Genetic engineering of a hypoallergenic trimer of the major birch pollen allergen Bet v 1

Past, present, and future of allergen immunotherapy vaccines

Allergen-specific immunotherapy (AIT) is an allergen-specific form of treatment for patients suffering from immunoglobulin E (IgE)-associated allergy; the most common and important immunologically mediated hypersensitivity disease. AIT is based on the administration of the disease-causing allergen with the goal to induce a protective immunity consisting of allergen-specific blocking IgG antibodies and alterations of the cellular immune response so that the patient can tolerate allergen contact. Major advantages of AIT over all other existing treatments for allergy are that AIT induces a long-lasting protection and prevents the progression of disease to severe manifestations. AIT is cost effective because it uses the patient´s own immune system for protection and potentially can be used as a preventive treatment. However, broad application of AIT is limited by mainly technical issues such as the quality of allergen preparations and the risk of inducing side effects which results in extremely cumbersome treatment schedules reducing patient´s compliance. In this article we review progress in AIT made from its beginning and provide an overview of the state of the art, the needs for further development, and possible technical solutions available through molecular allergology. Finally, we consider visions for AIT development towards prophylactic application.

Egg Allergy: Diagnosis and Immunotherapy

Hypersensitivity or an allergy to chicken egg proteins is a predominant symptomatic condition affecting 1 in 20 children in Australia; however, an effective form of therapy has not yet been found. This occurs as the immune system of the allergic individual overreacts when in contact with egg allergens (egg proteins), triggering a complex immune response. The subsequent instantaneous inflammatory immune response is characterized by the excessive production of immunoglobulin E (IgE) antibody against the allergen, T-cell mediators and inflammation. Current allergen-specific approaches to egg allergy diagnosis and treatment lack consistency and therefore pose safety concerns among anaphylactic patients. Immunotherapy has thus far been found to be the most efficient way to treat and relieve symptoms, this includes oral immunotherapy (OIT) and sublingual immunotherapy (SLIT). A major limitation in immunotherapy, however, is the difficulty in preparing effective and safe extracts from natural allergen sources. Advances in molecular techniques allow for the production of safe and standardized recombinant and hypoallergenic egg variants by targeting the IgE-binding epitopes responsible for clinical allergic symptoms. Site-directed mutagenesis can be performed to create such safe hypoallergens for their potential use in future methods of immunotherapy, providing a feasible standardized therapeutic approach to target egg allergies safely.

Allergen-specific IgE levels and the ability of IgE-allergen complexes to cross-link determine the extent of CD23-mediated T-cell activation

Background

CD23 mediates IgE-facilitated allergen presentation and subsequent allergen-specific T-cell activation in allergic patients.

Objective

We sought to investigate key factors regulating IgE-facilitated allergen presentation through CD23 and subsequent T-cell activation.

Methods

To study T-cell activation by free allergens and different types of IgE–Bet v 1 complexes, we used a molecular model based on monoclonal human Bet v 1–specific IgE, monomeric and oligomeric Bet v 1 allergen, an MHC-matched CD23-expressing B-cell line, and a T-cell line expressing a human Bet v 1–specific T-cell receptor. The ability to cross-link Fcε receptors of complexes consisting of either IgE and monomeric Bet v 1 or IgE and oligomeric Bet v 1 was studied in human FcεRI-expressing basophils. T-cell proliferation by monomeric or oligomeric Bet v 1, which cross-links Fcε receptors to a different extent, was studied in allergic patients’ PBMCs with and without CD23-expressing B cells.

Results

In our model non–cross-linking IgE–Bet v 1 monomer complexes, as well as cross-linking IgE–Bet v 1 oligomer complexes, induced T-cell activation, which was dependent on the concentration of specific IgE. However, T-cell activation by cross-linking IgE–Bet v 1 oligomer complexes was approximately 125-fold more efficient. Relevant T-cell proliferation occurred in allergic patients’ PBMCs only in the presence of B cells, and its magnitude depended on the ability of IgE–Bet v 1 complexes to cross-link CD23.

Conclusion

The extent of CD23-mediated T-cell activation depends on the concentration of allergen-specific IgE and the cross-linking ability of IgE-allergen complexes.

Fusion proteins consisting of Bet v 1 and Phl p 5 form IgE-reactive aggregates with reduced allergenic activity

The cross-linking of effector cell-bound IgE antibodies by allergens induces the release of inflammatory mediators which are responsible for the symptoms of allergy. We demonstrate that a recombinant hybrid molecule consisting of the major birch (Bet v 1) and grass (Phl p 5) pollen allergen exhibited reduced allergenic activity as compared to equimolar mixes of the isolated allergens in basophil activation experiments. The reduced allergenic activity of the hybrid was not due to reduced IgE reactivity as demonstrated by IgE binding experiments using sera from allergic patients. Physicochemical characterization of the hybrid by size exclusion chromatography, dynamic light scattering, negative-stain electron microscopy and circular dichroism showed that the hybrid occurred as folded aggregate whereas the isolated allergens were folded monomeric proteins. IgG antibodies raised in rabbits against epitopes of Bet v 1 and Phl p 5 showed reduced reactivity with the hybrid compared to the monomeric allergens. Our results thus demonstrate that aggregation can induce changes in the conformation of allergens and lead to the reduction of allergenic activity. This is a new mechanism for reducing the allergenic activity of allergens which may be important for modifying allergens to exhibit reduced side effects when used for allergen-specific immunotherapy.

Next-Generation of Allergen-Specific Immunotherapies: Molecular Approaches

PURPOSE OF REVIEW

The aim of this article is to discuss how allergen-specific immunotherapy (AIT) can be improved through molecular approaches. We provide a summary of next-generation molecular AIT approaches and of their clinical evaluation. Furthermore, we discuss the potential of next generation molecular AIT forms for the treatment of severe manifestations of allergy and mention possible future molecular strategies for the secondary and primary prevention of allergy.

RECENT FINDINGS

AIT has important advantages over symptomatic forms of allergy treatment but its further development is limited by the quality of the therapeutic antigen preparations which are derived from natural allergen sources. The field of allergy diagnosis is currently undergoing a dramatic improvement through the use of molecular testing with defined, mainly recombinant allergens which allows high-resolution diagnosis. Several studies demonstrate that molecular testing in early childhood can predict the development of symptomatic allergy later on in life. Clinical studies indicate that molecular AIT approaches have the potential to improve therapy of allergic diseases and may be used as allergen-specific forms of secondary and eventually primary prevention for allergy.

Molecular Aspects of Allergens and Allergy

Immunoglobulin E (IgE)-associated allergy is the most common immune disorder. More than 30% of the population suffer from symptoms of allergy which are often severe, disabling, and life threatening such as asthma and anaphylaxis. Population-based birth cohort studies show that up to 60% of the world population exhibit IgE sensitization to allergens, of which most are protein antigens. Thirty years ago the first allergen-encoding cDNAs have been isolated. In the meantime, the structures of most of the allergens relevant for disease in humans have been solved. Here we provide an update regarding what has been learned through the use of defined allergen molecules (i.e., molecular allergology) and about mechanisms of allergic disease in humans. We focus on new insights gained regarding the process of sensitization to allergens, allergen-specific secondary immune responses, and mechanisms underlying allergic inflammation and discuss open questions. We then show how molecular forms of diagnosis and specific immunotherapy are currently revolutionizing diagnosis and treatment of allergic patients and how allergen-specific approaches may be used for the preventive eradication of allergy.

Modified Allergens for Immunotherapy

PURPOSE OF REVIEW

During the past few decades, modified allergens have been developed for use in allergen-specific immunotherapy (AIT) with the aim to improve efficacy and reduce adverse effects. This review aims to provide an overview of the different types of modified allergens, their mechanism of action and their potential for improving AIT.

RECENT FINDINGS

In-depth research in the field of allergen modifications as well as the advance of recombinant DNA technology have paved the way for improved diagnosis and research on human allergic diseases. A wide range of structurally modified allergens has been generated including allergen peptides, chemically altered allergoids, adjuvant-coupled allergens, and nanoparticle-based allergy vaccines. These modified allergens show promise for the development of AIT regimens with improved safety and long-term efficacy. Certain modifications ensure reduced IgE reactivity and retained T cell reactivity, which facilities induction of immune tolerance to the allergen. To date, multiple clinical trials have been performed using modified allergens. Promising results were obtained for the modified cat, grass and birch pollen, and house dust mite allergens. The use of modified allergens holds promise for improving AIT efficacy and safety. There is however a need for larger clinical studies to reliably assess the added benefit for the patient of using modified allergens for AIT.

Safety and efficacy of immunotherapy with the recombinant B-cell epitope-based grass pollen vaccine BM32

Background

BM32 is a grass pollen allergy vaccine based on recombinant fusion proteins consisting of nonallergenic peptides from the IgE-binding sites of the 4 major grass pollen allergens and the hepatitis B preS protein.

Objective

We sought to study the safety and clinical efficacy of immunotherapy (allergen immunotherapy) with BM32 in patients with grass pollen–induced rhinitis and controlled asthma.

Methods

A double-blind, placebo-controlled, multicenter allergen immunotherapy field study was conducted for 2 grass pollen seasons. After a baseline season, subjects (n = 181) were randomized and received 3 preseasonal injections of either placebo (n = 58) or a low dose (80 μg, n = 60) or high dose (160 μg, n = 63) of BM32 in year 1, respectively, followed by a booster injection in autumn. In the second year, all actively treated subjects received 3 preseasonal injections of the BM32 low dose, and placebo-treated subjects continued with placebo. Clinical efficacy was assessed by using combined symptom medication scores, visual analog scales, Rhinoconjunctivitis Quality of Life Questionnaires, and asthma symptom scores. Adverse events were graded according to the European Academy of Allergy and Clinical Immunology. Allergen-specific antibodies were determined by using ELISA, ImmunoCAP, and ImmunoCAP ISAC.

Results

Although statistical significance regarding the primary end point was not reached, BM32-treated subjects, when compared with placebo-treated subjects, showed an improvement regarding symptom medication, visual analog scale, Rhinoconjunctivitis Quality of Life Questionnaire, and asthma symptom scores in both treatment years. This was accompanied by an induction of allergen-specific IgG without induction of allergen-specific IgE and a reduction in the seasonally induced increase in allergen-specific IgE levels in year 2. In the first year, more grade 2 reactions were observed in the active (n = 6) versus placebo (n = 1) groups, whereas there was almost no difference in the second year.

Conclusions

Injections of BM32 induced allergen-specific IgG, improved clinical symptoms of seasonal grass pollen allergy, and were well tolerated.

Recombinant Allergens in Structural Biology, Diagnosis, and Immunotherapy

The years 1988-1995 witnessed the beginning of allergen cloning and the generation of recombinant allergens, which opened up new avenues for the diagnosis and research of human allergic diseases. Most crystal and solution structures of allergens have been obtained using recombinant allergens. Structural information on allergens allows insights into their evolutionary biology, illustrates clinically observed cross-reactivities, and makes the design of hypoallergenic derivatives for allergy vaccines possible. Recombinant allergens are widely used in molecule-based allergy diagnosis such as protein microarrays or suspension arrays. Recombinant technologies have been used to produce well-characterized, noncontaminated vaccine components with known biological activities including a variety of allergen derivatives with reduced IgE reactivity. Such recombinant hypoallergens as well as wild-type recombinant allergens have been used successfully in several immunotherapy trials for more than a decade to treat birch and grass pollen allergy. As a more recent application, the development of antibody repertoires directed against conformational epitopes during immunotherapy has been monitored by recombinant allergen chimeras. Although much progress has been made, the number and quality of recombinant allergens will undoubtedly increase and keep improving our knowledge in basic scientific investigations, diagnosis, and therapy of human allergic diseases.

CD23 surface density on B cells is associated with IgE levels and determines IgE-facilitated allergen uptake, as well as activation of allergen-specific T cells

BACKGROUND

Increasing evidence suggests that the low-affinity receptor for IgE, CD23, plays an important role in controlling the activity of allergen-specific T cells through IgE-facilitated allergen presentation.

OBJECTIVE

We sought to determine the number of CD23 molecules on immune cells in allergic patients and to investigate whether the number of CD23 molecules on antigen-presenting cells is associated with IgE levels and influences allergen uptake and allergen-specific T-cell activation.

METHODS

Numbers of CD23 molecules on immune cells of allergic patients were quantified by using flow cytometry with QuantiBRITE beads and compared with total and allergen-specific IgE levels, as well as with allergen-induced immediate skin reactivity. Allergen uptake and allergen-specific T-cell activation in relation to CD23 surface density were determined by using flow cytometry in combination with confocal microscopy and T cells transfected with the T-cell receptor specific for the birch pollen allergen Bet v 1, respectively. Defined IgE-allergen immune complexes were formed with human monoclonal allergen-specific IgE and Bet v 1.

RESULTS

In allergic patients the vast majority of CD23 molecules were expressed on naive IgD⁺ B cells. The density of CD23 molecules on B cells but not the number of CD23⁺ cells correlated with total IgE levels (R_S = 0.53, P = .03) and allergen-induced skin reactions (R_S = 0.63, P = .008). Uptake of allergen-IgE complexes into B cells and activation of allergen-specific T cells depended on IgE binding to CD23 and were associated with CD23 surface density. Addition of monoclonal IgE to cultured PBMCs significantly (P = .04) increased CD23 expression on B cells.

CONCLUSION

CD23 surface density on B cells of allergic patients is correlated with allergen-specific IgE levels and determines allergen uptake and subsequent activation of T cells.

Allergen immunotherapy for birch pollen-allergic patients: recent advances

As of today, allergen immunotherapy is performed with aqueous natural allergen extracts. Recombinant allergen vaccines are not yet commercially available, although they could provide patients with well-defined and highly consistent drug substances. As Bet v 1 is the major allergen involved in birch pollen allergy, with more than 95% of patients sensitized to this allergen, pharmaceutical-grade recombinant Bet v 1-based vaccines were produced and clinically tested. Herein, we compare the clinical results and modes of action of treatments based on either a birch pollen extract or recombinant Bet v 1 expressed as hypoallergenic or natural-like molecules. We also discuss the future of allergen immunotherapy with improved drugs intended for birch pollen-allergic patients suffering from rhinoconjunctivitis.

Ligand Recognition of the Major Birch Pollen Allergen Bet v 1 is Isoform Dependent

Each spring millions of patients suffer from allergies when birch pollen is released into the air. In most cases, the major pollen allergen Bet v 1 is the elicitor of the allergy symptoms. Bet v 1 comes in a variety of isoforms that share virtually identical conformations, but their relative concentrations are plant-specific. Glycosylated flavonoids, such as quercetin-3-O-sophoroside, are the physiological ligands of Bet v 1, and here we found that three isoforms differing in their allergenic potential also show an individual, highly specific binding behaviour for the different ligands. This specificity is driven by the sugar moieties of the ligands rather than the flavonols. While the influence of the ligands on the allergenicity of the Bet v 1 isoforms may be limited, the isoform and ligand mixtures add up to a complex and thus individual fingerprint of the pollen. We suggest that this mixture is not only acting as an effective chemical sunscreen for pollen DNA, but may also play an important role in recognition processes during pollination.

Hypoallergenic derivatives of Fel d 1 obtained by rational reassembly for allergy vaccination and tolerance induction

BACKGROUND AND OBJECTIVE

The major cat allergen Fel d 1 represents one of the most important respiratory allergens. Aim of this study was to engineer recombinant Fel d 1 derivatives with reduced IgE reactivity and preserved T cell epitopes for vaccination and tolerance induction.

METHODS

Seven recombinant mosaic proteins were generated by reassembly of non-IgE-reactive peptides of Fel d 1 which contained the sequence elements for induction of allergen-specific blocking IgG antibodies and T cell epitopes. Mosaic proteins were expressed in Escherichia coli using codon-optimized synthetic genes and compared with Fel d 1 regarding structural fold by circular dichroism, IgE-binding capacity, activation of allergic patients' basophils and ability to induce allergen-specific blocking IgG antibodies upon immunization.

RESULTS

Although each of the mosaic proteins had lost the alpha-helical fold typical for Fel d 1, a strong reduction in IgE reactivity as well as allergenic activity in basophil activation assays was only obtained for three constructs, two reassembled fragments (Fel d 1 MB, Fel d 1 MC) and a fusion of the latter two (Fel d 1 MF) in which the cysteines of Fel d 1 MC were replaced by serines. Immunization of rabbits with Fel d 1 MB, MC and MF induced high levels of IgG antibodies that inhibited IgE reactivity of cat-allergic patients to Fel d 1 in a comparable manner as IgG induced with the wild-type allergen.

CONCLUSIONS

We report the development of hypoallergenic reassembled Fel d 1 proteins suitable for vaccination and tolerance induction in cat-allergic patients.

Prophylactic and therapeutic vaccination with carrier-bound Bet v 1 peptides lacking allergen-specific T cell epitopes reduces Bet v 1-specific T cell responses via blocking antibodies in a murine model for birch pollen allergy

Background

Vaccines consisting of allergen-derived peptides lacking IgE reactivity and allergen-specific T cell epitopes bound to allergen-unrelated carrier molecules have been suggested as candidates for allergen-specific immunotherapy.

Objective

To study whether prophylactic and therapeutic vaccination with carrier-bound peptides from the major birch pollen allergen Bet v 1 lacking allergen-specific T cell epitopes has influence on Bet v 1-specific T cell responses.

Methods

Three Bet v 1-derived peptides, devoid of Bet v 1-specific T cell epitopes, were coupled to KLH and adsorbed to aluminium hydroxide to obtain a Bet v 1-specific allergy vaccine. Groups of BALB/c mice were immunized with the peptide vaccine before or after sensitization to Bet v 1. Bet v 1- and peptide-specific antibody responses were analysed by ELISA. T cell and cytokine responses to Bet v 1, KLH, and the peptides were studied in proliferation assays. The effects of peptide-specific and allergen-specific antibodies on T cell responses and allergic lung inflammation were studied using specific antibodies.

Results

Prophylactic and therapeutic vaccination with carrier-bound Bet v 1 peptides induced a Bet v 1-specific IgG antibody response without priming/boosting of Bet v 1-specific T cells. Prophylactic and therapeutic vaccination of mice with the peptide vaccine induced Bet v 1-specific antibodies which suppressed Bet v 1-specific T cell responses and allergic lung inflammation.

Conclusion and Clinical Relevance

Vaccination with carrier-bound allergen-derived peptides lacking allergen-specific T cell epitopes induces allergen-specific IgG antibodies which suppress allergen-specific T cell responses and allergic lung inflammation.

The impact of nitration on the structure and immunogenicity of the major birch pollen allergen Bet v 1.0101

Allergy prevalence has increased in industrialized countries. One contributing factor could be pollution, which can cause nitration of allergens exogenously (in the air) or endogenously (in inflamed lung tissue). We investigated the impact of nitration on both the structural and immunological behavior of the major birch pollen allergen Bet v 1.0101 to determine whether nitration might be a factor in the increased incidence of allergy. Bet v 1.0101 was nitrated with tetranitromethane. Immune effects were assessed by measuring the proliferation of specific T-cell lines (TCLs) upon stimulation with different concentrations of nitrated and unmodified allergen, and by measurement of cytokine release of monocyte-derived dendritic cells (moDCs) and primary DCs (primDCs) stimulated with nitrated versus unmodified allergen. HPLC-MS, crystallography, gel electrophoresis, amino acid analysis, size exclusion chromatography and molecular dynamics simulation were performed to characterize structural changes after nitration of the allergen. The proliferation of specific TCLs was higher upon stimulation with the nitrated allergen in comparison to the unmodified allergen. An important structural consequence of nitration was oligomerization. Moreover, analysis of the crystal structure of nitrated Bet v 1.0101 showed that amino acid residue Y83, located in the hydrophobic cavity, was nitrated to 100%. Both moDCs and primDCs showed decreased production of T_H1-priming cytokines, thus favoring a T_H2 response. These results implicate that nitration of Bet v 1.0101 might be a contributing factor to the observed increase in birch pollen allergy, and emphasize the importance of protein modifications in understanding the molecular basis of allergenicity.

Recombinant allergens for pollen immunotherapy

Specific immunotherapy (IT) represents the only potentially curative therapeutic intervention of allergic diseases capable of suppressing allergy-associated symptoms not only during treatment, but also after its cessation. Presently, IT is performed with allergen extracts, which represent a heterogeneous mixture of allergenic, as well as nonallergenic, compounds of a given allergen source. To overcome many of the problems associated with extract-based IT, strategies based on the use of recombinant allergens or derivatives thereof have been developed. This review focuses on recombinant technologies to produce allergy therapeuticals, especially for allergies caused by tree, grass and weed pollen, as they are among the most prevalent allergic disorders affecting the population of industrialized societies. The reduction of IgE-binding of recombinant allergen derivatives appears to be mandatory to increase the safety profile of vaccine candidates. Moreover, increased immunogenicity is expected to reduce the dosage regimes of the presently cumbersome treatment. In this regard, it has been convincingly demonstrated in animal models that hypoallergenic molecules can be engineered to harbor inherent antiallergenic immunologic properties. Thus, strategies to modulate the allergenic and immunogenic properties of recombinant allergens will be discussed in detail. In recent years, several successful clinical studies using recombinant wild-type or hypoallergens as active ingredients have been published and, currently, novel treatment forms with higher safety and efficacy profiles are under investigation in clinical trials. These recent developments are summarized and discussed.

Molecular approach to allergy diagnosis and therapy

Presently, allergy diagnosis and therapy procedures are undergoing a transition phase in which allergen extracts are being step-by-step replaced by molecule-based products. The new developments will allow clinicians to obtain detailed information on sensitization patterns, more accurate interpretation of allergic symptoms, and thus improved patients' management. In this respect, recombinant technology has been applied to develop this new generation of molecule-based allergy products. The use of recombinant allergens allows full validation of identity, quantity, homogeneity, structure, aggregation, solubility, stability, IgE-binding and the biologic potency of the products. In contrast, such parameters are extremely difficult to assay and standardize for extract-based products. In addition to the possibility of bulk production of wild type molecules for diagnostic purposes, recombinant technology opened the possibility of developing safer and more efficacious products for allergy therapy. A number of molecule-based hypoallergenic preparations have already been successfully evaluated in clinical trials, bringing forward the next generation of allergy vaccines. In this contribution, we review the latest developments in allergen characterization, molecule-based allergy diagnosis, and the application of recombinant allergens in therapeutic setups. A comprehensive overview of clinical trials using recombinant allergens as well as synthetic peptides is presented.

Recombinant house dust mite allergens

House dust mites (HDM) are a globally important source of allergen responsible for the sensitization of more than 50% of allergic patients. Specific immunotherapy with HDM extracts is effective but allergen extracts cannot be fully standardized and severe side-effects can occur during the protracted course of treatment. The introduction of molecular biological techniques into allergy research allowed the indentification of more than 20 groups of HDM allergens. Recombinant HDM allergens can be produced in defined concentrations and consistent quality and allow the development of vaccines for HDM allergy with reduced allergenic activity and retained immunogenicity. The immunotherapy trials in pollen allergic patients with recombinant pollen allergens/hypoallergenic allergen derivatives have shown that this treatment is effective and indicated that recombinant HDM vaccines might improve immunotherapy of HDM allergic patients. Here we report the steps for the development of vaccines for HDM allergy. After selection of the most prevalent HDM species, the panel of allergens to be included into a therapeutic vaccine for HDM allergy needs to be determined. HDM allergens with high IgE-binding frequency and clinical relevance will be modified into hypoallergenic variants and evaluated for their allergenic activity and immunogenicity. Derivatives with reduced allergenic activity but with retained immunogenicity would be good candidates for a HDM vaccine for safe and efficient immunotherapy.

Transgenic rice seeds accumulating recombinant hypoallergenic birch pollen allergen Bet v 1 generate giant protein bodies

A versatile hypoallergenic allergen derivative against multiple allergens is an ideal tolerogen for allergen-specific immunotherapy. Such a tolerogen should exhibit high efficacy, without side effects, when administered at high doses and should be applicable to several allergens. Tree pollen chimera 7 (TPC7), a hypoallergenic Bet v 1 tolerogen against birch pollen allergy, was previously selected by DNA shuffling of 14 types of Fagales tree pollen allergens. In this study, transgenic rice seed accumulating TPC7 was generated as an oral vaccine against birch pollen allergy by expressing this protein as a secretory protein using the N-terminal signal peptide and the C-terminal KDEL tag under the control of an endosperm-specific glutelin promoter. The highest level of TPC7 accumulation was approximately 207 µg grain(-1). Recombinant TPC7 is a glycoprotein with high mannose-type N-glycan, but without β1,2-xylose or α1,3-fucose, suggesting that TPC7 is retained in the endoplasmic reticulum (ER). TPC7 is deposited as a novel, giant spherical ER-derived protein body, >20 µm in diameter, which is referred to as the TPC7 body. Removal of the KDEL retention signal or mutation of a cysteine residue resulted in an alteration of TPC7 body morphology, and deletion of the signal peptide prevented the accumulation of TPC7 in rice seeds. Therefore, the novel TPC7 bodies may have formed aggregates within the ER lumen, primarily due to the intrinsic physicochemical properties of the protein.

Characterization of mutants of a highly cross-reactive calcium-binding protein from Brassica pollen for allergen-specific immunotherapy

The major turnip (Brassica rapa) pollen allergen, belongs to a family of calcium-binding proteins (i.e., two EF-hand proteins), which occur as highly cross-reactive allergens in pollen of weeds, grasses and trees. In this study, the IgE binding capacity and allergenic activity of three recombinant allergen variants containing mutations in their calcium-binding sites were analyzed in sensitized patients with the aim to identify the most suitable hypoallergenic molecule for specific immunotherapy. Analysis of the wildtype allergen and the mutants regarding IgE reactivity and activation of basophils in allergic patients indicated that the allergen derivative mutated in both calcium-binding domains had the lowest allergenic activity. Gel filtration and circular dichroism experiments showed that both, the wildtype and the double mutant, occurred as dimers in solution and assumed alpha-helical fold, respectively. However, both fold and thermal stability were considerably reduced in the double mutant. The use of bioinformatic tools for evaluation of the solvent accessibility and charge distribution suggested that the reduced IgE reactivity and different structural properties of the double mutant may be due to a loss of negatively charged amino acids on the surface. Interestingly, immunization of rabbits showed that only the double mutant but not the wildtype allergen induced IgG antibodies which recognized the allergen and blocked binding of allergic patients IgE. Due to the extensive structural similarity and cross-reactivity between calcium-binding pollen allergens the hypoallergenic double mutant may be useful not only for immunotherapy of turnip pollen allergy, but also for the treatment of allergies to other two EF-hand pollen allergens.

New directions in immunotherapy

Allergen immunotherapy (AIT) is effective in reducing the clinical symptoms associated with allergic rhinitis, asthma and venom-induced anaphylaxis. Subcutaneous (SCIT) and sublingual immunotherapy (SLIT) with unmodified allergen extracts are the most widely prescribed AIT regimens. The efficacy of these 2 routes appears comparable, but the safety profile with SLIT is more favorable allowing for home administration and requiring less patient time. However, both require that the treatment is taken regularly over several years, e.g., monthly in a supervised medical setting with SCIT and daily at home with SLIT. Despite the difference in treatment settings, poor adherence has been reported with both routes. Emerging evidence suggests that AIT may be effective in other allergic conditions such as atopic dermatitis, venom sting-induced large local reactions, and food allergy. Research with oral immunotherapy (OIT) for food allergies suggest that many patients can be desensitized during treatment, but questions remain about whether this can produce long term tolerance. Further studies are needed to identify appropriate patients and treatment regimens with these conditions. Efforts to develop safer and more effective AIT for inhalant allergies have led to investigations with modified allergens and alternate routes. Intralymphatic (ILIT) has been shown to produce long-lasting clinical benefits after three injections comparable to a 3-year course of SCIT. Epicutaneous (EPIT) has demonstrated promising results for food and inhalant allergies. Vaccine modifications, such as T cell epitopes or the use of viral-like particles as an adjuvant, have been shown to provide sustained clinical benefits after a relatively short course of treatment compared to the currently available AIT treatments, SLIT and SCIT. These newer approaches may increase the utilization and adherence to AIT because the multi-year treatment requirement of currently available AIT is a likely deterrent for initiating and adhering to treatment.

Different modes of IgE binding to CD23 revealed with major birch allergen, Bet v 1-specific monoclonal IgE

We investigated the binding of IgE and different types of allergen-IgE complexes to CD23-expressing human B cells. We performed the experiments using chimeric Bip 1 (CB1), a chimeric humanized IgE specific for the major birch allergen, Bet v 1, together with monomeric and oligomeric forms of recombinant Bet v 1 (rBet v 1), and Bet v 1-specific IgG antibodies. In this model IgE binding to CD23 was independent of variations in antibody affinities towards monomeric and oligomeric Bet v 1 as demonstrated by plasmon surface resonance. CB1 alone or in the form of small immune complexes consisting of one molecule of CB1 plus allergen, showed comparable binding to CD23 on B cells. Using anti-IgE antibody probes discriminating CD23-bound from CD23-unbound IgE, it is demonstrated that in large immune complexes obtained with oligomeric Bet v 1 or by super-crosslinking of small immune complexes with Bet v 1-specific IgG, anti-IgE staining of B cells increased. This increase of staining was due to the presence of IgE antibodies in the immune complexes that were not directly engaged in CD23 binding, and thus available for IgE detection. Our study thus reveals that CD23 can bind in a comparable manner to free IgE and IgE-allergen complexes of different size and composition, which may also include allergen-specific IgG. The interplay of free IgE with IgE-allergen immune complexes of different sizes and composition with CD23 binding represents a mechanism for the modulation of CD23-mediated immune responses such as IgE-facilitated allergen presentation in allergic diseases.

Factors influencing the allergenicity and adjuvanticity of allergens

IgE-mediated allergic disorders affect up to 25% of the population in industrialized countries and result in a Th2-polarized immune response to innocuous environmental proteins, so-called allergens. Among a large number of proteins to which humans are exposed to, only a minute fraction are allergens. This observation suggests that allergens share special features of allergenicity (i.e., the capacity to induce the production of specific IgE antibodies in susceptible individuals). However, the question 'what makes a protein allergenic' still remains unanswered although some biochemical characteristics of allergens and their capacity to interact with the innate immune system could be associated with their allergenic potential. Allergen-specific immunotherapy aims at an alteration of the disease-eliciting immune response by repeated administration of allergens. Recently, approaches emerged to endow allergens with adjuvanticity, in particular aiming at an increase of their immunomodulatory capacity. This article summarizes factors of allergenicity and introduces recent concepts of adjuvanticity to improve allergen-specific immunotherapy.

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.

Peptide and recombinant immunotherapy

Because of the need to standardize allergen immunotherapy and the desire to reduce allergic adverse events during therapy, a transition to recombinant/synthetic hypoallergenic approaches is inevitable. Evidence supports the notion that effective therapy can be delivered using a limited panel of allergens or even epitopes, weakening the argument that all allergens must be present for optimal efficacy. Moreover, standardized products will allow direct comparisons between studies and, for the first time, immunotherapy studies will be truly blinded, allowing an accurate assessment of the actual treatment effect that can be achieved with this form of intervention.

Recombinant allergens for allergen-specific immunotherapy: 10 years anniversary of immunotherapy with recombinant allergens

The broad applicability of allergen-specific immunotherapy for the treatment and eventually prevention of IgE-mediated allergy is limited by the poor quality and allergenic activity of natural allergen extracts that are used for the production of current allergy vaccines. Today, the genetic code of the most important allergens has been deciphered; recombinant allergens equalling their natural counterparts have been produced for diagnosis and immunotherapy, and a large panel of genetically modified allergens with reduced allergenic activity has been characterized to improve safety of immunotherapy and explore allergen-specific prevention strategies. Successful immunotherapy studies have been performed with recombinant allergens and hypoallergenic allergen derivatives and will lead to the registration of the first recombinant allergen-based vaccines in the near future. There is no doubt that recombinant allergen-based vaccination strategies will be generally applicable to most allergen sources, including respiratory, food and venom allergens and allow to produce safe allergy vaccines for the treatment of the most common forms of IgE-mediated allergies.

Novel Strategies for the Development of a Vaccine for Parietaria Allergy

Specific immunotherapy is a well established and clinically proved strategy to cure allergic reactions. The impressive boost of knowledge derived from DNA recombinant technology applied to this field allowed the identification, cloning and expression of several clinically relevant allergens. Recombinant allergens can be easily produced in a pure and reproducible way with immunological properties comparable to natural allergens and matching the requirements of pharmaceutical companies. Parietaria pollinosis is a major health problem in the Mediterranean basin with prolonged symptoms. In this review we will discuss the rational approaches to design hypoallergenic derivatives of the major allergens of this pollen, their immunological properties and possible clinical future implications.

Genetic engineering of trimers of hypoallergenic fragments of the major birch pollen allergen, Bet v 1, for allergy vaccination

An immunotherapy trial performed in allergic patients with hypoallergenic recombinant fragments, comprising aa 1-74 and 75-160 of the major birch pollen allergen, Bet v 1, has indicated that the induction of allergen-specific IgG responses may be an important mechanism of this treatment. To investigate whether the immunogenicity of the rBet v 1 fragments can be increased, recombinant trimers of the fragments were produced. For this purpose, DNA trimers of rBet v 1 aa 1-74 as well as of rBet v 1 aa 75-160 were subcloned into expression plasmid pET 17b, expressed in Escherichia coli and purified. The fragments as well as the fragment trimers showed a reduced IgE-binding capacity and allergenic activity compared to rBet v 1 wildtype when tested in allergic patients. Both rBet v 1 aa 75-160 monomer and trimer induced high titers of allergen-specific IgG1 Abs in mice. Interestingly, rBet v 1 aa 1-74 trimer induced a much higher IgG(1) response to rBet v 1 than rBet v 1 aa 1-74 monomer. Consequently, IgG Abs induced with the rBet v 1 aa 1-74 trimer inhibited birch pollen allergic patients' IgE-binding 10-fold more efficiently than IgG Abs induced with the monomer. Our data show that the immunogenicity of allergy vaccines can be increased by oligomerization.

Altered IgE epitope presentation: A model for hypoallergenic activity revealed for Bet v 1 trimer

In order to reduce side effects in the course of allergen specific immunotherapy hypoallergenic allergen derivatives with reduced IgE reactivity have been made by genetic engineering. In contrast to other recombinant hypoallergenic allergen derivatives which showed reduced IgE reactivity, a recombinant trimer of the major birch pollen allergen Bet v 1 showed reduced allergenic activity despite preserved IgE reactivity. We studied rBet v 1 trimer by SDS-PAGE, mass spectrometry, circular dichroism and gel filtration. Furthermore we investigated IgE and IgG reactivity of the rBet v 1 trimer in solid and liquid phase assays and compared its allergenic activity with that of rBet v 1 wildtype using basophil activation assays. In solid phase immunoassays rBet v 1 trimer exhibited even stronger IgE reactivity than the rBet v 1 wildtype, whereas both proteins were equally well recognized by Bet v 1-specific IgG antibody probes. In fluid phase IgE experiments rBet v 1 trimer inhibited IgE reactivity to rBet v 1 wildtype but showed a more than 10-fold reduced allergenic activity compared to the rBet v 1 monomer. By analytical gel filtration it was demonstrated that, despite its monomeric appearance in SDS-PAGE the trimer occurred in fluid phase in the form of defined high molecular weight (>600 kDa) aggregates whereas rBet v 1 wildtype strictly appeared as monomeric protein. The results indicate that the hypoallergenic nature of the rBet v 1 trimer is due to formation of defined high molecular weight aggregates which may be responsible for an altered presentation of IgE epitopes in a form with reduced capacity to crosslink effector-cell bound IgE. We thus provide evidence for a novel mechanism for hypoallergenic activity.

Authentication of food allergen quality by physicochemical and immunological methods

Purified allergens are required to detect cross-contamination with other allergenic foods and to understand allergen interaction with other components of the food matrix. Pure allergens are also used for the diagnosis and treatment of food allergies. For example, serological methods are being developed to improve the quality of diagnosis, and to reduce the need for food challenge tests. In addition, recombinant allergens are being evaluated as candidate vaccines for safe and efficacious specific immunotherapy. Pure allergens are indispensable as reference materials for the calibration and standardization of methods between different laboratories and operators for risk assessment in the food industry. Therefore, there is a need for well-defined purified food allergens. In this context, a panel of 46 food allergens from plant and animal sources has been purified, from either the food sources or as recombinant forms, within the EU-funded EuroPrevall project. These allergens have been characterized by a battery of diagnostic tests demonstrating that they constitute an authentic, well-defined library of comparable quality. The review summarizes the applications, potentials and limitations of key techniques used for the characterization and authentication of these allergen preparations, with a special emphasis on protein purity and identity, folding, post-translational modifications and immunochemical properties. One key area identified is the development of powerful analytical techniques, such as mass spectrometry and nuclear magnetic resonance, to improve the authentication of allergens for routine applications in allergy management.

Hypoallergenic derivatives of the major birch pollen allergen Bet v 1 obtained by rational sequence reassembly

BACKGROUND

At least 100 million patients suffer from birch pollen allergy.

OBJECTIVE

Rational design of recombinant derivatives of the major birch pollen allergen, Bet v 1, characterized by reduced IgE reactivity, preservation of sequences relevant for the induction of allergen-specific blocking IgG, and maintenance of T-cell epitopes for immunotherapy of birch pollen allergy.

METHODS

Three recombinant mosaic proteins derived from Bet v 1 were generated by reassembly of codon-optimized genes coding for Bet v 1 fragments containing the elements for the induction of allergen-specific blocking IgG antibodies and the major T-cell epitopes. The proteins were expressed in Escherichia coli as recombinant mosaic molecules and compared with the Bet v 1 wild-type protein by chemical and structural methods, regarding IgE-binding and IgG-binding capacity, in basophil activation assays and tested for the in vivo induction of IgG responses.

RESULTS

Three recombinant Bet v 1 (rBet v 1) mosaic proteins with strongly reduced IgE reactivity and allergenic activity were expressed and purified. Immunization with the recombinant hypoallergens induced IgG antibodies that inhibited IgE reactivity of patients with allergy to Bet v 1 comparable to those induced with the rBet v 1 wild-type allergen.

CONCLUSION

We report the generation and preclinical characterization of 3 hypoallergenic rBet v 1 derivatives with suitable properties for immunotherapy of birch pollen allergy.

Transient dimers of allergens

Background

Allergen-mediated cross-linking of IgE antibodies bound to the FcεRI receptors on the mast cell surface is the key feature of the type I allergy. If an allergen is a homodimer, its allergenicity is enhanced because it would only need one type of antibody, instead of two, for cross-linking.

Methodology/Principal Findings

An analysis of 55 crystal structures of allergens showed that 80% of them exist in symmetric dimers or oligomers in crystals. The majority are transient dimers that are formed at high protein concentrations that are reached in cells by colocalization. Native mass spectrometric analysis showed that native allergens do indeed form transient dimers in solution, while hypoallergenic variants of them exist almost solely in the monomeric form. We created a monomeric Bos d 5 allergen and show that it has a reduced capability to induce histamine release.

Conclusions/Significance

The results suggest that dimerization would be a very common and essential feature for allergens. Thus, the preparation of purely monomeric variants of allergens could open up novel possibilities for specific immunotherapy.

Relevant B cell epitopes in allergic disease

The 3-dimensional structure of an allergen defines the accessible parts on the surface of the molecule or epitopes that interact with antibodies. Mapping the antigenic determinants for IgE antibody binding has been pursued through strategies based on the use of overlapping synthetic peptides, recombinant allergenic fragments or unfolded allergens. These approaches led to the identification of mostly linear epitopes and are useful for food allergens that undergo digestion or food processing. For inhaled allergens, conformational epitopes appear to be the primary targets of IgE responses. Knowledge of the molecular structure of allergens alone and in complex with antibodies that interfere with IgE antibody binding is important to understand the immune recognition of B cell-antigenic determinants on allergens and the design of recombinant allergens for immunotherapy. Starting with the molecular cloning and expression of allergens, and with the advent of X-ray crystallography and nuclear magnetic resonance techniques, we have been able to visualize conformational epitopes on allergens.

Engineering of major house dust mite allergens Der p 1 and Der p 2 for allergen-specific immunotherapy

BACKGROUND

Specifically designed recombinant allergens with reduced IgE reactivity are promising candidates for a more defined, effective, and safer specific immunotherapy (SIT).

OBJECTIVE

We sought to obtain hypoallergenic hybrid molecules which could potentially be applied to house dust mite (HDM) allergy treatment.

METHODS

Two hybrid molecules (QM1 and QM2) derived from the two major Dermatophagoides pteronyssinus allergens, Der p 1 and Der p 2, were engineered by PCR, produced in Escherichia coli, and purified. The overall IgE-binding capacity of the hybrids was compared with their single components by Western blot, specific IgE, skin prick test (SPT), and IgE-inhibition assays. T cell proliferation assay were performed to confirm their retention of T cell reactivity. Immune responses to the hybrid molecules were studied in BALB/c mice.

RESULTS

The IgE reactivity of both hybrid proteins was strongly reduced as evaluated by in vitro methods. Furthermore, in vivo SPTs performed on 106 HDM-allergic patients showed that the hybrid proteins had a significantly lower potency to induce cutaneous reactions than the individual components. Hybrid molecules induced higher T cell proliferation responses than those produced by an equimolecular mixture of Der p 1 and Der p 2. Immunization of mice with the hybrid proteins induced Der p 1- and Der p 2-specific IgG, which inhibited the binding of allergic patients' IgE to these natural allergens.

CONCLUSION

QM1 and QM2 hybrids exhibited less IgE-binding activity but preserved immunogenicity and fulfilled the basic requirements for hypoallergenic molecules suitable for a future SIT of HDM allergy.

A hypoallergenic variant of Der p 1 as a candidate for mite allergy vaccines

BACKGROUND

Recombinant hypoallergens that display reduced allergenicity but retain T-cell reactivity represent promising candidates to improve the safety and efficacy of allergen-specific vaccines or immunotherapy.

OBJECTIVE

The current study reports the immunologic characterization of a hypoallergenic variant of the major mite allergen Der p 1.

METHODS

The recombinant proform of Der p 1 (ProDer p 1) was expressed in Escherichia coli (ProDer p 1 coli), purified and characterized at the level of its secondary structure, and IgE and T-cell reactivities. Moreover, the prophylactic potential of ProDer p 1 coli vaccinations was evaluated in a murine Der p 1 sensitization model.

RESULTS

After purification and refolding, ProDer p 1 coli remained aggregated with a higher beta-sheet content and altered Der p 1 conformational epitopes compared with the correctly folded monomeric ProDer p 1 produced in Chinese hamster ovary cells. Both ProDer p 1 forms were able to retain the Der p 1-specific T-cell reactivity but direct ELISA, competitive inhibition, and rat basophil leukemia assays clearly showed that ProDer p 1 coli displays a very weak IgE reactivity. Mice vaccinations with aggregated ProDer p 1 adjuvanted with alum induced a T(H)1-biased immune response that prevented the subsequent allergic response after Der p 1 sensitization and airway challenge with aerosolized mite extracts. Furthermore, ProDer p 1 coli treatment inhibited the development of airway eosinophilia and airway hyperresponsiveness to inhaled methacholine.

CONCLUSION

Aggregated forms of Der p 1 could represent hypoallergens suitable for the prevention of mite allergy.

Disruption of allergenic activity of the major grass pollen allergen Phl p 2 by reassembly as a mosaic protein

The recognition of conformational epitopes on respiratory allergens by IgE Abs is a key event in allergic inflammation. We report a molecular strategy for the conversion of allergens into vaccines with reduced allergenic activity, which is based on the reassembly of non-IgE-reactive fragments in the form of mosaic proteins. This evolution process is exemplified for timothy grass pollen-derived Phl p 2, a major allergen for more than 200 million allergic patients. In a first step, the allergen was disrupted into peptide fragments lacking IgE reactivity. cDNAs coding for these peptides were reassembled in altered order and expressed as a recombinant mosaic molecule. The mosaic molecule had lost the three-dimensional structure, the IgE reactivity, and allergenic activity of the wild-type allergen, but it induced high levels of allergen-specific IgG Abs upon immunization. These IgG Abs crossreacted with group 2 allergens from other grass species and inhibited allergic patients' IgE binding to the wild-type allergen. The mosaic strategy is a general strategy for the reduction of allergenic activity of protein allergens and can be used to convert harmful allergens into safe vaccines.

From allergen genes to new forms of allergy diagnosis and treatment

Type I allergy represents an important health problem that affects more than 25% of the population in industrialized countries. Specific immunotherapy is one of the few causative treatment approaches for type I allergy and is currently performed with crude allergen extracts, which consist of a mixture of allergenic and nonallergenic components, are difficult to standardize and cannot be applied according to the patient's reactivity profile. With the introduction of molecular biological techniques into allergy research, a large panel of individual recombinant allergens has become available. Recombinant allergens can be used for improved diagnosis of allergy to determine the patient's sensitization profile, which is a prerequisite to select the allergens for patient-tailored immunotherapy. They allow the elucidation of the properties of allergens and of the mechanisms of allergy as well as of the mechanisms of immunotherapy. Moreover, recombinant allergens allow the development of hypoallergenic allergen derivatives with reduced allergenic activity and retained immunogenicity. First immunotherapy trials with hypoallergenic allergen derivatives have shown that this treatment might improve immunotherapy in the near future. This review summarizes the results, which were obtained with recombinant allergens and hypoallergenic allergen derivatives. The experiences from the in vitro and in vivo evaluation of the hypoallergenic derivatives and from clinical studies as well as the contribution of hypoallergenic derivatives to develop new treatment strategies and possibly prophylactic vaccination strategies are discussed.

Biotechnology-based allergy diagnosis and vaccination

The diagnosis and immunotherapy currently applied to allergic diseases involve the use of crude extracts of the allergen source without defining the allergy-eliciting molecule(s). Advances in recombinant DNA technology have made identification, cloning, expression and epitope mapping of clinically significant allergens possible. Recombinant allergens that retain the immunological features of natural allergens form the basis of accurate protein-chip-based methods for diagnosing allergic conditions. The ability to produce rationally designed hypoallergenic forms of allergens is leading to the development of novel and safe forms of allergy vaccines with improved efficacy. The initial clinical tests on recombinant-allergen-based vaccine preparations have provided positive results, and ongoing developments in areas such as alternative routes of vaccine delivery will enhance patient compliance.

Analysis of Epitope-Specific Immune Responses Induced by Vaccination with Structurally Folded and Unfolded Recombinant Bet v 1 Allergen Derivatives in Man

Previously, we have constructed recombinant derivatives of the major birch pollen allergen, Bet v 1, with a more than 100-fold reduced ability to induce IgE-mediated allergic reactions. These derivatives differed from each other because the two recombinant Bet v 1 fragments represented unfolded molecules whereas the recombinant trimer resembled most of the structural fold of the Bet v 1 allergen. In this study, we analyzed the Ab (IgE, IgG subclass, IgA, IgM) response to Bet v 1, recombinant and synthetic Bet v 1-derived peptides in birch pollen allergic patients who had been vaccinated with the derivatives or adjuvant alone. Furthermore, we studied the induction of IgE-mediated skin responses in these patients using Bet v 1 and Bet v 1 fragments. Both types of vaccines induced a comparable IgG1 and IgG4 response against new sequential epitopes which overlap with the conformational IgE epitopes of Bet v 1. This response was 4- to 5-fold higher than that induced by immunotherapy with birch pollen extract. Trimer more than fragments induced also IgE responses against new epitopes and a transient increase in skin sensitivity to the fragments at the beginning of therapy. However, skin reactions to Bet v 1 tended to decrease one year after treatment in both actively treated groups. We demonstrate that vaccination with folded and unfolded recombinant allergen derivatives induces IgG Abs against new epitopes. These data may be important for the development of therapeutic as well as prophylactic vaccines based on recombinant allergens.

Genetic Engineering of the Major Timothy Grass Pollen Allergen, Phl p 6, to Reduce Allergenic Activity and Preserve Immunogenicity

On the basis of IgE epitope mapping data, we have produced three allergen fragments comprising aa 1-33, 1-57, and 31-110 of the major timothy grass pollen allergen Phl p 6 aa 1-110 by expression in Escherichia coli and chemical synthesis. Circular dichroism analysis showed that the purified fragments lack the typical alpha-helical fold of the complete allergen. Superposition of the sequences of the fragments onto the three-dimensional allergen structure indicated that the removal of only one of the four helices had led to the destabilization of the alpha helical structure of Phl p 6. The lack of structural fold was accompanied by a strong reduction of IgE reactivity and allergenic activity of the three fragments as determined by basophil histamine release in allergic patients. Each of the three Phl p 6 fragments adsorbed to CFA induced Phl p 6-specific IgG Abs in rabbits. However, immunization of mice with fragments adsorbed to an adjuvant allowed for human use (AluGel-S) showed that only the Phl p 6 aa 31-110 induced Phl p 6-specific IgG Abs. Anti-Phl p 6 IgG Abs induced by vaccination with Phl p 6 aa 31-110 inhibited patients' IgE reactivity to the wild-type allergen as well as Phl p 6-induced basophil degranulation. Our results are of importance for the design of hypoallergenic allergy vaccines. They show that it has to be demonstrated that the hypoallergenic derivative induces a robust IgG response in a formulation that can be used in allergic patients.

Genetically engineered hybrid proteins from Parietaria judaica pollen for allergen-specific immunotherapy

BACKGROUND

Despite the use of conventional allergen-specific immunotherapy in clinical practice, more defined, efficient, and safer allergy vaccines are required.

OBJECTIVE

The aim of the study was to obtain hypoallergenic molecules by deleting B-cell epitopes, which could potentially be applied to Parietaria judaica pollen allergy treatment.

METHODS

Three hybrid molecules (Q1, Q2, and Q3) derived from fragments of the 2 major P judaica pollen allergens, Par j 1 and Par j 2, were engineered by means of PCR. Hybrid structures were compared with their natural components by means of circular dichroism, and their biologic activities were compared by using T-cell proliferation assays. Their IgE-binding activity was determined with Western blotting, skin prick tests, and enzyme allergosorbent and ELISA inhibition tests.

RESULTS

The hybrid proteins, especially Q2 and Q3, revealed significantly reduced IgE reactivity compared with the natural allergens, as well as with the whole P judaica extract. Furthermore, in vivo skin prick tests showed that the hybrid proteins had a significantly lower potency to induce cutaneous reactions than the whole P judaica extract. Two (Q1 and Q2) of the 3 hybrid proteins induced a comparable T-cell proliferation response as that produced by the whole extract and natural allergens.

CONCLUSION

Considering its reduced anaphylactogenic potential, together with its conserved T-cell reactivity, the engineered Q2 protein could be used in safe and shortened schedules of allergen-specific immunotherapy against P judaica pollen allergy.

CLINICAL IMPLICATIONS

Recombinant hybrid Q2 is able to induce T-cell proliferation, thus evidencing a potential therapeutic effect. Its reduced IgE-binding capacity envisages an excellent safety profile.

Recombinant allergens for immunotherapy

Recombinant allergens can be produced as defined molecules in consistent quality and unlimited amounts according to the corresponding DNA template. Furthermore, they can be modified to reduce their allergenic activity and to foster certain advantageous immunologic properties. Recombinant allergens equaling the natural allergens are available for diagnostic and therapeutic purposes, and modified versions have been developed with the aim to to reduce IgE-mediated side effects during immunotherapy. First injection immunotherapy trials conducted with recombinant vaccines for birch pollen and grass pollen allergy show that recombinant allergen-based immunotherapy has vaccination characteristics and is clinically effective. The obtained results hold promise that recombinant allergen-based immunotherapy will improve current immunotherapy practice and may open possibilities for new treatment strategies and possibly even for prophylactic vaccination.