Imatinib mesylate for lymphocytic variant of hypereosinophilic syndrome
To the editor: With a great interest I read a paper by Christoforidou et al. showing the high efficacy of imatinib mesylate (IM) in a patient with L-HES and undetectable FIP1L1-PDGFRA (F/P) fusion transcript. However, after reading this case description, it seems that several issues need to be clarified and commented. The diagnosis of L-HES requires the detection of the abnormal T-cell phenotype in peripheral blood by flow cytometry and the presence of T-cell receptor clonal rearrangement . It was demonstrated that clonal TCR rearrangement was detectable in patients with F/P mutation and treatment with IM resulted in disappearance of the clonal TCR pattern . In this publication, the authors described a patient with lymphocytosis involving clonal but phenotypically normal CD41 cell population, but these cells were detected in marrow. I wonder if these cells were also found in peripheral blood? The presence of CD41 cells in patients with hypereosinophilic syndromes has already been demonstrated by other study groups, but it should be highlighted that this finding is extremely rare. The occurrence of such a T-cell population is usually associated with other features of T-cell mediated hypereosinophilia, e.g., increased serum IgE levels or cytokine and chemokine overproduction . These results are needed to better characterize this variant but they are lacking in this report.
Corticosteroids (CS) remain a treatment of choice for patients with L-HES [2]. The authors reported severe side effects after therapy with steroids so they were discontinued. It was demonstrated in most studies that CS resulted in decrease of blood eosinophilia and resolution of clinical symptoms but the proportion of abnormal T-cell remained unaffected . In relation to this observation, I would expect such data from the authors of this presentation. We should keep in mind that treatment with IM, especially at a dose of 400 mg daily is expensive and associated with numerous side effects. Therefore, it seems rational to initiate IM only for patients who developed severe steroid-related complications and still require the continuation of treatment. Based on the presented case, it is difficult to judge that IM led to remission in a patient with L-HES. The therapy resulted in decrease of blood eosinophilia and withdrawal of some clinical symptoms, but in fact IM did not affect eosinophilic infiltration of the colon. The proportion of a clonal T-cell population remained intact. This case has shown that IM may remain an interesting therapeutic option but only for those patients who are resistant or intolerant to CS. As the abnormal T-cell subset remained unchanged after IM, we may expect that IM and CS will not prevent those patients from lymphoma transformation.