It is documented that omalizumab treatment reduces the cell surface expression of immunoglobulin E high-affinity receptor (FcRI) on several cell types. This has not been investigated in patients with uncontrolled severe persistent allergic asthma.

In a double-blind, randomized, placebo-controlled study, patients with severe allergic asthma uncontrolled by high dose inhaled corticosteroids and long-acting β₂-agonist received either omalizumab (n = 20) or placebo (n = 11) over 16 weeks at appropriate doses and frequencies. Baseline and end of study (week 16) FcRI expression on basophils and plasmacytoid dendritic cells was determined by flow cytometry for the primary endpoint. Secondary efficacy endpoints included asthma control and lung function as part of an initial investigation into the use of FcRI expression as a marker of response.

In the omalizumab group, and with respect to placebo, FcRI expression was significantly reduced at end of study on basophils (−82.6%, p < 0.01) and plasmacytoid dendritic cells (−44.2%, p = 0.029). FcRI expression reduction was not found to be correlated with clinical response.

Long-term omalizumab treatment induced reduction of FcRI expression on circulating basophils and plasmacytoid dendritic cells. These changes were not associated with those of clinical features related to severe asthma, which does not support further investigation into its use as a predictive marker of response.

The study was registered with clinicaltrials.gov (identifier: NCT00454051) and the European Clinical Trials Database, EudraCT (identifier: 2006-003591-35)