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Investigational Asthma Drug Is Effective in Treating Chronic Hypereosinophilic Syndrome

A multicenter team, including NIAID investigators, has found that an antibody currently being tested to treat asthma is a safe and effective long-term therapy for a rare chronic disorder called hypereosinophilic syndrome (HES). The results of this study appear in the October 4, 2012, issue of the Journal of Allergy and Clinical Immunology.


micrograph of human eosinophils

Micrograph of human eosinophils. Dark staining shows granules within the cells that contain chemicals such as histamine.
Credit: CDC/Dr. Mae Melvin

HES is characterized by increased numbers in the bloodstream of a type of immune cell called an eosinophil. Normally, eosinophils comprise a small portion of the white blood cell population, helping to fight infections caused by parasites and playing a role in allergic diseases by releasing chemicals, such as histamine, that cause allergic reactions. However, in HES, the significantly elevated numbers of eosinophils can damage the heart, bone marrow, and nervous system, and, if left untreated, can cause death.

People with HES are frequently prescribed corticosteroids, such as prednisone, to lower their eosinophil count. Although prednisone reduces the eosinophil count in most cases of HES, its long-term use has several harmful side-effects, including bone loss, fractures, weight gain, depression, and diabetes.

From 2004 to 2006, investigators at NIAID and research centers around the world conducted a clinical study in which people with HES were given an antibody called mepolizumab that blocked interleukin-5 (IL-5), a molecule that mediates the activation of eosinophils in the blood. At the conclusion of the 36-week trial, the investigators found that mepolizumab safely and effectively reduced participants' eosinophil counts as well as their need for high doses of corticosteroids. But because HES is a chronic condition, the study team wanted to determine the safety and efficacy of mepolizumab use over a longer period of time.

Results of Study

In this follow-up study, the researchers, including Amy Klion, M.D., chief of the Eosinophil Pathology Unit in the NIAID Laboratory of Parasitic Diseases, followed 78 of the adults who were enrolled in the previous study and who had taken mepolizumab for up to five years.

At the beginning of the study, the average daily dose of prednisone was 20 mg. After 24 weeks of treatment with mepolizumab, the average daily dose of prednisone was reduced to approximately 5 mg. By the end of the study, more than half of the participants were prednisone-free.

After four weeks of mepolizumab treatment, investigators observed in all participants a decrease in circulating eosinophils. The researchers did not observe any signs of drug resistance or any major side effects associated with the long-term use of the antibody.


For people affected by chronic HES, mepolizumab is a potential treatment option that appears to have fewer side effects than lifelong, high-dose prednisone therapy.

Eosinophils also may play a role in other conditions such as autoimmune diseases, certain types of cancers, and severe asthma, so the results of this study suggest that mepolizumab may be useful in reducing the need for corticosteroids when treating these disorders.

Next Steps

The major challenge to giving mepolizumab to more people with HES is that the drug is still being evaluated to treat asthma and has not yet been approved by the Food and Drug Administration for widespread use.

Recognizing people's need for mepolizumab now, investigators at NIAID and the other participating clinical sites are working with the drug manufacturer, GlaxoSmithKline, to allow patients with HES to continue receiving the drug. Currently, the manufacturer is supporting a compassionate-use trial of mepolizumab to treat people with life-threatening HES who have failed treatment with available therapies. The purpose of the study is to provide life-saving treatment for people with HES.


Roufosse FE, Kahn J, Gleich GJ, Schwartz LB, Singh AD, Rosenwasser LJ, Denburg JA, Ring J, Rothenberg ME, Sheikh J, Haig AE, Mallett SA, Templeton DN, Ortega HG, Klion AD. Long-term safety of mepolizumab for the treatment of hypereosinophilic syndrome. J Allergy Clin Immunol. Oct. 4, 2012 [online ahead of print].

Compassionate Use of Mepolizumab in Subjects With Hypereosinophilic Syndrome (HES)

Dr. Klion's Lab

Last Updated October 29, 2012