Investigation of different recombinant isoforms of grass group-V allergens (timothy grass pollen) isolated by low-stringency cDNA hybridization--antibody binding capacity and allergenic activity

Multiple grass mixes as opposed to single grasses for allergen immunotherapy in allergic rhinitis

Grass pollen allergy affects approximately 40% of allergic patients. Subcutaneous allergen immunotherapy (SCIT) is the only allergen-specific and disease-modifying treatment available. Currently available therapeutic vaccines for the treatment of grass pollen allergy are based on natural grass pollen extracts which are either made from pollen of one cross-reactive grass species or from several related grass species. Clinical studies have shown that SCIT performed with timothy grass pollen extract is effective for the treatment of grass pollen allergy. Moreover, it has been demonstrated that recombinant timothy grass pollen allergens contain the majority of relevant epitopes and can be used for SCIT in clinical trials. However, recent in vitro studies have suggested that mixes consisting of allergen extracts from several related grass species may have advantages for SCIT over single allergen extracts. Here, we review current knowledge regarding the disease-relevant allergens in grass pollen allergy, available clinical studies comparing SCIT with allergen extracts from timothy grass or from mixes of several related grass species of the Pooideae subfamily, in vitro cross-reactivity studies performed with natural allergen extracts and recombinant allergens and SCIT studies performed with recombinant timothy grass pollen allergens. In vitro and clinical studies performed with natural allergen extracts reveal no relevant advantages of using multiple grass mixes as opposed to single grass pollen extracts. Several studies analysing the molecular composition of natural allergen extracts and the molecular profile of patients' immune responses after SCIT with allergen extracts indicate that the major limitation for the production of a high quality grass pollen vaccine resides in intrinsic features of natural allergen extracts which can only be overcome with recombinant allergen-based technologies.

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.

Generation of a low immunoglobulin E-binding mutant of the timothy grass pollen major allergen Phl p 5a

BACKGROUND

Immunotherapy of grass pollen allergy is currently based on the administration of pollen extracts containing natural allergens. Specifically designed recombinant allergens with reduced IgE reactivity could be used in safer and more efficacious future therapy concepts.

OBJECTIVES

This study aimed to generate hypoallergenic variants of the timothy grass major allergen Phl p 5a as candidates for allergen-specific immunotherapy.

METHODS

Three deletion mutants were produced in Escherichia coli and subsequently purified. The overall IgE-binding capacity of the mutants was compared with the recombinant wild-type allergen by membrane blot and IgE-inhibition assays. The capacity for effector cell activation was determined in basophil activation assays. T cell proliferation assays with allergen-specific T cell lines were performed to confirm the retention of T cell reactivity. Structural properties were characterized by circular dichroism analysis and homogeneity by native isoelectric focusing. The deletion sites were mapped on homology models comprising the N- and C-terminal halves of Phl p 5a, respectively.

RESULTS

The double-deletion mutant rPhl p 5a Delta(94-113, 175-198) showed strongly diminished IgE binding in membrane blot and IgE-inhibition assays. Both deletions affect predominantly alpha-helical regions located in the N- and C-terminal halves of Phl p 5a, respectively. Whereas deletion of Delta175-198 alone was sufficient to cause a large reduction of the IgE reactivity in a subgroup of allergic sera, only the combination of both deletions was highly effective for all the sera tested. rPhl p 5a Delta(94-113, 175-198) consistently showed at least an 11.5-fold reduced capacity to activate basophils compared with the recombinant wild-type molecule, and the T cell proliferation assays demonstrated retention of T cell reactivity.

CONCLUSION

The mutant rPhl p 5a Delta(94-113, 175-198) fulfils the basic requirements for a hypoallergenic molecule suitable for a future immunotherapy of grass pollen allergy; it offers substantially reduced IgE binding and maintained T cell reactivity.

Lysine as a Critical Amino Acid for IgE Binding in Phl p 5b C Terminus

BACKGROUND

Allergens induce the formation of specific immunoglobulin (Ig)E and harbor at least two IgE-binding regions (epitopes) to facilitate crosslinking of basophilic or mast-cell-bound specific IgE antibodies. Studies mapping linear epitopes have shown that these regions often contain charged or hydrophobic amino acids. Nevertheless, these studies are hampered by limited significance due to the often conformational nature of IgE epitopes. This prompted us to study the role of lysines in the context of an intact 3-dimensional model.

METHODS

Major allergen Phl p 5b from timothy grass bears 12 lysines in its C-terminal half. Using site-directed mutagenesis, we substituted all 10 surface-exposed lysines by alanines.

RESULTS

Although structural integrity of the lysine-deficient mutant was not altered, IgE-binding capacity measured by ELISA inhibition tests and crosslinking activity in ex vivo basophil stimulation and in vivo skin prick tests were significantly diminished. Interestingly, binding of specific IgG antibodies was considerably less reduced by loss of lysines.

CONCLUSION

Lysine is an important amino acid for IgE binding in more than one epitope of major grass pollen allergen Phl p 5b C terminus. Allergenicity, but not IgG binding of the molecule, is substantially diminished by single amino acid substitutions without structural integrity being hampered.

The Major Grass Pollen Group 5 Allergen from Dactylis glomerata and Its C-Terminal Split Product Both Behave as Dimers: Implications for Allergen Standardization

BACKGROUND

On SDS-PAGE grass pollen group-5 allergens migrate as a doublet with an apparent molecular mass (M(r)) of 25 kDa. Immunoblot analysis revealed additional group 5 reactivity at double and half this M(r). The aim of this study was to investigate these group 5 molecular entities and to compare their allergenicity and behavior in quantitative immunoassays.

METHODS

Group-5-specific monoclonal antibodies were produced and used for the development of a group-5-specific sandwich ELISA. Affinity-purified Dac g 5 was separated by SDS-PAGE/Western blotting; individual bands were analyzed by N-terminal sequencing. Size exclusion chromatography (SEC) in conjunction with group-5-specific ELISA, competitive RIA and RAST inhibition were used to analyze the size distribution of Dac g 5. Basophil histamine release assays were used to assess biological activity.

RESULTS

The lower band of the typical group 5 doublet was identified as a truncated form lacking the typical group 5 N-terminus AD(L)/(A)GY, observed in the upper band. The 12-kDa peptide was shown to be the C-terminal half of Dac g 5 (amino acid 127 onwards). SEC in conjunction with competitive RIA revealed that around 45% of Dac g 5 is represented by the 12-kDa peptide. Both the C-terminal half and the whole allergen dimerize under nondenaturing conditions. In competitive RIA and RAST inhibition both forms are equally well detected. In contrast, the half molecule is poorly recognized in sandwich ELISA and displays negligible biological activity in basophil histamine release tests with purified IgE.

CONCLUSIONS

These observations stress the need to evaluate the performance of allergen standardization protocols in detail, with special attention to allergen size distribution.

Characterization of immunoglobulin E responses in Balb/c mice against the major allergens of timothy grass (Phleum pratense) pollen

BACKGROUND

Grass pollen, such as that from timothy grass (Phleum pratense), represents a major cause of type I allergy.

OBJECTIVE

To characterize the IgE immune response and to identify the major allergens eliciting an IgE response in a mouse model using pollen extract of P. pratense for sensitization, in order to assess analogies to human hyperreactivity and to gain information on the allergenic potential as determined by the IgE-reactivity kinetics of defined allergens.

METHODS

Balb/c mice were sensitized with pollen extract or with purified natural allergens. Serum IgE levels, the induction of specific IgE antibodies and immediate hypersensitivity were monitored by ELISA, Western blot and a skin test, respectively.

RESULTS

The sensitized mice mounted a strong IgE response and showed IgE-reactivity first against Phl p 5a and 5b, then Phl p 4 and 13 and lastly against Phl p 6. No IgE response was mounted against Phl p 1. However, all purified fractions examined (Phl p 5a, 5b, 6 and 1) induced specific IgE and showed similar kinetics of IgE induction as pollen extract (first Phl p 5a and 5b, then Phl p 6). Skin test experiments demonstrated positive reactivity only in sensitized mice.

CONCLUSION

The IgE reactivity induced by the major allergens in Balb/c mice was very similar to that found in allergic patients, with the exception of Phl p 1. The kinetics of the specific IgE response was comparable using either pollen extract or the purified major allergens, indicating that the intrinsic properties of the allergens are of importance rather than their proportionate amounts in pollen extract. This model should prove to be suitable for investigations regarding the mechanisms of induction and manifestation of timothy grass pollen allergy and for the evaluation of therapeutic strategies.

Purification strategy for recombinant Phl p 6 is applicable to the natural allergen and yields biochemically and immunologically comparable preparations

The recombinant major grass pollen allergen Phl p 6 has been expressed with a N-terminal 6 x His-tag sequence and subsequently purified using nickel-chelating Sepharose. After cleavage of the tag-sequence, a second pass over the affinity chromatography revealed that even untagged rPhl p 6 bound tightly. In order to determine if that property is typical for Phl p 6, the natural allergen was purified in the same way starting with a grass pollen extract. Indeed, nPhl p 6 could be highly enriched in one step using nickel-chelating Sepharose. In addition to this new powerful purification method, the results provide further information in that the recombinant and natural allergens share a lot of properties, since biochemical characteristics are reflected in the purification strategies. The preparations of natural and recombinant Phl p 6 were used for comparative electrophoretic, chromatographic and immunological analysis which demonstrated high similarity.

Hypoallergenic derivatives of major grass pollen allergens for allergy vaccination

Grass pollen-induced hay-fever and allergic asthma represent a major health problem in industrialized countries. Whereas the symptoms of these allergic conditions can be controlled by pharmacotherapy, specific immunotherapy vaccination is the only causative approach towards the treatment of these type 1 allergies. Specific immunotherapy is based on administration of increasing amounts of the disease-causing allergens in the form of allergen-containing extracts. However, the extracts used for immunotherapy consist of allergenic and non-allergenic components and may induce severe anaphylactic side-effects upon therapeutic administration. With recent developments in molecular biology of pollen allergens it has become feasible to produce modified hypoallergenic derivatives of recombinant allergens with abrogated or greatly reduced likelihood of anaphylactic side-effects as compared to extract-based treatments. We have demonstrated this concept through reducing the anaphylactic potential of major rye grass pollen allergens by introducing a few point mutations which leave the overall structural fold of the molecule unaltered. These modified forms are expected to make allergen-specific immunotherapy more widely used in the future.

The molecular basis of antigenic cross-reactivity between the group 2 mite allergens

BACKGROUND

Mite group 2 allergens Der p 2, Der f 2, and Eur m 2 are 14-kDa proteins of unknown function that share 83% to 85% amino acid sequence identity. Isoforms of the allergens within each genus have been identified which differ by 3 or 4 amino acids, but little is known of the influence of group 2 polymorphisms on human IgE antibody binding.

OBJECTIVE

The purpose of this study was to investigate the importance of interspecies and isoform substitutions on murine mAb and IgE antibody binding and on the molecular structure of the group 2 allergens.

METHODS

Site-directed mutagenesis was used to incorporate the isoform amino acid substitutions onto the Der p 2.0101 sequence. Recombinant allergens were expressed and purified from Escherichia coli and used to evaluate antibody binding by enzyme-linked immunosorbent assay (ELISA). Molecular modeling of the tertiary structure was used to analyze structural differences between the various group 2 allergens.

RESULTS

The substitution of asparagine for aspartic acid at position 114 restored mAb binding of rDer p 2.0101; the other Der p 2 isoforms and the 3 rDer f 2 isoforms also reacted in the 2-site ELISA. The correlation of IgE binding to the Der p 2 isoforms was excellent and tended to be higher in the isoforms with the asparagine 114 substitution (r (2) = 0.87 vs r (2) = 0.95). rEur m 2.0101 bound to all mAb except 7A1; when compared with rDer p 2 for IgE binding, rEur m 2.0101 gave a correlation coefficient of r (2) = 0.68. Molecular modeling revealed that Eur m 2 and the storage mite homologs Lep d 2 and Tyr p 2 retain the tertiary fold of Der p 2. Eur m 2 has a conserved surface, whereas Lep d 2 and Tyr p 2 present most of the amino acid substitutions on this surface. Lep d 2 and Tyr p 2 did not react with mAb or with sera from patients with IgE to Dermatophagoides species.

CONCLUSION

The isoform substitutions of rDer p 2 can be distinguished by mAb. The allergenic cross-reactivity between Der p 2, Der f 2, and Eur m 2 is a direct result of the conserved antigenic surface, whereas the lack of cross-reactivity with Lep d 2 and Tyr p 2 is a result of the multiple substitutions across this surface.

Identification of isoform-specific T-cell epitopes in the major timothy grass pollen allergen, Phl p 5

BACKGROUND

The involvement of CD4+ T cells in the pathophysiology of atopic disease is well established.

OBJECTIVE

To gain further insight into the activation requirements for allergen-specific T cells, we characterized epitope specificity, HLA restriction and T-cell receptor (TCR) usage for T cells specific to Phl p 5, the group 5 major allergen of the grass Phleum pratense.

METHODS

To identify the T-cell epitopes of Phl p 5, three Phl p 5-specific T-cell lines (TCLs) and 15 T-cell clones (TCCs) generated from the peripheral blood of three grass-allergic patients were tested with recombinant truncated Phl p 5a fragments and synthetic Phl p 5b peptides representing these two different recombinant Phl p 5 isoallergens. Additional activation experiments with HLA-subtyped antigen-presenting cells and flow cytometry analysis with TCR V-specific mAb were performed to further characterize the activation requirements for Phl p 5-specific TCCs.

RESULTS

At least nine distinct T-cell specificities were identified and the T-cell epitopes recognized differed considerably among the three patients. Most of the epitopes found were isoform-specific, whereas three epitopes were shared between Phl p 5a and 5b. Several human leucocyte antigen (HLA) class II molecules were involved in the recognition of Phl p 5. Different HLA restriction specificities were even found among TCCs specific to the same epitope region. All TCCs were TCR-alpha/beta positive, and an overrepresentation of TCR Vbeta 3.1+ clones among TCCs specific to Phl p 5 appear to exists as 31% (4/13) of the TCCs expressed TCR Vbeta 3.1 (compared with 5% TCR Vbeta 3.1+ T cells in human peripheral blood) with no correlation with epitope specificity or HLA restriction.

CONCLUSION

The T-cell reactivity of the three grass-allergic patients investigated shows that isoallergen-specific T-cell epitopes are found throughout the peptide backbone of Phl p 5a and Phl p 5b, and dominant T-cell epitopes of Phl p 5 were not identified. This indicates that a mixture of at least full-length rPhl p 5a and rPhl p 5b may be required to target the total Phl p 5-specific T-cell response of atopic patients.

Rapid and efficient purification of Phleum pratense major allergens Phl p 1 and group Phl p 2/3 using a two-step procedure

The standardization of natural allergenic extracts and the characterization of recombinant allergens ensures a continuing requirement for highly purified natural allergens. The extraction and purification methods have to be reproducible and also preserve the biological and immunological activity of the allergen. A simple two-step purification system has been established in order to provide milligram amounts of purified natural Phl p 1 and Phl p 2/3. Both major allergens were separated from other proteins of timothy grass pollen extract in one step by hydrophobic interaction chromatography (HIC) under mild conditions. The allergens elute in the flow-through fraction while the rest of the proteins remain bound to the column. The very different molecular weights of Phl p 1 and Phl p 2/3 permitted separation of the allergens by a second step using gel filtration.

A nonspecific, single-stranded nuclease activity with characteristics of a topoisomerase found in a major grass pollen allergen: possible biological significance

The major allergen from timothy grass pollen, Phlp5b (Phleum pratense), was shown to exhibit ribonuclease activity. It turned out that the C-terminal portion of this molecule was the biologically active domain. Here evidence is presented that the allergen is a single-stranded, sugar-nonspecific nuclease with topoisomerase activity. An isomerase-specific active site was identified, and a non-active mutant was constructed by site directed mutagenesis, and showed no nucleolytic activity. In contrast to the wild type (WT), the mutant did not dimerize. Although the binding capacity of IgE antibodies toward the mutant was reduced as compared to the WT, the allergenic activity was retained. We conclude that the allergen Phlp5b is a single-stranded nuclease with an unusual topoisomerase-like activity. This biological activity is not by itself connected to the allergenicity of the molecule. Whether the enzymatic activity is responsible for the induction of the allergic sensitization and inflammation remains an open question.

Monitoring allergen immunotherapy of pollen-allergic patients: the ratio of allergen-specific IgG4 to IgG1 correlates with clinical outcome

BACKGROUND

Although allergen immunotherapy has been established as a treatment of type I allergy back in 1911, until now the underlying mechanisms have not been fully understood, nor are there any parameters which would allow one to monitor an ongoing treatment or to assess therapeutic success in the meantime.

OBJECTIVE

We wanted to define allergen-specific parameters that change due to treatment in correlation with the clinical outcome.

METHODS

We conducted a controlled study with grass pollen-allergic children and compared allergen-specific antibody titres before and 1 year after the onset of immunotherapy in contrast with untreated allergic and healthy children. Two recombinant forms of the major allergen group V of Phleum pratense (Phl p 5) served as model allergens.

RESULTS

No change in IgE levels and no significant reduction of skin prick test (SPT) reactivity were seen. On the other hand, a significant reduction of symptom scores in the treated group and a significant rise in allergen-specific IgG1, IgG2 and IgG4 due to the treatment could be observed, but in neither case could we establish a correlation between the increasing amounts of the single antibody classes and the reduction of symptom scores. But most interestingly, when comparing the ratio of IgG4 to IgG1 with the symptom scores, we found significant correlations. Nevertheless, treated allergic patients still differ considerably from healthy controls as nonatopics have hardly any measurable allergen-specific IgG antibodies and no IgE antibodies at all.

CONCLUSION

The ratio of IgG4 to IgG1 can serve as a valuable parameter that allows us to assess the success of immunotherapy already 1 year after the onset. The increase of specific IgG1 in relation to IgG4 during treatment reflects a possible influence of this subclass on the induction of tolerance towards allergens.

“Allergen Engineering”: Variants of the Timothy Grass Pollen Allergen Phl p 5b with Reduced IgE-Binding Capacity but Conserved T Cell Reactivity

One problem of conventional allergen-specific immunotherapy is the risk of anaphylactic reactions. A new approach to make immunotherapy safer and more efficient might be the application of engineered allergens with reduced IgE-binding capacity but retained T cell reactivity. Using overlapping dodeca-peptides, the dominant T cell epitopes of the timothy grass pollen allergen Phl p 5b were identified. By site-directed mutagenesis outside these regions, point and deletion mutants were generated. Allergen variants were analyzed for IgE-binding capacity with sera of different grass pollen allergic patients by Western blotting, Dot blotting, and EAST inhibition test, and for histamine releasing capacity with peripheral blood basophils from different patients. The deletion mutants revealed significantly reduced IgE reactivity and histamine releasing capacity, compared with the wild-type Phl p 5b. Furthermore, in vivo skin prick tests showed that the deletion mutants had a significantly lower potency to induce cutaneous reactions than the wild-type Phl p 5b. On the other hand, T cell clones and T cell lines from different allergic patients showed comparable proliferation after stimulation with allergen variants and wild-type Phl p 5b. Considering their reduced anaphylactogenic potential together with their conserved T cell reactivity, the engineered allergens could be important tools for efficient and safe allergen-specific immunotherapy.

Mapping of T-cell epitopes of Phl p 5: evidence for crossreacting and non-crossreacting T-cell epitopes within Phl p 5 isoallergens

BACKGROUND

Group 5 allergens represent major grass pollen allergens because of their high sensitization indices. The identification of T-cell epitopes of these allergens is a prerequisite for the design of immunotherapeutic strategies based on peptide vaccination or modified allergens with conserved T-cell epitopes.

OBJECTIVE

This study was undertaken to determine T-cell epitopes on Phl p 5 major pollen allergen of timothy grass (Phleumn pratense).

METHODS

T-cell lines (TCLs) and T-cell clones (TCCs), specific to Phl p 5, were established from the peripheral blood of 18 patients allergic to grass pollen. All TCCs were mapped for epitope specificities using 178 overlapping dodecapeptides representing the primary structures of two isoforms of Phl p 5 (Phl p 5a and Phl p 5b). Phenotype and cytokine production profiles of TCCs were tested. Selected TCCs were analysed for HLA class II restriction.

RESULTS

A total of 82 TCCs were isolated. All TCCs displayed the helper cell (TH) phenotype. Their reactivity with two recombinant expressed isoforms of Phl p 5a and Phl p 5b was heterogeneous. The epitope specificity of the TCCs was then revealed. Nineteen T-cell epitopes could be identified on Phl p 5. Eighty-one percent of mapped TCCs recognized three T-cell reactive regions on the Phl p 5 allergen. Some TCCs were reactive with isoepitopes presenting on Phl p 5a as well as Phl p 5b. Allergen-specific stimulation induced a TH0-like type of cytokine production in 25 of 50 TCCs. Almost all TCCs secreted high concentrations of interleukin-13.

CONCLUSION

Phl p 5, a major grass pollen allergen, contains several T-cell epitopes. Some epitope regions were recognized by several patients. Epitope recognition pattern could not be correlated with special HLA class II haplotypes. T-cell stimulating isoepitopes were found at corresponding regions of Phl p 5a and Phl p 5b isoforms.

Allergenic activity of a major grass pollen allergen is elevated in the presence of nasal secretion

Phl p5 is a major allergen of timothy grass and causes rhinitis and bronchial asthma in nearly all patients allergic to grass pollen. The biochemical processing of this molecule by the nasal mucosa at its first encounter and possible changes of its biologic activity are unknown. Two isoforms of the allergen were expressed in Escherichia coli and subsequently purified. Conversion of these preparations to various forms with molecular size between 10 and 20 kD in the presence of nasal secretion was observed. Surprisingly, in skin prick test assays with allergic patients the mixture of converted peptides caused significantly higher allergic response when compared with the parent protein. Allergenic activity of the recombinant N-terminal Phl p5a and the C-terminal Phl p5b as measured by skin prick test and histamine release assays was significantly higher than that of the respective parent molecules. Using pancreatic rather than nasal secretion, Phl p5b was completely degraded and its allergenicity was almost completely reduced. Proteolytic degradation converts Phl p5 to defined fragments with increased allergenicity. Complete degradation of Phl p5 on the mucosa could be a preventive strategy to destroy its potency for the induction of an allergic response.