Identification of a highly promiscuous and an HLA allele-specific T-cell epitope in the birch major allergen Bet v 1: HLA restriction, epitope mapping and TCR sequence comparisons

Management of Cow's Milk Allergy from an Immunological Perspective: What Are the Options?

The immunological mechanism underlying Immunoglobuline E (IgE)-mediated cow’s milk allergy has been subject to investigations for many years. Identification of the key immune cells (mast cells, B cells) and molecules (IgE) in the allergic process has led to the understanding that avoidance of IgE-crosslinking epitopes is effective in the reduction of allergic symptoms but it cannot be envisioned as a treatment. For the treatment and prevention of IgE-mediated cow’s milk allergy, it is thought that the induction of a sustained state of immunological tolerance is needed. In this review, we will discuss various approaches aimed at achieving immunological tolerance and their success. Furthermore, we will speculate on the involved immunological mechanism.

T Cell Epitope Peptide Therapy for Allergic Diseases

Careful selection of dominant T cell epitope peptides of major allergens that display degeneracy for binding to a wide array of MHC class II molecules allows induction of clinical and immunological tolerance to allergen in a refined treatment strategy. From the original concept of peptide-induced T cell anergy arising from in vitro studies, proof-of-concept murine models and flourishing human trials followed. Current randomized, double-blind, placebo-controlled clinical trials of mixtures of T cell-reactive short allergen peptides or long contiguous overlapping peptides are encouraging with intradermal administration into non-inflamed skin a preferred delivery. Definitive immunological mechanisms are yet to be resolved but specific anergy, Th2 cell deletion, immune deviation, and Treg induction seem implicated. Significant efficacy, particularly with short treatment courses, in a range of aeroallergen therapies (cat, house dust mite, grass pollen) with inconsequential non-systemic adverse events likely heralds a new class of therapeutic for allergy, Synthetic Peptide Immuno-Regulatory Epitopes (SPIRE).

Immunoregulatory T cell epitope peptides: the new frontier in allergy therapy

Allergen immunotherapy (AIT) has been practised since 1911 and remains the only therapy proven to modify the natural history of allergic diseases. Although efficacious in carefully selected individuals, the currently licensed whole allergen extracts retain the risk of IgE-mediated adverse events, including anaphylaxis and occasionally death. This together with the need for prolonged treatment regimens results in poor patient adherence. The central role of the T cell in orchestrating the immune response to allergen informs the choice of T cell targeted therapies for down-regulation of aberrant allergic responses. Carefully mapped short synthetic peptides that contain the dominant T cell epitopes of major allergens and bind to a diverse array of HLA class II alleles, can be delivered intradermally into non-inflamed skin to induce sustained clinical and immunological tolerance. The short peptides from allergenic proteins are unable to cross-link IgE and possess minimal inflammatory potential. Systematic progress has been made from in vitro human models of allergen T cell epitope-based peptide anergy in the early 1990s, through proof-of-concept murine allergy models and early human trials with longer peptides, to the current randomized, double-blind, placebo-controlled clinical trials with the potential new class of synthetic short immune-regulatory T cell epitope peptide therapies. Sustained efficacy with few adverse events is being reported for cat, house dust mite and grass pollen allergy after only a short course of treatment. Underlying immunological mechanisms remain to be fully delineated but anergy, deletion, immune deviation and Treg induction all seem contributory to successful outcomes, with changes in IgG4 apparently less important compared to conventional AIT. T cell epitope peptide therapy is promising a safe and effective new class of specific treatment for allergy, enabling wider application even for more severe allergic diseases.

Novel birch pollen specific immunotherapy formulation based on contiguous overlapping peptides

Background

Synthetic contiguous overlapping peptides (COPs) may represent an alternative to allergen extracts or recombinant allergens for allergen specific immunotherapy. In combination, COPs encompass the entire allergen sequence, providing all potential T cell epitopes, while preventing IgE conformational epitopes of the native allergen.

Methods

Individual COPs were derived from the sequence of Bet v 1, the major allergen of birch pollen, and its known crystal structure, and designed to avoid IgE binding. Three sets of COPs were tested in vitro in competition ELISA and basophil degranulation assays. Their in vivo reactivity was determined by intraperitoneal challenge in rBet v 1 sensitized mice as well as by skin prick tests in volunteers with allergic rhinoconjunctivitis to birch pollen.

Results

The combination, named AllerT, of three COPs selected for undetectable IgE binding in competition assays and for the absence of basophil activation in vitro was unable to induce anaphylaxis in sensitized mice in contrast to rBet v 1. In addition no positive reactivity to AllerT was observed in skin prick tests in human volunteers allergic to birch pollen. In contrast, a second set of COPs, AllerT4-T5 displayed some residual IgE binding in competition ELISA and a weak subliminal reactivity to skin prick testing.

Conclusions

The hypoallergenicity of contiguous overlapping peptides was confirmed by low, if any, IgE binding activity in vitro, by the absence of basophil activation and the absence of in vivo induction of allergic reactions in mouse and human.

Trial registration

ClinicalTrials.gov NCT01719133

Peptide immunotherapy for childhood allergy - addressing translational challenges

Allergic sensitisation usually begins early in life. The number of allergens a patient is sensitised to can increase over time and the development of additional allergic conditions is increasingly recognised. Targeting allergic disease in childhood is thus likely to be the most efficacious means of reducing the overall burden of allergic disease. Specific immunotherapy involves administering protein allergen to tolerise allergen reactive CD4⁺ T cells, thought key in driving allergic responses. Yet specific immunotherapy risks allergic reactions including anaphylaxis as a consequence of preformed allergen-specific IgE antibodies binding to the protein, subsequent cross-linking and mast cell degranulation. CD4⁺ T cells direct their responses to short "immunodominant" peptides within the allergen. Such peptides can be given therapeutically to induce T cell tolerance without facilitating IgE cross-linking. Peptide immunotherapy (PIT) offers attractive treatment potential for allergic disease. However, PIT has not yet been shown to be effective in children. This review discusses the immunological mechanisms implicated in PIT and briefly covers outcomes from adult PIT trials. This provides a context for discussion of the challenges for the application of PIT, both generally and more specifically in relation to children.

Interaction of allergens, major histocompatibility complex molecules, and T cell receptors: a 'ménage à trois' that opens new avenues for therapeutic intervention in type I allergy

T cells are major players in the initiation and perpetuation of the allergic immune response. In this review, we summarize the current knowledge on allergen recognition by T lymphocytes and address the components of the trimeric recognition complex: T cell receptors, major histocompatibility complex molecules, and allergen-derived peptides. Furthermore, possible implications of this scientific background for future therapeutic developments are discussed.

Naturally processed T cell-activating peptides of the major birch pollen allergen

BACKGROUND

Although antigen processing and presentation of allergens to CD4(+)T lymphocytes are key events in the pathophysiology of allergic disorders, they still remain poorly understood.

OBJECTIVE

To investigate allergen processing and presentation by dendritic cells using the major birch pollen allergen Bet v 1 as a model.

METHODS

Endolysosomal extracts of dendritic cells derived from patients with birch pollen allergy were used to digest Bet v 1. Dendritic cells were pulsed with Bet v 1, and peptides were eluted from MHC class II molecules. Peptides obtained by either approach were sequenced by tandem mass spectrometry. Bet v 1-specific T-cell cultures were stimulated with HLA-DR-eluted Bet v 1-derived peptides. Bet v 1-specific T-cell lines were generated from each patient and analyzed for epitope recognition.

RESULTS

A high proportion of Bet v 1 remained intact for a long period of endolysosomal degradation. The peptides that appeared early in the degradation process contained frequently recognized T-cell epitopes. Bet v 1-derived peptides eluted from MHC class II molecules corresponded to those generated by endolysosomal degradation, matched known T-cell epitopes, and showed T cell-activating capacity. The Bet v 1-specific T-cell line of each individual harbored T cells reactive with peptides located within the MHC class II-eluted Bet v 1-derived sequences demonstrating their occurrence in vivo.

CONCLUSION

We report for the first time how epitopes of allergens are generated and selected for presentation to T lymphocytes. The limited susceptibility of Bet v 1 to endolysosomal processing might contribute to its high allergenic potential.

Three-dimensional structure determines the pattern of CD4+ T-cell epitope dominance in influenza virus hemagglutinin

The structural context of a CD4(+) T-cell epitope is known to influence immunodominance at the level of antigen processing, but general rules have not emerged. Dominant epitopes of influenza virus hemagglutinin are found to be localized to the C-terminal flanks of conformationally stable segments identified by low crystallographic B-factors or high COREX residue stabilities. The bias toward C-terminal flanks is distinctive for antigens from the influenza virus. Dominant epitopes in antigens/allergens from other sources also localize to the flanks of stable segments but are found on either N- or C-terminal flanks. Thus, dominance arises from preferential endoproteolytic nicking between stable segments followed by loading of fragment terminal regions into antigen-presenting proteins. This mechanism probably arose in order to direct CD4(+) responses onto sequences that are conserved for structure and function. Structure-guided presentation could enhance protection against genetically drifting influenza virus variants but most likely reduces protection against new viral subtypes.

Nitration Enhances the Allergenic Potential of Proteins

BACKGROUND

Recent investigations have shown that proteins, including Bet v 1a, are nitrated by exposure to polluted urban air. We have investigated immunogenic and allergenic properties of in vitro nitrated allergens in in vivo models.

METHODS

Untreated and nitrated samples of ovalbumin or Bet v 1a were compared for their ability to stimulate proliferation and cytokine secretion in splenocytes from DO11.10 or from sensitized BALB/c mice, and for their ability to induce specific immunoglobulin (Ig)G1, IgG2a and IgE in sensitized mice. Additionally, sera from birch pollen-allergic individuals were analysed for IgE and IgG specific for nitrated Bet v 1a.

RESULTS

Upon splenocyte stimulation with nitrated as compared with unmodified allergens, proliferation as well as interleukin 5 and interferon-gamma production were enhanced. Sera of mice sensitized with nitrated allergens showed elevated levels of specific IgE, IgG1 and IgG2a, compared with sera from mice sensitized with unmodified allergens. Moreover, cross-reactivity of antibodies against unrelated, nitrated allergens was observed in mice. We also found higher amounts of functional, specific IgE against nitrated than against untreated Bet v 1a in sera from birch pollen-allergic patients.

CONCLUSIONS

Our findings suggest that nitration enhances allergic responses, which may contribute to an increased prevalence of allergic diseases in polluted urban environments.

T-cell epitopes of food allergens

During recent years, a great deal of research has focused on the identification of food allergens, their characterization at the molecular level, and the investigation of immunological mechanisms responsible for food hypersensitivity. Allergen-reactive T-helper 2 cells play a central role in the pathophysiology of allergic diseases. After activation with allergens, this subset of CD4(+) T-lymphocytes produces a spectrum of cytokines that induce high serum levels of immunoglobulin E and eosinophilia, which, in turn, mediate the clinical symptoms. Furthermore, T-helper 2 cells are present in target organs during the late response to allergen exposure. The analysis of the allergic T-cell response, including cytokine production and the identification of T-cell epitopes, provides important information on the characteristics of food allergens. Therefore, in vitro cultures of allergen-specific T-cells derived from peripheral blood or different target organs have been of indispensable help. Results obtained from such studies may not only contribute to the understanding of cellular mechanisms underlying different types of food allergy but also to the development of novel strategies for immunotherapy of food allergy.

Computational tools for the study of allergens

Allergy is a major cause of morbidity worldwide. The number of characterized allergens and related information is increasing rapidly creating demands for advanced information storage, retrieval and analysis. Bioinformatics provides useful tools for analysing allergens and these are complementary to traditional laboratory techniques for the study of allergens. Specific applications include structural analysis of allergens, identification of B- and T-cell epitopes, assessment of allergenicity and cross-reactivity, and genome analysis. In this paper, the most important bioinformatic tools and methods with relevance to the study of allergy have been reviewed.

Cytokine profile, HLA restriction and TCR sequence analysis of human CD4+ T clones specific for an immunodominant epitope of Mycobacterium tuberculosis 16-kDa protein

The identification of immunodominant and universal mycobacterial peptides could be applied to vaccine design and have an employment as diagnostic reagents. In this paper we have investigated the fine specificity, clonal composition and HLA class II restriction of CD4+ T cell clones specific for an immunodominant epitope spanning amino acids 91-110 of the 16-kDa protein of Mycobacterium tuberculosis. Twenty-one of the tested 28 clones had a Th1 profile, while seven clones had a Th0 profile. None of the clones had a Th2 profile. While the TCR AV gene usage of the clones was heterogeneous, a dominant TCR BV2 gene family was used by 18 of the 28 clones. The CDR3 regions of BV2+ T cell clones showed variation in lengths, but a putative common motif R-L/V-G/S-Y/W-E/D was detected in 13 of the 18 clones. Moreover, the last two to three residues of the putative CDR3 loops, encoded by conserved BJ sequences, could also play a role in peptide recognition. Antibody blockade and fine restriction analysis using HLA-DR homozygous antigen-presenting cells established that 16 of 18 BV2+ peptide-specific clones were DR restricted and two clones were DR-DQ and DR-DP restricted. Additionally, five of the 18 TCRBV2+ clones recognized peptide 91-110 in association with both parental and diverse HLA-DR molecules, indicating their promiscuous recognition pattern. The ability of peptide 91-110 to bind a wide range of HLA-DR molecules, and to stimulate a Th1-type interferon (IFN)-gamma response more readily, encourage the use of this peptide as a subunit vaccine component.

Interaction among human leucocyte antigen-peptide-T cell receptor complexes in cow's milk allergy: the significance of human leucocyte antigen and T cell receptor-complementarity determining region 3 loops

BACKGROUND

Allergic individuals respond to only a few specific antigens, therefore allergic diseases are characterized by antigen specificity. Clarification of the mechanism of antigen specificity will lead to progress in the therapy of allergic diseases.

OBJECTIVES

The purpose of this study is to determine the specific association among T cell epitopes, antigen-presenting molecules and T cell receptor (TCR), and to determine the TCR usage in the pathogenesis of allergies using antigen-specific T cell clones (TCCs). The results can clarify the mechanism of the antigen specificity of allergic diseases, and provide new therapeutic possibilities using analogue peptides.

METHODS

Short-term T cell clones specific to beta-lactoglobulin (BLG) were established from peripheral blood mononuclear cells (PBMCs) collected from five patients allergic to cow's milk. We then identified the T cell epitopes and antigen-presenting molecules, and examined TCR usage. We also determined the sequence of the TCR-complementarity-determining region 3 (CDR3).

RESULTS

Six TCCs established from the five patients recognized three different peptides, and BLGp97-117 was recognized by four of the six TCCs. BLGp101-112 (KYLLFCMENSAE) was the core sequence in the fragment. Sequence analysis of TCR by the RT-PCR method revealed a marked heterogeneity in TCR usage, and similar amino acid sequences were recognized in the CDR3 region. Four of the six TCCs recognized BLG in association with human leucocyte antigen (HLA)-DRB1*0405 as antigen-presenting molecules.

CONCLUSION

We proposed the motif of the interaction between the HLA-DRB1*0405 allele and antigen peptide, and suggested that HLA-DRB1*0405 is an immunoregulatory gene product for T cell responses to BLG.

T cell receptor Vbeta expression in patients with allergic asthma before and after repeated low-dose allergen inhalation

The objective of this study was to identify disease-associated T cell subsets by characterizing the lung and blood T cell receptor (TCR) repertoires in allergic asthmatics before and after repeated low-dose allergen challenge. Peripheral blood lymphocyte (PBL) and bronchoalveolar lavage (BAL) samples were obtained from eight patients with allergic asthma before and after a period of repeated low-dose allergen inhalations. RT-PCR followed by Southern blot allowed the quantification of relative Vbeta gene segment usage. Thirteen healthy individuals served as controls at PBL level. PBL as well as BAL T cells of asthmatics displayed a higher usage of Vbeta3, Vbeta5.2, and Vbeta6.1-3 and a lower usage of Vbeta16, Vbeta18, and Vbeta19 compared to PBL of healthy controls. Interestingly, TCR Vbeta7 and Vbeta9 usage was significantly higher in BAL than in PBL in asthmatics before as well as after challenge. TCR repertoire alterations after allergen challenge differed between individuals, with relatively mild changes.

Identification of isoform-specific T-cell epitopes in the major timothy grass pollen allergen, Phl p 5

BACKGROUND

The involvement of CD4+ T cells in the pathophysiology of atopic disease is well established.

OBJECTIVE

To gain further insight into the activation requirements for allergen-specific T cells, we characterized epitope specificity, HLA restriction and T-cell receptor (TCR) usage for T cells specific to Phl p 5, the group 5 major allergen of the grass Phleum pratense.

METHODS

To identify the T-cell epitopes of Phl p 5, three Phl p 5-specific T-cell lines (TCLs) and 15 T-cell clones (TCCs) generated from the peripheral blood of three grass-allergic patients were tested with recombinant truncated Phl p 5a fragments and synthetic Phl p 5b peptides representing these two different recombinant Phl p 5 isoallergens. Additional activation experiments with HLA-subtyped antigen-presenting cells and flow cytometry analysis with TCR V-specific mAb were performed to further characterize the activation requirements for Phl p 5-specific TCCs.

RESULTS

At least nine distinct T-cell specificities were identified and the T-cell epitopes recognized differed considerably among the three patients. Most of the epitopes found were isoform-specific, whereas three epitopes were shared between Phl p 5a and 5b. Several human leucocyte antigen (HLA) class II molecules were involved in the recognition of Phl p 5. Different HLA restriction specificities were even found among TCCs specific to the same epitope region. All TCCs were TCR-alpha/beta positive, and an overrepresentation of TCR Vbeta 3.1+ clones among TCCs specific to Phl p 5 appear to exists as 31% (4/13) of the TCCs expressed TCR Vbeta 3.1 (compared with 5% TCR Vbeta 3.1+ T cells in human peripheral blood) with no correlation with epitope specificity or HLA restriction.

CONCLUSION

The T-cell reactivity of the three grass-allergic patients investigated shows that isoallergen-specific T-cell epitopes are found throughout the peptide backbone of Phl p 5a and Phl p 5b, and dominant T-cell epitopes of Phl p 5 were not identified. This indicates that a mixture of at least full-length rPhl p 5a and rPhl p 5b may be required to target the total Phl p 5-specific T-cell response of atopic patients.

The role of allergen-specific T cells in the allergic immune response: relevance to allergy vaccination

Recent research has elucidated many of the immunologic mechanisms that underlie atopic allergies. In particular, it has become clear that the role of CD4+ allergen-specific T cells is crucial for the induction of IgE and eosinophilia, factors that mediate the immediate hypersensitivity reaction and late-phase responses, respectively. Therefore, the reactivity patterns and activation requirements of allergen-specific T cells are important parameters for understanding and manipulating the allergic immune response. This review addresses these issues and discusses their relevance to the further development of allergy vaccines.