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, induces remission and decreases the daily corticosteroid dose; however, the clinical efficacy of mepolizumab in EGPA and the prognosis with long-term treatment with this drug are unknown. Methods Seventy-one EGPA patients were treated at Hiratsuka City Hospital, Japan, between April 2018 and March 2022. We administered mepolizumab for a mean of 2.8 ± 1.7 years to 43 patients in whom remission could not be induced by conventional treatment. After excluding 18 patients who had received mepolizumab for less than 3 years, we classified 15 patients into a “super-responder group” (the daily dose of corticosteroids or other immunosuppressant could be decreased, or the interval between IVIG treatments could be prolonged) and 10 patients into a “responder group” (neither of these changes was achievable). Eosinophil numbers, serum IgG levels, daily doses of corticosteroids and other immunosuppressants, Birmingham Vasculitis Activity Score (BVAS), and relapse frequency before and after mepolizumab initiation were determined. Results Blood eosinophil count at diagnosis and the lowest serum IgG level before mepolizumab treatment were significantly higher in super-responders than in responders (p < 0.05). In super-responders, the prednisolone dose at last visit on mepolizumab treatment was lower than that before treatment (p < 0.01) and lower than that at last visit in the responders (p < 0.01). In both groups, peripheral blood eosinophil numbers and BVAS were lower after starting mepolizumab than before (p < 0.01). BVAS before mepolizumab (p < 0.05) and at last visit (p < 0.01) were lower in super-responders than in responders. Relapse rates every year after the start of mepolizumab were lower in super-responders than in responder groups (p < 0.01). In super-responders, relapse rates were lower during the 3 years following mepolizumab initiation (p < 0.01) and at last visit (p < 0.01) were significantly lower than after 1 year of treatment. Conclusion Mepolizumab treatment of super-responders sustainably reduced the relapse rate.

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.