Characterization of allergoids

Abstract

So far it has not been possible to measure the amount of major allergens in the complexes after chemical modification. Furthermore, the presence of minor allergens remained obscure, unless antibodies were successfully generated by animal immunization with allergoids and shown to be reactive with purified natural or recombinant allergens in immunological assays. Thus, we adapted and employed a set of physicochemical methods with the aim of elucidating the molecular size and allergen composition of allergoids. Using online-HPSEC light scattering and DLS, it was shown that two thirds of depigmented allergoid prepared from birch pollen extracts adopted a MW between 1000 and 2000 kDa. The question of reproducibility of the polymerization reaction was addressed by investigating four batches of P. pratense allergoid. Three out of the four batches contained 73 to 77% of polymerized molecules in the above-mentioned range of molecular sizes. One batch showed a significantly higher content of molecules with a MW exceeding 2 MDa. Analysis of allergen composition in B. alba allergoids revealed the presence of all relevant Bet v 1 isoforms and minor allergens except for Bet v 3 and Bet v 4, which was in good agreement with the allergens detected in the native extracts. It should be noted that Bet v 3 has not been detected at the protein level before. Similarly, good agreement in allergen composition between allergoid and native extract was also found for D. pteronyssinus. Presently, the European Directorate for Quality of Medicines and Healthcare (EDQM) is committed to the application of the 3R principles (i. e. replace, reduce, refine the use of animals) for the quality control of medicines wherever possible. This is reflected by the regular review of the monographs of the European Pharmacopoeia and the introduction of alternative tests. For instance, recently it was decided to replace the rabbit pyrogen test by an in vitro test. Furthermore, through the Biological Standardisation Programme the EDQM develops, validates, and establishes alternative test methods in the field of quality control of biologicals (personal communication with Karl-Heinz Buchheit, EDQM). Therefore, the approach presented here for the characterization of allergoids relying on physicochemical methods shall also serve the growing needs for alternative methods to animal testing.