Mepolizumab approved by European Commission for the treatment of hypereosinophilic syndrome

On November 17, 2021, it was announced that the European Commission has approved mepolizumab, an anti-interleukin-5 (IL-5) monoclonal antibody, for the treatment of hypereosinophilic syndrome (HES) as an add-on treatment for adult patients with inadequately controlled HES without an identifiable non-hematologic secondary cause.¹ Mepolizumab is the first approved targeted therapy for patients with HES in Europe. Approval by the U.S. Food and Drug Administration (FDA) was granted in October 2020; read more here.

The approval is based on favorable results of a phase III trial, where a significantly lower number of patients experienced a HES flare, defined by worsening of symptoms or high eosinophil levels requiring an escalation in therapy, when treated with mepolizumab (as an add-on to standard of care) compared with placebo (28% vs 56%, respectively; p = 0.002). The key results from this trial are summarized here.

HES is characterized by elevated eosinophil levels, which may lead to inflammation and, ultimately, organ damage. Patients may experience a variety of complications, including fever, malaise, respiratory, or cardiac problems, which may be life-threatening. The diagnosis of HES can be a challenge, and patients may experience disease flares due to limited therapeutic options. IL-5 is known to play a role in eosinophil growth but the mechanism of action for mepolizumab has not been demonstrated; however, it is thought that mepolizumab prevents IL-5 from binding to its specific receptor on the eosinophil surface, decreasing and maintaining the levels of blood eosinophils.

Mepolizumab also has been approved for the treatment of eosinophilic granulomatosis with polyangiitis and chronic rhinosinusitis with nasal polyps.