This study focuses on people with Hypereosinophilic Syndrome (HES), a rare blood condition where there are too many white blood cells called eosinophils in the blood and tissues. These elevated levels can cause damage to various organs in the body. The study will test a new medication called depemokimab, which is given as an injection under the skin, along with standard treatments that may include prednisolone tablets.

The purpose of this research is to determine if depemokimab is effective in controlling HES when compared to placebo in people who are already receiving standard care. The study will last for 52 weeks, during which participants will receive either depemokimab injections or placebo injections. Some participants will also receive prednisolone tablets or matching placebo tablets as part of their treatment.

Throughout the study, doctors will monitor how often participants experience HES flares, which are periods when symptoms get worse or blood eosinophil counts increase. The medication will be provided in a pre-filled syringe for injection under the skin. Participants will be regularly checked for any changes in their condition and any effects of the treatment.