Use of phage display technology to investigate allergen-antibody interactions

Human Monoclonal IgE Antibodies-a Major Milestone in Allergy

PURPOSE OF REVIEW

Bound to its high affinity receptor on mast cells and basophils, the IgE antibody molecule plays an integral role in the allergic reaction. Through interactions with the allergen, it provides the sensitivity and specificity parameters for cell activation and mediator release that produce allergic symptoms. Advancements in human hybridoma technologies allow for the generation and molecular definition of naturally occurring allergen-specific human IgE monoclonal antibodies.

RECENT FINDINGS

A high-resolution structure of dust mite allergen Der p 2 in complex with Fab of the human IgE mAb 2F10 was recently determined using X-ray crystallography. The structure reveals the fine molecular details of IgE 2F10 binding its 750 Å2 conformational epitope on Der p 2. This review provides an overview of this major milestone in allergy, the first atomic resolution structure of an authentic human IgE epitope. The molecular insights that IgE epitopes provide will allow for structure-based design approaches to the development of novel diagnostics, antibody therapeutics, and immunotherapies.

IgE Epitope Profiling for Allergy Diagnosis and Therapy - Parallel Analysis of a Multitude of Potential Linear Epitopes Using a High Throughput Screening Platform

Immunoglobulin E (IgE) is pivotal for manifestation and persistence of most immediate-type allergies and some asthma phenotypes. Consequently, IgE represents a crucial target for both, diagnostic purposes as well as therapeutic approaches. In fact, allergen-specific immunotherapy – aiming to re-route an IgE-based inflammatory response into an innocuous immune reaction against the allergen – is the only curative approach for IgE-mediated allergic diseases known so far. However, this requires the cognate allergen to be known. Unfortunately, even in well-characterized allergics or asthmatics, often just a small fraction of total IgE can be assigned to specific target allergens. To overcome this knowledge gap, we have devised an analytical platform for unbiased IgE target epitope detection. The system relies on chemically produced random peptide libraries immobilized on polystyrene beads (“one-bead-one-compound (OBOC) libraries”) capable to present millions of different peptide motifs simultaneously to immunoglobulins from biological samples. Beads binding IgE are highlighted with a fluorophore-labeled anti-IgE antibody allowing fluorescence-based detection and isolation of positives, which then can be characterized by peptide sequencing. Setting-up this platform required an elaborate optimization process including proper choice of background suppressants, secondary antibody and fluorophore label as well as incubation conditions. For optimal performance our procedure involves a sophisticated pre-adsorption step to eliminate beads that react nonspecifically with anti-IgE secondary antibodies. This step turned out to be important for minimizing detection of “false positive” motifs that otherwise would erroneously be classified as IgE epitopes. In validation studies we were able to retrieve artificial test-peptide beads spiked into our library by using IgE directed against those test-peptides at physiological concentrations (≤20 IU/ml of specific IgE), and disease-relevant bead-bound epitopes of the major peanut allergen Ara h 2 by screening with sera from peanut allergics. Thus, we established a platform with which one can find and validate new immunoglobulin targets using patient material which displays a largely unknown immunoglobulin repertoire.

Structural Aspects of the Allergen-Antibody Interaction

The development of allergic disease involves the production of IgE antibodies upon allergen exposure in a process called sensitization. IgE binds to receptors on the surface of mast cells and basophils, and subsequent allergen exposure leads to cross-linking of IgE antibodies and release of cell mediators that cause allergy symptoms. Although this process is quite well-understood, very little is known about the epitopes on the allergen recognized by IgE, despite the importance of the allergen-antibody interaction for the allergic response to occur. This review discusses efforts to analyze allergen-antibody interactions, from the original epitope mapping studies using linear peptides or recombinant allergen fragments, to more sophisticated technologies, such as X-ray crystallography and nuclear magnetic resonance. These state-of-the-art approaches, combined with site-directed mutagenesis, have led to the identification of conformational IgE epitopes. The first structures of an allergen (egg lysozyme) in complex with Fab fragments from IgG antibodies were determined in the 1980s. Since then, IgG has been used as surrogate for IgE, due to the difficulty of obtaining monoclonal IgE antibodies. Technical developments including phage display libraries have contributed to progress in epitope mapping thanks to the isolation of IgE antibody constructs from combinatorial libraries made from peripheral blood mononuclear cells of allergic donors. Most recently, single B cell antibody sequencing and human hybridomas are new breakthrough technologies for finally obtaining human IgE monoclonal antibodies, ideal for epitope mapping. The information on antigenic determinants will facilitate the design of hypoallergens for immunotherapy and the investigation of the fundamental mechanisms of the IgE response.

Alternaria B Cell Mimotope Immunotherapy Alleviates Allergic Responses in a Mouse Model

Alternaria is a major outdoor allergen. Immunotherapy with Alternaria extracts has been documented to be effective in the sensitized patients. However, Alternaria extracts are notoriously difficult to standardize. Our aim is to screen the B cell mimotopes of Alternaria and to evaluate the therapeutic effects of B cell mimotope peptides on a BALB/c mouse model of Alternaria allergy. After a human sera pool from Alternaria monosensitized patients was established, B cell mimotopes were screened by a phage-displayed random heptamer peptide library that was identified via mixed Alternaria-specific IgE in the sera pool. B cell mimotopes with phage as a carrier were used to perform immunotherapy in an Alternaria allergy mouse model. Serological Ab levels, lung histology, and cytokine profiles were compared in the mimotope immunotherapy group, natural extract immunotherapy group, irrelevant phage control group, Alternaria-sensitized model group, and saline-blank group. Two mimotopes (MISTSRK and QKRNTIT) presented high binding ability with the sera of the Alternaria-allergic patients and mice and, therefore, were selected for immunotherapy in the mouse model. Compared with irrelevant phage control, model, and natural extract immunotherapy group, mimotope immunotherapy group significantly reduced serum IgE levels, inflammatory cells infiltration in the lung tissue, and IL-4 levels in bronchoalveolar lavage fluid, whereas serum IgG1 and IFN-γ levels in bronchoalveolar lavage fluid were increased. Our results indicate that B cell mimotopes of Alternaria alleviates allergic response in a mouse model and have potential as novel therapeutic agents for IgE-mediated Alternaria-allergic diseases.

Application of phage peptide display technology for the study of food allergen epitopes

Phage peptide display technology has been used to identify IgE-binding mimotopes (mimics of natural epitopes) that mimic conformational epitopes. This approach is effective in the characterization of those epitopes that are important for eliciting IgE-mediated allergic responses by food allergens and those that are responsible for cross-reactivity among allergenic food proteins. Application of this technology will increase our understanding of the mechanisms whereby food allergens elicit allergic reactions, will facilitate the discovery of diagnostic reagents and may lead to mimotope-based immunotherapy.

Phage display peptide libraries in molecular allergology: from epitope mapping to mimotope-based immunotherapy

Identification of allergen epitopes is a key component in proper understanding of the pathogenesis of type I allergies, for understanding cross-reactivity and for the development of mimotope immunotherapeutics. Phage particles have garnered recognition in the field of molecular allergology due to their value not only in competitive immunoscreening of peptide libraries but also as immunogenic carriers of allergen mimotopes. They integrate epitope discovery technology and immunization functions into a single platform. This article provides an overview of allergen mimotopes identified through the phage display technique. We discuss the contribution of phage display peptide libraries in determining dominant B-cell epitopes of allergens, in developing mimotope immunotherapy, in understanding cross-reactivity, and in determining IgE epitope profiles of individual patients to improve diagnostics and individualize immunotherapy. We also discuss the advantages and pitfalls of the methodology used to identify and validate the mimotopes.

Uses of phage display in agriculture: a review of food-related protein-protein interactions discovered by biopanning over diverse baits

This review highlights discoveries made using phage display that impact the use of agricultural products. The contribution phage display made to our fundamental understanding of how various protective molecules serve to safeguard plants and seeds from herbivores and microbes is discussed. The utility of phage display for directed evolution of enzymes with enhanced capacities to degrade the complex polymers of the cell wall into molecules useful for biofuel production is surveyed. Food allergies are often directed against components of seeds; this review emphasizes how phage display has been employed to determine the seed component(s) contributing most to the allergenic reaction and how it has played a central role in novel approaches to mitigate patient response. Finally, an overview of the use of phage display in identifying the mature seed proteome protection and repair mechanisms is provided. The identification of specific classes of proteins preferentially bound by such protection and repair proteins leads to hypotheses concerning the importance of safeguarding the translational apparatus from damage during seed quiescence and environmental perturbations during germination. These examples, it is hoped, will spur the use of phage display in future plant science examining protein-ligand interactions.

Phage display--a powerful technique for immunotherapy: 2. Vaccine delivery

Phage display is a powerful technique in medical and health biotechnology. This technology has led to formation of antibody libraries and has provided techniques for fast and efficient search of these libraries. The phage display technique has been used in studying the protein-protein or protein-ligand interactions, constructing of the antibody and antibody fragments and improving the affinity of proteins to receptors. Recently phage display has been widely used to study immunization process, develop novel vaccines and investigate allergen-antibody interactions. This technology can provide new tools for protection against viral, fungal and bacterial infections. It may become a valuable tool in cancer therapies, abuse and allergies treatment. This review presents the recent advancements in diagnostic and therapeutic applications of phage display. In particular the applicability of this technology to study the immunization process, construction of new vaccines and development of safer and more efficient delivery strategies has been described.

Mimotope vaccination--from allergy to cancer

BACKGROUND

Mimotopes are peptides mimicking protein, carbohydrates or lipid epitopes and can be generated by phage display technology. When selected by antibodies, they represent exclusively B-cell epitopes and are devoid of antigen/allergen-specific T-cell epitopes. Coupled to carriers or presented in a multiple antigenic peptide form mimotopes achieve immunogenicity and induce epitope-specific antibody responses upon vaccination.

OBJECTIVE/METHODS

In allergy IgG antibodies may block IgE binding to allergens, whereas other IgG antibody specificities enhance this and support the anaphylactic reaction. In cancer, inhibitory antibody specificities prevent growth signals derived from overexpressed oncogenes, whereas growth-promoting specificities enhance signalling and proliferation. Therefore, the mimotope concept is applicable to both fields for epitope-specific vaccination and analysis of conformational B-cell epitopes for the allergen/antigen.

RESULTS/CONCLUSIONS

Mimotope technology is a relatively young theme in allergology and oncology. Still, proof of concept studies testing allergen and tumour mimotope vaccines suggest that mimotopes are ready for clinical trials.

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.

Molecular basis of allergen cross-reactivity: non-specific lipid transfer proteins from wheat flour and peach fruit as models

Peach non-specific lipid transfer protein (Pru p 3; nsLTP) has been characterized as the major food allergen in the adult Mediterranean population. Its wheat homologous protein, Tri a 14 has a relevant inhalant allergen in occupational baker's asthma. Different sensitization patterns to these allergens have been found in patients with this latter disorder. The objective of the present study was to characterize IgE epitopes of Tri a 14 and to compare them with those of Pru p 3 using three complementary strategies: the analysis of IgE-binding capacity of decapeptides bound to membrane, the identification of mimotopes using a phage display random peptide library, and the analysis of the surface electrostatic potential of both allergens. Thus, synthetic overlapping decapeptides, covering the Pru p 3 and Tri a 14 amino acid sequences, were used to identify sequential regions involved in recognition of IgE from baker's asthma patients sensitized to both nsLTPs. A phage display library was screened with total IgE from the same patients, and positive clones sequentially selected using the purified allergens, allowed to identify mimotopes (conformational epitopes) of Tri a 14 and Pru p 3. Both sequential regions and mimotopes were localized in the corresponding 3D molecular surface and their electrostatic properties were analyzed. Common sequential regions with strong IgE-binding capacity (residues 31-40 and 71-80) were identified in Tri a 14 and Pru p 3, whereas regions Tri a 14(51-60) and Pru p 3(11-20) were found specific of each allergen. A major conformational epitope (mimotope), L34H35N36R39S40S42D43G74V75L77P78Y79T80, which comprised the two common sequential epitopes, was located in Tri a 14, and a very similar one in Pru p 3. However, differences were detected on the surface electrostatic potential of both mimotopes: a first part (around residues 31-45) showed similar positive features in both allergens, whereas a second part (around residues 74-80) was markedly negative in Tri a 14 but neutral-positive in Pru p 3. Tri a 14 and Pru p 3 have a similar conformational region involved in IgE-binding, although their electrostatic features are different. Additionally, common and specific sequential IgE-binding regions were mapped in both allergens. These findings could be instrumental in understanding the cross-reactivity and specificity of sensitization to both homologous allergens.

Allergen structures and biologic functions: the cutting edge of allergy research

Studies of structure and function of allergens using state-of-the-art technologies have led to a better understanding of allergenicity, including aspects related to cross-reactivity, allergen nomenclature, and the identification of antigenic determinants. This information is being applied to the design and production of allergy vaccines, some of which already have proven efficacy and safety in clinical trials.

Analysis of B-cell epitopes from the allergen Hev b 6.02 revealed by using blocking antibodies

Hev b 6.02 (hevein), identified as a major allergen from natural rubber latex (NRL), is involved in the latex-fruit syndrome and also acts as a pathogenesis defense-related protein. Its 3D structure has been solved at high resolution, and its linear epitopes have already been reported. However, information about conformational epitopes is still controversial, even though it is relevant for an accurate diagnosis and treatment, as well as for the study of allergen-antibody molecular interactions. We sought to analyze the B-cell epitopes of Hev b 6.02 at a molecular and structural level, using specific recombinant antibodies. We obtained a murine monoclonal antibody (mAb 6E7) and three human single chain fragments (scFvs A6, H8, and G7) anti-Hev b 6.02 that were able to compete for hevein binding with serum IgEs from latex allergic patients. In vitro assays showed that the mAb 6E7 and scFv H8 recognized the area of Hev b 6.02 where the aromatic residues are exposed; while the scFv G7 defined the amino and carboxy-terminal regions that lie close to each other, as a different epitope. The structural modeling of the Hev b 6.02-scFv H8 and Hev b 6.02-scFv G7 complexes revealed the putative regions of two conformational epitopes. In one of these, the aromatic residues, as well as polar side chains are important for the interaction, suggesting that they are part of a dominant conformational epitope also presented on the Hev b 6.02-IgE interactions. Antibodies recognizing this important allergen have potential to be used to diagnose and ultimately treat latex allergy.

Molecular determinants of allergen-induced effector cell degranulation

BACKGROUND

Allergen-induced effector cell degranulation is a key event in allergic inflammation and leads to early-phase symptoms, such as allergic rhinitis, conjunctivitis, urticaria, or bronchial asthma.

OBJECTIVE

We sought to study molecular determinants of effector cell degranulation using a monoclonal IgE antibody specific for a peptide epitope of one of the most important respiratory allergens, the major grass pollen allergen Phl p 1, as a model system.

METHODS

A hybridoma cell line producing a monoclonal IgE antibody against a Phl p 1-derived peptide, P1, was established by means of immunization of mice and used to sensitize rat basophil leukemia cells, which were exposed to P1 monomer, P1 dimer, and P1 polymer.

RESULTS

It is demonstrated that the number of IgE epitopes on an allergen molecule and the concentration of allergen-specific IgE antibodies determine the extent of degranulation. The P1 monomer did not cause mediator release and prevented degranulation induced by polymeric P1.

CONCLUSION

Our results suggest that the number of IgE epitopes on an allergen molecule determines its allergenic activity and explains why increases of allergen-specific IgE levels make patients more sensitive to allergens. Allergen-derived monomeric structures isolated by means of combinatorial chemistry might be used to develop new therapeutic strategies for allergy.

CLINICAL IMPLICATIONS

Our study reveals molecular factors that determine the immediate allergenic activity of allergens and hence influence clinical sensitivity to these allergens.

Exploiting the avian immunoglobulin system to simplify the generation of recombinant antibodies to allergenic proteins

BACKGROUND

Monoclonal antibodies are a valuable tool in the study of allergens, but the technology used in their generation can be slow and labour-intensive. Therefore, we have examined recombinant antibody development by phage-display against single allergens and protein mixtures.

OBJECTIVE

We used the avian immunoglobulin system (generated from single V(H) and V(L) genes) to provide a rapid method for generating highly specific recombinant antibody fragments from a minimal number of animals.

METHODS

A single-chain antibody fragment (scFv) library was generated from a single chicken immunized with model allergens. ScFvs were isolated by phage-display and their properties investigated by ELISA and Western blot.

RESULTS

Mono-specific scFvs were generated against recombinant Fel d 1 and native Amb a 1. Pannings against yellow jacket venom extracts only yielded clones that reacted with multiple proteins in the venom extract. The scFvs from each panning type were effectively expressed in Escherichia coli and readily purified. Highly specific and sensitive recognition of Fel d 1 and Amb a 1 was demonstrated in ELISA, with scFvs displaying antibody-concentration-dependent absorbance curves down to picogram levels of antibody. The specificity of selected antibodies for their cognate antigen was further confirmed in Western blot analysis, with scFvs directed to either Fel d 1 or Amb a 1 showing no reactivity for the other antigens used in immunization. Anti-Amb a 1 scFvs also mapped Amb a 1-isoform location in Western blot of ragweed extracts separated by 2D SDS-PAGE. DNA sequence analysis of scFvs showed that multiple different clones had been generated against Fel d 1 and Amb a 1. Using two anti-Fel d 1 scFv for ELISA analysis of Fel d 1 content in crude cat pelt extracts, we could produce data which were highly similar (P=0.33 and 0.89 by paired t-test analysis) to those obtained using conventional assays (radial immunodiffusion).

CONCLUSION

Phage-display technology may generate multiple allergen-specific recombinant antibody fragments from a single chicken, to allergens from mammalian, plant and insect sources. The resulting antibody fragments are of demonstrable use in allergen identification and quantification, in comparison with standard immunoassays.

Mapping of conformational IgE epitopes on Phl p 5a by using mimotopes from a phage display library

BACKGROUND

Phl p 5 represents a major allergen of timothy grass pollen (Phleum pratense). Detailed knowledge about the structures responsible for IgE binding would allow the design of a novel generation of allergy vaccines.

OBJECTIVE

We aimed to characterize the IgE epitopes of Phl p 5a using phage display combined with a molecular modeling approach.

METHODS

Phl p 5a-specific IgE from sera of patients with grass pollen allergy was used for screening of a random peptide phage library displaying constrained decamers.

RESULTS

Fifteen phage clones that shared sequence motifs and could be grouped into families were selected by using Phl p 5a-specific IgE. Peptide alignment with the solvent-accessible amino acids of Phl p 5a revealed 3 sequence sections with frequent hits of identical or similar amino acids. On the surface of Phl p 5a, these sections assembled in compact patches, most likely representing conformational IgE epitopes, whereas no matching clusters were found on the back sides of the 2 Phl p 5a halves. In surface plasmon resonance experiments, the high-affinity interaction between IgE and Phl p 5 could be competed by phage-displayed peptides up to 24%, indicating that they represent true epitope mimics (ie, mimotopes). Allergen-specific immunogenicity of the mimotopes was proved in Biozzi mice.

CONCLUSION

The selected mimotopes facilitated the localization of conformational IgE epitopes of Phl p 5. We suggest them to be suitable candidates for the development of an epitope-specific immunotherapy.

Allergen mimotopes

The causative treatment of type I allergies is a long pursued goal in immunology. To design safe and efficient vaccine preparations, the interaction of the allergen and the symptom-inducing IgE antibodies still needs to be better understood. In this article, we describe the use of the phage display technique in allergy. It yields epitope mimics, so-called mimotopes, which can be employed for both, investigation of allergen-IgE interactions and definition of safe novel vaccines.

IL-9 in allergic inflammation

Th2 type cytokines such as interleukin (IL)-4, IL-5, IL-9, and IL-13 are important mediators in allergic inflammation. The present review will focus on the role of IL-9 in allergic inflammation. The structure and genomic architecture of IL-9 and its receptor, the source of IL-9 and its regulation as well as its effects on different cell types will be reviewed. Furthermore, the specific role of IL-9 in allergic diseases and the potential therapeutic approach of blocking IL-9 will be discussed.

A novel grass pollen allergen mimotope identified by phage display peptide library inhibits allergen-human IgE antibody interaction

The aim of this study was to investigate the molecular basis of human IgE-allergen interaction by screening a phage-displayed peptide library with an allergen-specific human IgE-mimicking monoclonal antibody (mAb). A mAb that reacted with major grass pollen allergens was successfully identified and shown to inhibit human IgE-allergen interaction. Biopanning of a phage-displayed random peptide library with this mAb yielded a 12 amino acid long mimotope. A synthetic peptide based on this 12-mer mimotope inhibited mAb and human IgE binding to grass pollen extracts. Our results indicate that such synthetic peptide mimotopes of allergens have potential as novel therapeutic agents.