Evaluation of Potential Allergenicity of New Wheat Varieties

The prevalence of food allergy is increasing in the pediatric population. A diagnosis of food allergy carries significant medical, nutritional, and psychological implications for both patients and their families. Therefore, making an accurate diagnosis is critical. However, the diagnosis of symptomatic food allergy continues to be a challenge for allergists and other practicing physicians. The patient's clinical history remains a key component in diagnosing food allergy. Skin prick testing and food-specific immunoglobulin-e (IgE) testing act as secondary tools to aid in the evaluation process, but these tests also suffer from a high rate of false positivity. For specific IgE levels below the cutoffs to these foods, however, supervised oral food challenges (OFCs) may be necessary to establish the diagnosis of symptomatic food allergy, as the sensitivity of these values is relatively low. Currently, the double-blind, placebo-controlled food challenge (DBPCFC) remains the gold standard for the diagnosis of food allergy. OFCs have their own inherent drawbacks: they are not always readily available to all patients, they are time-consuming, and they are potentially dangerous due to their risk of anaphylaxis.

Wheat is one of the eight allergenic foods that are responsible for approximately 90% of all food allergies. Wheat is less allergenic than other foods in this group and less likely to cause multi-organ, severe, life-threatening reactions. Allergy to wheat is more prevalent in children than adults and is considered a transient allergy of infancy/childhood. Wheat allergy is often outgrown in early childhood, in most cases by age 3-5 years, but 35% show a persistent allergy into adolescence. While previous studies using food-specific IgE antibodies have determined diagnostic decision points that indicate a high likelihood of clinical reactivity for certain foods, namely milk, egg, peanut, and fish, wheat-specific IgE levels do not seem to be useful predictors of food challenge outcome, enabling reduction in need for food challenges. Furthermore, false-positive IgE reactions to wheat and other cereals are frequently seen in grass-allergic patients due to insignificant cross-reactivity between water/salt-soluble proteins. Therefore, identification of wheat proteins associated with symptoms to wheat is of importance.

Gliadins in particular have been implicated in allergy to wheat, both in IgE-mediatedallergy and the non-IgE mediated celiac allergy. IgE antibodies to ω-5-gliadin have been found in children with immediate reactions to ingested wheat, and published results show that increased levels of IgE to ω-5-gliadin correlate with the outcome of food challenges. In a Finnish study, all children with IgE antibodies to ω-5-gliadin reacted with immediate symptoms to wheat challenges, while all patients with delayed or negative challenge test results showed no detectable IgE antibodies to ω-5-gliadin.15 In a Japanese cohort, the presence of elevated ω-5-gliadin-specific IgE antibodies was associated with immediate symptoms with wheat food challenges and also in patients with a strong convincing history of wheat allergy who were not challenged due to risk of anaphylaxis. Furthermore, patients with severe reactions upon challenge had significantly higher levels of ω-5-gliadin-specific IgE antibodies compared to children with mild or moderate symptoms. In a multicenter Japanese study, Ebisawa et al. showed a significant relationship between the probability of wheat allergy and the concentration of ω-5-gliadin-specific IgE antibodies with 2.6-fold increased risk. In a study of mixed German and American subjects, ω-5-gliadin-specific IgE antibodies did not correlate with food challenge outcomes in patients with suspected allergy. However, the sample size in this study was much smaller than in others, and the German population included more patients with non-IgE mediated wheat allergy with delayed symptoms, almost half of the German cohort. Nonetheless, ω-5-gliadin-specific IgE antibodies may differ among populations in Asia, Europe, and the United States due to dietary habits and genetics, and further study is warranted, especially in a larger U.S. cohort.

Food crops that have been developed through agricultural biotechnology for commercial use are thoroughly assessed for their safety. One of the key elements in the safety assessment of a genetically improved crop is an evaluation of potential changes in their allergenic properties. Allergenic properties of the crop can potentially be altered if a known allergen or a protein that has high potential to become an allergen is introduced. In addition, the level of expression of endogenous allergens might be altered as a result of transformation and insertion of the new gene into the plant genome.

Since wheat is a known allergenic food crop, international guidelines require analyses to determine if the introduction of the genes and production of the recombinant proteins in wheat cause an unintended change in the levels of endogenous allergenic proteins. To address this question, levels of wheat-specific IgE binding observed in the biotechnology derived wheat varieties are compared to the set of binding values observed in reference wheat varieties that are already on the market. Determining the levels of direct IgE binding using an enzyme linked immuno-sorbent assay (ELISA) has been shown to be an appropriate method to perform such comparisons, especially when the assay is validated and calibrated prior to the production of data. This comparison is important as it will enable determinations of whether there is heterogeneity in wheat-allergic patients with wheat allergy in terms of a predominant trigger. Ultimately, crops may be engineered to eliminate culprit components if predominant.

Food challenge outcomes and standard ImmunoCAP IgE assays to wheat will be compared to CRD wheat testing in this study (Thermo Fisher Scientific, Waltham, MA). When evaluated together with clinical history, skin test reactivity, and OFC outcomes, responses to individual components may be able be used to predict food challenge responsiveness. With respect to intact wheat-specific IgE levels, in two previous studies using these, a true 95% positive predictive value cutoff to predict reactivity at OFC could not be determined to wheat, although a physician challenge was suggested at an estimated wheat level of 26 kU/L to determine possible reactivity.6,7 However, these studies are now over a decade old and pre-dated component resolved diagnostics (CRD). CRD to major proteins ω-5-gliadin may prove to be more beneficial in determining predictive levels of IgE and positive OFC outcomes to wheat. Therefore, in addition to determining wheat component patterns that could predict OFC outcomes, the investigators hope to determine 95% predictive decision points for each of the individual components and compare these to the decision points estimated by the ImmunoCAP assay to wheat.