Precision engineering for localization, validation, and modification of allergenic epitopes

Antigenic determinants underlying IgE-mediated anaphylaxis to peanut

BACKGROUND

Studies of human IgE and its targeted epitopes on allergens have been very limited. We established a method to immortalize IgE-encoding B cells from patients with allergy.

OBJECTIVE

We sought to develop an unbiased and comprehensive panel of peanut-specific human IgE mAbs to characterize key immunodominant antigenic regions and epitopes on peanut allergens to map molecular interactions responsible for inducing anaphylaxis.

METHODS

Using human hybridoma technology to immortalize IgE-encoding B cells from peripheral blood of subjects with severe peanut allergy, we generated a panel of naturally occurring human IgE mAbs in an unbiased manner. Isolated IgE mAbs were characterized extensively in allergen binding assays, peptide array analysis, antigenic mapping, binding kinetic analysis, serum blocking, skin testing inhibition, and functional assessment using human FCεRI transgenic mice.

RESULTS

We created a large panel of 54 peanut-specific IgE mAbs, of which 63% were specific for Ara h 2 and/or Ara h 6. Pairs of IgE mAbs with the same antigen specificity but different binding sites were able to mediate passive systemic anaphylaxis in FCεRI transgenic mice. A single mAb targeting the repetitive motif on Ara h 2 was able to induce degranulation and anaphylaxis on its own. IgG1 switch variant immunoglobulins of the IgE mAb inhibited binding of 30% to 60% of patients' IgE to peanut extract (ImmunoCAP) and reduced peanut extract-induced skin wheal sizes by 1.6 to 7.4 mm in patients with peanut allergy.

CONCLUSION

We created a molecular map of the IgE antibody response to the most important peanut allergen proteins to enable the design of new allergy immunotherapies and vaccines.

Identification and Validation of Key Amino Acids in IgE Linear Epitopes of β-Lactoglobulin: Comparison of Recognition Patterns of Chinese Bovine Milk-Allergic Sera with Different Symptoms

β-lactoglobulin (BLG) is the primary allergen in bovine milk allergy. The identification of key amino acids in the BLG epitopes has not been comprehensive due to differences in identification methods, patient symptoms, and population characteristics. In this study, bioinformatics predictions were conducted for key amino acids based on two potential IgE linear epitopes in BLG. Then, the peptide AA30-43 was confirmed as an IgE linear epitope through alanine scanning mutagenesis and peptide microarray assays, with four key amino acids (A34, A37, R40, and V41) common to different symptoms being identified. Moreover, symptom-specific key amino acids were identified. Serine (S30) and aspartic acid (D33) are the key amino acids for cutaneous allergy, while food allergy sera showed a preference for recognizing leucines in different positions (L31 and L39). Additionally, mutant peptides (R40, V41, L39, and D33) showed an obvious decrease in digestive stability compared with the epitope. Finally, the results of the KU812 cell degranulation model validated the critical role of the amino acids in allergenicity. These findings offer significant advantages for advancing both immune tolerance therapies and hypoallergenic milk product development, which hold significant implications for further research, prevention, and treatment of bovine milk allergy.

The Potential of Human Monoclonal IgE Antibodies to Establish Biological Potency and Stability of Allergen Extracts

PURPOSE OF REVIEW

Allergenic extracts are often standardized to control for potency, either by measuring concentrations of major allergens or "overall allergenicity" by competition for IgE in pooled sera from highly allergic subjects with a reference extract. Recent developments present an opportunity to use human mAb cloned from highly allergic subjects to define potency of allergenic extracts.

RECENT FINDINGS

Two recent developments present an opportunity for revising potency measurements of allergen extracts: cloning allergen specific IgE from allergic subjects and extensive epitope mapping of major allergenic proteins. Because human IgE mAb recognize biologically relevant epitopes, they present a novel opportunity to determine the potencies of allergenic extracts and may contribute to the science base for allergen standardization.

Structural analysis of human IgE monoclonal antibody epitopes on dust mite allergen Der p 2

BACKGROUND

Human IgE (hIgE) mAbs against major mite allergen Der p 2 developed using human hybridoma technology were used for IgE epitope mapping and analysis of epitopes associated with the hIgE repertoire.

OBJECTIVE

We sought to elucidate the new hIgE mAb 4C8 epitope on Der p 2 and compare it to the hIgE mAb 2F10 epitope in the context of the allergenic structure of Der p 2.

METHODS

X-ray crystallography was used to determine the epitope of anti-Der p 2 hIgE mAb 4C8. Epitope mutants created by targeted mutagenesis were analyzed by immunoassays and in vivo using a human high-affinity IgE receptor (FcεRIα)-transgenic mouse model of passive systemic anaphylaxis.

RESULTS

The structure of recombinant Der p 2 with hIgE mAb 4C8 Fab was determined at 3.05 Å. The newly identified epitope region does not overlap with the hIgE mAb 2F10 epitope or the region recognized by 3 overlapping hIgE mAbs (1B8, 5D10, and 2G1). Compared with wild-type Der p 2, single or double 4C8 and 2F10 epitope mutants bound less IgE antibodies from allergic patients by as much as 93%. Human FcεRIα-transgenic mice sensitized by hIgE mAbs, which were susceptible to anaphylaxis when challenged with wild-type Der p 2, could no longer cross-link FcεRI to induce anaphylaxis when challenged with the epitope mutants.

CONCLUSIONS

These data establish the structural basis of allergenicity of 2 hIgE mAb nonoverlapping epitopes on Der p 2, which appear to make important contributions to the hIgE repertoire against Der p 2 and provide molecular targets for future design of allergy therapeutics.

Research gaps and future needs for allergen prediction in food safety

The allergenicity and protein risk assessments in food safety are facing new challenges. Demands for healthier and more sustainable food systems have led to significant advances in biotechnology, the development of more complex foods, and the search for alternative protein sources. All this has increased the pressure on the safety assessment prediction approaches anchored into requirements defined in the late 90's. In 2022, the EFSA's Panel on Genetically Modified Organisms published a scientific opinion focusing on the developments needed for allergenicity and protein safety assessments of new products derived from biotechnology. Here, we further elaborate on the main elements described in this scientific opinion and prioritize those development needs requiring critical attention. The starting point of any new recommendation would require a focus on clinical relevance and the development of a fit-for-purpose database targeted for specific risk assessment goals. Furthermore, it is imperative to review and clarify the main purpose of the allergenicity risk assessment. An internationally agreed consensus on the overall purpose of allergenicity risk assessment will accelerate the development of fit-for-purpose methodologies, where the role of exposure should be better clarified. Considering the experience gained over the last 25 years and recent scientific developments in the fields of biotechnology, allergy, and risk assessment, it is time to revise and improve the allergenicity safety assessment to ensure the reliability of allergenicity assessments for food of the future.