An FDA-approved drug to treat severe asthma also drastically improves the health of those individuals with hypereosinophilic syndromes (HES), rare types of chronic immune disorders.

HES is caused by extremely high counts of white blood cells known as eosinophils in the blood or tissues. Symptoms for the disease vary, but can affect the skin, heart, lungs, central nervous system and other organs.

Almost all current therapies for treating HES involve drugs not approved for HES in particular, and have significant side effects. Their usefulness also in some cases reduces over time.

Scientists from the National Institute of Allergy and Infections Diseases, in partnership with AstraZeneca, tested the asthma drug Benralizumab in only the second-ever randomised, placebo-controlled trial for a drug specifically for treating HES. Benralizumab consists of an antibody which binds to a protein found on the surface of eosinophils. Once this binding occurs, natural killer cells find and destroy the eosinophils.

In the trial 20 participants went through three phases of testing over a period of 48 weeks. During the first phase they were randomly assigned either 30 milligrams of benralizumab or a placebo once every four weeks. In the second phase, all participants were given 30 milligrams of benralizumab over the same time period. In the final phase, those participants with improving symptoms could continue receiving benralizumab until the last week of the trial.

After 12 weeks of benralizumab therapy during the first and second phases, 17 of 19 participants had undetectable levels of eosinophils in their blood and reduced HES symptoms, with few or no side effects. Fourteen of those participants saw beneficial responses last until the end of the third phase. Nine of these tapered off other HES therapies during the third phase.