Luc Vander Elst

Major T cell epitope-containing peptides can elicit strong antibody responses

Peptides containing major T cell epitopes have the capacity to induce T cell anergy and have therefore been proposed for the treatment of allergic and autoimmune diseases. Such peptides should not be immunogenic, i.  e. should not contain a B cell recognition site. We have evaluated in BALB / c mice the therapeutic potential of a 15‐mer peptide (p21 – 35) derived from Der p2, a major allergen of the house dust mite Dermatophagoides pteronyssinus, which contains a dominant T cell epitope but is not recognized by antibodies to Der p2. Unexpectedly, p21 – 35 elicited strong immune responses, suggesting the presence of a cryptic B cell epitope. Similar results were obtained with mice of three additional MHC haplotypes. A core sequence of four amino acids (Ile‐Ile‐His‐Arg) corresponding to residues 28 – 31 was shared by the B and T cell epitopes. Critical residues for B cell recognition were Arg31 and Lys33, while Ile28 was essential for T cell recognition. A Lys33Ala mutant of p21 – 35 still activated T cells but had much reduced immunogenic properties, making it a suitable alternative peptide for T cell anergy induction. Careful investigation of the immunogenic potential of peptides used to induce T cell anergy should be carried out prior to their clinical application.

The Dermatophagoides pteronyssinus Group 2 Allergen Contains a Universally Immunogenic T Cell Epitope

The use of T cell epitope-containing peptides for the induction of anergy in allergen sensitization is limited by genetic restriction that could be circumvented by using universally immunogenic epitopes. We attempted to identify such epitopes on Dermatophagoides pteronyssinus group 2 allergen (Der p 2), a major allergen of D. pteronyssinus T cells from BALB/c (H-2d), C57BL/6 (H-2b), C3H (H-2k), and SJL (H-2s) mice that were immunized with rDer p 2, recognized an immunodominant region encompassing residues 21–35. A synthetic 21–35 peptide (p21–35) induced strong dose-dependent in vitro T cell proliferation with cells of the four mouse strains and required processing for MHC class II presentation. Substitution of Ile28 with Ala resulted in reduction of T cell proliferation in each strain. Ile28 could represent an important MHC class II anchoring residue for T cell response to p21–35. An immunodominant T cell epitope of Der p 2 therefore behaves as a universal epitope and could be a suitable candidate for T cell anergy induction.

Establishing an allergic eczema model employing recombinant house dust mite allergens Der p 1 and Der p 2 in BALB/c mice

The major house dust mite allergens Der p 1 and Der p 2 are prevalent inducers of eczema. Der p 1 is a cysteine protease disrupting epithelial barriers, whereas Der p 2 functionally mimics the LPS‐binding compound MD‐2 within the TLR4 complex. In this work, we tested the percutaneous sensitizing capacity of recombinant (r) Der p 1 and Der p 2 in BALB/c mice. Mice were sensitized by percutaneous application of low (10 μg/application) and high dose (100 μg) rDer p 1 or rDer p 2, or with rDer p 1 followed by rDer p 2. Allergen‐specific and total IgE antibodies were determined by ELISA. Eczema of BALB/c was classified by the itching score and corresponded to erosions. Infiltrating immune cells were identified by haematoxylin/eosin and Giemsa staining for eosinophils or mast cells, CD3 staining for T lymphocytes. Percutaneous treatments with rDer p 1, but not rDer p 2‐induced specific IgG1. However, cotreatment with rDer p 1 led to increase in anti‐Der p 2 IgG titres. Both allergens elicited skin erosions because of scratching, thickening of the epidermis, and eosinophil and T‐cell infiltration. Our data indicate that recombinant mite allergens in the absence of adjuvant are sufficient for inducing eczema in BALB/c mice. As the enzymatic activity of an allergen might be an important cofactor for specific sensitization via the skin, Der p 1 may act as adjuvant for other allergens too. The presented mouse model is suitable for investigating the mechanisms of allergic eczema.

MHC Class II-Restricted Epitopes Containing an Oxidoreductase Activity Prompt CD4+ T Cells with Apoptosis-Inducing Properties

Abrogating an unwanted immune response toward a specific antigen without compromising the entire immune system is a hoped-for goal in immunotherapy. Instead of manipulating dendritic cells and suppressive regulatory T cells, depleting effector T cells or blocking their co-stimulatory pathways, we describe a method to specifically inhibit the presentation of an antigen eliciting an unwanted immune reaction. Inclusion of an oxidoreductase motif within the flanking residues of MHC class II epitopes polarizes CD4+ T cells to cytolytic cells capable of inducing apoptosis in antigen presenting cells (APCs) displaying cognate peptides through MHC class II molecules. This novel function results from an increased synapse formation between both cells. Moreover, these cells eliminate by apoptosis bystander CD4+ T cells activated at the surface of the APC. We hypothesize that they would thereby block the recruitment of cells of alternative specificity for the same autoantigen or cells specific for another antigen associated with the pathology, providing a system by which response against multiple antigens linked with the same disease can be suppressed. These findings open the way toward a novel form of antigen-specific immunosuppression.

Thioreductase containing epitopes inhibit the development of type 1 diabetes in the NOD mouse model

Autoreactive CD4+ T cells recognizing islet-derived antigens play a primary role in type 1 diabetes. Specific suppression of such cells therefore represents a strategic target for the cure of the disease. We have developed a methodology by which CD4+ T cells acquire apoptosis-inducing properties on antigen-presenting cells after cognate recognition of natural sequence epitopes. We describe here that inclusion of a thiol-disulfide oxidoreductase (thioreductase) motif within the flanking residues of a single MHC class II-restricted GAD65 epitope induces GAD65-specific cytolytic CD4+ T cells (cCD4+ T). The latter, obtained either in vitro or by active immunization, acquire an effector memory phenotype and lyse APCs by a Fas–FasL interaction. Furthermore, cCD4+ T cells eliminate by apoptosis activated bystander CD4+ T cells recognizing alternative epitopes processed by the same APC. Active immunization with a GAD65 class II-restricted thioreductase-containing T cell epitope protects mice from diabetes and abrogates insulitis. Passive transfer of in vitro-elicited cCD4+ T cells establishes that such cells are efficient in suppressing autoimmunity. These findings provide strong evidence for a new vaccination strategy to prevent type 1 diabetes.

A Naturally-Processed Universal T Cell Epitope Is Located Within a Conserved Region of Der p 2: Implications for Allergen Sensitization and Immunotherapy

Background: Major allergens could represent a ‘port of entry’ to allergen polysensitization. The immunogenic properties of Der p 2 T cell epitopes were evaluated to test this hypothesis. Material and Methods: T cells were obtained from regional lymph nodes of mice belonging to four different haplotypes and used in proliferation assays using Der p 2 or synthetic peptides. Results: T cells from recombinant (r) Der p 2-immunized Balb/c mice (H-2d) proliferated to an immunodominant region encompassing residues 21–35, which also stimulates T cells of mice expressing three alternative haplotypes (H-2b, H-2k and H-2s), indicating the presence of a universal T cell epitope. Epitope mapping identified Ile28 as a critical H-2-binding residue for all four different haplotypes. p21–35 presents a sequence homology with FIS, another universal T cell epitope. FIS priming boosts immune responses to distinct weak immunogens. Balb/c mice primed with p21–35 or FIS produced stronger immune responses to transferrin upon administration of the latter than unprimed mice. Besides, this procedure profoundly affected the overall B cell response to rDer p 2. Conclusion: An immunodominant T cell epitope of Der p 2 behaves as a universal epitope and enhances responses to related and unrelated coadministered antigens. These findings have implications for the understanding of allergen polysensitization and for immunotherapy.