Depemokimab in Participants With Hypereosinophilic Syndrome, Efficacy, and Safety Trial

This is a 52-week, randomized, placebo-controlled, double-blind, parallel group, multicenter study of depemokimab in adults with uncontrolled HES receiving standard of care (SoC) therapy. The study will recruit patients with a confirmed diagnosis of HES and who are on stable HES therapy for at least 4 weeks prior to randomization (Visit 2). Eligible participants must have uncontrolled HES with a history of repeated flare (≥2 flares in the previous 12 months) and blood eosinophil count of ≥1,000 cells/ microliter (μL) during Screening. Historical HES flares are defined as documented HES-related worsening of clinical symptoms or blood eosinophil counts requiring an escalation in therapy. Participants who meet the inclusion and exclusion criteria will be randomized in a 2:1 ratio to receive either depemokimab or placebo while continuing their SoC HES therapy.

Inclusion Criteria: * Participants who are greater than or equal (\>=) 40 kilogram (kg) at Screening Visit 1. * Participants who have a documented diagnosis of HES prior to Visit 2. * A history of 2 or more HES flares within the past 12 months prior to Visit 1. * A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: a) woman of non-childbearing potential (WONCBP) Or b) woman of childbearing potential (WOCBP) and using a contraceptive method that is highly effective, with a failure rate of less than (\