GSK’s First-in-Class Anti-IL-5 Monoclonal Antibody Mepolizumab Approved in China for Hypereosinophilic Syndrome

On June 23, GlaxoSmithKline (GSK) announced that the National Medical Products Administration of China has approvedMepolizumab InjectionFor adults and adolescents aged 12 years and older without a clear non-hematologic secondary causeTreatment of Hypereosinophilic Syndrome (HES).

Hypereosinophilic Syndrome (HES) is characterized by elevated eosinophil levels in the blood and/or tissues, frequently involving the skin, lungs, gastrointestinal tract, and cardiovascular system. Organ and tissue damage progressively worsens over time, potentially leading to death. Traditional therapies, such as glucocorticoids and cytotoxic/immunosuppressive agents, demonstrate variable efficacy and are often associated with significant adverse effects and high relapse rates.

According to publicly available information,Mepolizumab is a “first-in-class” humanized monoclonal antibody against IL-5, and the first anti-IL-5 monoclonal antibody approved globally.. The reason why mepolizumab stands out among numerous drugs lies in its unique mechanism of action. ItPrecision Targeting of Interleukin-5 (IL-5)IL-5 plays a crucial role in the human immune system. It is a core cytokine in type 2 inflammation, which is the underlying driver of various diseases.

The approval of this new indication for the drug is based on the NCT02836496 Phase III international, multicenter, randomized, double-blind, placebo-controlled clinical study. This study evaluated the efficacy and safety of subcutaneous mepolizumab versus placebo in patients with HES, in addition to prior standard therapy.

This study enrolled a total of 108 adult patients with hypereosinophilic syndrome (HES), who were randomized in a 1:1 ratio to receive subcutaneous injections of mepolizumab 300 mg or placebo every 4 weeks for 32 weeks, in addition to their existing therapy (including but not limited to oral corticosteroids, immunosuppressants, and/or cytotoxic agents).

The study results showed that compared with placebo, mepolizumabSignificantly reduced the risk of HES patients experiencing exacerbations or withdrawing from the study by 50%(Incidence/withdrawal rate: 28% vs. 56%, P=0.002);66% Reduction in Risk of First Episode(HR 0.34, P=0.002); the proportion of exacerbations during weeks 20–32 was significantly lower (17% vs 35%, P=0.02; OR 0.33, 95% CI 0.13–0.85);Annualized seizure rate significantly reduced by 66%(0.50 times/year vs. 1.46 times/year, P<0.001); peripheral blood eosinophil (EOS) count dropped sharply by approximately 88% at week 2 of treatment (from 1,460/μL to 170/μL), reached its lowest level at week 8, and remained sustained through week 32.

In terms of safety, the overall incidence of adverse events was comparable to that in the placebo group (89% vs 87%), and no new safety signals were identified in the study.

Previously, the indications approved for mepolizumab in China includedEosinophilic Granulomatosis with Polyangiitis (EGPA), Severe Eosinophilic Asthma (SEA), Chronic Rhinosinusitis with Nasal Polyps (CRSwNP), and Chronic Obstructive Pulmonary Disease (COPD)Among them, the indications for EGPA, SEA, and CRSwNP have all been included in the National Reimbursement Drug List.

Currently, drugs targeting IL-5 mainly includeReslizumab (Teva Pharmaceutical), Benralizumab (AstraZeneca), Depemokimab (GSK)etc.

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