Comparison of intact allergen extracts and allergoids for subcutaneous immunotherapy – the effect of chemical modification differs both between species and between individual allergen molecules

Abstract

Background: Allergen products for subcutaneous immunotherapy (SCIT) contain intact allergen extracts or chemically modified allergoids. Chemical modification was introduced to reduce allergenicity while retaining immunogenicity and thereby enable safer and more efficient allergy immunotherapy. Methods: Experimental allergoids were produced from intact allergen extract for birch, grass and house dust mite (HDM) to evaluate the effects of chemical modification. Preparations were compared with commercial allergoids and analysed by SDS-PAGE/immunoblotting, IgE-inhibition assays, and crossed immunoelectrophoresis (CIE). Dermatophagoides pteronyssinus (Der p) vaccines were also tested for protease activity and immunizing capacity in a mouse model. Results: The composition of IgE-binding epitopes in allergoids differed from intact allergen vaccines. Birch and grass allergoids produced smears of protein aggregates on SDS-PAGE, whereas intact allergen preparations showed distinct protein bands as expected. Der p allergoid vaccines, however, showed a distinct protein band corresponding to major allergen Der p 1 in both SDS-PAGE and CIE analysis, and commercial Der p allergoid vaccines showed Der p 1-related cysteine protease activity. Conclusion: Allergoids and intact allergen preparations differ with respect to the composition of IgE-binding epitopes, however, chemical cross-linking does not affect every allergen molecule to a similar degree. Der p 1, for example remains largely unmodified. Furthermore, the investigational HDM allergoid vaccines showed reduced and delayed immune responses when used for immunisation of mice.