Interleukin-3 receptor alpha chain (CD123) is widely expressed in hematologic malignancies

Background and Objectives. The hematopoietic system is controlled by growth factors (cytokines) which can influence cell survival, proliferation, diff erentiation and functional activation, The study of cytokine receptor expre ssion by flow cytometry could allow us to differentiate between normal and tumoral cells. Design and Methods. We analyzed the expression of the interleukin-3 (IL-3) receptor alpha chain (CD123) in 22 normal samples and in a wide panel of he matologic malignancies using flow cytometry. We found that CD123 was expres sed in the myeloid progenitor subpopulation but in contrast, normal lymphoi d progenitors lacked CD123. We analyzed the CD123 expression pattern in 64 patients with acute leukemia, 45 with acute myeloid leukemia (AML) and 19 w ith acute lymphocytic leukemia (ALL) (13 B-cell lineage ALL and 6 T-cell li neage ALL). Results. All the AML cases except two patients with M7 and all the B-cell l ineage ALL patients were CD123 positive. In contrast, all the T-cell lineag e ALL cases tested were CD123 negative. We also studied the CD123 expressio n pattern in 122 patients with a B-cell chronic lymphoproliferative disease (B-CLPD). CD123 was positive in three situations: 1) typical cases of hair y cell leukemia showed a specific, strong CD123 expression, 2) a subgroup o f atypical chronic lymphocytic leukemia with a marked CD11c expression was also CD123 positive, and finally 3) transformed B-CLPD showed the phenomeno n of transition from CD123 negativity to CD123 positivity simultaneuosly wi th morphologic changes. Interpretation and Conclusions. In summary, our data show high expression o f IL-3 receptor a chain in hematologic malignancies. Given the high frequen cy of CD123 reactivity in blast cells in contrast to in normal precursors, this antigen could be applied to the study of minimal residual disease in a cute leukemia. CD123 is expressed with a characteristic pattern in cases of hairy cell leukemia. (C) 2001, Ferrata Storti Foundation.