2-CHLORODEOXYADENOSINE THERAPY FOR IDIOPATHIC HYPEREOSINOPHILIC SYNDROME

Idiopathic hypereosinophilic syndrome (HES) is a rare disease with no established effective therapy. It has been reported that interleukin-5 (IL-5) produced by helper T cells plays a major role in the prolifera tion of eosinophils. The nucleotide analogue 2-chlorodeoxyadenosine (2 -CdA), which induces excellent clinical responses in hairy cell leukem ia, is known to suppress helper T cells; therefore, we used 2-CdA, alo ne or in combination with cytarabine, to treat patients with idiopathi c HES. 2-CdA alone and combined with cytarabine resulted in a rapid an d sustained decrease in circulating eosinophils in two patients with i diopathic HES that was refractory to steroids, hydroxyurea and cytarab ine. The efficacy of 2-CdA alone and combined with cytarabine exceeded by far that of cytarabine alone. However, reverse transcription-polym erase chain reaction (RT-PCR) did not show production of IL-5 or granu locyte-macrophage colony-stimulating factor mRNA in T cells as previou sly reported, and multiple cytokine receptors were found on eosinophil s in idiopathic HES, suggesting that IL-5 may not be the sole cytokine involved in the regulation of idiopathic HES. The clinical efficacy o f 2-CdA in idiopathic HES needs to be established on a large group of patients.