Sustained low disease activity during long-term mepolizumab treatment in FIP1L1::PDGFRA-negative hypereosinophilic syndrome: a multicenter real-world study

Background Mepolizumab reduces relapses and glucocorticoid exposure in hypereosinophilic syndrome (HES), but evidence on long-term effectiveness remains limited. Growing consensus emphasizes sustained low disease activity over single-timepoint response in chronic inflammatory diseases. Objective To evaluate the long-term safety and effectiveness of mepolizumab in HES using a pragmatic definition of Eosinophilic Low Disease Activity State (EoLDAS). Methods We conducted a retrospective multicenter study of 67 patients with glucocorticoid-responsive FIP1L1::PDGFRA -negative HES treated with mepolizumab between 2003 and 2022 through clinical trials or compassionate use programs. Clinical manifestations, blood eosinophil counts, treatments, and serious adverse events were assessed at three-month intervals. EoLDAS was defined as absence of relapse, an absolute eosinophil count <0.5×10 9 /L (complete hematologic response, [CHR]), and a prednisone dose ≤5 mg/day. Results After a median follow-up of 51 months, 12 patients (18%) relapsed and CHR was maintained during a median of 93% of visits. Patients spent a median of 79% (IQR, 40–88) of follow-up visits in EoLDAS, and 51% maintained EoLDAS for at least 75% of visits. Poor EoLDAS attainment (<25% of visits; n=11) was associated with lymphocytic HES and more prior treatment lines. Extending mepolizumab dosing intervals was associated with modest increases in eosinophil counts, but not with relapse or increased glucocorticoid exposure. No serious adverse event was considered related to mepolizumab. Conclusion Mepolizumab provided sustained long-term disease control with low glucocorticoid exposure in FIP1L1::PDGFRA -negative HES. EoLDAS offers a pragmatic measure of longitudinal disease control that warrants prospective validation and may inform future treat-to-target strategies.

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Journal
The Journal of Allergy and Clinical Immunology In Practice
Published
2026-10-01
DOI
https://doi.org/10.1016/j.jaip.2026.09.021
Primary Topic
Eosinophilic Disorders and Syndromes
Type
article
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article

Sustained low disease activity during long-term mepolizumab treatment in FIP1L1::PDGFRA-negative hypereosinophilic syndrome: a multicenter real-world study

Dorine Canu, F. Barde, Bernard Bonnotte, Kévin Chevalier et al.
The Journal of Allergy and Clinical Immunology In Practice
Eosinophilic Disorders and Syndromes
article

Sustained low disease activity during long-term mepolizumab treatment in FIP1L1::PDGFRA-negative hypereosinophilic syndrome: a multicenter real-world study

Dorine Canu, F. Barde, Bernard Bonnotte, Kévin Chevalier, Divi Cornec, Camille Ravaiau, Jean‐Emmanuel Kahn, N. Freymond, Guillaume Lefèvre, Emmanuel Ledoult, ARNAUD AB BOURDIN, Stanislas Faguer, Matthieu Groh, Ibrahim Marroun, Zakaria Mohamed Lahmar, Sébastien Trouiller, Julien Rohmer, Pascal Chanez, Daniele Belgodere, Julien Sénéschal, Félix Ackermann, Lucile Grange, Antoine Néel, Camille Taillé, Alpha Oumar Diallo
article en

Abstract

Background Mepolizumab reduces relapses and glucocorticoid exposure in hypereosinophilic syndrome (HES), but evidence on long-term effectiveness remains limited. Growing consensus emphasizes sustained low disease activity over single-timepoint response in chronic inflammatory diseases. Objective To evaluate the long-term safety and effectiveness of mepolizumab in HES using a pragmatic definition of Eosinophilic Low Disease Activity State (EoLDAS). Methods We conducted a retrospective multicenter study of 67 patients with glucocorticoid-responsive FIP1L1::PDGFRA -negative HES treated with mepolizumab between 2003 and 2022 through clinical trials or compassionate use programs. Clinical manifestations, blood eosinophil counts, treatments, and serious adverse events were assessed at three-month intervals. EoLDAS was defined as absence of relapse, an absolute eosinophil count <0.5×10 9 /L (complete hematologic response, [CHR]), and a prednisone dose ≤5 mg/day. Results After a median follow-up of 51 months, 12 patients (18%) relapsed and CHR was maintained during a median of 93% of visits. Patients spent a median of 79% (IQR, 40–88) of follow-up visits in EoLDAS, and 51% maintained EoLDAS for at least 75% of visits. Poor EoLDAS attainment (<25% of visits; n=11) was associated with lymphocytic HES and more prior treatment lines. Extending mepolizumab dosing intervals was associated with modest increases in eosinophil counts, but not with relapse or increased glucocorticoid exposure. No serious adverse event was considered related to mepolizumab. Conclusion Mepolizumab provided sustained long-term disease control with low glucocorticoid exposure in FIP1L1::PDGFRA -negative HES. EoLDAS offers a pragmatic measure of longitudinal disease control that warrants prospective validation and may inform future treat-to-target strategies.

The Journal of Allergy and Clinical Immunology In Practice
Centre National de la Recherche Scientifique (FR), Inserm (FR), Université de Bourgogne (FR), Université de Versailles Saint-Quentin-en-Yvelines (FR), Université de Montpellier (FR), Université Paris Cité (FR), Aix-Marseille Université (FR), Université Paris-Saclay (FR), Centre Hospitalier Universitaire de Lille (FR), Centre Hospitalier Universitaire de Nantes (FR), Centre Hospitalier Universitaire de Toulouse (FR), Physiologie et Médecine Expérimentale du Coeur et des Muscles (FR), Centre Hospitalier Universitaire de Montpellier (FR), Assistance Publique – Hôpitaux de Paris (FR), Center for Infection and Immunity of Lille (FR), Hospices Civils de Lyon (FR), Centre de recherche en Epidémiologie et Santé des Populations (FR), Hôpital Saint-André (FR), Centre Hospitalier Universitaire d'Angers (FR), CHU Dijon Bourgogne (FR), Lille Inflammation Research International Center (FR), Hôpitaux Universitaires Henri-Mondor (FR), Institut Régional d'Administration de Bastia (FR), Centre Hospitalier Régional Universitaire de Brest (FR), Hôpital Ambroise-Paré (FR), Hôpital Bichat-Claude-Bernard (FR), Hôpitaux Universitaires de Strasbourg (FR), Centre Hospitalier Universitaire de Saint-Étienne (FR), Institut de recherche Saint-Louis (FR), Université d'Angers (FR)
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