Mechanistic Correlates of Clinical Responses to Omalizumab in the Setting of Oral Immunotherapy for Milk Allergy

In our recent clinical trial, the addition of omalizumab to oral immunotherapy (OIT) for milk allergy improved safety but no significant clinical benefit was detected. To investigate mechanisms by which omalizumab modulates immunity in the context of OIT, and to identify baseline biomarkers that predict subgroups of patients most likely to benefit from omalizumab. Blood was obtained at baseline and multiple time-points during a placebo-controlled trial of OIT for milk allergy where subjects were randomized to receive omalizumab or placebo. Immunologic outcomes included measurement of basophil CD63 expression and histamine release (HR), and casein-specific CD4(+) T regulatory (Treg) cell proliferation. Biomarkers were analyzed in relationship to measurements of safety and efficacy. Milk-induced basophil CD63 expression was transiently reduced in whole blood samples from both omalizumab and placebo subjects. However, IgE-dependent HR increased in washed cell preparations from omalizumab but not placebo subjects. No increase in Treg frequency was evident in either group. Subjects with lower rates of adverse reactions, regardless of arm, experienced better clinical outcomes. Pre-OIT basophil reactivity positively associated with occurrence of symptoms during OIT, while the baseline milk IgE/total IgE ratio correlated with the likelihood of achieving sustained unresponsiveness (SU). A combination of baseline basophil and serologic biomarkers defined a subset of patients where adjunctive therapy with omalizumab was associated with attainment of SU and a reduction in adverse reactions. Combining omalizumab therapy with milk OIT led to distinct alterations in basophil reactivity but not T cell responses. Baseline biomarkers may identify subjects most likely to benefit from adjunctive therapy with omalizumab. Copyright © 2017 American Academy of Allergy, Asthma & Immunology. All rights reserved.

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