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 response, ex vivo, to crosslinking 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 To determine if the increase in response to anti-IgE Ab is a reflection of an increased cellular sensitivity, expressed as molecules of antigen-specific IgE per basophil required to produce a 50% of maximal response. Methods Patients were treated with omalizumab or placebo agent for 12 weeks (NCT01003301 at ClinicalTrials.gov) and the metric of basophil sensitivity was assessed at 4 time points, baseline, 6–8 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 histamine release induced by crosslinking anti-IgE Ab. 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 histamine release. The increased cellular sensitivity also occurred when using LTC4 secretion as a metric of the basophil response. 12 weeks after the end of treatment, cellular sensitivity was found to shift towards the baseline level 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 implications both mechanistic and clinical.

Immunotherapy in allergy and cellular tests

“…91,92 BAT used in sub-cutaneous immunotherapy against wasp venom allergy, showed an increase in sensitivity during the up-dosing phase of SCIT, an evidence reported by others also for humanized anti-IgE allergy therapy. 93,94 This transient increase has not yet fully elucidated. Basophils increased their sensitivity after 3 wk of specific imunotherapy, probably due to a mechanism reflecting competing amounts of immunoglobulin on basophil membrane (IgE) and free immunoglobulin in circulation 93 and coincides with the observed early decrease in histamine release and increase in IgG4 and IgA immunoglobulins.…”

“…31,40 For example, recent evidence showed that treatment with omalizumab results in a markedly increased sensitivity of basophils to an IgE-mediated stimulation in terms of the number of IgE molecules required to produce a given response. 41 Treatment with omalizumab in patients suffering from cat or peanut allergy enhanced the intrinsic sensitivity of circulating basophils as evaluated by histamine and LTC 4 release. 41 The mechanism underlying this increase in IgE-mediated response is yet unclear.…”

“…41 Treatment with omalizumab in patients suffering from cat or peanut allergy enhanced the intrinsic sensitivity of circulating basophils as evaluated by histamine and LTC 4 release. 41 The mechanism underlying this increase in IgE-mediated response is yet unclear. During the formation of omalizumab-IgE heterodimers in the serum, 42 the monoclonal IgG 1 -anti-Cε3(IgE) complex, can be recognized by FcγRs in immune and dendritic cells and removed from systemic circulation.…”

“…Although basophil response to further allergens during anti-IgE immunotherapy has not been yet investigated, the accepted model suggests that clearance of allergens by immunocomplexes (ICs)-mediated competition or trap mechanism, elicits also a downregulation mechanism of FcεRI on basophil membrane, then reducing basophil IgE-mediated response and allergy symptoms. 41,46 The use of humanized antiIgE antibodies, such as omalizumab, 44,45 may raise some concern about the role of mast cell and basophil Fc-gamma receptors in resolving allergy by an anti-IgE immunotherapy approach. 46 Mast cells, as like as basophils, compete for FcRβ in the allergy IgEmediated mechanism.…”

“…First, the use of an anti-IgE-fluorochrome labeled to gate basophils, such as using Orpegen Basotest®, may give bias because of the dramatic effect caused by anti-IgE monoclonal antibodies on membrane FcεRIs. 41 Khan and colleagues used a BAT where cells were captured following the expression of IgE (anti-IgE-FITC) and CD123-PECy5 and non-expression of HLA-DR-APC, besides the absence of CD3, CD8, CD14, CD19. While they excluded subjects undergoing omalizumab treatment, their BAT was affected by a significant proportion of false-positive results, due to the anti-IgE phenotyping approach.…”