Isoforms of atopic allergens with reduced allergenicity but conserved T cell antigenicity: possible use for specific immunotherapy

Prospects for a vaccine in allergic diseases and asthma

Allergen-specific immunotherapy is widely used to treat allergic diseases, and current research is now focusing on the development of therapeutic vaccines acting on the IgE immune response following allergen challenge. The IgE immune response is dependent on genetic and environmental factors; production of IgE results from complex interactions among B cells, T cells, mast cells, basophils,surface and adhesion molecules and various cytokines. New vaccination methods under investigation involve allergen-specific or nonspecific methodology. Allergen-specific methods currently being developed include allergoids, passive saturation of effector cells, plasmid DNA immunisation and antigen-antibody complexes. The mechanisms of immunotherapy using allergen-specific methods differ with the allergens and the route of immunisation used (parenteral, intranasal, sublingual, oral or bronchial). Many vaccines being developed at present comprise synthetic, recombinant or highly purified subunit antigens, which although they have increased safety may also be less immunogenic.It is hoped that the addition of adjuvants will overcome this drawback. Methods of increasing the dose of allergen while reducing the possibility of an anaphylactic reaction include the use of non-anaphylactic isoforms of the allergens, alteration of the tertiary structure of the allergens and construction of minimal allergen-derived T cell peptides. Nonspecific approaches include humanised anti-IgE antibodies,moderation of the T(H)2 cytokine network and antisense oligodeoxynucleotide therapy.

The influence of recombinant production on the immunologic behavior of birch pollen isoallergens

BACKGROUND

Allergic reactions towards the birch major pollen allergen Bet v 1 are among the most common causes of spring pollinosis in the temperate climate zone of the Northern hemisphere. Natural Bet v 1 is composed of a complex mixture of different isoforms. Detailed analysis of recombinant Bet v 1 isoforms revealed striking differences in immunologic as well as allergenic properties of the molecules, leading to a classification of Bet v 1 isoforms into high, medium, and low IgE binding proteins. Especially low IgE binding Bet v 1 isoforms have been described as ideal candidates for desensitizing allergic patients with allergen specific immunotherapy (SIT). Since diagnosis and therapy of allergic diseases are highly dependent on recombinant proteins, continuous improvement of protein production is an absolute necessity.

METHODOLOGY

Therefore, two different methods for recombinant production of a low IgE binding Bet v 1 isoform were applied; one based on published protocols, the other by implementing latest innovations in protein production. Both batches of Bet v 1.0401 were extensively characterized by an array of physicochemical as well as immunological methods to compare protein primary structure, purity, quantity, folding, aggregation state, thermal stability, and antibody binding capacity.

CONCLUSION

The experiments demonstrated that IgE antibody binding properties of recombinant isoallergens can be significantly influenced by the production method directly affecting possible clinical applications of the molecules.

Antigen aggregation decides the fate of the allergic immune response

Previously, defined naturally occurring isoforms of allergenic proteins were classified as hypoallergens and therefore suggested as an agent for immunotherapy in the future. In this paper, we report for the first time the molecular background of hypoallergenicity by comparing the immunological behavior of hyperallergenic Betula verrucosa major Ag 1a (Bet v 1a) and hypoallergenic Bet v 1d, two isoforms of the major birch pollen allergen Betula verrucosa 1. Despite their cross-reactivity, Bet v 1a and Bet v 1d differ in their capacity to induce protective Ab responses in BALB/c mice. Both isoforms induced similar specific IgE levels, but only Bet v 1d expressed relevant titers of serum IgGs and IgAs. Interestingly, hypoallergenic Bet v 1d activated dendritic cells more efficiently, followed by the production of increased amounts of Th1- as well as Th2-type cytokines. Surprisingly, compared with Bet v 1a, Bet v 1d-immunized mice showed a decreased proliferation of regulatory T cells. Crystallographic studies and dynamic light scattering revealed that Bet v 1d demonstrated a high tendency to form disulfide-linked aggregates due to a serine to cysteine exchange at residue 113. We conclude that aggregation of Bet v 1d triggers the establishment of a protective Ab titer and supports a rationale for Bet v 1d being a promising candidate for specific immunotherapy of birch pollen allergy.

Coordinated and standardized production, purification and characterization of natural and recombinant food allergens to establish a food allergen library

Reliable diagnosis of food allergy is dependent on the analytes used. Approaches based on well-defined individual molecules of either natural or recombinant origin are likely to replace those based on food extracts in the future. Therefore, a library comprising well-characterized authentic natural and recombinant allergens was formed within the EC funded IP EuroPrevall. The advantages and disadvantages of including either natural or recombinant proteins are summarized, together with inclusion criteria such as purity and the implications of both allergenic and nonallergenic impurities for the performance of diagnostic assays. In order to harmonize quality criteria of the individual food allergens included in the library, as suite of characteristics and associated methodologies used to define them, was agreed. The application of these methods and impact on the quality and performance of the final purified food allergens included in the EuroPrevall allergen library is discussed.

Bioinformatics approaches to classifying allergens and predicting cross-reactivity

Allergenic proteins from very different environmental sources have similar sequences and structures. This fact may account for multiple allergen syndromes, whereby a myriad of diverse plants and foods may induce a similar IgE-based reaction in certain patients. Identifying the common triggering protein in these sources, in silico, can aid designing individualized therapy for allergen sufferers. This article provides an overview of databases on allergenic proteins, and ways to identify common proteins that may be the cause of multiple allergy syndromes. The major emphasis is on the relational Structural Database of Allergenic Proteins (SDAP []), which includes cross-referenced data on the sequence, structure, and IgE epitopes of over 800 allergenic proteins, coupled with specially developed bioinformatics tools to group all allergens and identify discrete areas that may account for cross-reactivity. SDAP is freely available on the Web to clinicians and patients.

A single amino acid substitution on the surface of a natural hevein isoform (Hev b 6.0202), confers different IgE recognition

Decreased immune reactivity of isoforms of major allergens has been reported. However, such claims have always been based on experiments with recombinant proteins. This work describes the molecular and physicochemical characterization of a hevein (Hev b 6.0201) natural isoform (Hev b 6.0202), which is present in rubber latex from Hevea brasiliensis. The isoallergen has a single substitution Asn14Asp, which gives rise to local differences in the surface potential, as observed from the crystal structure presented here. Besides, ELISA inhibition using serum pools of adult and pediatric patients showed reduced IgE-binding capacity ( approximately 27%) with the isoallergen. Overall, these results are relevant to delineate crucial residues involved in this dominant discontinuous epitope.

Emerging anti-inflammatory agents for allergic rhinitis

Allergic rhinitis (AR) is a high-prevalence disease, affecting 10-15% of the general population. AR is sustained by an IgE-mediated reaction, and by a complex inflammatory network of cells, mediators and cytokines that becomes chronic when exposure to allergen persists. A T helper 2 (TH2)-biased immune response is the basis for the allergic inflammation. The current therapeutic strategy is mainly based on drugs (antihistamines, nasal corticosteroids, cromones, decongestants) and allergen immunotherapy. Drugs are overall effective in controlling symptoms, but do not modify the immune background that leads to allergic inflammation, and safety concerns may be present especially for prolonged treatments. Immunotherapy can modify the allergic response, but there is still space for improvement. Nowadays, several approaches are under investigation to optimise the management of AR. On one hand, new drugs and antimediators are being developed; on the other hand, attempts are made to selectively block relevant signal pathways of allergic reaction. Finally, one of the major goals is to modify the TH2-biased immune response by improving the characteristics and modes of action of allergen immunotherapy.

Mutational analysis of amino acid positions crucial for IgE-binding epitopes of the major apple (Malus domestica) allergen, Mal d 1

BACKGROUND

Individual amino acid residues of the major birch pollen allergen, Bet v 1, have been identified to be crucial for IgE recognition. The objective of the present study was to evaluate whether this concept was applicable for the Bet v 1-homologous apple allergen, Mal d 1.

METHODS

A Mal d 1 five-point mutant was produced by PCR techniques, cloned into pMW 172 and expressed in Escherichia coli BL21(DE3) cells. To evaluate the allergenic properties of the engineered protein compared to Mal d 1 wild-type IgE immunoblotting, ELISA, peripheral blood monocytes proliferation assays, and skin prick tests were performed.

RESULTS

The Mal d 1 mutant showed reduced capacity to bind specific IgE as compared to wild-ype Mal d 1 in in vitro assays in the majority of the sera tested. In ELISA, 10 out of 14 serum samples displayed an 88-30% decrease in IgE binding to Mal d 1 mutant compared to wild-type Mal d 1. Skin prick tests in apple-allergic patients (n = 2) confirmed the markedly decreased ability of the Mal d 1 mutant to induce allergic reactions in vivo. However, the relevant T cell epitopes were present in the mutated molecule according to peripheral blood mononuclear cell proliferation assays.

CONCLUSIONS

Our findings suggest that it is possible to modulate the IgE-binding properties of allergens by single amino acid substitutions at crucial positions which might be useful for future immunotherapy of birch-pollen-associated food allergies which are not ameliorated by birch pollen immunotherapy.

Immunoglobulin E reactivity of native Blo t 5, a major allergen of Blomia tropicalis

BACKGROUND

Blo t 5 is a major allergen of Blomia tropicalis and its complementary DNA (cDNA) has been expressed in both prokaryotic and eukaryotic expression systems. Although the recombinant Blo t 5 has been well characterized, relatively less is known about its native counterparts and the allergenicity comparison of the native and recombinant Blo t 5 allergens has not been reported.

OBJECTIVE

The aims of this study are to characterize the native counterpart of Blo t 5, and compare the allergenicity of native and recombinant Blo t 5 by in vivo and in vitro assays.

METHODS

Native Blo t 5 were purified by immuno-affinity chromatography and characterized by proteomic means. The allergenicity of the allergen was evaluated by skin prick tests, human IgE ELISA, ELISA inhibition and histamine release assays.

RESULTS

Native Blo t 5 consists of at least five distinct isoforms, ranging from pI 3 to 5.5. Allergenicity assessment of recombinant and native Blo t 5 based on skin reaction, IgE-binding capacity and histamine release in allergic individuals indicated that there was a good correlation between both forms of Blo t 5 in general. However, data from IgE ELISA inhibition assay revealed the presence of additional unique IgE epitopes in native Blo t 5.

CONCLUSIONS

At least five distinct isoforms of Blo t 5 have been identified. Comparative assessment of native and recombinant Blo t 5 revealed that the allergenicity of these two forms was similar but not completely identical suggesting that the various isoforms of native Blo t 5 may exhibit additional unique IgE epitopes.

Monoclonal IgE antibodies against birch pollen allergens: novel tools for biological characterization and standardization of allergens

BACKGROUND

IgE antibodies are key players in immediate hypersensitivity reactions. Allergen characterization and standardization is usually based on the sera of allergic patients, whereas monoclonal IgE antibodies specific for clinically relevant allergens are very rare.

OBJECTIVE

The aim of this study was to establish IgE mAbs specific for birch pollen allergens, because these are important inhalant allergens.

METHODS

IgE-producing hybridomas were identified by using the highly sensitive rat basophilic leukemia cell mediator release assay with enhanced allergen stimulation by additional cross-linking with birch pollen-specific IgG antibodies. The obtained IgE mAbs were characterized by immunologic methods and by cDNA sequencing.

RESULTS

Seven IgE mAbs specific for the birch pollen allergens Bet v 1 or Bet v 6 were obtained and were all biologically active in mast cell-based assays. Mediator release experiments with mAb combinations indicated that 2 different epitope regions were recognized on Bet v 1, whereas the 2 Bet v 6-specific mAbs bound to the same epitope region. After sensitization of rat basophilic leukemia cells with IgE mAbs, different amounts of Bet v 1 or Bet v 6 were detected in commercial diagnostic allergen reagents, whereas sensitization with polyclonal IgE resulted in similar allergenic potency of all products.

CONCLUSIONS

IgE mAbs represent promising novel tools for allergen characterization and component-resolved standardization of allergen extracts.

Molecular cloning and sequence analysis of full-length cDNAs encoding new group of Cyn d 1 isoallergens

BACKGROUND

Cyn d 1, the major allergen of Bermuda grass pollen, contains some acidic/basic isoforms. The N-terminal amino acid sequences of some acidic Cyn d 1 isoforms were found to be different from those of Cyn d 1 cDNA clones identified previously.

METHODS

A predicted 17-meric oligonucleotide probe was designed to fish the unidentified isoallergen cDNAs out of BGP cDNA library. The reactive clones were isolated and verified by sequencing. Two of them were expressed in the yeast Pichia pastoris to obtain recombinant Cyn d 1 proteins.

RESULTS

All four cDNA clones encode the full-length Cyn d 1 with mature proteins of 244 amino acid residues. A 97-99% identity was found among the deduced amino acids of these four clones while an 86% identity was elicited between the four clones and the ones previously identified. The predicted isoelectric focusing (pI) values of the newly identified Cyn d 1s are acidic while pIs of the previously identified Cyn d 1s are basic. The two recombinant acidic Cyn d 1 proteins possess the epitopes recognized by mouse and rabbit polyclonal anti-Cyn d 1 antibodies, and have human IgE-binding capacity as revealed by immunodot assay.

CONCLUSIONS

The present study identified full-length cDNAs encoding new isoallergens of Cyn d 1, and separated Cyn d 1 gene into an acidic group and a basic group.

Use of altered peptide ligands to modulate immune responses as a possible immunotherapy for allergies

Allergies are dramatically increasing in prevalence, and the management of these diseases is a heavy burden on the health-care systems of developed countries. In recent years, many efforts have been made to improve the therapy of allergies and to develop new approaches for immunotherapy. Here we briefly review the use of peptides to modulate T-cell responses to allergens. We focus mainly on the possibility of using altered peptide ligands (APLs), i.e., peptides tailored on immunodominant T epitopes and bearing a single amino-acid substitution, as a tool to modulate immune responses to allergens. These peptides may be recognized by the specific T cells triggered by the agonist peptides, but they are unable to elicit T-cell responses; thus, they could be ideal candidates to modulate immune responses to allergens. The availability of these peptides could allow new approaches for immunotherapies.

Future directions for allergen immunotherapy

Over the last 30 years several approaches to modify immunotherapy have been tested, including allergoids, alum precipitation, and most recently peptides. However, none of these have replaced the traditional regimens. Over the same period our scientific understanding of allergic disease has been transformed. Today it is possible to identify and monitor changes occurring during treatment and to target many different aspects of the immune system. Recombinant technology provides a powerful technique both for sequencing proteins and producing allergens in commercial quantities. The recombinant proteins can be modified by site-directed mutagenesis so as to decrease their reactivity with IgE antibodies while maintaining reactivity with T cells. Knowledge of the tertiary structure of allergens will make it simpler to identify and change surface epitopes. A completely different approach is to use plasmids to introduce the genes for an allergen. The strength of this technique is that the plasmid can be designed to control expression and also to influence the cytokine profile of the response or the isotype of antibodies produced. Finally, different adjuvants can be used with proteins to alter the response. These include IL-12, immunostimulatory sequences of DNA, and bacterial proteins such as those used in HibVax. It is now possible to identify the cells that control the immune response to allergens and to design treatments that will either downregulate or change the response of T cells. The challenge is to transform this information into an effective treatment for allergic disease.