Long-term follow-up of patients with hypereosinophilic syndrome treated with alemtuzumab, an anti-CD52 antibody

Background: Relapsing, refractory patients with idiopathic hypereosinophilic syndrome (I-HES) and chronic eosinophilic leukemia-not otherwise specified (CEL-NOS) do not have many effective, durable therapeutic options. Alemtuzumab, an anti-CD52 antibody, has been reported to be an effective therapy due to inherent expression of CD52 on eosinophils. Methods: A retrospective chart review of 12 patients treated with alemtuzumab at our center until 2012. Results: Ten (83%) of 12 patients achieved complete hematologic response (CHR) after a median of 1 week for a median duration of 66 weeks, with the elimination of disease-related symptoms; 2 patients achieved partial hematologic remission hematologic remission (PHR). Patients with CHR who received alemtuzumab maintenance (n = 5) had a significantly longer time to progression than those patients who were only observed (n = 5) (P =.01). Eleven patients relapsed (only one while on maintenance), and 6 were rechallenged with alemtuzumab. Five (83%) achieved second CHR after a median of 3.5 weeks, for a median duration of 123 weeks. Again, those given maintenance (n = 3) had a longer time to progression than those who were only observed (P =.04). Adverse effects were mostly related to infusion reactions and lymphopenia-related viral infections (despite antibiotic prophylaxis). One patient developed Epstein-Barr virus-related lymphoma. Conclusions: Alemtuzumab is an effective treatment for patients with relapsed, refractory idiopathic hypereosinophilic syndrome and chronic eosinophilic leukemia-not otherwise specified, in terms of both CHR achievement (even after repeated rechallenges) and duration (particularly if provided as a maintenance therapy). Common adverse effects are related to infusion reactions and immunosuppression.