Mechanistic correlates of clinical responses to omalizumab in the setting of oral immunotherapy for milk allergy

Abstract

Background: 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.

Objective: We sought 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.

Methods: Blood was obtained at baseline and multiple time points during a placebo-controlled trial of OIT for milk allergy in which subjects were randomized to receive omalizumab or placebo. Immunologic outcomes included measurement of basophil CD63 expression and histamine release and casein-specific CD4⁺ regulatory T-cell proliferation. Biomarkers were analyzed in relationship to measurements of safety and efficacy.

Results: Milk-induced basophil CD63 expression was transiently reduced in whole blood samples from both omalizumab- and placebo-treated subjects. However, IgE-dependent histamine release increased in washed cell preparations from omalizumab- but not placebo-treated subjects. No increase in regulatory T-cell 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, whereas the baseline milk IgE/total IgE ratio correlated with the likelihood of achieving sustained unresponsiveness. A combination of baseline basophil and serologic biomarkers defined a subset of patients in which adjunctive therapy with omalizumab was associated with attainment of sustained unresponsiveness and a reduction in adverse reactions.

Conclusions: Combining omalizumab therapy with milk OIT led to distinct alterations in basophil reactivity but not T-cell responses. Baseline biomarkers can identify subjects most likely to benefit from adjunctive therapy with omalizumab.

Keywords: Oral immunotherapy; basophil activation; biomarker; desensitization; food allergy; milk allergy; omalizumab; regulatory T cells; sustained unresponsiveness.

Fig 1

Whole blood basophil %CD63 expression in omalizumab (blue) and placebo (red) subjects following stimulation with milk (0.001, 0.01, 0.11, 10 μg/mL) or anti-lgE at baseline (BL) and visits M4, 16, 22, 28, 30 and 32. Statistically significant p-values are indicated in the text. These data were previously presented in Reference 5.

Fig 2

Percent histamine release from washed basophil-enriched suspensions from omalizumab (blue) and placebo (red) subjects stimulated with the 5 concentrations of milk (0.001, 0.01, 0.11, 10 μg/mL), anti-lgE, or media alone (Spont Med) at baseline (BL) and visits M4, 16, 22, 28, 30, and 32. Statistically significant p-values are indicated in the text.

Fig 3

Percent of MOIT doses given during the escalation or maintenance phase of MOIT, or over the course of the entire study, that led to moderate-severe (Mod/Severe) symptoms, Gl symptoms, or any symptom excluding oropharyngeal (Symptoms excl. oral) in subjects who achieved sustained unresponsiveness (SU), were desensitized only (D), or failed the M28 desensitization OFC (F). P-values for a difference in ordinal outcomes (SU/D/F; ord. pval) are presented.

Fig 4

Relationship between percent of MOIT doses that led to moderate-severe (Mod/Severe) symptoms, Gl symptoms, or any symptom excluding oropharyngeal (Symptoms excl. oral) over the course of MOIT and basophil %CD63 expression at milk stimulant concentration 10 μg/mL (%CD63+: Milk 10) measured at the baseline (BL) or M4 visit. Statistically significant p-values are discussed in the text. The gray vertical line at %CD63 expression at baseline illustrates the proposed threshold for greatest treatment difference.

Fig 5

Percent of MOIT doses that led to moderate-severe (Mod/Severe) symptoms, Gl symptoms, or any symptom excluding oropharyngeal (Symptoms excl. oral) over the course of MOIT in subjects whose baseline basophil %CD63 expression at milk stimulant concentration 10μg/mL was less than or greater than 40% (%CD63 Milk 10>40 or <40, respectively). P-values are indicated in the graphs.

Fig 6

Ratio of basophil %CD63 expression at milk stimulant concentration 10 μg/mL over %CD63 anti-lgE (%CD63: Milk10/anti-lgE) or ratio of milk IgE over total IgE (IgE Ratio: Milk/Total) in placebo (red) and omalizumab (blue) subjects who achieved sustained unresponsiveness (SU), were desensitized only (D) or failed (F). Statistically significant p-values are discussed in the text.

Fig 7

A Baseline values of the ratio of %CD63 to milk stimulant concentration 10 μg/mL over %CD63 to anti-lgE (%CD63: Milk10/anti-lgE) were evaluated in relation to the baseline milk IgE/total IgE ratio (IgE Ratio: Milk/Total) in a logistic interaction model. Shaded area indicates region of numerically positive treatment estimate in terms of likelihood of achieving SU. Subjects who achieved SU are shown in open points; those who were desensitized only or failed are depicted in closed points (Not SU). B Number of omalizumab or placebo subjects whose baseline biomarker values fell above (%CD63 Milk10/anti-lgE > 0.091+10.98× IgE Ratio: Milk/Total) or below (%CD63 Milk10/anti-lgE < 0.091+10.98× IgE Ratio: Milk/Total) the line of positive effect described in A who achieved sustained unresponsiveness (SU), were desensitized only (D) or failed (F). P-values for a difference in SU (SU. p), and for a difference in ordinal outcomes (SU/D/F; ord. p) are presented. C Percent of MOIT doses that led to moderate-severe (Mod/Severe) symptoms, GI symptoms, or any symptom excluding oropharyngeal (Symptoms excl. oral) over the course of MOIT in the two subsets of subjects described in B. P-values are indicated in the graphs.