Omalizumab increases the intrinsic sensitivity of human basophils to IgE-mediated stimulation

Abstract

Background: Treatment of allergic patients with omalizumab results in a paradoxical increase in their basophil histamine release (HR) response ex vivo to cross-linking anti-IgE antibody. It is not known whether this change in response is associated with an increase in intrinsic cellular sensitivity, which would be a paradoxical response.

Objective: We sought to determine whether the increase in response to anti-IgE antibody is a reflection of an increased cellular sensitivity expressed as molecules of antigen-specific IgE per basophil required to produce 50% of the maximal response.

Methods: Patients were treated with omalizumab or placebo for 12 weeks (NCT01003301 at ClinicalTrials.gov), and the metric of basophil sensitivity was assessed at 4 time points: baseline, 6 to 8 weeks, 12 weeks (after which treatment stopped), and 24 weeks (12 weeks after the end of treatment).

Results: As observed previously, treatment with omalizumab resulted in a marked increase in the maximal HR induced by cross-linking anti-IgE antibody. This change was accompanied by a marked shift in intrinsic basophil sensitivity, ranging from 2.5- to 125-fold, with an average of 6-fold at the midpoint of the treatment to 12-fold after 12 weeks. The magnitude of the increase in cellular sensitivity was inversely related to the starting sensitivity or the starting maximum HR. The increased cellular sensitivity also occurred when using leukotriene C4 secretion as a metric of the basophil response. Twelve weeks after the end of treatment, cellular sensitivity was found to shift toward the baseline value, although the return to baseline was not yet complete at this time point.

Conclusions: Treatment with omalizumab results in a markedly increased sensitivity of basophils to IgE-mediated stimulation in terms of the number of IgE molecules required to produce a given response. These results provide a better quantitative sense of the phenotypic change that occurs in basophils during omalizumab treatment, which has both mechanistic and clinical implications.

Keywords: ED(50); Effective density for 50% maximum response; Fc receptors; HR; HSA; Histamine release; Human; Human serum albumin; IL-3 receptor; IL-3R; LTC(4); Leukotriene C(4); PAG; PIPES; PIPES-albumin-glucose; Piperazine-N,N′-bis(2-ethanesulfonic acid); Spleen tyrosine kinase; Syk; allergy; basophil.

Copyright © 2013 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.

Figures

Figure 1

Sensitivity curves for subjects treated with omalizumab or placebo. Panel A; placebo treated subjects (n=9), () average baseline sensitivity curve, () average sensitivity curve at the midpoint of the study (approximately 6–8 weeks) and () average sensitivity curve at approximately 12 weeks, just prior to cessation of drug dosing. Panel B; omalizumab treated subjects (n=10), () average baseline sensitivity curve, () average sensitivity curve at the midpoint of the study (approximately 6–8 weeks) and () average sensitivity curve at approximately 12 weeks. The dotted line provides visual reference for the change in sensitivity.

Figure 2

Relationships in change in sensitivity and starting sensitivity or starting maximum histamine release. Panel A; starting sensitivity (ED50) as measured in units of MFI from the flow cytometric measurements. Panel B; relationship between starting maximum histamine release and change in sensitivity.

Figure 3

Sensitivity measurements using LTC4 secretion as the outcome. LTC4 was measured in the same supernatants as used to measure histamine release. The data shows only subjects treated with omalizumab (n=7) and for which data was available at each of the 3 time points (baseline, 6–8 weeks, 12 weeks).

Figure 4

Recovery of baseline sensitivity after cessation of omalizumab treatment (n=7); () average baseline sensitivity curve for the 7 subjects that completed the recovery period, () average sensitivity curve at 12 weeks, () average sensitivity curve 3 months after cessation of omalizumab.