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.