FLOW CYTOMETRIC ANALYSIS OF THY-1 EXPRESSION IN CD34-POSITIVE ACUTE-LEUKEMIA

We analyzed the expression of the Thy-1 antigen (CD90) in CD34(+) acut e leukemia using two-color how cytometry. Leukemic cells were obtained from the bone marrow (BM) and/or the peripheral blood (PB) of 57 pati ents: 37 with acute myelogenous leukemia (AML) including nine with sec ondary AML following myelodysplastic syndrome (MDS/AML), and 20 with a cute lymphoblastic leukemia (ALL) including three with chronic myeloge nous leukemia in blast crisis (CML-BC) of the lymphoid type. Among the se patients, one (3.6%) with de novo AML, two (22.2%) with MDS/AML, th ree (17.6%) with de novo ALL, and two (66.7%) with CML-BC coexpressed CD34 and Thy-1 (CD34(+) Thy-1(+)) on more than 20% of the mononuclear cells within 'lymph' plus 'blast' window. Thy-1 was rarely expressed i n de novo acute leukemia especially in AML. Interestingly, in 1 patien t with CML-BC, the leukemic cells in BM were divided into two subpopul ations (CD34(+) Thy-1(low) and CD34(+) Thy-1(high)), whereas most of t he CD34(+) leukemic cells in PB were Thy-1(high). However, the mechani sm for the mobilization of CD34(+) Thy-1(high) leukemic cells into the PB is unknown. (C) 1997 Elsevier Science Ireland Ltd.