Standardization of allergen products: 1. Detailed characterization of GMP-produced recombinant Bet v 1.0101 as biological reference preparation

Standardization of allergen extracts requires the availability of well-characterized recombinant allergens, which can be used as reference standards provided by the European regulatory authorities. The objective of this study was the detailed physicochemical and immunological characterization of rBet v 1.0101, which shall be used in a ring trial within the framework of the Biological Standardization Programme BSP090 of the European Directorate for Quality of Medicines and Healthcare. Recombinant Bet v 1.0101 Y0487 was produced under good manufacturing practice conditions and analysed by an array of physicochemical and immunological methods for identity, quantity, homogeneity, folding and denaturation, aggregation state and stability in solution, as well as biological activity. Batch Y0487 was shown to contain monomeric and well-folded protein being identical with rBet v 1.0101, as determined by mass spectrometry. SDS-PAGE, isoelectric focusing, deamidation analysis and size-exclusion chromatography with light scattering revealed sample homogeneity of > 99.9%. Upon storage at +4 degrees C batch Y0487 retained the monomeric state up to 3 months. Protein quantification determined by amino acid analysis was found coinciding with half-maximal inhibition of serum IgE in ELISA. Biological activity of batch Y0487 was shown to be comparable to natural Bet v 1 by IgG and IgE immunoblotting, as well as basophil and T-cell activation. Recombinant Bet v 1.0101 Y0487 was characterized extensively by physicochemical and immunological methods. It was shown highly stable, monomeric and immunologically equivalent to its natural counterpart. Thus, it represents an appropriate candidate reference standard for Bet v 1.