potential of these immune modulatory cells. We highlight preclinical studies that have been performed to induce oral tolerance to therapeutic proteins or enzymes for single gene disorders, such as hemophilia or Pompe disease. These studies mainly utilize a transgenic plant-based system for oral delivery of antigen in conjugation with fusion protein technology that favors the prevention of antigen degradation in the stomach while enhancing uptake in the small intestine by antigen presenting cells and regulatory T cell induction, thereby promoting antigen specific systemic tolerance.

Strategies of adoptive T -cell transfer to treat refractory viral infections post allogeneic stem cell transplantation

Background

Allogeneic hematopoietic stem cell transplantation (HSCT) can expose patients to a transient but marked immunosuppression, during which viral infections are an important cause of morbidity and mortality. Adoptive transfer of virus-specific T cells is an attractive approach to restore protective T -cell immunity in patients with refractory viral infections after allogeneic HSCT.

Objectives

This narrative review summarizes clinical evidence and developments of almost 30 years of adoptive T -cell transfer. The review is based on evidence extracted from PubMed searches and the clinical and experimental work of the authors.

Content

Viral infections after HSCT are frequently caused by the endogenous reactivation of persistent pathogens such as cytomegalovirus (CMV), Epstein-Barr virus (EBV), and adenovirus (AdV). Current antiviral medication is not satisfactory and does not treat the underlying pathophysiology which is the lack of specific T -cell immunity. Adoptive transfer of virus-specific T cells could be a potentially curative, pathogen-specific, and non-toxic treatment providing long-term immunity against the virus. The isolation of virus-specific T cells from a healthy donor and infusion into a recipient is known as adoptive T -cell transfer and has been performed in many patients using different treatment protocols. Based on basic research, new isolation protocols aim at a safe and fast availability of cellular products for adoptive T -cell transfer. We summarize preclinical and clinical data on each of the main pathogens and on the technical approaches currently available to target either single antigens or even multiple pathogens.

Conclusion

Cellular therapy is considered as one of the major recent breakthroughs in medicine. Translation of this individualized treatment into first-line clinical routine is still limited. Main hurdles are availability of the technique, limited compatibility of classical phase III designs with cellular therapy, and regulatory restrictions. Multinational efforts are required to clarify the status of cellular treatment in first-line clinical routine with the overall objective to strengthen evidence-based treatment guidelines for the treatment of refractory viral infections post HSCT.

A selective window after the food-intake period favors tolerance induction in mesenteric lymph nodes

Biological rhythms are periodic oscillations that occur in the physiology of the organism and the cells. The rhythms of the immune system are strictly regulated and the circadian alteration seems to have serious consequences. Even so, it is not clear how the immune cells of the intestinal mucosa synchronize with the external environment. Besides, little is known about the way in which biological rhythms affect the critical functions of intestinal immunity, such as oral tolerance. We studied fluctuations in the relevant parameters of intestinal immunity at four different times throughout the day. By using multivariate statistical tools, we found that these oscillations represent at least three different time frames with different conditions for tolerance induction that are altered in Per2ko mice lacking one of the clock genes. Our results allowed us to characterize a window in the final stage of the dark phase that promotes the induction of specific regulatory populations and favors its location in the lamina propria. We show here that, at the end of the intake, the entry of luminal antigens, soluble factors, and leukocyte populations converge in the mesenteric lymph nodes (MLN) and display the greatest potential of the tolerogenic machinery.

V-set and Ig domain-containing 4 (VSIG4)-expressing hepatic F4/80+ cells regulate oral antigen-specific responses in mouse

Oral tolerance can prevent unnecessary immune responses against dietary antigens. Members of the B7 protein family play critical roles in the positive and/or negative regulation of T cell responses to interactions between APCs and T cells. V-set and Ig domain-containing 4 (VSIG4), a B7-related co-signaling molecule, has been known to act as a co-inhibitory ligand and may be critical in establishing immune tolerance. Therefore, we investigated the regulation of VSIG4 signaling in a food allergy and experimental oral tolerance murine models. We analyzed the contributions of the two main sites involved in oral tolerance, the mesenteric lymph node (MLN) and the liver, in VSIG4-mediated oral tolerance induction. Through the comparative analysis of major APCs, dendritic cells (DCs) and macrophages, we found that Kupffer cells play a critical role in inducing regulatory T cells (Tregs) and establishing immune tolerance against oral antigens via VSIG4 signaling. Taken together, these results suggest the possibility of VSIG4 signaling-based regulation of orally administered antigens.

Mucosal immune tolerance at the ocular surface in health and disease

The ocular surface is constantly exposed to environmental irritants, allergens and pathogens, against which it can mount a prompt immune response to preserve its integrity. But to avoid unnecessary inflammation, the ocular surface's mucosal immune system must also discriminate between harmless and potentially dangerous antigens, a seemingly complicated task. Despite its unique features, the ocular surface is a mucosal lining, and as such, it shares some homeostatic and pathophysiological mechanisms with other mucosal surfaces. The purpose of this review is to explore the mucosal homeostatic immune function of the ocular surface in both the healthy and diseased states, with a special focus on mucosal immunology concepts. The information discussed in this review has been retrieved by PubMed searches for literature published from January 1981 to October 2016.

Food allergy: immune mechanisms, diagnosis and immunotherapy

Food allergy is a pathological, potentially deadly, immune reaction triggered by normally innocuous food protein antigens. The prevalence of food allergies is rising and the standard of care is not optimal, consisting of food-allergen avoidance and treatment of allergen-induced systemic reactions with adrenaline. Thus, accurate diagnosis, prevention and treatment are pressing needs, research into which has been catalysed by technological advances that are enabling a mechanistic understanding of food allergy at the cellular and molecular levels. We discuss the diagnosis and treatment of IgE-mediated food allergy in the context of the immune mechanisms associated with healthy tolerance to common foods, the inflammatory response underlying most food allergies, and immunotherapy-induced desensitization. We highlight promising research advances, therapeutic innovations and the challenges that remain.

Peptide-MHC multimer-based monitoring of CD8 T-cells in HIV-1 infection and AIDS vaccine development

The use of MHC multimers allows precise and direct detecting and analyzing of antigen-specific T-cell populations and provides new opportunities to characterize T-cell responses in humans and animals. MHC-multimers enable us to enumerate specific T-cells targeting to viral, tumor and vaccine antigens with exceptional sensitivity and specificity. In the field of HIV/SIV immunology, this technique provides valuable information about the frequencies of HIV- and SIV-specific CD8(+) cytotoxic T lymphocytes (CTLs) in different tissues and sites of infection, AIDS progression, and pathogenesis. Peptide-MHC multimer technology remains a very sensitive tool in detecting virus-specific T -cells for evaluation of the immunogenicity of vaccines against HIV-1 in preclinical trials. Moreover, it helps to understand how immune responses are formed following vaccination in the dynamics from priming point until T-cell memory is matured. Here we review a diversity of peptide-MHC class I multimer applications for fundamental immunological studies in different aspects of HIV/SIV infection and vaccine development.

Analysis, Isolation, and Activation of Antigen-Specific CD4(+) and CD8(+) T Cells by Soluble MHC-Peptide Complexes

T cells constitute the core of adaptive cellular immunity and protect higher organisms against pathogen infections and cancer. Monitoring of disease progression as well as prophylactic or therapeutic vaccines and immunotherapies call for conclusive detection, analysis, and sorting of antigen-specific T cells. This is possible by means of soluble recombinant ligands for T cells, i.e., MHC class I-peptide (pMHC I) complexes for CD8(+) T cells and MHC class II-peptide (pMHC II) complexes for CD4(+) T cells and flow cytometry. Here we review major developments in the development of pMHC staining reagents and their diverse applications and discuss perspectives of their use for basic and clinical investigations.

Antigen-specific regulation of IgE antibodies by non-antigen-specific γδ T cells

We re-examined the observation that γδ T cells, when transferred from mice tolerized to an inhaled conventional Ag, suppress the allergic IgE response to this Ag specifically. Using OVA and hen egg lysozyme in crisscross fashion, we confirmed the Ag-specific IgE-regulatory effect of the γδ T cells. Although only Vγ4(+) γδ T cells are regulators, the Ag specificity does not stem from specificity of their γδ TCRs. Instead, the Vγ4(+) γδ T cells failed to respond to either Ag, but rapidly acquired Ag-specific regulatory function in vivo following i.v. injection of non-T cells derived from the spleen of Ag-tolerized mice. This correlated with their in vivo Ag acquisition from i.v. injected Ag-loaded splenic non-T cells, and in vivo transfer of membrane label provided evidence for direct contact between the injected splenic non-T cells and the Vγ4(+) γδ T cells. Together, our data suggest that Ag itself, when acquired by γδ T cells, directs the specificity of their IgE suppression.

Self-reactive human CD4 T cell clones form unusual immunological synapses

Compared with influenza-specific T cells, self-reactive T cells from patients with multiple sclerosis or type 1 diabetes fail to slow down and do not form normal immunological synapses upon encounter with cognate self-peptide presented by MHC.

Recognition of self–peptide-MHC (pMHC) complexes by CD4 T cells plays an important role in the pathogenesis of many autoimmune diseases. We analyzed formation of immunological synapses (IS) in self-reactive T cell clones from patients with multiple sclerosis and type 1 diabetes. All self-reactive T cells contained a large number of phosphorylated T cell receptor (TCR) microclusters, indicative of active TCR signaling. However, they showed little or no visible pMHC accumulation or transport of TCR–pMHC complexes into a central supramolecular activation cluster (cSMAC). In contrast, influenza-specific T cells accumulated large quantities of pMHC complexes in microclusters and a cSMAC, even when presented with 100-fold lower pMHC densities. The self-reactive T cells also maintained a high degree of motility, again in sharp contrast to virus-specific T cells. 2D affinity measurements of three of these self-reactive T cell clones demonstrated a normal off-rate but a slow on-rate of TCR binding to pMHC. These unusual IS features may facilitate escape from negative selection by self-reactive T cells encountering very small amounts of self-antigen in the thymus. However, these same features may enable acquisition of effector functions by self-reactive T cells encountering large amounts of self-antigen in the target organ of the autoimmune disease.

Induced CD4+Foxp3+ regulatory T cells in immune tolerance

Regulatory T lymphocytes are essential to maintain homeostasis of the immune system, limiting the magnitude of effector responses and allowing the establishment of immunological tolerance. Two main types of regulatory T cells have been identified--natural and induced (or adaptive)-and both play significant roles in tuning down effector immune responses. Adaptive CD4(+)Foxp3(+) regulatory T (iTreg) cells develop outside the thymus under a variety of conditions. These include not only antigen presentation under subimmunogenic or noninflammatory conditions, but also chronic inflammation and infections. We speculate that the different origin of iTreg cells (noninflammatory versus inflammatory) results in distinct properties, including their stability. iTreg cells are also generated during homeostasis of the gut and in cancer, although some cancers also favor expansion of natural regulatory T (nTreg) cells. Here we review how iTreg cells develop and how they participate in immunological tolerance, contrasting, when possible, iTreg cells with nTreg cells.

Interrogating the repertoire: broadening the scope of peptide-MHC multimer analysis

Labelling antigen-specific T cells with peptide-MHC multimers has provided an invaluable way to monitor T cell-mediated immune responses. A number of recent developments in this technology have made these multimers much easier to make and use in large numbers. Furthermore, enrichment techniques have provided a greatly increased sensitivity that allows the analysis of the naive T cell repertoire directly. Thus, we can expect a flood of new information to emerge in the coming years.

Function of mucosa-associated lymphoid tissue in antibody formation

Abundant evidence supports the notion that human intestinal plasma cells are largely derived from B cells initially activated in gut-associated lymphoid tissue (GALT). Nevertheless, insufficient knowledge exists about the uptake, processing, and presentation of luminal antigens occurring in GALT to accomplish priming and sustained expansion of mucosal B cells. Also, it is unclear how the germinal center reaction so strikingly promotes class switch to IgA and expression of J chain, although the commensal microbiota appears to contribute to both diversification and memory. B-cell migration from GALT to the intestinal lamina propria is guided by rather well-defined adhesion molecules and chemokines/chemokine receptors, but the cues directing homing to secretory effector sites beyond the gut require better definition. In this respect, the role of human Waldeyer's ring (including adenoids and the palatine tonsils) as a regional mucosa-associated lymphoid tissue must be better defined, although the balance of evidence suggests that it functions as nasopharynx-associated lymphoid tissue (NALT) like the characteristic NALT structures in rodents. Altogether, data suggest a remarkable compartmentalization of the mucosal immune system that must be taken into account in the development of effective local vaccines to protect specifically the airways, small and large intestines, and the female genital tract.

Signals elicited at the intestinal epithelium upon chitosan feeding contribute to immunomodulatory activity and biocompatibility of the polysaccharide

Chitosan is a copolymer of N-acetylglucosamine and glucosamine derived from chitin with several applications in pharmaceutical and medical fields. This polysaccharide exhibits adjuvant properties in mucosal immune responses of humans, rats and mice. Characterization of signals elicited by chitosan at the intestinal epithelium could explain its immunomodulatory activity and biocompatibility. We fed normal rats with single doses of chitosan and 16h later, we purified intestinal epithelial cells (IECs) to assess immune and biochemical parameters. Following chitosan administration, mRNA expression and release of several cytokines and chemokines increased, injury markers maintained constitutive levels and MHC type II molecule expression was augmented. IEC supernatants showed higher levels of IL-10, IL-6 and TGF-beta. Arginase activity of IECs increased upon chitosan interaction in vivo and in vitro. Together, after chitosan feeding, mild activation of IECs occurs in vivo, with production of regulatory factors that could be relevant for its biocompatibility and immunomodulatory effects.

T-bet and pSTAT-1 expression in PBMC from coeliac disease patients: new markers of disease activity

Coeliac disease (CD) is considered a T cell-mediated autoimmune disease, and up-regulation of T-bet and phosphorylated signal transducers and activators of transcription (pSTAT)1, key transcription factors for the development of T helper type 1 (Th1) cells, has been described in the mucosa of patients with untreated CD. Using transcription factor analysis, we investigated whether T-bet and pSTAT1 expressions are up-regulated in the peripheral blood of CD patients and correlate with disease activity. Using flow cytometry, we analysed T-bet, pSTAT1 and pSTAT3 expression in CD4(+), CD8(+) T cells, CD19(+) B cells and monocytes from peripheral blood of 15 untreated and 15 treated CD patients and 30 controls, and longitudinally in five coeliac patients before and after dietary treatment. We evaluated using enzyme-linked immunosorbent assay (ELISA), interferon (FN)-gamma, interleukin (IL)-17 and IL-10 production by peripheral blood mononuclear cell (PBMC) cultures. T-bet expression in CD4(+), CD8(+) T cells, CD19(+) B cells and monocytes and IFN-gamma production by PBMC was higher in untreated than in treated CD patients and controls. pSTAT1 expression was higher in CD4(+)T cells, B cells and monocytes from untreated than from treated CD patients and controls. pSTAT3 was increased only in monocytes from untreated patients compared with CD-treated patients and controls. The data obtained from the longitudinal evaluation of transcription factors confirmed these results. Flow cytometric analysis of pSTAT1 and T-bet protein expression in peripheral blood mononuclear cells could be useful and sensible markers in the follow-up of CD patients to evaluate disease activity and response to dietary treatment.

Sequential role of plasmacytoid dendritic cells and regulatory T cells in oral tolerance

BACKGROUND & AIMS

Orally induced tolerance to environmental allergens prevents deleterious, systemic, delayed-type hypersensitivity responses via immune suppression mechanisms believed to include either anergy/deletion of specific effector T cells or active suppression by CD4(+)CD25(+) regulatory T cells (Tregs). The aim of this study was to investigate whether and how antigen (Ag) penetration through the gut orchestrates these 2 distinct mechanisms.

METHODS

Using a model of allergic contact dermatitis (ACD) mediated by hapten-specific cytolytic CD8(+) T cells and a T-cell transfer model of contact hypersensitivity in CD3epsilon-deficient mice, we studied the outcome of Ag gavage on CD8(+) effectors and Tregs.

RESULTS

Full protection from ACD by gavage with the relevant allergen required 2 coordinated events taking place first in gut-associated lymphoid tissues and then systemically. Allergen gavage induced deletion by plasmacytoid dendritic cells of a large fraction of Ag-specific CD8(+) T cells in liver and mesenteric lymph nodes and also triggered the suppressive function of Treg of secondary lymphoid organs. Residual Ag-specific CD8(+) T cells conditioned during this mucosal step are fully susceptible to suppression by activated Treg, which completely prevented their differentiation into ACD effectors, upon re-exposure to the allergen via the skin.

CONCLUSIONS

Thus, oral tolerance initiated in gut-associated lymphoid tissues by the plasmacytoid dendritic cells-mediated deletion of Ag-specific T cells is completed systemically by CD4(+)CD25(+) T cells. Biotherapies able to increase the susceptibility of effector T cells to the suppressive function of Treg may be valuable for the treatment of autoimmune and inflammatory diseases.

The biocompatible polysaccharide chitosan enhances the oral tolerance to type II collagen

Chitosan is a mucoadhesive polysaccharide that promotes the transmucosal absorption of peptides and proteins. At mucosal sites chitosan exhibits immunomodulatory activities and stimulates the release of regulatory cytokines. Herein we evaluated the effect of the co-administration of chitosan in the tolerance to type II collagen (CII) using an experimental model of arthritis. Rats were fed diluent (acetic acid), 1 mg CII, 1 mg chitosan or 1 mg CII + 1 mg chitosan during 5 days before immunization with CII in Freund's complete adjuvant. Systemic effects were evaluated in draining lymph nodes after antigenic challenge or during the clinical evolution of arthritis. Specific antibodies, proliferation against CII and the production of interferon (IFN)-gamma and interleukin-10 were assessed. Clinical signs were observed 13-15 days after primary immunization. The CII : chitosan group presented the lowest incidence and developed moderate arthritis, with reduced levels of immunoglobulin (Ig)G2a anti-CII, a limited proliferation in draining lymph nodes and a lower release of IFN-gamma after restimulation with CII. Our results demonstrate that chitosan enhances the tolerance to an articular antigen with a decrease in the inflammatory responses and, as a consequence, an improvement in clinical signs.

Autochthonous liver tumors induce systemic T cell tolerance associated with T cell receptor down-modulation

The reason the adaptive immune system fails in advanced liver tumors is largely unclear. To address this question, we have developed a novel murine model that combines c-myc-induced autochthonous tumorigenesis with expression of a cognate antigen, ovalbumin (OVA). When c-myc/OVA transgenic mice were crossed with liver-specific inducer mice, multifocal hepatocellular carcinomas co-expressing OVA developed in a tetracycline-dependent manner with a short latency and 100% penetrance. Transferred OVA-specific T cells, although infiltrating the tumor at high numbers, were hyporesponsive, as evidenced by a lack of in vivo cytotoxicity and interferon gamma production. This allowed the tumor to progress even in the presence of large numbers of antigen-specific T cells and even after vaccination (OVA+CpG-DNA). Interestingly, T cell receptor down-modulation was observed, which may explain antigen-specific hyporesponsiveness. This model is helpful in understanding liver cancer-specific mechanisms of T cell tolerance and dissection of antigen-specific and nonspecific mechanisms of immunotherapies in the preclinical phase.

Splenic Dendritic Cells from Antigen-Fed Mice Induced Antigen-Specific T Cell Unresponsiveness in vivo

While it is well-known that orally fed antigens induce systemic T cell tolerance (oral tolerance), the mechanism by which this occurs, however, remains unclear. In the present study, we examined the role of splenic dendritic cells (DCs) in the process of oral tolerance induction and/or maintenance, by using an adoptive transfer system of antigen (Ag)-specific CD4(+) T cells from ovalbumin (OVA)-specific T cell receptor transgenic mice and DCs from OVA-fed BALB/c mice. Transfer of splenic DCs from OVA-fed mice reduced IL-2 productivity and the proliferative activity of pre-transferred Ag-specific CD4(+) T cells to ex vivo Ag stimulation. There were no changes in expression levels of costimulatory molecules on DCs from OVA-fed mice. Our results show that orally administered Ags induce systemic T cell unresponsiveness through splenic DCs without inducing cell division of T cells, thus providing evidence that splenic DCs are involved in oral tolerance induction.

Plasmacytoid dendritic cells mediate oral tolerance

Oral tolerance prevents oral sensitization to dietary antigens (Ags), including proteins and haptens, and development of delayed-type hypersensitivity (DTH) responses. We showed here that plasmacytoid dendritic cells (pDCs) prevented oral T cell priming and were responsible for systemic tolerance to CD4(+) and CD8(+) T cell-mediated DTH responses induced by Ag feeding. Systemic depletion of pDCs prevented induction of tolerance by antigen feeding. Transfer of oral Ag-loaded liver pDCs to naive recipient mice induced Ag-specific suppression of CD4(+) and CD8(+) T cell responses to protein and hapten, respectively. Liver is a site of oral Ag presentation, and pDCs appeared to induce anergy or deletion of Ag-specific T cells in the liver relatively rapidly via a CD4(+) T cell-independent mechanism. These data demonstrate that oral tolerance relies on Ag presentation by pDC to T cells and suggest that pDC could represent a key therapeutic target for intestinal and systemic inflammatory diseases.

Ovalbumin-protein sigma 1 M-cell targeting facilitates oral tolerance with reduction of antigen-specific CD4+ T cells

BACKGROUND & AIMS

The follicle-associated epithelium (FAE) plays key roles in antigen uptake and subsequent induction of mucosal immunity. In this study, we examined whether M-cell targeting using a protein antigen (Ag) delivery system would induce oral tolerance instead of enhancement of Ag-specific mucosal antibody (Ab) responses.

METHODS

Mice were fed different doses of a recombinant protein sigma 1 of reovirus genetically conjugated to ovalbumin (OVA-psigma1), psigma1 only, or phosphate-buffered saline (PBS) before oral challenge with OVA plus cholera toxin as mucosal adjuvant. OVA-specific Ab and CD4-positive (CD4(+)) T-cell responses were determined.

RESULTS

A low dose of OVA-psigma1 reduced anti-OVA Ab and CD4(+) T-cell responses in both mucosal and systemic lymphoid tissues. OVA/MHC I-A(d) tetramer staining showed that the numbers of OVA-specific CD4(+) T cells were significantly reduced in lamina propria of mice fed OVA-psigma1 than those fed psigma1 only or PBS only. In fact, Foxp3 expressing CD25(+) CD4(+) T cells were markedly increased in this tissue. Nonetheless, CD25(+) CD4(+) T cells from the spleen, mesenteric lymph nodes, and Peyer's patches of orally tolerized mice showed increased transforming growth factor beta1 (TGF-beta1) and interleukin-10 (IL-10) production compared with nontolerized mice.

CONCLUSIONS

These results show that an FAE M-cell targeting protein Ag delivery system facilitates oral tolerance induction because of a reduction in Ag-specific CD4(+) T cells and increased levels of TGF-beta1 and IL-10 producing, CD25(+) CD4(+) regulatory T cells in both systemic and mucosal lymphoid tissues.

MHC-peptide tetramers to visualize antigen-specific T cells

Mature T lymphocytes of the CD8 or CD4 classes bear alphabeta T cell receptors (TCR) that are specific for a molecular complex consisting of a major histocompatibility complex class I or II (MHC class I or II) molecule bound to a unique self or foreign peptide. Until recently, methods for monitoring the T cell immune response to a viral or tumor antigen were restricted primarily to functional assays based on limiting dilution analysis, because the lack of specific molecular reagents to identify clonal T cells obviated approaches to identify and enumerate specific T cells. Development of efficient methods to express and refold MHC class I molecules with synthetic peptides coincided with identification of specific protein sequences that provide the substrate for enzymatic biotinylation. This combination has led to the development of a straightforward method for generating synthetic TCR ligands, making them tetravalent to provide increased avidity, and labeling them through a streptavidin moiety with useful fluorescent tags such as fluorescein or phycoerythrin. This unit describes the preparation of MHC class I/peptide tetramers in detail, including bacterial expression and refolding of the MHC class I light chain, beta2-microglobulin (beta2m), as well as the formation of a complex consisting of the MHC class I heavy chain of interest, beta2m, and a chosen peptide.

Tracking antigen specific CD4+ T-cells with soluble MHC molecules

The advent of soluble MHC multimer technology has allowed for the flow-cytometric direct identification of specific-MHC restricted antigen-specific T cells in mixed cell populations and also enabled the direct phenotyping and cloning of these cells at the same time. To date, MHC multimers have been used in characterizing the adaptive T cell repertoire under infectious, cancerous, and autoimmune states and has increased our understanding of the dynamics of T-cell immunity. Recombinant MHC multimers have been produced where MHC-binding peptide antigens are either covalently or noncovalently bound to the MHC, with the latter having the advantage of the ability to use a single recombinant MHC to investigate multiple MHC-binding peptides and their interacting T cells. In this method we describe how to generate recombinant non-covalently bound peptide MHC-multimers in insect cells. MHC multimers are generated as tetravalent complexes using a streptavidin scaffold.

The impact of cell-bound antigen transport on mucosal tolerance induction

Mucosal surfaces are exposed continuously to a flood of foreign antigens demanding a tightly controlled balance between immunity and tolerance induction. Tolerance toward food and inhaled antigens, known as oral and respiratory tolerance, respectively, evokes a body-wide nonresponsiveness against the plethora of environmental antigens. Key issues in understanding the induction of mucosal tolerance relate to the site of antigen entrance, the mechanisms of antigen transport, and the exact anatomical location where lymphocytes meet their cognate antigens. In this regard, opposing ideas have been put forward: In one scenario, antigens taken up at mucosal surfaces are considered to spread throughout the body, thus potentially evoking tolerogenic immune responses in all secondary lymphoid organs. Alternatively, tolerance induction might be confined to the draining regional lymph nodes (LN). Recent observations strongly supported the latter scenario, emphasizing the importance of regional LN and their network of afferent lymphatics in this process. In this model, air-borne and intestinal antigens are captured at mucosal sites by dendritic cells, which then migrate exclusively in a CCR7-dependent way to draining regional LN. Tolerance is then induced actively by the activation of antigen-specific T cells, which are subsequently deleted, become anergic, or alternatively, differentiate into regulatory T cells. Thus, the concept of local induction of immune responses seems to hold true for the majority of immune reactions, regardless of whether they are tolerogenic or defensive in their outcome.

TCRβ Chain That Forms Peptide-Independent Alloreactive TCR Transfers Reduced Reactivity with Irrelevant Peptide/MHC Complex

A major feature of the TCR repertoire is strong alloreactivity. Peptides presented by allogeneic MHC are irrelevant for recognition by a subset of alloreactive T cells. To characterize peptide-independent TCRs at the molecular level, we forced the expression of a TCRbeta chain isolated from a peptide-independent alloreactive CD8+ T cell line. The alloreactive TCR repertoire in the transgenic mouse was peptide dependent. However, analysis of essential TCR contacts formed during the recognition of self-MHC-restricted Ag showed that fewer contacts with peptide were established by the transgenic TCRbeta chain, and that this was compensated by additional contacts formed by endogenous TCRalpha chains. Thus, reduced interaction with the peptide appears to be a transferable feature of the peptide-independent TCRbeta chain. In addition, these findings demonstrate that reactivity to peptides is preferred over the reactivity to MHC during the formation of the TCR repertoire.

The stimulatory potency of T cell antigens is influenced by the formation of the immunological synapse

T cell activation is predicated on the interaction between the T cell receptor and peptide-major histocompatibility (pMHC) ligands. The factors that determine the stimulatory potency of a pMHC molecule remain unclear. We describe results showing that a peptide exhibiting many hallmarks of a weak agonist stimulates T cells to proliferate more than the wild-type agonist ligand. An in silico approach suggested that the inability to form the central supramolecular activation cluster (cSMAC) could underlie the increased proliferation. This conclusion was supported by experiments that showed that enhancing cSMAC formation reduced stimulatory capacity of the weak peptide. Our studies highlight the fact that a complex interplay of factors determines the quality of a T cell antigen.

CD25+CD4+ Regulatory T Cells Develop in Mice Not Only During Spontaneous Acceptance of Liver Allografts but Also After Acute Allograft Rejection

BACKGROUND

Liver grafts transplanted across a major histocompatibility barrier are accepted spontaneously and induce donor specific tolerance in some species. Here, we investigated whether liver allograft acceptance is characterized by, and depends upon, the presence of donor reactive CD25CD4 regulatory T cells.

METHODS

CD25 and CD25CD4 T cells, isolated from CBA. Ca (H2) recipients of C57BL/10 (B10; H2) liver and heart allografts 10 days after transplantation, were transferred into CBA. Rag1 mice to investigate their influence on skin allograft rejection mediated by CD45RBCD4 effector T Cells.

RESULTS

Fully allogeneic B10 liver allografts were spontaneously accepted by naive CBA.Ca recipient mice, whereas B10 cardiac allografts were acutely rejected (mean survival time=7 days). Strikingly, however, CD25CD4 T cells isolated from both liver and cardiac allograft recipients were able to prevent skin allograft rejection in this adoptive transfer model. Interestingly, CD25CD4 T cells isolated from liver graft recipients also showed suppressive potency upon adoptive transfer. Furthermore, depletion of CD25CD4 T cells in primary liver allograft recipients did not prevent the acceptance of a secondary donor-specific skin graft.

CONCLUSIONS

Our data provide evidence that the presence of CD25CD4 regulatory T cells is not a unique feature of allograft acceptance and is more likely the result of sustained exposure to donor alloantigens in vivo.

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A defect in epithelial barrier integrity is not required for a systemic response to bacterial antigens or intestinal injury in T cell receptor-alpha gene-deficient mice

BACKGROUND AND AIMS

Genetically induced disruption of the intestinal epithelial barrier leads to development of intestinal inflammation. In the interleukin-10 gene-deficient inflammatory bowel disease (IBD) mouse model, for instance, a primary defect in intestinal epithelial integrity occurs before the development of enterocolitis. In humans, a causal role for epithelial barrier disruption is still controversial. Although studies with first-degree relatives of IBD patients suggests an underlying role of impaired barrier function, a primary epithelial barrier defect in IBD patients has not been confirmed. The purpose of this article is to examine whether a primary epithelial barrier disruption is a prerequisite for the development of intestinal inflammation or whether intestinal inflammation can develop in the absence of epithelial disruption. We examined the intestinal epithelial integrity of the T cell receptor (TCR)-alpha gene-deficient mouse model of IBD.

MATERIALS AND METHODS

In vivo colonic permeability, determined by mannitol transmural flux, was assessed in 6-week-, 12-week-, and 25-week-old TCR-alpha gene-deficient and wild-type control mice using a single-pass perfusion technique. Mice were scored for intestinal histological injury and intestinal cytokine levels measured in organ cultures. Systemic responses to bacterial antigens were determined through 48-h spleen cell cultures stimulated with sonicate derived from endogenous bacterial strains.

RESULTS

In contrast with previous findings in the interleukin-10 gene-deficient IBD model, TCR-alpha gene-deficient mice did not demonstrate evidence of primary intestinal epithelial barrier disruption at any age, despite developing a moderate to severe colitis within 12 weeks. A rise in intestinal interferon (IFN)-gamma levels preceded the onset of mucosal inflammation and then correlated closely with the degree of intestinal inflammation and injury. Spleen cells from TCR-alpha gene-deficient mice released IFN-gamma in response to stimulation with endogenous luminal bacterial antigens, a finding that suggests that the systemic response to bacterial antigens occurred independently of epithelial barrier disruption.

CONCLUSIONS

Intestinal inflammation and a systemic response to bacterial antigens can develop in the absence of a measurable disruption of intestinal permeability.

Chondroitin sulfate intake inhibits the IgE-mediated allergic response by down-regulating Th2 responses in mice

Chondroitin sulfate (CS) was administered orally to BALB/c mice immunized intraperitoneally with ovalbumin (OVA) and/or dinitrophenylated OVA. The titers of antigen-specific IgE and IgG1 in mouse sera were determined. The antigen-specific IgE production by mice fed ad libitum with CS was significantly inhibited. We also examined the effect of feeding CS on immediate-type hypersensitivity. One hour after antigen stimulation, the ears of mice fed with CS swelled less than those of the control mice. Furthermore, the rise in serum histamine in the mice fed with CS under active systemic anaphylaxis was significantly lower than that in the controls. We next examined the pattern of cytokine production by splenocytes from mice followed by re-stimulation with OVA in vitro. The splenocytes from the mice fed with CS produced less interleukin (IL)-5, IL-10, and IL-13 than those from the control group. In contrast, the production of interferon-gamma and IL-2 by the splenocytes of mice fed with CS was not significantly different from those in the control mice. In addition, the production of transforming growth factor-beta from the splenocytes of mice fed with CS was significantly higher than that of the control mice. Furthermore, we showed that the percentages of CD4(+) cells, CD8(+) cells, and CD4(+)CD25(+) cells in the splenocytes of mice fed with CS are significantly higher than those of the control. These findings suggest that oral intake of CS inhibits the specific IgE production and antigen-induced anaphylactic response by up-regulating regulatory T-cell differentiation, followed by down-regulating the Th2 response.

Cognate interaction between endothelial cells and T cells

Endothelial cells lining the blood vessels form a barrier between circulating immune cells and parenchymal tissue. While the molecular mechanisms involved in antigen-independent recruitment of leukocytes into infected tissue have been extensively studied, the mechanisms involving antigen-specific recruitment of T cells into tissue have remained largely elusive. Here I shall review the experimental evidence that endothelial cells function as antigen-presenting cells and in this function contribute first to regulation of immune responses and second, to antigen-specific recruitment of T cells.

Oral tolerance originates in the intestinal immune system and relies on antigen carriage by dendritic cells

Oral tolerance induction is a key feature of intestinal immunity, generating systemic nonresponsiveness to ingested antigens. In this study, we report that orally applied soluble antigens are exclusively recognized in the intestinal immune system, particularly in the mesenteric lymph nodes. Consequently, the initiation of oral tolerance is impeded by mesenteric lymphadenectomy. Small bowel transplantation reveals that mesenteric lymph nodes require afferent lymph to accomplish the recognition of orally applied antigens. Finally, oral tolerance cannot be induced in CCR7-deficient mice that display impaired migration of dendritic cells from the intestine to the mesenteric lymph nodes, suggesting that immunologically relevant antigen is transported in a cell-bound fashion. These results demonstrate that antigen transport via afferent lymphatics into the draining mesenteric lymph nodes is obligatory for oral tolerance induction, inspiring new therapeutic strategies to exploit oral tolerance induction for the prevention and treatment of autoimmune diseases.

Generation of functional HLA-DR*1101 tetramers receptive for loading with pathogen- or tumour-derived synthetic peptides

BACKGROUND

MHC class I-peptide tetramers are currently utilised to characterize CD8+ T cell responses at single cell level. The generation and use of MHC class II tetramers to study antigen-specific CD4+ T cells appears less straightforward. Most MHC class II tetramers are produced with a homogeneously built-in peptide, reducing greatly their flexibility of use. We attempted the generation of "empty" functional HLA-DR*1101 tetramers, receptive for loading with synthetic peptides by incubation. No such reagent is in fact available for this HLA-DR allele, one of the most frequent in the Caucasian population.

RESULTS

We compared soluble MHC class II-immunoglobulin fusion proteins (HLA-DR*1101-Ig) with soluble MHC class II protein fused with an optimised Bir site for enzymatic biotynilation (HLA-DR*1101-Bir), both produced in insect cells. The molecules were multimerised by binding fluorochrome-protein A or fluorochrome-streptavidin, respectively. We find that HLA-DR*1101-Bir molecules are superior to the HLA-DR*1101-Ig ones both in biochemical and functional terms. HLA-DR*1101-Bir molecules can be pulsed with at least three different promiscuous peptide epitopes, derived from Tetanus Toxoid, influenza HA and the tumour associated antigen MAGE-3 respectively, to stain specific CD4+ T cells. Both staining temperature and activation state of CD4+ T cells are critical for the binding of peptide-pulsed HLA-DR*1101-Bir to the cognate TCR.

CONCLUSION

It is therefore possible to generate a soluble recombinant HLA-DR*1101 backbone that is receptive for loading with different peptides to stain specific CD4+ T cells. As shown for other HLA-DR alleles, we confirm that not all the strategies to produce soluble HLA-DR*1101 multimers are equivalent.

Cross-presentation of oral antigens by liver sinusoidal endothelial cells leads to CD8 T cell tolerance

After ingestion, oral antigens distribute systemically and provoke T cell stimulation outside the gastrointestinal tract. Within the liver, scavenger liver sinusoidal endothelial cells (LSEC) eliminate blood-borne antigens and induce T cell tolerance. Here we investigated whether LSEC contribute to oral tolerance. Oral antigens were efficiently cross-presented on H-2K(b) by LSEC to naive CD8 T cells. Cross-presentation efficiency in LSEC but not dendritic cells was increased by antigen-exposure to heat or low pH. Mechanistically, cross-presentation in LSEC requires endosomal maturation, involves hsc73 and proteasomal degradation. H-2K(b)-restricted cross-presentation of oral antigens by LSEC in vivo induced CD8 T cell priming and led to development of CD8 T cell tolerance in two independent experimental systems. Adoptive transfer of LSEC from mice fed with antigen (ovalbumin) into RAG2-/- knockout mice, previously reconstituted with naive ovalbumin-specific CD8 T cells, prevented development of specific cytotoxicity and expression of IFN-gamma in CD8 T cells. Using a new transgenic mouse line expressing H-2K(b) only on endothelial cells, we have demonstrated that oral antigen administration leads to tolerance in H-2K(b)-restricted CD8 T cells. Collectively, our data demonstrate a participation of the liver, in particular scavenger LSEC, in development of CD8 T cell tolerance towards oral antigens.

MHC multimer technology: current status and future prospects

The detection of antigen-specific T cell responses by MHC multimer staining is rapidly becoming one of the core immunological techniques, and the technology to produce MHC multimers has been optimized substantially in recent years. Furthermore, recent work demonstrates the potential of high-throughput detection of T cell responses and suggests that manipulation of T cell responses through the use of multimeric MHC reagents is also feasible.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.