Dupilumab as Add-On Therapy for Hypereosinophilic Syndrome With Partial Clinical Response to Eosinophil-Depleting Biologic Agents

Background: Hypereosinophilic syndrome (HES) is a blood disorder that causes high levels of white blood cells called eosinophils. HES can damage the lungs and airways, intestines, skin, and other organs. The current primary treatment for HES can cause serious side effects. Secondary treatments do not work in all people. Objective: To test an approved drug (dupilumab), combined with other drugs, in people with HES. Eligibility: People aged 18 years and older who take drugs (mepolizumab, reslizumab, or benralizumab) to treat HES. Design: Participants will have up to 6 clinic visits and 7 remote visits in up to 48 weeks. Participants will be screened. They will have blood and urine tests. They will have a test of their heart function. They will take surveys about how HES affects their daily life. Some participants may have a bone marrow biopsy: A sample of tissue and fluid from inside a bone will be removed with a large needle. Participants will have other tests specific to their symptoms. For example, those with symptoms affecting their lungs will have breathing tests. Others may have tests that target symptoms in their sinuses, gastrointestinal tract, or skin. Dupilumab is injected under the skin once every 1 or 2 weeks. Dose and timing will vary among participants. They will be taught how to inject themselves at home between clinic visits. They will take dupilumab plus their current medications for 24 weeks. If the drug is helping them, they will continue taking it for another 24 weeks. Participants will have a final visit 12 weeks after their last dose.