Affinity-CIEF has been applied to characterize a recombinant product of the major birch pollen allergen Betula verrucosa isoform 1a (Bet v 1a) immuno-chemically. For this purpose mAbs of the IgG-type have been produced in-lab from two murine hybridoma lines, specified as clones 2 and 5.1. Both IgG clones were characterized by SDS-PAGE, MALDI-TOF-MS and CIEF. The purified IgG solutions had to be dialysed against 10 mmol/L phosphate (pH 7.4) to prevent IgG precipitation and to ensure appropriate CIEF separation. Both tested monoclonal IgGs (mIgGs) comprised four constituents covering pI ranges of 6.98-7.09 and 6.78-7.03 for clones 2 and 5.1 with major peaks at pI 7.09 and 7.03, respectively. When increasing amounts of Bet v 1a (pI 4.95) were incubated with 2.0 mumol/L mIgG, novel peaks were progressively induced in a pI range slightly more acidic than the focusing region of mIgGs. These peaks grew on the expense of original mIgG peaks. All pI values were calculated using two pI marker compounds with a repeatability of better than 0.03 units. New peaks represent complexes between Bet v 1a and mIgG either of 1:1 or of 2:1 binding stoichiometry. At a molar ratio of 2:1, saturation of both IgG paratopes with allergen (Ag) molecules was achieved as indicated by unbound Bet v 1a. The current CIEF approach addresses the proof of single epitope integrity in the course of immuno-chemical characterization of Bet v 1a. Contrary to traditional immunoassays, affinity CIEF allows for a distinction and relative quantification of mAbs, Ag-antibody complexes and Ag variants coexisting in one sample.

CZE and CIEF separation systems, both developed previously for a quality control of two recombinant products of the major birch pollen allergen Bet v 1a of Betula verrucosa, were validated including aspects of the International Conference on Harmonization. One product contained carbamylated variants as impurities. Linearity of response was confirmed by Mandel's fitting test between 0.028 and 1.90 mg/mL for CZE and between 0.016 and 0.26 mg/mL for CIEF. Repeatability and intermediate precision were evaluated for the effective mobility (mu(eff)) in CZE, for relative mobilization time in CIEF and the peak area ratio of Bet v 1a. LOQ for Bet v 1a was between 10 and 23 microg/mL for both methods. Evaluation of robustness for CZE revealed susceptibility of micro(eff) of Bet v 1a to alterations in of buffer pH and separation temperature. Selectivity was impaired by an increase in temperature, pH, and buffer concentration. In addition, pH variations influenced the separation profile of impurities. For CIEF, the ratio of narrow pH range carrier ampholytes is the critical parameter to retain robustness. Results demonstrate the suitability of both separation systems to discriminate between nonmodified Bet v 1a and carbamylated variants in the selected recombinant allergen products.