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Immunological methods for quantifying free and total serum IgE levels in allergy patients receiving omalizumab (Xolair) therapy.

Hamilton RG, Marcotte GV, Saini SS

Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA. rhamilto@jhmi.edu

Omalizumab (humanized-IgG1 anti-human IgE Fc, Xolair) complexes circulating IgE, blocking IgE binding to high affinity epsilon Fc receptors (FcepsilonR1) on mast cells and basophils. Free (non-Omalizumab bound) IgE levels in serum are a measure of effective Omalizumab dosing. The goal of this study was to quantify free (non-Omalizumab-complexed) and total serum IgE levels in asthma patients on Xolair. The concentration of (non-Omalizumab bound) free IgE in human serum was measured using a solid phase immunoenzymetric assay (IEMA) in which IgE was captured from serum with monoclonal anti-human IgE (clone HP6061) and detected with labeled-FcepsilonR1alpha. In a companion total human serum IEMA, IgE was captured from serum with the same anti-human IgE (clone HP6061) and all bound IgE was detected with labeled monoclonal anti-human IgE Fc (clone HP6029). Free and total IgE levels were quantified in pre- and 1 and 3 months post Omalizumab therapy sera from 12 allergic asthma patients. In the absence of Omalizumab, working ranges of the free and total IgE IEMAs were comparable (10-1000 kIU/l), with excellent precision, reproducibility and parallelism. Pre-Omalizumab total and free IgE levels by IEMA were highly correlated (r2=0.99, Y=0.9X+0.32, p<0.001), as were total serum IgE levels by IEMA and ImmunoCAP-250 (r2=0.98, Y=1.1X-0.05, p<0.001, n=33). In vitro reduction of free IgE (>90%) occurred at [Omalizumab:IgE] molar ratios of 2-20. Total IgE levels in 12 asthmatics increased from pre-therapy levels (52-658 kIU/l) by 1.5-5.5-fold at 1 month and 1.7-8.6 fold at 3 months of uninterrupted Omalizumab treatment. Free IgE levels fell by 49%-97% at 1 month and 45%-98% by 3 months of Omalizumab treatment. Free and total IgE levels by IEMA aid in monitoring patients receiving Omalizumab therapy.

Published 22 August 2005 in J Immunol Methods, 303(1): 81-91.
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