Long-term treatment by mepolizumab reduces the relapse rate in patients with eosinophilic granulomatosis with polyangiitis

Abstract Background: The mainstay of treatment for eosinophilic granulomatosis with polyangiitis (EGPA) is systemic corticosteroid therapy; some patients also receive intravenous immunoglobulins, other immunosuppressive agents, and biologics. Mepolizumab, an anti-interleukin-5 monoclonal antibody, in EGPA patients induces remission and decreases the daily dose of corticosteroids; however, the prognosis of long-term mepolizumab treatment for EGPA and its clinical efficacy are unknown. Methods: Seventy-one EGPA patients were treated at Hiratsuka City Hospital, Japan, between April 2018 and March 2022. We administered mepolizumab for mean 2.8±1.7 years to 43 patients in whom remission could not be induced by conventional treatment. After excluding 18 patients who received mepolizumab for less than 3 years, we classified 15 patients in the “super-responder group” (the daily dose of corticosteroids or another immunosuppressant could be decreased, or the interval between IVIG treatments could be prolonged) and 10 patients in the “responder group” (neither of these changes could be achieved). Eosinophil numbers, serum IgG levels, daily doses of corticosteroids and other immunosuppressants, the Birmingham Vasculitis Activity Score (BVAS), and relapse frequency before and after mepolizumab initiation were determined. Results: Eosinophil numbers at diagnosis or the lowest serum IgG level before mepolizumab treatment were higher in the super-responder group than in the responder group ( p < 0.05). In the super-responder group, the prednisolone dose at last visit after mepolizumab initiation was lower than before treatment ( p < 0.01) and in the responder group ( p < 0.01). In both groups, the number of peripheral blood eosinophils and BVAS decreased after starting mepolizumab compared to before treatment ( P < 0.01). BVAS before mepolizumab ( p < 0.05) and at the last visit ( p < 0.01) in the super-responder group were lower than in the responder group. Relapse rates every year after the start of mepolizumab were lower in the super-responder group than in the responder group ( p <0.01). Relapse rates decreased during the 3 years following initiation of mepolizumab treatment ( p <0.05) and at the last visit ( p <0.01) compared with those at the start of mepolizumab treatment. Conclusions: Treatment with mepolizumab in the super-responder group durably reduced the relapse rate.