Peanut allergy diagnosis: Moving from basic to more elegant testing

Precision allergy molecular diagnosis applications in food allergy

PURPOSE OF REVIEW

Precision medicine has become important in the diagnosis and management of food allergies. This review summarizes the latest information regarding molecular allergology, an essential component of food allergy managements.

RECENT FINDINGS

Component-resolved diagnostics (CRD) can be used to investigate sensitization to allergens based on symptoms and to reveal co-sensitization and/or cross-sensitization in patients with allergies. The following allergen components are known to be associated with symptoms: ovomucoid from eggs, omega-5 gliadin from wheat, and many storage proteins (Gly m 8 from soy, Ara h 2 from peanut, Cor a 14 from hazelnut, Ana o 3 from cashew nut, Jug r 1 from walnut, and Ses i 1 from sesame). Recent studies on allergens of macadamia nuts (Mac i 1 and Mac i 2), almonds (Pru du 6), fish (parvalbumin and collagen), and shrimp (Pem m 1 and Pem m 14) have provided additional information regarding CRD. In addition, Pru p 7 is a risk factor for systemic reactions to peaches and has recently been found to cross-react with cypress and Japanese cedar pollen.

SUMMARY

CRD provides information of individualized sensitization profiles related to symptoms and severity of allergies in patients. Clinical practice based on CRD offers many benefits, such as higher diagnostic accuracy and improved management of individual patients.

NOVEOS and ImmunoCAP Have Similar Performances for Diagnosing Food Allergies

BACKGROUND

The clinical significance of newly available platforms for specific IgE measurement must be evaluated. However, data are lacking for NOVEOS (Hycor), especially for food allergens.

OBJECTIVE

We compared the technical and clinical performance of two platforms (ImmunoCAP and NOVEOS) to measure specific IgE to 10 food allergens.

METHODS

Sera from 289 clinically characterized patients were tested for IgE specific for six food allergen extracts (egg white, cow's milk, peanut, hazelnut, fish, and shrimp) and four molecular allergens (Gal d 1, Bos d 8, Ara h 2, and Cor a 14). Specific IgE measurements were carried out using ImmunoCAP and NOVEOS methods. Food allergy diagnoses were established according to international guidelines.

RESULTS

A strong correlation (ρ > 0.9) was present between the two platforms whereas specific IgE concentrations measured with NOVEOS were consistently lower (mean, -15%) than with ImmunoCAP. NOVEOS and ImmunoCAP provided similar overall odds ratios and relative risks for food allergy diagnosis with both allergen extracts and molecular allergens. When all 10 allergens were considered, NOVEOS provided better receiver operating characteristic curves (P = .04). Finally, we found that the most discordant results were observed with hazelnut and peanut extracts and were related to cross-reactive carbohydrate determinants for these two with ImmunoCAP.

CONCLUSIONS

Specific IgE determination by either ImmunoCAP or NOVEOS (odds ratios of allergy, 25.1 or 33.0, respectively) is highly informative regarding the risk of allergy in the selected population. The NOVEOS platform presents the advantage of being less affected by unwanted reactivity owing to carbohydrate determinant-specific IgE while requiring a 10-fold lower test sample volume.

Current state and advances in desensitization for peanut allergy in pediatric age

Peanut allergy affects about 1%-3% of the pediatric population in the world, with an important increase in the last decades. Nowadays, international guidelines recommend the early introduction of peanuts in the infant diet, with poor information about the quantity and the frequency of the intake. Allergen immunotherapy may represent the only therapeutic strategy able to modify the natural history of peanut allergy. In particular, oral immunotherapy showed the most promising results in terms of efficacy, but with significant rates of adverse reactions, mostly gastrointestinal. In 2020, the Food and Drug Administration and the European Medicines Agency approved Palforzia®, an oral drug for patients aged 4-17 years. Several studies are ongoing to improve the tolerability of oral immunotherapy and standardize the desensitization protocols. Sublingual immunotherapy permits to offer much lower doses than oral immunotherapy, but fewer adverse events are shown. Subcutaneous immunotherapy is associated with the greatest systemic adverse effects. Epicutaneous immunotherapy, for which Viaskin® patch was approved, has the highest safety profile. Innovative studies are evaluating the use of biological drugs, such as omalizumab or dupilumab, and probiotics, such as Lactobacillus rhamnosus, in monotherapy or associated with oral immunotherapy. Therapy for peanut allergy is constantly evolving, and new perspectives are ongoing to develop.

From Skin to Solution: Exploring Epicutaneous Immunotherapy for Peanut Allergy-A Systematic Review and Meta-Analysis

Peanut allergy is a leading cause of severe food reactions. This meta-analysis evaluates the efficacy and safety of epicutaneous immunotherapy (EPIT) compared to placebo for peanut-allergic individuals. After prospectively registering on PROSPERO, we searched three databases (PubMed, Google Scholar, and Cochrane CENTRAL) and 2 trial registries till September 2023. Analysis was conducted via RevMan where data was computed using risk ratios (RR). The Cochrane Risk of Bias tool and GRADE criteria were used to appraise and evaluate the evidence. From 4927 records, six multicenter randomized placebo-controlled trials comprising 1453 participants were included. The 250 µg EPIT group had a significant increase in successful desensitization compared to placebo (RR: 2.13 (95% C.I: 1.72, 2.64), P < 0.01, I2 = 0%), while the 100 µg EPIT group did not (RR: 1.54 (95% C.I: 0.92, 2.58), P = 0.10, I2 = 0%) (moderate certainty evidence). Moreover, there was a significant increase in local (RR: 1.69 (95% C.I: 1.06, 2.68), P = 0.03, I2 = 89%) and systemic adverse events (RR: 1.75 (95% C.I: 1.14, 2.69), P = 0.01, I2 = 0%) with EPIT. Additionally, individuals administered EPIT have an increased probability of requiring rescue medications like epinephrine (RR: 1.91 (95% C.I: 1.12, 3.28), P = 0.02, I2 = 0%) and topical corticosteroids (RR: 1.49 (95% C.I: 1.29, 1.73), P < 0.01, I2 = 0%) to treat adverse events. The association of adverse events post-treatment including anaphylaxis (RR: 2.31 (95% C.I: 1.00, 5.33), P = 0.05, I2 = 36%), skin/subcutaneous disorders like erythema or vesicles (RR: 0.93 (95% C.I: 0.79, 1.08), P = 0.33, I2 = 0%), and respiratory disorders like dyspnea or wheezing (RR: 0.94 (95% C.I: 0.77, 1.15), P = 0.55, I2 = 0%) with EPIT is inconclusive. EPIT, although effective in desensitization, is linked to an increased risk of adverse events. PROSPERO registration: CRD42023466600.

The combination of Ara h 2-sIgE and basophil activation test could be an alternative to oral food challenge in cases of suspected peanut allergy

BACKGROUND

Most children with peanut sensitisation do not have a clinical peanut allergy (PA). Oral food challenge (OFC) is then necessary to diagnose PA and assess the reactive dose of the allergen. However, OFC is laborious to perform, expensive and stressful. We evaluated whether in vitro tests, such as basophil activation test (BAT), allergen-specific IgE (sIgE) and their combination, could be used to replace OFC for the diagnosis of PA in children.

METHODS

Ninety-one patients aged 6 months to 18 years with suspected PA were prospectively recruited. These patients then underwent an OFC to assess PA. Whole peanut-sIgE, Ara h 2-sIgE, Ara h 8-sIgE and %CD63+ basophils (CCR3+ /SCClow ) to peanut measured by BAT were investigated for PA diagnosis.

RESULTS

Forty-one patients had a positive peanut OFC, and the remaining 50 were only sensitised. All patients with Ara h 2-sIgE >7 kUA /L were allergic to peanut. A threshold of 6% for activated basophils yielded a sensitivity of 95% and a specificity of 54%. All patients with Ara h 2-sIgE ≤7 kUA /L and BAT ≤6% (n = 22) had a negative OFC except for one who presented an oral syndrome due to PR-10 sensitisation.

CONCLUSIONS

We have shown that Ara h 2-sIgE >7 kUA/L is a discriminating threshold for the diagnosis of PA. Furthermore, when Ara h 2-sIgE ≤7 kUA/L and BAT ≤6%, patients do not need to adjust their diet and, thus, do not need an OFC.

Are peanut oral food challenges still useful? An evaluation of children with suspected peanut allergy, sensitization to Ara h 2 and controlled asthma

BACKGROUND

Sensitization to Ara h 2 has been proposed as a promising biological marker for the severity of peanut allergy and may reduce the need for oral food challenges. This study aimed to evaluate whether peanut oral food challenge is still a useful diagnostic tool for children with suspected peanut allergy and an elevated level of Ara h 2-specific IgE. Additionally, we assessed whether well-controlled asthma is an additional risk for severe reactions.

METHODS

A retrospective analysis of 107 children with sensitization to Ara h 2-specific IgE (> 0.35 kU/l) undergoing open peanut challenges during 2012-2018 in the Tampere University Hospital Allergy Centre, Finland.

RESULTS

Of the 107 challenges, 82 (77%) were positive. Serum levels of Ara h 2 -sIgE were higher in subjects with a positive challenge than in those who remained negative (median 32.9 (IQR 6.7-99.8) vs. 2.1 (IQR 1.0-4.9) kU/l), p < 0.001) but were not significantly different between subjects with and without anaphylaxis. No correlation was observed between the serum level of Ara h 2-sIgE and reaction severity grading. Well-controlled asthma did not affect the challenge outcome.

CONCLUSIONS

Elevated levels of Ara h 2-specific IgE are associated with a positive outcome in peanut challenges but not a reliable predictor of reaction severity. Additionally, well-controlled asthma is not a risk factor for severe reactions in peanut challenges in children with sensitization to Ara h 2.

Peanut oral immunotherapy – current trends in clinical trials

Immunotherapy for allergy has been practised for over 100 years. Low-dose repeated exposure to specific allergen extracts over several months to years can successfully induce clinical tolerance in patients with allergy to insect venoms, pollen, house dust mite and domestic animals. Different regimens and routes for immunotherapy include subcutaneous, sublingual, oral and intralymphatic. Food allergies have been difficult to treat in this way due to high anaphylactic potential and only recently the first immunotherapy for peanut allergy has received regulatory approval. Several clinical trials have indicated high efficacy in desensitisation of peanut-allergic individuals using oral immunotherapy, which allows for safer administration of relatively high allergen concentrations. Still, the risk of adverse events including serious allergic reactions and high anxiety levels for patients remains, demonstrating the need for further optimisation of treatment protocols. Here we discuss the design and outcomes of recent clinical trials with traditional oral immunotherapy, and consider alternative protocols and formulations for safer and more effective oral treatment strategies for peanut allergy.

The Major Peanut Allergen Ara h 2 Produced in Nicotiana benthamiana Contains Hydroxyprolines and Is a Viable Alternative to the E. Coli Product in Allergy Diagnosis

Peanut allergy is a potentially life-threatening disease that is mediated by allergen-specific immunoglobulin E (IgE) antibodies. The major peanut allergen Ara h 2, a 2S albumin seed storage protein, is one of the most dangerous and potent plant allergens. Ara h 2 is posttranslationally modified to harbor four disulfide bridges and three hydroxyprolines. These hydroxyproline residues are required for optimal IgE-binding to the DPYSPOHS motifs representing an immunodominant IgE epitope. So far, recombinant Ara h 2 has been produced in Escherichia coli, Lactococcus lactis, Trichoplusia ni insect cell, and Chlamydomonas reinhardtii chloroplast expression systems, which were all incapable of proline hydroxylation. However, molecular diagnosis of peanut allergy is performed using either natural or E. coli-produced major peanut allergens. As IgE from the majority of patients is directed to Ara h 2, it is of great importance that the recombinant Ara h 2 harbors all of its eukaryotic posttranslational modifications. We produced hydroxyproline-containing and correctly folded Ara h 2 in the endoplasmic reticulum of leaf cells of Nicotiana benthamiana plants, using the plant virus-based magnICON® transient expression system with a yield of 200 mg/kg fresh biomass. To compare prokaryotic with eukaryotic expression methods, Ara h 2 was expressed in E. coli together with the disulfide-bond isomerase DsbC and thus harbored disulfide bridges but no hydroxyprolines. The recombinant allergens from N. benthamiana and E. coli were characterized and compared to the natural Ara h 2 isolated from roasted peanuts. Natural Ara h 2 outperformed both recombinant proteins in IgE-binding and activation of basophils via IgE cross-linking, the latter indicating the potency of the allergen. Interestingly, significantly more efficient IgE cross-linking by the N. benthamiana-produced allergen was observed in comparison to the one induced by the E. coli product. Ara h 2 from N. benthamiana plants displayed a higher similarity to the natural allergen in terms of basophil activation due to the presence of hydroxyproline residues, supporting so far published data on their contribution to the immunodominant IgE epitope. Our study advocates the use of N. benthamiana plants instead of prokaryotic expression hosts for the production of the major peanut allergen Ara h 2.

The Importance of Diet in Predicting the Remission of Urticaria-Determination of Allergen-Specific IgE

Background and Objectives: Different types of food introduced gradually in the diet will expose children to different food allergens, increasing the chance of developing allergic diseases. The aim of our study was to determine if allergen-specific IgE values can influence, depending on the diet, the prediction of remission of urticaria in children. Materials and Methods: This prospective study was conducted in 132 patients diagnosed over two years with urticaria, admitted to "Sf. Maria" Clinical Pediatric Hospital Iaşi. Total IgE assay was performed by ELISA, and determination of specific serum IgE by the CLA System Quanti Scan method (Innogenetics, Heiden, Germany). Data were gathered and statistical analysis was performed using statistical software SPSS, using descriptive and inferential statistics. Results: The determination of specific IgE to food allergens was performed on a total of 132 cases. The values of specific IgE were positive for one or more food allergens in 84 patients (63.64%). The most common allergens involved were: cow's milk in 33.3% cases, egg white in 22.6% cases, and hazelnuts in 11.9% cases. The specific IgE values for the different types of food included in our study had a predictive value for disease remission. Conclusions: The determination of specific IgE confirms the presence of a particular food allergen and may have predictive value for the future development of an allergic manifestation.

Biomarkers of diagnosis and resolution of food allergy

Food allergy is increasing in prevalence, affecting up to 10% of children in developed countries. Food allergy can significantly affect the quality of life and well-being of patients and their families; therefore, an accurate diagnosis is of extreme importance. Some food allergies can spontaneously resolve in 50%-60% of cow's milk and egg-allergic, 20% of peanut-allergic and 9% of tree nut-allergic children by school age. For that reason, food-allergic status should be monitored over time to determine when to reintroduce the food back into the child's diet. The gold-standard to confirm the diagnosis and the resolution of food allergy is an oral food challenge; however, this involves the risk of causing an acute-allergic reaction and requires clinical experience and resources to treat allergic reactions of any degree of severity. In the clinical setting, biomarkers have been used and validated to enable an accurate diagnosis when combined with the clinical history, deferring the oral food challenge, whenever possible. In this review, we cover the tools available to support the diagnosis of food allergies and to predict food allergy resolution over time. We review the latest evidence on different testing modalities and how effective they are in guiding clinical decision making in practice. We also evaluate predictive test cut-offs for the more common food allergens to try and provide guidance on when challenges might be most successful in determining oral tolerance in children.

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.