IgE binding to linear epitopes of Ara h 2 in peanut allergic preschool children undergoing oral Immunotherapy

Novel post-translationally cleaved Ara h 2 proteoforms: Purification, characterization and IgE-binding properties

The 2S albumins Ara h 2 and Ara h 6 have been shown to be the most important source of allergenicity in peanut. Several isoforms of these allergens have been described. Using extraction and liquid chromatography we isolated proteins with homology to Ara h 2 and characterized hitherto unknown Ara h 2 proteoforms with additional post-translational cleavage. High-resolution mass spectrometry located the cleavage site on the non-structured loop of Ara h 2 while far UV CD spectroscopy showed a comparable structure to Ara h 2. The cleaved forms of Ara h 2 were present in genotypes of peanut commonly consumed. Importantly, we revealed that newly identified Ara h 2 cleaved proteoforms showed comparable IgE-binding using sera from 28 peanut-sensitized individuals, possessed almost the same IgE binding potency and are likely similarly allergenic as intact Ara h 2. This makes these newly identified forms relevant proteoforms of peanut allergen Ara h 2.

Alanine Scanning of the Unstructured Region of Ara h 2 and of a Related Mimotope Reveals Critical Amino Acids for IgE Binding

SCOPE

The unstructured region of Ara h 2, referred to as epitope 3, contains a repeated motif, DYPSh (h = hydroxyproline) that is important for IgE binding.

METHODS AND RESULTS

IgE binding assays to 20mer and shorter peptides of epitope 3, defines a 16mer core sequence containing one copy of the DPYSh motif, DEDSYERDPYShSQDP. This study performs alanine scanning of this and a related 12mer mimotope, LLDPYAhRAWTK. IgE binding, using a pool of 10 sera and with individual sera, is greatly reduced when alanine is substituted for aspartate at position 8 (D8; p < 0.01), tyrosine at position 10 (Y10; p < 0.01), and hydroxyproline at position 12 (h12; p < 0.001). IgE binding to alanine-substituted peptides of a mimotope containing the DPY_h motif confirm the critical importance of Y (p < 0.01) and h (p < 0.01), but not D. Molecular modeling of the core and mimotope suggests an h-dependent conformational basis for the recognition of these sequences by polyclonal IgE.

CONCLUSIONS

IgE from pooled sera and individual sera differentially bound amino acids throughout the sequences of Epitope 3 and its mimotope, with Y10 and h12 being most important for all sera. These results are highly significant for designing hypoallergenic forms of Ara h 2.

The updated Structural Database of Allergenic Proteins (SDAP 2.0) provides 3D models for allergens and incorporated bioinformatics tools

Background

Allergenic proteins can cause IgE-mediated adverse reactions in sensitized individuals. Although the sequences of many allergenic proteins have been identified, bioinformatics data analysis with advanced computational methods and modeling is needed to identify the basis for IgE binding and cross-reactivity.

Objective

We aim to present the features and use of the updated Structural Database of Allergenic Proteins 2.0 (SDAP 2.0) webserver, a unique, publicly available resource to compare allergens using specially designed computational tools and new high-quality 3-D models for most known allergens.

Methods

Previously developed and novel software tools for identifying cross-reactive allergens using sequence and structure similarity are implemented in SDAP 2.0. A comprehensive set of high-quality 3-D models of most allergens was generated with the state-of-the-art AlphaFold 2 software. A graphics tool enables the interactive visualization of IgE epitopes on experimentally determined and modeled 3-D structures.

Results

A user can search for allergens similar to a given input sequence with the FASTA algorithm or the window-based World Health Organization/International Union of Immunological Societies (WHO/IUIS) guidelines on safety concerns of novel food products. Peptides similar to known IgE epitopes can be identified with the property distance tool and conformational epitopes by the Cross-React method. The updated database contains 1657 manually curated sequences including all allergens from the IUIS database, 334 experimentally determined X-ray or NMR structures, and 1565 3-D models. Each allergen/isoallergen is classified according to its protein family.

Conclusions

SDAP provides access to the steadily increasing information on allergenic structures and epitopes with integrated bioinformatics tools to identify and analyze their similarities. In addition to serving the research and regulatory community, it provides clinicians with tools to identify potential coallergies in a sensitive patient and can help companies to design hypoallergenic foods and immunotherapies.

Oral immunotherapy as a curative treatment for food-allergic preschool children: Current evidence and potential underlying mechanisms

The worldwide rising prevalence of food allergy is a major public health concern. Standard care consists of allergen avoidance and rescue medication upon accidental exposure. Oral immunotherapy (OIT) is increasingly being studied as a treatment option. Although desensitization (an increased reaction threshold) is often achieved during OIT, sustained unresponsiveness (SU; clinical nonreactivity after finishing OIT) is not achieved in most patients. A few studies have investigated the effectiveness of OIT in children younger than 4 years of age (early = e-OIT) and have shown a much more favorable outcome in terms of SU development. Together with food allergy prevention studies, which have demonstrated high efficacy of early oral allergen exposure, the outcomes of e-OIT studies indicate an early-life window of opportunity to achieve SU, allowing unrestricted dietary intake. However, the underlying mechanism of the high effectiveness of e-OIT is not understood yet. Both cohort and OIT studies indicate early-life immune plasticity. An immature food-allergic response in the first years of life seems to be a major driver of this immune plasticity, along with a higher tolerogenic immunological state. Allergy maturation can likely be disrupted effectively by early intervention, preventing the development of persistent food allergy. Upcoming studies will provide important additional data on the safety, feasibility, and effectiveness of e-OIT. Combined with immune mechanistic studies, this should inform the implementation of e-OIT.

Immune signatures predicting the clinical outcome of peanut oral immunotherapy: where we stand

Peanut allergy is a growing health concern that can cause mild to severe anaphylaxis as well as reduced quality of life in patients and their families. Oral immunotherapy is an important therapeutic intervention that aims to reshape the immune system toward a higher threshold dose reactivity and sustained unresponsiveness in some patients. From an immunological point of view, young patients, especially those under 3 years old, seem to have the best chance for therapy success. To date, surrogate markers for therapy duration and response are evasive. We provide a comprehensive overview of the current literature state regarding immune signatures evolving over the course of oral immunotherapy as well as baseline immune conditions prior to the initiation of treatment. Although research comparing clinical and immune traits in the first years of life vs. later stages across different age groups is limited, promising insights are available on immunological endotypes among peanut-allergic patients. The available data call for continued research to fill in gaps in knowledge, possibly in an integrated manner, to design novel precision health approaches for advanced therapeutic interventions in peanut allergy.

Epitope-Based IgE Assays and Their Role in Providing Diagnosis and Prognosis of Food Allergy

With advances in molecular and computational science, epitope-specific IgE antibody profiling has been developed and recently brought into clinical practice. Epitope-based testing detects IgE antibodies that directly bind to antigenic sites of an allergen, providing increased resolution specificity and fewer false-positive results for diagnosing food allergy. Epitope-binding profiles may also serve as prognostic markers of food allergy and help predict quantities of allergen that would provoke a reaction (ie, eliciting dose, possible severity of a reaction after allergen ingestion, and outcomes of treatment options such as oral immunotherapy [OIT]). Future studies are under way to discover additional applications of epitope-specific antibodies for multiple food allergens.

An update on recent developments and highlights in food allergy

While both the incidence and general awareness of food allergies is increasing, the variety and clinical availability of therapeutics remain limited. Therefore, investigations into the potential factors contributing to the development of food allergy (FA) and the mechanisms of natural tolerance or induced desensitization are required. In addition, a detailed understanding of the pathophysiology of food allergies is needed to generate compelling, enduring, and safe treatment options. New findings regarding the contribution of barrier function, the effect of emollient interventions, mechanisms of allergen recognition, and the contributions of specific immune cell subsets through rodent models and human clinical studies provide novel insights. With the first approved treatment for peanut allergy, the clinical management of FA is evolving toward less intensive, alternative approaches involving fixed doses, lower maintenance dose targets, coadministration of biologicals, adjuvants, and tolerance-inducing formulations. The ultimate goal is to improve immunotherapy and develop precision-based medicine via risk phenotyping allowing optimal treatment for each food-allergic patient.

IgE and IgG4 Epitope Mapping of Food Allergens with a Peptide Microarray Immunoassay

Peptide microarrays are a powerful tool to identify linear epitopes of food allergens in a high-throughput manner. The main advantages of the microarray-based immunoassay are as follows: the possibility to assay thousands of targets simultaneously, the requirement of a low volume of serum, the more robust statistical analysis, and the possibility to test simultaneously several immunoglobulin subclasses. Among them, the last one has a special interest in the field of food allergy, because the development of tolerance to food allergens has been associated with a decrease in IgE and an increase in IgG4 levels against linear epitopes. However, the main limitation to the clinical use of microarray is the automated analysis of the data. Recent studies mapping the linear epitopes of food allergens with peptide microarray immunoassays have identified peptide biomarkers that can be used for early diagnosis of food allergies and to predict their severity or the self-development of tolerance. Using this approach, we have worked on epitope mapping of the two most important food allergens in the Spanish population, cow's milk, and chicken eggs. The final aim of these studies is to define subsets of peptides that could be used as biomarkers to improve the diagnosis and prognosis of food allergies. This chapter describes the protocol to produce microarrays using a library of overlapping peptides corresponding to the primary sequences of food allergens and data acquisition and analysis of IgE and IgG4 binding epitopes.

Management of Anaphylaxis During Peanut Oral Immunotherapy

BACKGROUND

Peanut oral immunotherapy (POIT) has emerged as an active management option for peanut allergy, with an FDA-approved product now available for therapy. Allergic reactions, including anaphylaxis, can occur during therapy and their management is key in optimizing this treatment and patient outcomes.

PURPOSE OF REVIEW

In this manuscript, we will review the rates of allergic reactions and anaphylaxis in seminal peanut oral immunotherapy research studies. We will examine factors that can alter the risk of anaphylaxis and describe various strategies, including adjunct therapies, that have the potential to mitigate anaphylaxis risk based on published evidence.

RECENT FINDINGS

Rates of anaphylaxis and epinephrine administration vary in different research studies, but there is consensus that most POIT-related allergic reactions are mild or moderate and not severe. Certain external factors (for example, tiredness, exercise, viral illness) as well as uncontrolled allergic co-morbidities (asthma, allergic rhinitis) have been shown to increase the risk of anaphylaxis during OIT. The search of biomarkers who may predict who is at risk for severe allergic reactions is ongoing. Adjunct therapies have shown promise, but further studies are required to optimize their use alongside POIT. Our understanding of anaphylaxis during POIT has increased in recent years, resulting in better management strategies. However, future plans will need to involve all stakeholders, including physicians, patients and families, researchers, public health authorities, and the food, hospitality, and catering industries.

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.

Ara h 2-Specific IgE Presence Rather Than Its Function Is the Best Predictor of Mast Cell Activation in Children

BACKGROUND

Ara h 2-specific IgE (Arah2-sIgE) is an excellent serologic marker for peanut allergy. However, not all subjects with detectable Arah2-sIgE react clinically.

OBJECTIVE

To assess the importance of functional characteristics of Arah2-sIgE for Ara h 2-induced mast cell activation.

METHODS

We studied a cohort of children assessed for peanut allergy. We determined Arah2-sIgE levels, Ara h 2/total IgE ratios and IgE avidity for Ara h 2 using ImmunoCAP (Thermo Fisher) and mast cell activation to Ara h 2 using flow cytometry.

RESULTS

Samples from 61 of 100 children (46 peanut-allergic [PA] and 15 peanut-sensitized tolerant) who had Arah2-sIgE levels 0.10 kU/L or greater were studied. Arah2-sIgE and Ara h 6-specific IgE levels, Ara h 2/total IgE ratios, and the diversity of IgE for Ara h 2 epitopes were higher in PA compared with peanut-sensitized tolerant samples. The levels of IgE to peanut, Ara h 1, and Ara h 3 were not significantly different between groups. Results from the mast cell activation test to Ara h 2 strongly correlated with Arah2-sIgE levels (r = 0.722; P < .001) and Ara h 2/total IgE ratios (r = 0.697; P < .001) and moderately with Arah2-sIgE diversity (r = 0.540; P < .001). On a linear regression model, Arah2-sIgE levels (standardized β-coefficient = 0.396; P = .008) and Ara h 2/total IgE ratios (standardized β-coefficient = 0.0.669; P = .002) were the main determinants of mast cell response to Ara h 2.

CONCLUSIONS

Most children sensitized to Ara h 2 are PA. Ara h 2-specific IgE titers and specific activity are the major determinants of mast cell response to Ara h 2.

Mechanisms and biomarkers of successful allergen-specific immunotherapy

Allergen-specific immunotherapy (AIT) is considered the only curative treatment for allergic diseases mediated by immunoglobulin E (IgE). Currently, the route of administration depends both on the different types of causal allergens and on its effectiveness and safety profile. Several studies have reported the mechanisms and changes in humoral and cellular response underlying AIT; however, the full picture remains unknown. Knowledge of who can benefit from this type of treatment is urgently needed due to the patient safety risks and costs of AIT. In vivo or in vitro biomarkers have become a strategy to predict clinical outcomes in precision medicine. There are currently no standardized biomarkers that allow determining successful responses to AIT, however, some studies have found differences between responders and nonresponders. In addition, different candidates have been postulated that may have the potential to become biomarkers. In this review, we aim to summarize the findings to date related to biomarkers in different IgE-mediated allergic diseases (respiratory, food, and venom allergy) with the potential to define who will benefit from AIT.

Biomarkers in oral immunotherapy

Food allergy (FA) is a global health problem that affects a large population, and thus effective treatment is highly desirable. Oral immunotherapy (OIT) has been showing reasonable efficacy and favorable safety in most FA subjects. Dependable biomarkers are needed for treatment assessment and outcome prediction during OIT. Several immunological indicators have been used as biomarkers in OIT, such as skin prick tests, basophil and mast cell reactivity, T cell and B cell responses, allergen-specific antibody levels, and cytokines. Other novel indicators also could be potential biomarkers. In this review, we discuss and assess the application of various immunological indicators as biomarkers for OIT.

Differences in Linear Epitopes of Ara h 9 Recognition in Peanut Allergic and Tolerant, Peach Allergic Patients

Background

Peanut-allergic patients from the Mediterranean region are predominantly sensitized to the lipid transfer protein (LTP) Ara h 9, and the peach LTP Pru p 3 seems to be the primary sensitizer. However, LTP sensitization in peanut allergy is not a predictive marker for clinically relevant symptoms.

Objective

We aimed to identify sequential epitopes of IgE and IgG4 from Pru p 3 and Ara h 9 in peach-allergic patients sensitized to peanuts. We also sought to determine the differences in IgE and IgG4 binding between patients who had developed peanut allergy and those tolerating peanuts.

Methods

A total of 46 peach-allergic patients sensitized to peanuts were selected. A total of 35 patients were allergic to peanuts (peanut-allergic group) and 11 were tolerant to peanuts (peanut-tolerant group). We measured sIgE and sIgG4 in peanut, peach, and their recombinant allergen (Ara h 1, Ara h 2, Ara h 3, Ara h 8, and Ara h 9) with fluorescence enzyme immunoassay. We examined the IgE and IgG4 binding to sequential epitopes using a peptide microarray corresponding to linear sequences of the LTPs Ara h 9 and Pru p 3 with a library of overlapping peptides with a length of 20 amino acids (aa) and an offset of 3 aa.

Results

The frequency and the intensity of IgE recognition of Ara h 9 and Pru p 3 peptides were higher in the peanut-tolerant group than in the peanut-allergic group. We found four Ara h 9 peptides (p4, p14, p21, and p25) and four Pru p 3 peptides (p1, p3, p21, and p24) with a significantly elevated IgE recognition in peanut-tolerant patients. Only one peptide of Ara h 9 (p4) recognized by IgG4 was significantly elevated in the peanut-tolerant group. The IgG4/IgE ratio of Ara h 9 peptide 4 was significantly higher in peanut-tolerant patients than in peanut-allergic patients, while no significant differences were observed in the IgG4/IgE ratio of this peptide in Pru p 3.

Conclusion

Although we found significant differences in IgE and IgG4 recognition of Ara h 9 and Pru p 3 between peanut-tolerant and peanut-allergic patients (all of whom were allergic to peach), polyclonal IgE peptide recognition of both LTPs was observed in peach-allergic patients tolerating peanuts. However, the IgG4 blocking antibodies against Ara h 9 peptide 4 could provide an explanation for the absence of clinical reactivity in peanut-tolerant peach-allergic patients. Further studies are needed to validate the usefulness of IgG4 antibodies against Ara h 9 peptide 4 for peanut allergy diagnosis.

Immunodominant conformational and linear IgE epitopes lie in a single segment of Ara h 2

BACKGROUND

Contribution of conformational epitopes to the IgE reactivity of peanut allergens Ara h 2 and Ara h 6 is at least as important as that of the linear epitopes. However, little is known about these conformational IgE-binding epitopes.

OBJECTIVE

We investigated the distribution of conformational epitopes on chimeric 2S-albumins.

METHODS

Recombinant chimeras were generated by exchanging structural segments between Ara h 2 and Ara h 6. Well-refolded chimeras, as verified by circular dichroism analysis, were then used to determine the epitope specificity of mAbs by performing competitive inhibition of IgG binding. Furthermore, we delineated the contribution of each segment to the overall IgE reactivity of both 2S-albumins by measuring the chimeras' IgE-binding capacity with sera from 21 patients allergic to peanut. We finally assessed chimeras' capacity to trigger mast cell degranulation.

RESULTS

Configuration of the conformational epitopes was preserved in the chimeras. Mouse IgG mAbs, raised against natural Ara h 6, and polyclonal human IgE antibodies recognized different conformational epitopes distributed all along Ara h 6. In contrast, we identified human IgG mAbs specific to different Ara h 2 linear or conformational epitopes located in all segments except the C-terminal one. The major conformational IgE-binding epitope of Ara h 2 was located in a segment located between residues 33 and 81 that also contains the major linear hydroxyproline-containing epitope. Accordingly, this segment is critical for the capacity of Ara h 2 to induce mast cell degranulation.

CONCLUSIONS

Chimeric 2S-albumins provide new insights on the conformational IgE-binding epitopes of Ara h 2 and Ara h 6. Proximity of the immunodominant linear and conformational IgE-binding epitopes probably contributes to the high allergenic potency of Ara h 2.

IgE-Mediated food allergy: Current diagnostic modalities and novel biomarkers with robust potential

Food allergy (FA) is a serious public health issue afflicting millions of people globally, with an estimated prevalence ranging from 1-10%. Management of FA is challenging due to overly restrictive diets and the lack of diagnostic approaches with high accuracy and prediction. Although measurement of serum-specific antibodies combined with patient medical history and skin prick test is a useful diagnostic tool, it is still an imprecise predictor of clinical reactivity with a high false-positive rate. The double-blind placebo-controlled food challenge represents the gold standard for FA diagnosis; however, it requires large healthcare and involves the risk of acute onset of allergic reactions. Improvement in our understanding of the molecular mechanism underlying allergic disease pathology, development of omics-based methods, and advances in bioinformatics have boosted the generation of a number of robust diagnostic biomarkers of FA. In this review, we discuss how traditional diagnostic modalities guide appropriate diagnosis and management of FA in clinical practice, as well as uncover the potential of the latest biomarkers for the diagnosis, monitoring, and prediction of FA. We also raise perspectives for precise and targeted medical intervention to fill the gap in the diagnosis of FA.

Bringing the Next Generation of Food Allergy Diagnostics into the Clinic

Food allergy diagnosis has a massive impact on the lives of patients and their families. Despite recent developments with specific IgE to component allergens, a significant proportion of patients assessed for possible food allergy require oral food challenge to ensure an accurate diagnosis. More precise diagnostic methods are required to reduce the need for oral food challenges. Bead-based epitope assays and cellular tests, such as basophil activation and mast cell tests are the most novel and promising tests on the horizon. There is a pathway to pursue to enable their incorporation in clinical practice, including standardization, technical validation, clinical validation, external validation, overcoming practical and logistical issues, and regulatory approval. Valuable clinical application of these tests goes beyond diagnosis and includes risk assessment to identify allergic patients who are most sensitive and at risk for severe allergic reactions, and to define prognosis and assess clinical response to immunomodulatory treatments.

Improving Diagnostic Accuracy in Food Allergy

The diagnosis of food allergy can have a major impact on the lives of patients and families, imposing dietary restrictions and limitations on social activities. On the other hand, misdiagnosis can place the patient at risk of a potentially severe allergic reaction. Therefore, an accurate diagnosis of food allergy is of utmost importance. The diagnosis of food allergy is often established by the combination of the clinical history and allergen-specific IgE; however, without a clear history of an allergic reaction, the interpretation of IgE sensitization tests can be difficult. There are also rare cases of clinical food allergy in the absence of IgE sensitization. For that reason, testing for suspected food allergy ideally requires access to oral food challenges (OFCs), which are currently the gold standard tests to diagnose food allergy. As OFCs are time consuming and involve the risk of acute allergic reactions of unpredictable severity, the question remains: how can we improve the accuracy of diagnosis before referring the patient for an OFC? Herein, we review the predictive value of different tests used to support the diagnosis of food allergy, discuss implications for therapy and prognosis, and propose a diagnostic approach to be applied in clinical practice.

Emerging Food Allergy Biomarkers

The management of food allergy is complicated by the lack of highly predictive biomarkers for diagnosis and prediction of disease course. The measurement of food-specific IgE is a useful tool together with clinical history but is an imprecise predictor of clinical reactivity. The gold standard for diagnosis and clinical research is a double-blind placebo-controlled food challenge. Improvement in our understanding of immune mechanisms of disease, development of high-throughput technologies, and advances in bioinformatics have yielded a number of promising new biomarkers of food allergy. In this review, we will discuss advances in immunoglobulin measurements, the utility of the basophil activation test, T-cell profiling, and the use of -omic technologies (transcriptome, epigenome, microbiome, and metabolome) as biomarker tools in food allergy.

Peanut oral immunotherapy in a pediatric allergy clinic: Patient factors associated with clinical outcomes

BACKGROUND

Additional information is needed to inform optimal patient selection, expected outcomes, and treatment end points for clinical peanut oral immunotherapy (OIT).

OBJECTIVE

To provide insight into the optimal patient selection, expected outcomes, and treatment end points for clinical peanut oral immunotherapy by analyzing a real-world peanut OIT cohort.

METHODS

Records were reviewed for 174 children undergoing peanut OIT at a pediatric allergy clinic. Patient age, peanut skin prick test results, and peanut-specific immunoglobulin E (sIgE) results, with inclusion of additional foods in OIT, were analyzed for correlations with OIT outcomes.

RESULTS

To date, 144 patients have achieved maintenance dosing, 50 of whom transitioned to ad lib twice-weekly peanut ingestion. A total of 30 discontinued OIT. In addition, 47 patients who underwent multifood OIT had no significant difference in reactions (FDR-adjusted P = .48) or time-to-reach maintenance (FDR-adjusted P = .48) compared with those on peanut OIT alone. Age at initiation inversely correlated with achievement of maintenance: 92% of patients 0.5 to less than 5 years, 81% of those 5 to less than 11 years, and 70% of those 11 to less than 18 years reached and continued maintenance (P = .01). Baseline peanut-sIgE level positively correlated with number of reactions during updosing (P < .001) and maintenance (P = .005), though it was not significantly different in patients achieving successful maintenance vs those who discontinued OIT (P = .09). Furthermore, 66% of patients experienced greater than or equal to 1 adverse reaction during OIT. Of those on ad lib peanut ingestion, 2 reported mild reactions after lapses in peanut consumption.

CONCLUSION

Clinical peanut OIT has similar outcomes to research protocols. OIT can be successful in older children and those with high peanut-sIgE levels, though these factors affect outcomes. Clinical and laboratory criteria can guide successful transition to intermittent ad lib peanut consumption.

The importance of the 2S albumins for allergenicity and cross-reactivity of peanuts, tree nuts, and sesame seeds

Allergies to peanuts, tree nuts, and sesame seeds are among the most important food-related causes of anaphylaxis. Important clinical questions include: Why is there a variable occurrence of coallergy among these foods and Is this immunologically mediated? The clinical and immunologic data summarized here suggest an immunologic basis for these coallergies that is based on similarities among the 2S albumins. Data from component resolved diagnostics have highlighted the relationship between IgE binding to these allergens and the presence of IgE-mediated food allergy. Furthermore, in vitro and in vivo experiments provide strong evidence that the 2S albumins are the most important allergens in peanuts for inducing an allergic effector response. Although the 2S albumins are diverse, they have a common disulfide-linked core with similar physicochemical properties that make them prime candidates to explain much of the observed coallergy among peanuts, tree nuts, and sesame seeds. The well-established frequency of cashew and pistachio nut coallergy (64%-100%) highlights how the structural similarities among their 2S albumins may account for observed clinical cross-reactivity. A complete understanding of the physicochemical properties of the 2S albumins in peanuts, tree nuts, and sesame seeds will enhance our ability to diagnose, treat, and ultimately prevent these allergies.

Mechanisms of oral immunotherapy

Food allergy presents a significant global health concern with up to 10% of the population affected in developed nations and a steadily increasing prevalence. In many cases, particularly with peanut, tree nut and shellfish, food allergy is a lifelong and potentially life-threatening diagnosis. While no 'cure' for IgE-mediated food allergy exists, oral immunotherapy (OIT) is a promising treatment modality with the peanut OIT drug Palforzia (Aimmune Therapeutics) the only treatment for food allergy that is currently approved by the United States Food and Drug Administration. OIT primarily induces a state of desensitization with only a minority of subjects achieving sustained unresponsiveness, a state of limited clinical remission that appears to be immunologically distinct from natural tolerance. Early humoural changes during OIT include an initial increase in allergen-specific IgE, which eventually decreases to below baseline levels as OIT progresses, and a gradual increase in allergen-specific IgA and IgG4 that continues throughout the course of OIT. Basophil hyporesponsiveness and decreased skin prick test wheal size are observed within the first year of OIT, and persistence after completion of therapy has been associated with sustained unresponsiveness. In the T-cell compartment, there is an initial expansion followed by a decline in the number and activity of T helper 2 (TH 2) cells, the latter of which may be dependent on an expansion of IL-10-producing cells, including regulatory T-cells. Our understanding of the immunomodulatory effects of OIT continues to evolve, with new technologies such as single-cell transcriptional profiling and antibody epitope analysis allowing for more detailed study of T-cell and B-cell responses to OIT. In this review, we present evidence to illustrate what is currently known about the immunologic changes induced by OIT, explore potential mechanisms and emphasize knowledge gaps where future research is needed.

IgE-Mediated Peanut Allergy: Current and Novel Predictive Biomarkers for Clinical Phenotypes Using Multi-Omics Approaches

Food allergy is a collective term for several immune-mediated responses to food. IgE-mediated food allergy is the best-known subtype. The patients present with a marked diversity of clinical profiles including symptomatic manifestations, threshold reactivity and reaction kinetics. In-vitro predictors of these clinical phenotypes are evasive and considered as knowledge gaps in food allergy diagnosis and risk management. Peanut allergy is a relevant disease model where pioneer discoveries were made in diagnosis, immunotherapy and prevention. This review provides an overview on the immune basis for phenotype variations in peanut-allergic individuals, in the light of future patient stratification along emerging omic-areas. Beyond specific IgE-signatures and basophil reactivity profiles with established correlation to clinical outcome, allergenomics, mass spectrometric resolution of peripheral allergen tracing, might be a fundamental approach to understand disease pathophysiology underlying biomarker discovery. Deep immune phenotyping is thought to reveal differential cell responses but also, gene expression and gene methylation profiles (eg, peanut severity genes) are promising areas for biomarker research. Finally, the study of microbiome-host interactions with a focus on the immune system modulation might hold the key to understand tissue-specific responses and symptoms. The immune mechanism underlying acute food-allergic events remains elusive until today. Deciphering this immunological response shall enable to identify novel biomarker for stratification of patients into reaction endotypes. The availability of powerful multi-omics technologies, together with integrated data analysis, network-based approaches and unbiased machine learning holds out the prospect of providing clinically useful biomarkers or biomarker signatures being predictive for reaction phenotypes.

Immunological Outcomes of Allergen-Specific Immunotherapy in Food Allergy

IgE-mediated food allergies are caused by adverse immunologic responses to food proteins. Allergic reactions may present locally in different tissues such as skin, gastrointestinal and respiratory tract and may result is systemic life-threatening reactions. During the last decades, the prevalence of food allergies has significantly increased throughout the world, and considerable efforts have been made to develop curative therapies. Food allergen immunotherapy is a promising therapeutic approach for food allergies that is based on the administration of increasing doses of culprit food extracts, or purified, and sometime modified food allergens. Different routes of administration for food allergen immunotherapy including oral, sublingual, epicutaneous and subcutaneous regimens are being evaluated. Although a wealth of data from clinical food allergen immunotherapy trials has been obtained, a lack of consistency in assessed clinical and immunological outcome measures presents a major hurdle for evaluating these new treatments. Coordinated efforts are needed to establish standardized outcome measures to be applied in food allergy immunotherapy studies, allowing for better harmonization of data and setting the standards for the future research. Several immunological parameters have been measured in food allergen immunotherapy, including allergen-specific immunoglobulin levels, basophil activation, cytokines, and other soluble biomarkers, T cell and B cell responses and skin prick tests. In this review we discuss different immunological parameters and assess their applicability as potential outcome measures for food allergen immunotherapy that may be included in such a standardized set of outcome measures.