RELAPSE OF ACUTE MYELOGENOUS LEUKEMIA DURING LOW-DOSE INTERLEUKIN-2 (IL-2) THERAPY - PHENOTYPIC EVOLUTION ASSOCIATED WITH STRONG EXPRESSION OF THE IL-2 RECEPTOR-ALPHA CHAIN

Background. Interleukin-2 (IL-2) has produced remissions in patients with solid tumors, predominantly malignant melanoma and renal cell carcinoma. Recently, clinical trials have assessed the therapeutic benefit of this cytokine in acute myelogenous leukemia (AML). However, little is known about the potential of IL-2 to promote the growth of leukemic cells in vivo. Methods. A patient with acute myelocytic leukemia whose leukemic blasts displayed lymphoid (TdT+ and CD4+) and myeloid features (myeloperoxidase [MPO]+ and CD13+) is reported. The IL-2 receptor alpha chain (CD25 antigen) was present on 28.9% of his blasts. After entering complete remission with chemotherapy, he was treated on a protocol using IL-2 maintenance. Results. Six weeks after beginning low-dose IL-2, his leukocyte count increased to 448,000/mu l with 86% blasts. The phenotype of these blasts was different from that at diagnosis with expression of the CD25 antigen and the CD33 antigen on 75.9% and 74.8 of the blasts, respectively. Furthermore, 30% of the cells were TdT+, whereas MPO was not detectable. Conclusion. The rapid course of relapse, phenotypic evolution, and the high expression of CD25 antigen on the blasts after IL-2 therapy raise the possibility that the cytokine therapy may have promoted the growth of leukemic cells.