The size of the disease relevant IgE antibody fraction in relation to 'total-IgE' predicts the efficacy of anti-IgE (Xolair) treatment.

Background: Some patients with allergic asthma treated with anti-IgE (Xolair) do not become symptom free. Better criteria for response assessment than allergy skin tests or IgE determination are needed. The impact of the size of the disease relevant allergen-specific IgE antibody fraction, i.e. the percentage of IgE antibody of total IgE, was evaluated in cat allergic patients treated with the recommended doses of Xolair. Results were measured as changes in basophil allergen threshold sensitivity (CD-sens).

Methods: In a double-blind placebo controlled trial 20 patients with a high (>3.8%) and 18 with a low (<1%) percentage of IgE antibodies to cat were given Xolair for 16 weeks and the change in CD-sens was compared to 11 and 10 patients, respectively, in each group receiving placebo.

Results: The CD-sens dropped significantly in both the high (P < 0.001) and low (P < 0.001) group on Xolair but did not change significantly after placebo. For Xolair-treated patients, at the end of the trial there was a highly significant (P < 0.001) difference in CD-sens between the high group, where no patients, and the low group, where 13/18 patients, had become negative.

Conclusions: The currently recommended doses of Xolair very efficiently eliminate IgE antibodies if the IgE antibody fraction is <1% of total IgE but has not enough effect on allergen sensitivity if the fraction is >3-4%. Further studies will show if increased doses of Xolair would help also these patients, who seem to represent about 1/3 of the patient population.