Allergy Vaccine Engineering: Epitope Modulation of Recombinant Bet v 1 Reduces IgE Binding but Retains Protein Folding Pattern for Induction of Protective Blocking-Antibody Responses

T cells specific to multiple Bet v 1 peptides are highly cross-reactive toward the corresponding peptides from the homologous group of tree pollens

Background

Allergens from Fagales trees frequently cause spring allergy in Europe, North America, and some parts of Asia. The definition of the birch homologous group, which includes birch (Bet v), oak (Que a), alder (Aln g), hazel (Cor a), hornbeam (Car b), beech (Fag s), and chestnut (Cas s), is based on high allergen sequence identity and extensive IgE cross-reactivity. Clinical effect was seen during the alder/hazel, birch, and oak pollen seasons after treatment with tree SLIT-tablets containing only birch allergen extract. Here, we characterize T-cell reactivity with respect to epitope specificities and cross-reactivity toward various Bet v 1 family members, (PR-10/group 1 major allergens). This cross-reactivity may be part of the immunological basis of clinical effect or cross-protection when exposed to birch homologous tree species.

Method

T-cell lines were generated from 29 birch-allergic individuals through stimulation of peripheral blood mononuclear cells (PBMCs) with birch/Bet v or oak/Que a allergen extracts. T-cell responses to allergen extracts, purified group 1 allergens, and overlapping 20-mer peptides (Bet v 1, Aln g 1, Cor a 1, and Que a 1) were investigated by T-cell proliferation and cytokine production. Cross-reactivity was evaluated based on Pearson's correlations of response strength and further investigated by flow cytometry using tetramer staining for homologous peptide pairs.

Results

T-cell reactivity toward extracts and group 1 allergens from across the birch homologous group was observed for birch/Bet v as well as oak/Que a T-cell lines. T-cell lines responded to multiple Bet v 1 homologous peptides from Aln g 1 and Cor a 1 and a subset of Que a 1 peptides. Significant Pearson's correlations between frequently recognized peptides derived from Bet v 1 and the corresponding peptides derived from alder, hazel, and oak strongly supported the T-cell cross-reactivity toward these allergens. Cross-reactivity between birch and birch homologous peptides was confirmed by pMHCII tetramer staining.

Conclusion

T cells from birch tree pollen allergic individuals respond to multiple trees within the birch homologous group in accordance with the level of sequence homology between Bet v 1 family members, (PR-10 allergens) from these allergen sources, confirming the basis for clinical cross-protection.

Structural Bases for the Allergenicity of Fra a 1.02 in Strawberry Fruits

Although strawberries are highly appreciated fruits, their intake can induce allergic reactions in atopic patients. These reactions can be due to the patient's previous sensitization to the major birch pollen allergen Bet v 1, by which IgE generated in response to Bet v 1 cross-reacts with the structurally related strawberry Fra a 1 protein family. Fra a 1.02 is the most expressed paralog in ripe strawberries and is highly allergenic. To better understand the molecular mechanisms regulating this allergic response, we have determined the three-dimensional structure of Fra a 1.02 and four site-directed mutants that were designed based on their positions in potential epitopes. Fra a 1.02 and mutants conform to the START fold. We show that the cross-reactivity of all the mutant variants to IgE from patients allergic to Bet v 1 was significantly reduced without altering the conserved structural fold, so that they could potentially be used as hypoallergenic Fra a 1 variants for the generation of vaccines against strawberry allergy in atopic patients.

Conformational IgE Epitope Mapping of Der p 2 and the Evaluations of Two Candidate Hypoallergens for Immunotherapy

Epitope mapping of Der p 2, a clinically important dust-mite allergen is the first step in designing immunotherapy hypoallergen vaccine candidates. Twenty-one single alanine mutants of Der p 2 were generated and their secondary structure was analysed using circular dichroism spectra. Only one mutant, K96A resulted in a misfolded protein. All mutants were tested for serum IgE reactivity using serum from dust mite allergic individuals by immuno dot-blots. Mutations to five residues, N10, E25, K77, K96 and E102 consistently showed reduced IgE reactions compared to wild-type Der p 2, and therefore these residues constitute the major IgE epitopes of Der p 2. Two mutants with consistent low IgE binding, K96A and E102A, were subsequently evaluated as hypoallergen candidates. IgG antibodies raised in mice against both mutants could inhibit human IgE-binding to WT Der p 2. Both mutants had intact T-cell epitopes as they were able to stimulate peripheral blood mononuclear cell proliferation similar to WT Der p 2. However, a switch in Th1:Th2 cytokine profile was not observed. In summary, we have identified the major conformational epitopes of Der p 2, and evaluated two Der p 2 hypoallergen vaccine candidates for immunotherapy.

Combination of two epitope identification techniques enables the rational design of soy allergen Gly m 4 mutants

Detailed IgE-binding epitope analysis is a key requirement for the understanding and development of diagnostic and therapeutic agents to address food allergies. An IgE-specific linear peptide microarray with random phage peptide display for the high-resolution mapping of IgE-binding epitopes of the major soybean allergen Gly m 4, which is a homologue to the birch pollen allergen Bet v 1 is combined. Three epitopes are identified and mapped to a resolution of four key amino acids, allowing the rational design and the production of three Gly m 4 mutants with the aim to abolish or reduce the binding of epitope-specific IgE. In ELISA, the binding of the mutant allergens to polyclonal rabbit-anti Gly m 4 serum as well as IgE purified from Gly m 4-reactive soybean allergy patient sera is reduced by up to 63% compared to the wild-type allergen. Basophil stimulation experiments using RBL-SX38 cells loaded with patient IgE are showed a decreased stimulation from 25% for the wild-type Gly m 4 to 13% for one mutant. The presented approach demonstrates the feasibility of precise mapping of allergy-related IgE-binding epitopes, allowing the rational design of less allergenic mutants as potential therapeutic agents.

Six years of INSTAND e. V. sIgE proficiency testing: An evaluation of in vitro allergy diagnostics

Background

Even though allergies are an important health issue, wide manufacturer-dependent differences in the detected amounts of allergen-specific IgE (sIgE) have repeatedly been found. These discrepancies hinder diagnostics and research into clinically significant cutoff points for life-threatening symptoms.

Methods

To evaluate whether the reported differences have led to changes in diagnostic testing, we analyzed data from six years of round robin testing (RRT, also known as proficiency testing) at the Gesellschaft zur Förderung der Qualitätssicherung in medizinischen Laboratorien e.V.  (Society for Promoting Quality Assurance in medical Laboratories) for the important allergen sources bee venom, wasp venom, and birch pollen. The results of the four main suppliers of in vitro diagnostic sIgE testing were compared in a pseudo-anonymized form using overlay images of box plot graphs for the semiquantitative data and allergen class results. Coefficients of variation (CV) were obtained to study the development of interlaboratory comparability.

Results

We found that the large differences between the manufacturer collectives remained constant between January 2010 and April 2015 without any real improvement. The CVs were good for two of the four analyzed suppliers, one was marginal and one above the quality level of 20%.

Conclusion

The numerous publications that have found discrepancies in the sIgE results of the different suppliers did not change the status quo within the last six years. Unfortunately, this is unlikely to change until there is a characterized standard material with known values of sIgE.

Allergen Valency, Dose, and FcεRI Occupancy Set Thresholds for Secretory Responses to Pen a 1 and Motivate Design of Hypoallergens

Ag-mediated crosslinking of IgE-FcεRI complexes activates mast cells and basophils, initiating the allergic response. Of 34 donors recruited having self-reported shrimp allergy, only 35% had significant levels of shrimp-specific IgE in serum and measurable basophil secretory responses to rPen a 1 (shrimp tropomyosin). We report that degranulation is linked to the number of FcεRI occupied with allergen-specific IgE, as well as the dose and valency of Pen a 1. Using clustered regularly interspaced palindromic repeat-based gene editing, human RBL^rαKO cells were created that exclusively express the human FcεRIα subunit. Pen a 1-specific IgE was affinity purified from shrimp-positive plasma. Cells primed with a range of Pen a 1-specific IgE and challenged with Pen a 1 showed a bell-shaped dose response for secretion, with optimal Pen a 1 doses of 0.1-10 ng/ml. Mathematical modeling provided estimates of receptor aggregation kinetics based on FcεRI occupancy with IgE and allergen dose. Maximal degranulation was elicited when ∼2700 IgE-FcεRI complexes were occupied with specific IgE and challenged with Pen a 1 (IgE epitope valency of ≥8), although measurable responses were achieved when only a few hundred FcεRI were occupied. Prolonged periods of pepsin-mediated Pen a 1 proteolysis, which simulates gastric digestion, were required to diminish secretory responses. Recombinant fragments (60-79 aa), which together span the entire length of tropomyosin, were weak secretagogues. These fragments have reduced dimerization capacity, compete with intact Pen a 1 for binding to IgE-FcεRI complexes, and represent a starting point for the design of promising hypoallergens for immunotherapy.

IgE and allergen-specific immunotherapy-induced IgG4 recognize similar epitopes of Bet v 1, the major allergen of birch pollen

BACKGROUND

Allergen-specific immunotherapy (AIT) with birch pollen generates Bet v 1-specific immunoglobulin (Ig)G₄ which blocks IgE-mediated hypersensitivity mechanisms. Whether IgG₄ specific for Bet v 1a competes with IgE for identical epitopes or whether novel epitope specificities of IgG₄ antibodies are developed is under debate.

OBJECTIVE

We sought to analyze the epitope specificities of IgE and IgG₄ antibodies from sera of patients who received AIT.

METHODS

15 sera of patients (13/15 received AIT) with Bet v 1a-specific IgE and IgG₄ were analyzed. The structural arrangements of recombinant (r)Bet v 1a and rBet v 1a_{_11x} , modified in five potential epitopes, were analyzed by circular dichroism and nuclear magnetic resonance spectroscopy. IgE binding to Bet v 1 was assessed by ELISA and mediator release assays. Competitive binding of monoclonal antibodies specific for Bet v 1a and serum IgE/IgG₄ to rBet v 1a and serum antibody binding to a non-allergenic Bet v 1-type model protein presenting an individual epitope for IgE was analyzed in ELISA and western blot.

RESULTS

rBet v 1a_{_11x} had a Bet v 1a - similar secondary and tertiary structure. Monomeric dispersion of rBet v 1a_{_11x} was concentration and buffer-dependent. Up to 1500-fold increase in the EC₅₀ for IgE-mediated mediator release induced by rBet v 1a_{_11x} was determined. The reduction of IgE and IgG₄ binding to rBet v 1a_{_11x} was comparable in 67% (10/15) of sera. Bet v 1a-specific monoclonal antibodies inhibited binding of serum IgE and IgG₄ to 66.1% and 64.9%, respectively. Serum IgE and IgG₄ bound specifically to an individual epitope presented by our model protein in 33% (5/15) of sera.

CONCLUSION AND CLINICAL RELEVANCE

Patients receiving AIT develop Bet v 1a-specific IgG₄ which competes with IgE for partly identical or largely overlapping epitopes. The similarities of epitopes for IgE and IgG₄ might stimulate the development of epitope-specific diagnostics and therapeutics.

The conformational IgE epitope profile of soya bean allergen Gly m 4

BACKGROUND

Birch pollen-related soya allergy is mediated by Gly m 4. Conformational IgE epitopes of Gly m 4 are unknown.

OBJECTIVE

To identify the IgE epitope profile of Gly m 4 in subjects with birch pollen-related soya allergy utilizing an epitope library presented by Gly m 4-type model proteins.

METHODS

Sera from patients with (n = 26) and without (n = 19) allergy to soya as determined by oral provocation tests were studied. Specific IgE (Bet v 1/Gly m 4) was determined by ImmunoCAP. A library of 59 non-allergenic Gly m 4-type model proteins harbouring individual and multiple putative epitopes for IgE was tested in IgE binding assays. Primary, secondary and tertiary protein structures were assessed by mass spectrometry, circular dichroism and nuclear magnetic resonance spectroscopy.

RESULTS

All subjects were sensitized to Gly m 4 and Bet v 1. Allergen-specific serum IgE levels ranged from 0.94 to > 100 kU_A /L. The avidities of serum IgE were 5.06 ng (allergic) and 1.8 ng (tolerant) as determined by EC₅₀ for IgE binding to Gly m 4. 96% (46/48) of the protein variants bound IgE. Model proteins had Gly m 4-type conformation and individual IgE binding clustered in six major surface areas. Gly m 4-specific IgE binding could be inhibited to up to 80% by model proteins harbouring individual IgE binding sites in an epitope-wise equimolar fashion. Receiver operating curve analysis revealed an area under fitted curve of up to 0.88 for model proteins and 0.66 for Gly m 4.

CONCLUSION AND CLINICAL RELEVANCE

Serum levels and avidity of Gly m 4-specific IgE do not correlate with clinical reactivity to soya. Six IgE-binding areas, represented by 23 amino acids, account for more than 80% of total IgE binding capacity of Gly m 4. Model proteins may be used for epitope-resolved diagnosis to differentiate birch-soya allergy from clinical tolerance.

Epitope Mapping of Rhi o 1 and Generation of a Hypoallergenic Variant: A CANDIDATE MOLECULE FOR FUNGAL ALLERGY VACCINES

Efficacy of allergen-specific immunotherapy is often severely impaired by detrimental IgE-mediated side effects of native allergen during vaccination. Here, we present the molecular determinants for IgE recognition of Rhi o 1 and eventually converting the allergen into a hypoallergenic immunogen to restrain health hazards during desensitization. Rhi o 1 is a respiratory fungal allergen. Despite having cross-reactivity with cockroach allergen, we observed that non-cross-reactive epitope predominantly determined IgE binding to Rhi o 1. Denaturation and refolding behavior of the allergen confirmed that its IgE reactivity was not essentially conformation-dependent. A combinatorial approach consisting of computational prediction and a peptide-based immunoassay identified two peptides ((44)TGEYLTQKYFNSQRNN and (311)GAEKNWAGQYVVDCNK) of Rhi o 1 that frequently reacted with IgE antibodies of sensitized patients. Interestingly, these peptides did not represent purely linear IgE epitopes but were presented in a conformational manner by forming a spatially clustered surface-exposed epitope conferring optimal IgE-binding capacity to the folded allergen. Site-directed alanine substitution identified four residues of the IgE epitope that were crucial for antibody binding. A multiple mutant (T49A/Y52A/K314A/W316A) showing 100-fold lower IgE binding and reduced allergenic activity was generated. The TYKW mutant retained T-cell epitopes, as evident from its lymphoproliferative capacity but down-regulated pro-allergic IL-5 secretion. The TYKW mutant induced enhanced focusing of blocking IgG antibodies specifically toward the IgE epitope of the allergen. Anti-TYKW mutant polyclonal IgG antibodies competitively inhibited binding of IgE antibodies to Rhi o 1 up to 70% and suppressed allergen-mediated histamine release by 10-fold. In conclusion, this is a simple yet rational strategy based on epitope mapping data to develop a genetically modified hypoallergenic variant showing protective antibody response for immunotherapeutic applications.

Antigenic Determinants of the Bilobal Cockroach Allergen Bla g 2

Bla g 2 is a major indoor cockroach allergen associated with the development of asthma. Antigenic determinants on Bla g 2 were analyzed by mutagenesis based on the structure of the allergen alone and in complex with monoclonal antibodies that interfere with IgE antibody binding. The structural analysis revealed mechanisms of allergen-antibody recognition through cation-π interactions. Single and multiple Bla g 2 mutants were expressed in Pichia pastoris and purified. The triple mutant K132A/K251A/F162Y showed an ∼100-fold reduced capacity to bind IgE, while preserving the native molecular fold, as proven by x-ray crystallography. This mutant was still able to induce mast cell release. T-cell responses were assessed by analyzing Th1/Th2 cytokine production and the CD4(+) T-cell phenotype in peripheral blood mononuclear cell cultures. Although T-cell activating capacity was similar for the KKF mutant and Bla g 2 based on CD25 expression, the KKF mutant was a weaker inducer of the Th2 cytokine IL-13. Furthermore, this mutant induced IL-10 from a non-T-cell source at higher levels that those induced by Bla g 2. Our findings demonstrate that a rational design of site-directed mutagenesis was effective in producing a mutant with only 3 amino acid substitutions that maintained the same fold as wild type Bla g 2. These residues, which were involved in IgE antibody binding, endowed Bla g 2 with a T-cell modulatory capacity. The antigenic analysis of Bla g 2 will be useful for the subsequent development of recombinant allergen vaccines.

Epicutaneous immunotherapy with a hypoallergenic Bet v 1 suppresses allergic asthma in a murine model

BACKGROUND

Due to reduced allergic potency, hypoallergenic variants have been suggested as safer and potentially more efficacious alternative to the corresponding wild-type allergens in allergen-specific immunotherapy. Here, we aimed at investigating the efficacy of recombinant Bet v 1B2, a hypoallergenic folding variant of Bet v 1, in epicutaneous immunotherapy to suppress asthmatic features using a murine model of birch pollen allergy.

METHODS AND RESULTS

Before, or after sensitization with rBet v 1 plus ALUMW and intranasal challenges with birch pollen extract, BALB/c mice received epicutaneous immunization (EPI) with rBet v 1, or rBet v 1B2 on their depilated back. Prophylactic EPI with rBet v 1B2, but not with rBet v 1, suppressed serum levels of Bet v 1-specific IgE antibodies and reduced the number of eosinophils and the concentrations of Th2 cytokines in bronchoalveolar lavage. In an established allergic condition, serum levels of Bet v 1-specific IgE antibodies were similar between PBS-treated control mice and EPI-treated mice. However, therapeutic EPI with rBet v 1B2, but not with rBet v 1, significantly suppressed the development of airway inflammation and lung function impairment.

CONCLUSION

This study is the first to show the effect of therapeutic EPI with a recombinant form of a hypoallergenic folding variant on the suppression of asthmatic features. Our results suggest that rBet v 1B2 along with its reduced IgE-binding capacity could be a preferred therapeutic allergen than wild-type rBet v 1 in epicutaneous immunotherapy of birch pollen-induced allergic asthma, in particular due to a lower risk of allergic side effect.

Folded or Not? Tracking Bet v 1 Conformation in Recombinant Allergen Preparations

BACKGROUND

Recombinant Bet v 1a (rBet v 1a) has been used in allergy research for more than three decades, including clinical application of so-called hypoallergens. Quantitative IgE binding to rBet v 1a depends on its native protein conformation, which might be compromised upon heterologous expression, purification, or mutational engineering of rBet v 1a.

OBJECTIVE

To correlate experimental/theoretical comparisons of IgE binding of defined molar ratios of folded/misfolded recombinant Bet v 1a variants and to determine accuracy and precision of immuno- and physicochemical assays routinely used to assess the quality of recombinant allergen preparations.

METHODS

rBet v 1a and its misfolded variant rBet v 1aS112P/R145P were heterologously expressed and purified from Escherichia coli. Structural integrities and oligomerisation of the recombinant allergens were evaluated by 1H-nuclear magnetic resonance (1H-NMR), circular dichroism (CD) spectroscopy, and dynamic light scattering (DLS). IgE binding of defined combinations of rBet v 1a and rBet v 1aS112P/R145P was assessed using immunoblotting (IB), enzyme-linked immunosorbent assay (ELISA) and mediator release (MR) of humanized rat basophilic leukemia cells sensitized with serum IgE of subjects allergic to birch pollen. Experimental and theoretically expected results of the analyses were compared.

RESULTS

1H-NMR spectra of rBet v 1a and rBet v 1aS112P/R145P demonstrate a native and highly disordered protein conformations, respectively. The CD spectra suggested typical alpha-helical and beta-sheet secondary structure content of rBet v 1a and random coil for rBet v 1aS112P/R145P. The hydrodynamic radii (RH) of 2.49 ± 0.39 nm (rBet v 1a) and 3.1 ± 0.56 nm (rBet v 1aS112P/R145P) showed monomeric dispersion of both allergens in solution. Serum IgE of birch pollen allergic subjects bound to 0.1% rBet v 1a in the presence of 99.9% of non-IgE binding rBet v 1aS112P/R145P. Immunoblot analysis overestimated, whereas ELISA and mediator release assay underestimated the actual quantity of IgE-reactive rBet v 1a in mixtures of rBet v 1a/rBet v 1aS112P/R145P with a molar ratio of rBet v 1a ≤ 10%.

CONCLUSION

Valid conclusions on quantitative IgE binding of recombinant Bet v 1a preparations depend on the accuracy and precision of physico- and immunochemical assays with which natively folded allergen is detected.

Isolation, expression and characterization of a minor allergen from Penicillium crustosum

A ribosomal P1 protein, Pen b 26 from Penicillium brevicompactum, was previously identified as a major allergen. A homolog protein was isolated and characterized from Penicillium crustosum which is not known to be allergenic mold. A cDNA library of P. crustosum was constructed and screened using a probe based on the DNA sequence of Pen b 26. A positive clone was isolated, expressed in Escherichia coli, purified and characterized by comparing its immunological and physical properties to Pen b 26. It was designated as Pen cr 26 and had a 321 nt ORF corresponding to 107 amino acids with a MW of 11 kDa. Pen cr 26 had strong sequence homology to Pen b 26 (92% for nucleotides and 86% for amino acids) and its physical and predicted structural properties were similar to the latter. The level of expression of Pen cr 26 was much lower than that of Pen b 26 in the same expression vector. Both proteins were recognized equally well by the IgG class specific antibodies, but Pen cr 26 was poorly recognized by Penicillium-sensitive atopic sera (IgE), suggesting striking antigenic difference in IgE epitopes, i.e., 87% were positive for Pen b 26 while only 23% were positive for Pen cr 26. The allergenicity of Pen cr 26 seems to be minor in nature and it could be a hypoallergenic variant of Pen b 26.

Enlarging the toolbox for allergen epitope definition with an allergen-type model protein

BACKGROUND

Birch pollen-allergic subjects produce polyclonal cross-reactive IgE antibodies that mediate pollen-associated food allergies. The major allergen Bet v 1 and its homologs in plant foods bind IgE in their native protein conformation. Information on location, number and clinical relevance of IgE epitopes is limited. We addressed the use of an allergen-related protein model to identify amino acids critical for IgE binding of PR-10 allergens.

METHOD

Norcoclaurine synthase (NCS) from meadow rue is structurally homologous to Bet v 1 but does not bind Bet v 1-reactive IgE. NCS was used as the template for epitope grafting. NCS variants were tested with sera from 70 birch pollen allergic subjects and with monoclonal antibody BV16 reported to compete with IgE binding to Bet v 1.

RESULTS

We generated an NCS variant (Δ29NCSN57/I58E/D60N/V63P/D68K) harboring an IgE epitope of Bet v 1. Bet v 1-type protein folding of the NCS variant was evaluated by 1H-15N-HSQC NMR spectroscopy. BV16 bound the NCS variant and 71% (50/70 sera) of our study population showed significant IgE binding. We observed IgE and BV16 cross-reactivity to the epitope presented by the NCS variant in a subgroup of Bet v 1-related allergens. Moreover BV16 blocked IgE binding to the NCS variant. Antibody cross-reactivity depended on a defined orientation of amino acids within the Bet v 1-type conformation.

CONCLUSION

Our system allows the evaluation of patient-specific epitope profiles and will facilitate both the identification of clinically relevant epitopes as biomarkers and the monitoring of therapeutic outcomes to improve diagnosis, prognosis, and therapy of allergies caused by PR-10 proteins.

Human IgE against the major allergen Bet v 1--defining an epitope with limited cross-reactivity between different PR-10 family proteins

Background

The interaction between IgE and allergen is a key event at the initiation of an allergic response, and its characteristics have substantial effects on the clinical manifestation. Despite this, the molecular details of the interaction between human IgE and the major birch allergen Bet v 1, one of the most potent tree allergens, still remain poorly investigated.

Objective

To isolate Bet v 1-specific human monoclonal IgE and characterize their interaction with the allergen.

Methods

Recombinant human IgE were isolated from a combinatorial antibody fragment library and their interaction with Bet v 1 assessed using various immunological assays. The structure of one such IgE in the single-chain fragment variable format was determined using X-ray crystallography.

Results

We present four novel Bet v 1-specific IgE, for one of which we solve the structure, all with their genetic origin in the IGHV5 germline gene, and demonstrate that they target two non-overlapping epitopes on the surface of Bet v 1, thereby fulfilling the basic criteria for FcεRI cross-linkage. We further define these epitopes and for one epitope pinpoint single amino acid residues important for the interaction with human IgE. This provides a potential explanation, at the molecular level, for the differences in recognition of isoforms of Bet v 1 and other allergens in the PR-10 protein family displayed by IgE targeting this epitope. Finally, we present the first high-resolution structure of a human allergen-specific IgE fragment in the single-chain fragment variable (scFv) format.

Conclusions and Clinical Relevance

We here display the usefulness of allergen-specific human monoclonal IgE as a tool in studies of the crucial molecular interaction taking place at the initiation of an allergic response. Such studies may aid us in development of better diagnostic tools and guide us in the development of new therapeutic compounds.

Structure of allergens and structure based epitope predictions

The structure determination of major allergens is a prerequisite for analyzing surface exposed areas of the allergen and for mapping conformational epitopes. These may be determined by experimental methods including crystallographic and NMR-based approaches or predicted by computational methods. In this review we summarize the existing structural information on allergens and their classification in protein fold families. The currently available allergen-antibody complexes are described and the experimentally obtained epitopes compared. Furthermore we discuss established methods for linear and conformational epitope mapping, putting special emphasis on a recently developed approach, which uses the structural similarity of proteins in combination with the experimental cross-reactivity data for epitope prediction.

Chimeras of Bet v 1 and Api g 1 reveal heterogeneous IgE responses in patients with birch pollen allergy

BACKGROUND

Characterization of IgE-binding epitopes of allergens and determination of their patient-specific relevance is crucial for the diagnosis and treatment of allergy.

OBJECTIVE

We sought to assess the contribution of specific surface areas of the major birch pollen allergen Bet v 1.0101 to binding IgE of individual patients.

METHODS

Four distinct areas of Bet v 1 representing in total 81% of its surface were grafted onto the scaffold of its homolog, Api g 1.0101, to yield the chimeras Api-Bet-1 to Api-Bet-4. The chimeras were expressed in Escherichia coli and purified. IgE binding of 64 sera from Bet v 1-sensitized subjects with birch pollen allergy was determined by using direct ELISA. Specificity was assessed by means of inhibition ELISA.

RESULTS

rApi g 1.0101, Api-Bet-1, Api-Bet-2, Api-Bet-3, and Api-Bet-4 bound IgE from 44%, 89%, 80%, 78%, and 48% of the patients, respectively. By comparing the amount of IgE binding to the chimeras and to rApi g 1.0101, 81%, 70%, 75%, and 45% of the patients showed significantly enhanced IgE binding to Api-Bet-1, Api-Bet-2, Api-Bet-3, and Api-Bet-4, respectively. The minority (8%) of the sera revealed enhanced IgE binding exclusively to a single chimera, whereas 31% showed increased IgE binding to all 4 chimeras compared with rApi g 1.0101. The chimeras inhibited up to 70% of IgE binding to rBet v 1.0101, confirming the specific IgE recognition of the grafted regions.

CONCLUSION

The Bet v 1-specific IgE response is polyclonal, and epitopes are spread across the entire Bet v 1 surface. Furthermore, the IgE recognition profile of Bet v 1 is highly patient specific.

Modern approaches to therapeutic vaccination as treatment for Type 1 respiratory hypersensitivity (allergy) treatment

The incidence of respiratory and other allergies has increased dramatically in many countries over the last few decades. Drug treatment is symptomatic and has a minimal effect on the underlying immunological dysfunction. This disease process may, however, be modified by allergy vaccination, which is typically applied by injecting increasing strengths of the offending allergens. Its use has been fairly limited owing to long injection schedules involving many visits to the physician, occasional local or systemic side effects, perceived limited efficacy and poor compliance. A greater understanding of the immunological mechanisms involved in allergy vaccination has led recently to the development of new generations of products with properties that address some of these issues, and these advances are likely to increase the successful use of the therapy.

Structural and functional aspects of PR-10 proteins

Physical, chemical and biological stress factors, such as microbial infection, upregulate the transcription levels of a number of plant genes, coding for the so-called pathogenesis-related (PR) proteins. For PR proteins of class-10 (PR-10), the biological function remains unclear, despite two decades of scientific research. PR-10 proteins have a wide distribution throughout the plant kingdom and the class members share size and secondary structure organization. Throughout the years, we and other groups have determined the structures of a number of PR-10 proteins, both in the crystalline state by X-ray diffraction and in solution by NMR spectroscopy. Despite the accumulating structural information, our understanding of PR-10 function is still limited. PR-10 proteins are rather small (~ 160 amino acids) with a fold consisting of three α helices and seven antiparallel β strands. These structural elements enclose a large hydrophobic cavity that is most probably the key to their functional relevance. Also, the outer surface of these proteins is of extreme interest, as epitopes from a PR-10 subclass cause allergic reactions in humans.

Identification of critical amino acids in an immunodominant IgE epitope of Pen c 13, a major allergen from Penicillium citrinum

Background

Pen c 13, identified as a 33-kDa alkaline serine protease, is a major allergen secreted by Penicillium citrinum. Detailed knowledge about the epitopes responsible for IgE binding would help inform the diagnosis/prognosis of fungal allergy and facilitate the rational design of hypoallergenic candidate vaccines. The goal of the present study was to characterize the IgE epitopes of Pen c 13.

Methodology/Principal Findings

Serum samples were collected from 10 patients with mold allergy and positive Pen c 13 skin test results. IgE-binding epitopes on rPen c 13 were mapped using an enzymatic digestion and chemical cleavage method, followed by dot-blotting and mass spectrometry. A B-cell epitope-predicting server and molecular modeling were used to predict the residues most likely involved in IgE binding. Theoretically predicted IgE-binding regions were further confirmed by site-directed mutagenesis assays. At least twelve different IgE-binding epitopes located throughout Pen c 13 were identified. Of these, peptides S16 (A¹⁴⁸–E¹⁶⁶) and S22 (A²⁴³–K²⁷⁴) were recognized by sera from 90% and 100% of the patients tested, and were further confirmed by inhibition assays. Peptide S22 was selected for further analysis of IgE-binding ability. The results of serum screening showed that the majority of IgE-binding ability resided in the C-terminus. One Pen c 13 mutant, G270A (T²⁶¹–K²⁷⁴), exhibited clearly enhanced IgE reactivity, whereas another, K274A, exhibited dramatically reduced IgE reactivity.

Conclusions/Significance

Experimental analyses confirmed in silico-predicted residues involved in an important antigenic region of Pen c 13. The G270A mutant of Pen c 13 has the potential to serve as an additional tool for the diagnosis/prognosis of mold allergy, and the K274A mutant, as a hypoallergenic form of the epitope, may provide a framework for the design and development of a safe and efficient therapeutic strategy for treating human allergic diseases.

Allergen-specific immunotherapy with recombinant allergens

Subcutaneous immunotherapy is a well-documented treatment of allergic rhinitis and asthma. The major limitation is the risk of anaphylactic side effects. The documentation of clinical efficacy is based on crude allergenic extracts sometimes containing varying amounts of individual allergens including allergens to which the patient may not be sensitized. The introduction of recombinant allergens offer a possibility to use well-defined molecules with consistent pharmaceutical quality defined in mass units. The proof-of-concept of the clinical efficacy of recombinant allergens is based on two studies published as full articles. One study applied a mixture of five Phleum pratense major allergens in a maximum dose of 40 μg protein. The clinical efficacy showed a significant efficacy with about 40% reduction in disease severity. The second study compared a commercial birch extract with both recombinant Bet v 1 and purified Bet v 1 in dosages of 15 μg allergen. The clinical effect was around 60% additional efficacy. Systemic side effects occurred more frequently with grass allergens. A third study used hypoallergenic fragments and a trimer of Bet v 1. The study did not show efficacy and a rather high frequency of systemic side effects. The advantages of using recombinant allergens for immunotherapy are obvious but more large-scale clinical studies are needed before the overall value in terms of efficacy and safety can be determined.

Mechanisms underlying allergy vaccination with recombinant hypoallergenic allergen derivatives

Hundred years ago therapeutic vaccination with allergen-containing extracts has been introduced as a clinically effective, disease-modifying, allergen-specific and long-lasting form of therapy for allergy, a hypersensitivity disease affecting more than 25% of the population. Today, the structures of most of the disease-causing allergens have been elucidated and recombinant hypoallergenic allergen derivatives with reduced allergenic activity have been engineered to reduce side effects during allergen-specific immunotherapy (SIT). These recombinant hypoallergens have been characterized in vitro, in experimental animal models and in clinical trials in allergic patients. This review provides a summary of the molecular, immunological and preclinical evaluation criteria applied for this new generation of allergy vaccines. Furthermore, we summarize the mechanisms underlying SIT with recombinant hypoallergens which are thought to be responsible for their therapeutic effect.

In search of a vaccine for mouse allergy: significant reduction of Mus m 1 allergenicity by structure-guided single-point mutations

BACKGROUND

Mouse urinary proteins are relevant allergens from mice urine. We used the recombinant protein Mus m 1 as an allergen model to identify if, by altering Mus m 1 architecture via single-point mutations, we could effectively modify its allergenicity.

METHODS

Based on structural considerations, we synthesized two single-point mutants, Mus m 1-Y120A and Mus m 1-Y120F, which were expected to harbor large structural alterations. Circular dichroism and fluorescence analysis showed significant conformational rearrangements of the aromatic side chains in the internal cavity of Mus m 1-Y120A when compared to Mus m 1-Y120F and Mus m 1. Evaluation of the allergenic potential of the recombinant molecules was performed in vitro with both immunochemical approaches and assays based on the measurement of basophil degranulation. Moreover, to assess the integrity of the T cell epitopes and as an in vitro measure of immunogenicity, we tested the reactivity of T lymphocytes from subjects allergic to mouse urine against proteins and synthetic peptides encompassing the immunodominant linear epitope containing the mutation.

RESULTS

We found that the selected point mutation was able to modulate the protein allergenicity, and to severely impair the recognition of Mus m 1 by IgE, while T cell reactivity was fully maintained.

CONCLUSIONS

In silico predicted, minimum selected structural modifications allowed to design one protein with reduced allergenicity and preserved immunogenicity. Structurally guided mutations can direct the design of proteins with reduced allergenicity which can be used as vaccines for a safer and more effective immunotherapy of allergic disorders.

Kiwifruit Act d 11 is the first member of the ripening-related protein family identified as an allergen

BACKGROUND

Kiwifruit is an important cause of food allergy. A high amount of a protein with a molecular mass compatible with that of Bet v 1 was observed in the kiwifruit extract.

OBJECTIVE

To identify and characterize kirola, the 17-kDa protein of green kiwifruit (Act d 11).

METHODS

Act d 11 was purified from green kiwifruit. Its primary structure was obtained by direct protein sequencing. The IgE binding was investigated by skin testing, immunoblotting, inhibition tests, and detection by the ISAC microarray in an Italian cohort and in selected Bet v 1-sensitized Austrian patients. A clinical evaluation of kiwi allergy was carried out.

RESULTS

Act d 11 was identified as a member of the major latex protein/ripening-related protein (MLP/RRP) family. IgE binding to Act d 11 was shown by all the applied testing. Patients tested positive for Act d 11 and reporting symptoms on kiwifruit exposure were found within the Bet v 1-positive subset rather than within the population selected for highly reliable history of allergic reactions to kiwifruit. Epidemiology of Act d 11 IgE reactivity was documented in the two cohorts. IgE co-recognition of Act d 11 within the Bet v 1-like molecules is documented using the microarray IgE inhibition assay.

CONCLUSIONS

Act d 11 is the first member of the MLP/RRP protein family to be described as an allergen. It displays IgE co-recognition with allergens belonging to the PR-10 family, including Bet v 1.

The current state of recombinant allergens for immunotherapy

PURPOSE OF REVIEW

Subcutaneous immunotherapy is a well documented treatment of allergic rhinitis and asthma. The majority of the disadvantages of the treatment are related to the poor quality of the natural allergen extracts which can contain varying amounts of individual allergens including allergens to which the patient may not be sensitized. Recombinant allergens offer a possibility to use well defined molecules with consistent pharmaceutical quality defined in mass units. The proof of concept of the clinical efficacy of recombinant allergens is based on two studies published as full articles.

RECENT FINDINGS

One study applied a mixture of five Phleum pratense major allergens in a maximum dose of 40mcg protein. The clinical efficacy showed a significant efficacy with 40% reduction in disease severity. The second study compared a commercial birch extract with both recombinant Bet v 1 and purified Bet v 1 in dosages of 15mcg allergen. The clinical effect was 60% additional efficacy. Systemic side effects occurred more frequently with grass allergens. A third study used hypoallergenic fragments and a trimer of Bet v 1. The study did not show efficacy and a rather high frequency of systemic side effects.

SUMMARY

The advantages of using recombinant allergens for immunotherapy are obvious but more studies on a large scale are needed before the overall value in terms of efficacy and safety can be assessed. Clinical trials are also necessary for new combined vaccines based on recombinant allergens that in experimental studies have shown greatly enhanced immunogenicity and low allergen-specific reactivity.

Epitope grafting, re-creating a conformational Bet v 1 antibody epitope on the surface of the homologous apple allergen Mal d 1

Birch-allergic patients often experience oral allergy syndrome upon ingestion of vegetables and fruits, most prominently apple, that is caused by antibody cross-reactivity of the IgE antibodies in patients to proteins sharing molecular surface structures with the major birch pollen group 1 allergen from Betula verrucosa (Bet v 1). Still, to what extent two molecular surfaces need to be similar for clinically relevant antibody cross-reactivity to occur is unknown. Here, we describe the grafting of a defined conformational antibody epitope from Bet v 1 onto the surface of the homologous apple allergen Malus domestica group 1 (Mal d 1). Engineering of the epitope was accomplished by genetic engineering substituting amino acid residues in Mal d 1 differing between Bet v 1 and Mal d 1 within the epitope defined by the mAb BV16. The kinetic parameters characterizing the antibody binding interaction to Bet v 1 and to the mutated Mal d 1 variant, respectively, were assessed by Biacore experiments demonstrating indistinguishable binding kinetics. This demonstrates that a conformational epitope defined by a high affinity antibody-allergen interaction can successfully be grafted onto a homologous scaffold molecule without loss of epitope functionality. Furthermore, we show that increasing surface similarity to Bet v 1 of Mal d 1 variants by substitution of 6-8 residues increased the ability to trigger basophil histamine release with blood from birch-allergic patients not responding to natural Mal d 1. Conversely, reducing surface similarity to Bet v 1 of a Mal d 1 variant by substitution of three residues abolished histamine release in one patient reacting to Mal d 1.

Allergen-related approaches to immunotherapy

Allergic diseases, including asthma, rhinitis and eczema, represent a major health burden worldwide. Mainstay treatments are allergen avoidance where feasible and pharmacotherapy for symptom relief. For selected patients, allergen-specific immunotherapy (SIT) offers the prospect of long lasting clinical efficacy. SIT involves the administration of allergen extract using a standardized regimen, usually subcutaneously or increasingly sublingually. However, application of this potentially curative treatment is restricted, largely due to the risk of serious adverse events, especially in asthmatics and for potent allergens such as peanut, seafood and latex. New insights into immunological mechanisms underlying effective SIT and molecular characterization of allergens and their recognition by the immune system suggest strategies for refinement of SIT. Selective targeting of allergen-specific T cells, especially regulatory T cells, is likely to be pivotal for efficacy. Recombinant allergens lacking IgE reactivity and small T cell epitope-based peptides are being trialled clinically with evidence of efficacy without serious IgE-mediated adverse reactions. Adjuvants, either co-administered or incorporated into a recombinant allergen vaccine to target tolerogenic dendritic cells may also increase efficacy. The safer sublingual route of allergen administration is attracting interest and different allergen forms may be optimal for inducing tolerance by this route. Defined allergen-derived molecules or peptides offer ease of standardization and, coupled with appropriate targeting of immunoregulatory mechanisms, will result in more widespread clinical use of SIT. Adjunct therapies such as anti-IgE antibody and corticosteroids may minimize the likelihood of adverse reactions in those with severe allergic disease who would most benefit from this treatment.

Pediococcus pentosaceus NB-17 for probiotic use

The plant-derived Pediococcus pentosaceus NB-17 was isolated from Japanese traditional vegetable pickles. The production of cytokines from mouse spleen cells co-cultivated with heat-killed bacteria was investigated in vitro. The bacteria significantly induced secretion levels of interferon (IFN)-gamma and interleukin (IL)-12 p70, and suppressed IL-4 productions in ovalbumin (OVA) sensitized mouse spleen cells. Therefore, the bacteria could effectively stimulate immune activities and showed allergic inhibitory effects. Further study on acid tolerance was performed under simulated gastric conditions and NB-17 showed resistance to simulated gastric acidity at pH 3.0 and pH 2.5. Moreover, after oral administration of the intact cells to rats, bacterial colonies derived from feces were analyzed by random amplification polymorphic DNA (RAPD). It was confirmed that the administered strain NB-17 remained alive in feces. These results suggest the possibility to use the P. pentosaceus NB-17 as functional foods.

Crystallization and preliminary crystallographic studies of Hyp-1, a St John's wort protein implicated in the biosynthesis of hypericin

According to a debated hypothesis, the biosynthesis from emodin of the medicinally important natural compound hypericin is catalyzed in St John's wort (Hypericum perforatum) by the phenolic oxidative-coupling protein Hyp-1. Recombinant St John's wort Hyp-1 has been overexpressed in Escherichia coli and obtained in single-crystal form. The crystals belong to the orthorhombic system, space group P2(1)2(1)2(1), with unit-cell parameters a = 37.5, b = 76.7, c = 119.8 A, contain two protein molecules in the asymmetric unit and diffract X-rays to 1.73 A resolution.

Molecular and immunological characterization of cytochrome c: a potential cross-reactive allergen in fungi and grasses

BACKGROUND

Recombinant allergens are required for component-resolved diagnosis/therapy of allergic disorders. The study was aimed to express and characterize an allergenic protein from Curvularia lunata and study its cross-reactivity.

METHODS

A clone encoding a 12-kDa protein screened from the cDNA library of C. lunata was sequenced and expressed in pET22b+ vector. The purified protein was characterized by biophysical and immunological methods.

RESULTS

The sequence of gene encoding a 12-kDa protein showed homology to cytochrome c. It was expressed in Escherichia coli yielding 0.5 mg protein/l culture and designated as Cur l 3. The absorption and circular dichroism spectrum of Cur l 3 were similar to horse cytochrome c and the protein reacted with cytochrome c antibody. ELISA with different fungal-positive patients' sera showed > or = 3 times specific IgE to Cur l 3 compared with healthy controls. Mice anti-Cur l 3 reacted with tropical and temperate grass extracts. Protein also reacted with grass-positive patients' sera. In vitro stimulation of peripheral blood mononuclear cells from C. lunata, fungi or grass-positive patients with it released significant levels of Th2 cytokines. In vivo testing of this protein in allergic patients showed marked positive skin reactivity in 60% fungal and 43% grass-positive cases. Cross inhibition assays (EC(50)) demonstrated allergenic cross-reactivity of Cur l 3 with fungi and grasses.

CONCLUSIONS

Cytochrome c, a major allergen from C. lunata was cloned, sequenced and expressed. It was identified as a cross-reactive allergen among fungi and grasses and has potential for clinical application.

Characterization of a Hypoallergenic Recombinant Bet v 1 Variant as a Candidate for Allergen-Specific Immunotherapy

BACKGROUND

Recombinant allergens and especially their hypoallergenic variants are promising candidates for a more effective and safer specific immunotherapy.

METHODS

Physicochemical and immunological characteristics of a folding variant of recombinant Bet v 1 (rBet v 1-FV) were investigated in comparison to natural Bet v 1 (nBet v 1) and the correctly folded recombinant Bet v 1 (rBet v 1-WT) by SDS-PAGE, size exclusion chromatography, multi-angle light scattering, circular dichroism, immunoblotting and enzyme allergosorbent test inhibition assay for detection of IgE reactivity and ELISA with Bet v 1-specific monoclonal antibodies. The functional IgE reactivity of the different Bet v 1 proteins was investigated using basophil activation in terms of CD203c expression and histamine release. T cell reactivity was investigated using T cell lines raised from birch pollen-allergic subjects against nBet v 1. Immunogenicity was investigated in mice.

RESULTS

Physicochemical characterization revealed purity, homogeneity and monomeric properties of rBet v 1-FV. Unlike nBet v 1 and rBet v 1-WT, rBet v 1-FV showed almost no IgE binding in immunoblots. The reduction of allergenicity was further proved by IgE-binding inhibition assays, basophil activation and histamine release. T cell reactivity was completely conserved, as demonstrated by proliferation of Bet v 1-specific T cell lines with multiple epitope specificities. rBet v 1-FV showed strong immunogenicity in mice.

CONCLUSIONS

Due to its reduced IgE reactivity and decreased capacity to activate basophils, but retained T cell reactivity and strong immunogenicity, rBet v 1-FV proved to be a very promising candidate for specific immunotherapy in birch pollen-allergic subjects.

Allergenicity and antigenicity of wild-type and mutant, monomeric, and dimeric carrot major allergen Dau c 1: destruction of conformation, not oligomerization, is the roadmap to save allergen vaccines

BACKGROUND

Carrot allergy is caused by primary sensitization to birch pollen. Continuous carrot exposure results in additional Dau c 1-specific allergic responses. Thus, immunotherapy with birch pollen may not improve the food allergy.

OBJECTIVE

Evaluation of mutation and oligomerization of the major carrot allergen, Dau c 1, in regard to alteration of antibody binding capacities, structure, and the ability to induce blocking IgG antibodies.

METHODS

Measurement of IgE reactivities to monomers, dimers of wild-type and mutant Dau c 1.0104 and Dau c 1.0201, and Dau c 1.0104 trimer, their ability to induce blocking antibodies in mice, and their allergenic potency by histamine release.

RESULTS

The reactivity of human IgE to the mutant dimer was reduced on average by 81%. Sera of immunized Balb/c mice showed specific IgG similar to the human IgE antibody response; Dau c 1.01 was more antigenic than Dau c 1.02. Both wild-type and mutant Dau c 1 variants induced cross-reacting IgG, which blocked binding of human IgE. The mutants were more antigenic than the wild-type forms, and the dimers induced higher IgG responses in mice than the monomers. The results of the histamine release experiments corroborated the findings of the antibody binding studies.

CONCLUSION

Destruction of native conformation rather than oligomerization is the appropriate strategy to reduce the allergenicity of Bet v 1-homologous food allergens.

CLINICAL IMPLICATIONS

The dimer composed of mutants of Dau c 1.0104 and Dau c 1.0201 is a promising candidate vaccine for treatment of carrot allergy because of its high immunogenicity and drastically reduced allergenicity.

Hypoallergenic mutants of Ole e 1, the major olive pollen allergen, as candidates for allergy vaccines

BACKGROUND

The C-terminal region of Ole e 1, a major allergen from olive pollen, is a dominant IgE-reactive site and offers a target for site-directed mutagenesis to produce variants with reduced IgE-binding capability.

OBJECTIVE

To evaluate in vitro and in vivo the immunogenic properties of three engineered derivatives of Ole e 1.

METHODS

One point (Y141A) and two deletion (135Delta10 and 140Delta5) mutants were generated by site-directed mutagenesis of Ole e 1-specific cDNA and produced in Pichia pastoris. Ole e 1 mutants were analysed for IgE reactivity by ELISA using sera from olive pollen-allergic patients. Their allergenicity was also investigated in both a mouse model of allergic sensitization and in basophil activation assays. IgG1 response was assayed by immunoblotting and competitive ELISA. T cell reactivity was evaluated by proliferation assays and cytokine production in splenocyte cultures.

RESULTS

The 135Delta10 mutant showed the strongest reduction in the IgE-binding capability of sera from olive pollen-allergic patients. Rat basophil leukaemia assays identified the deletion mutant 135Delta10 as the variant with the lowest beta-hexosaminidase-releasing capacity. Furthermore, the same 135Delta10 mutant induced the lowest IgE levels in a BALB/c mouse model of sensitization. All Ole e 1 mutants retained their allergen-specific T cell reactivity. Immunization of mice with the mutants induced IgG1 antibodies, which cross-reacted with Ole e 1 and Ole e 1-like allergens from ash, lilac and privet pollens. The ability of the human IgE to block the binding of anti-Ole e 1 mutant-specific mouse IgG1 antibodies to natural Ole e 1 demonstrated that Ole e 1 mutants are able to induce in vivo antibodies reactive to the natural allergen.

CONCLUSION

The 135Delta10 mutant with reduced allergenicity, intact T cell reactivity and capacity to induce blocking antibodies could provide a suitable candidate vaccine for efficient and safer therapy of olive pollen allergy.

Mediator release assays based on human or murine immunoglobulin E in allergen standardization

BACKGROUND

The biological potency of allergens can be measured by provoking mediator release from effector cells. As established immunochemical methods in allergen standardization only determine inhibition potency or major allergen content, routine tests for biological potency may enhance standardization and batch control of allergen products.

OBJECTIVE

The general performance and application potential of biological in vitro assays in batch control and standardization of allergens and as a tool for verifying activity and stability of allergen standards were analysed.

METHODS

Allergen extracts of five clinically relevant allergens from three to five different manufacturers were investigated. A CAP-IgE-inhibition assay was compared with mediator release assay (MRA)s based on murine or human basophils. Rat basophilic leukaemia (RBL) cells were passively sensitized with pooled murine allergen-specific IgE-containing sera. Humanized RBL cells and human-stripped basophils were sensitized with pooled patient's sera, which were also used for the CAP-IgE-inhibition assay. Allergen specificity of the sera was determined by immunoblotting.

RESULTS

A good batch-to-batch consistency was found with each assay among all manufacturers and allergens tested. Between different manufacturers, the products showed differences in activity and the various assays indicated an almost identical ranking. However, the biological assays revealed qualitative differences of biological activity or composition of allergen preparations undetectable by IgE-inhibition assay.

CONCLUSIONS

MRAs provide refined information on allergen activity, either confirming the results of IgE-inhibition assay, or indicating differences requiring further investigation, and represent a highly sensitive novel tool in allergen standardization. By using permanently cultivated cell lines, repeated venepuncture to obtain human basophils is avoided. As in the RBL assay, the coefficient of variation for the release values were below 15% and for the ED50 below 25%, the assay is suitable to determine differences that are relevant for batch control purposes.

Hypoallergens for allergen-specific immunotherapy by directed molecular evolution of mite group 2 allergens

Allergen-specific immunotherapy is the only treatment that provides long lasting relief of allergic symptoms. Currently, it is based on repeated administration of allergen extracts. To improve the safety and efficacy of allergen extract-based immunotherapy, application of hypoallergens, i.e. modified allergens with reduced IgE binding capacity but retained T-cell reactivity, has been proposed. It may, however, be difficult to predict how to modify an allergen to create a hypoallergen. Directed molecular evolution by DNA shuffling and screening provides a means by which to evolve proteins having novel or improved functional properties without knowledge of structure-function relationships of the target molecules. With the aim to generate hypoallergens we applied multigene DNA shuffling on three group 2 dust mite allergen genes, two isoforms of Lep d 2 and Gly d 2. DNA shuffling yielded a library of genes from which encoded shuffled allergens were expressed and screened. A positive selection was made for full-length, high-expressing clones, and screening for low binding to IgE from mite allergic patients was performed using an IgE bead-based binding assay. Nine selected shuffled allergens revealed 80-fold reduced to completely abolished IgE binding compared with the parental allergens in IgE binding competition experiments. Two hypoallergen candidates stimulated allergen-specific T-cell proliferation and cytokine production at comparable levels as the wild-type allergens in patient peripheral blood mononuclear cell cultures. The two candidates also induced blocking Lep d 2-specific IgG antibodies in immunized mice. We conclude that directed molecular evolution is a powerful approach to generate hypoallergens for potential use in allergen-specific immunotherapy.

Novel vaccines and adjuvants for allergen-specific immunotherapy

Advances in genetic engineering and biotechnology, in parallel to increased understanding of disease processes and mechanisms of protective immunity, have facilitated the development of novel rational vaccination concepts for allergy. The spectrum ranges from utilizing recombinant proteins, peptides, new adjuvants, immunomodulatory therapy and DNA vaccines, to use of new application routes for both prophylaxis and treatment of allergic disease. New therapeutic concepts based on patient-tailored immunotherapy using recombinant allergens, anti-IgE and sublingual immunotherapies are slowly moving from the bench to the clinics. The additive value of new treatments above existing therapies must be, however, focused on the improvement of efficacy for long-term cure and increased patient compliance to warrant a broad applicability that has to compete with the symptomatic control of allergic and asthmatic diseases of currently available drugs.

Structural bioinformatic approaches to understand cross-reactivity

Cross-reactivity of allergens results from the presence of antibody-accessible conserved surface structures. These can best be studied when allergens have been structurally defined by X-ray crystallography or another structure determination method. When this is not the case, mimotope technology provides a useful alternative for elucidating antibody-binding sites on allergens. Structural bioinformatic approaches have been used to study the cross-reactivity of inhalant allergens with labile food allergens (Bet v 1 family) as well as the cross-reactivity between stable food allergens such as members of the nonspecific lipid transfer protein family. It was found that the degree of similarity of the structures correlated with the observed IgE cross-reactivities. However, IgE cross-reactivity between structurally unrelated allergens has not been demonstrated to date.

Standardization of allergen-specific immunotherapy vaccines

In the 1970s and 1980s, scientific methods were introduced in the standardization of allergen vaccines and, in combination with improved documentation of the clinical benefits obtained using standardized vaccines, specific allergy treatment as a scientifically based, reproducible, and safe treatment for allergic disease was established. This article describes important issues in the control of source materials and vaccine preparation as part of the European standardization of allergen vaccines, and also includes a discussion of vaccines that are based on recombinant allergens, which may appear on the market in the near future.

Nuclear magnetic resonance structure-based epitope mapping and modulation of dust mite group 13 allergen as a hypoallergen

IgE-mediated allergic response involves cross-linking of IgE bound on mast cells by specific surface epitopes of allergens. Structural studies on IgE epitopes of allergens are essential in understanding the characteristics of an allergen and for development of specific allergen immunotherapy. We have determined the structure of a group 13 dust mite allergen from Dermatophagoides farinae, Der f 13, using nuclear magnetic resonance. Sequence comparison of Der f 13 with homologous human fatty acid-binding proteins revealed unique surface charged residues on Der f 13 that may be involved in IgE binding and allergenicity. Site-directed mutagenesis and IgE binding assays have confirmed four surface charged residues on opposite sides of the protein that are involved in IgE binding. A triple mutant of Der f 13 (E41A_K63A_K91A) has been generated and found to have significantly reduced IgE binding and histamine release in skin prick tests on patients allergenic to group 13 dust mite allergens. The triple mutant is also able to induce PBMC proliferation in allergic patients with indices similar to those of wild-type Der f 13 and shift the secretion of cytokines from a Th2 to a Th1 pattern. Mouse IgG serum raised using the triple mutant is capable to block the binding of IgE from allergic patients to wild-type Der f 13, indicating potential for the triple mutant as a hypoallergen for specific immunotherapy. Findings in this study imply the importance of surface charged residues on IgE binding and allergenicity of an allergen, as was also demonstrated in other major allergens studied.

Biodegradable PLGA Particles for Improved Systemic and Mucosal Treatment of Type I Allergy

Although allergen immunotherapy is basically a story of success, it still needs improvement. The goal of this study was to optimize parenteral and oral allergen formulations through using the biocompatible polymer of lactic and glycolic acid (PLGA). Subcutaneous application of birch pollen allergen Bet v 1 encapsulated in nanoparticles biased the immune response toward Th1 in allergic mice and did not elicit granuloma formation in mice and in human volunteers. When oral immunotherapy of mice was tried with birch pollen-filled PLGA microparticles, mucosal targeting was indispensable for achieving any immune response, and targeting of M-cells was necessary for modulating an ongoing allergic response toward Th1. The authors suggest that biocompatible PLGA nano- or microparticles can be useful tools for upgrading therapy of type I allergy.

Genetic polymorphisms of major house dust mite allergens

BACKGROUND

Polymorphic sequence substitutions in the major mite allergens can markedly affect immunoglobulin E binding and T cell responses, but there are few studies on environmental isolates from Dermatophagoides pteronyssinus and none for D. farinae.

OBJECTIVE

To determine the sequence variation of the group 1 and 2 allergens from environmental D. pteronyssinus and D. farinae.

METHODS

RNA from each species was isolated from homes in Bangkok and the sequence of Der p 1, Der p 2, Der f 1, and Der f 2 determined from cDNA produced by high fidelity polymerase chain reactions.

RESULTS

The enlarged data set revealed preferred amino acid substitutions in residues 19, 81, and 215 of Der p 1 as well as sporadic changes. Der p 2 showed frequent variations with clusters of amino acid substitutions, but the canonical Der p 2.0101 was not found in any of 17 sequences. Der f 2 showed variants with clusters of substitutions similar to Der p 2 but in different amino acid positions and without any structural concordance. Der f 1 in contrast to the other allergens had few amino acid sequence substitutions.

CONCLUSIONS

The sequence information on variants provides data important for the optimal design of allergen formulations and useful for the genetic engineering and structure-function analyses of the major allergens.

Reduced Allergenic Potency of VR9-1, a Mutant of the Major Shrimp Allergen Pen a 1 (Tropomyosin)

The major shrimp allergen, tropomyosin, is an excellent model allergen for studying the influence of mutations within the primary structure on the allergenic potency of an allergen; Pen a 1 allows systematic evaluation and comparison of Ab-binding epitopes, because amino acid sequences of both allergenic and nonallergenic tropomyosins are known. Individually recognized IgE Ab-binding epitopes, amino acid positions, and substitutions critical for IgE Ab binding were identified by combinatorial substitution analysis, and 12 positions deemed critical were mutated in the eight major epitopes. The mutant VR9-1 was characterized with regard to allergenic potency by mediator release assays using sera from shrimp-allergic subjects and sera from BALB/c, C57BL/6J, C3H/HeJ, and CBA/J mice sensitized with shrimp extract using alum, cholera toxin, and Bordetella pertussis, as adjuvants. The secondary structure of VR9-1 was not altered; however, the allergenic potency was reduced by 90-98% measuring allergen-specific mediator release from humanized rat basophilic leukemia (RBL) cells, RBL 30/25. Reduced mediator release of RBL-2H3 cells sensitized with sera from mice that were immunized with shrimp extract indicated that mice produced IgE Abs to Pen a 1 and to the same epitopes as humans did. In conclusion, data obtained by mapping sequential epitopes were used to generate a Pen a 1 mutant with significantly reduced allergenic potency. Epitopes that are relevant for human IgE Ab binding are also major binding sites for murine IgE Abs. These results indicate that the murine model might be used to optimize the Pen a 1 mutant for future therapeutic use.

The crystal structure of recombinant proDer p 1, a major house dust mite proteolytic allergen

Allergy to house dust mite is among the most prevalent allergic diseases worldwide. Most house dust mite allergic patients react to Der p 1 from Dermatophagoides pteronyssinus, which is a cysteine protease. To avoid heterogeneity in the sample used for crystallization, a modified recombinant molecule was produced. The sequence of the proDer p 1 allergen was modified to reduce glycosylation and to abolish enzymatic activity. The resulting rproDer p 1 preparation was homogenous and stable and yielded crystals diffracting to a resolution of 1.61 A. The active site is located in a large cleft on the surface of the molecule. The 80-aa pro-peptide adopts a unique fold that interacts with the active site cleft and a substantial adjacent area on the mature region, excluding access to the cleft and the active site. Studies performed using crossed-line immunoelectrophoresis and IgE inhibition experiments indicated that several epitopes are covered by the pro-peptide and that the epitopes on the recombinant mature molecule are indistinguishable from those on the natural one. The structure confirms previous results suggesting a preference for aliphatic residues in the important P2 position in substrates. Sequence variations in related species are concentrated on the surface, which explains the existence of cross-reacting and species-specific antibodies. This study describes the first crystal structure of one of the clinically most important house dust mite allergens, the cysteine protease Der p 1.