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Hypereosinophilia during 2‐chlorodeoxyadenosine treatment for hairy cell leukaemia

A 43‐year‐old male with newly diagnosed hairy cell leukaemia underwent a single course of 2‐chlorodeoxyadenosine (2‐CdA). Skin rash, facial swelling and marked eosinophilia developed 20 d after treatment and were resolved by 7 d of steroid therapy. Eosinophil peak in peripheral blood reached 1230 cells/μl. Flow cytometric analysis of the eosinophil population showed a high expression of the IL‐2 receptor α‐chain (CD25), representing up to 94% of gated cells. HLA‐DR and CD4 antigens were constantly negative; eosinophils strongly reacted with the secretory form of the eosinophil cationic protein (ECP), recognized by EG2 monoclonal antibody. IL‐5 serum levels were markedly elevated at the onset of eosinophilia, returned to normal levels after its disappearance and positively correlated with eosinophil count (r = 0.94, P = 0.016). Eosinophilia is an uncommon finding after treatment with 2‐CdA. It is unclear whether these phenomena represented a true allergic reaction to the drug or the effect of massive tumour cell lysis and haemopoietic pancytopenia with immunosuppression, which induced the release of IL‐5 and possibly other cytokines.