CHARACTERIZATION OF THY-1 (CDW90) EXPRESSION IN CD34(-LEUKEMIA() ACUTE)

Thy-1 (CDw90) is a phosphatidylinositol-anchored cell surface molecule which, when coexpressed with CD34 in normal human bone marrow, identi fies a population of immature cells that includes putative hematopoiet ic stem cells. To date, the characterization of Thy-1 expression has b een confined largely to normal tissues and cell lines. In this study, we evaluated the frequency and intensity of Thy-1 expression as define d by reactivity with the anti-Thy-1 antibody 5E10 in 38 cases of CD34( +) acute leukemia (21 acute myelogenous leukemia [AML], 8 chronic myel ogenous leukemia [CML] in blast crisis, and 9 acute lymphoblastic leuk emia [ALL]). In 34 of 38 cases (89%) the CD34(+) cells lacked expressi on of the Thy-1 antigen. High-density Thy-1 expression was found in 1 case of CML in lymphoid blast crisis, and low-density Thy-1 expression was identified on a portion of the leukemic cells in 2 cases of AML w ith myelodysplastic features, and 1 case of CML in myeloid blast crisi s, suggesting a possible correlation between Thy-1 expression and cert ain instances of stem cell disorders such as CML and AML with dysplast ic features. In contrast, the dissociation of Thy-1 and CD34 expressio n in the majority of acute leukemias studied suggests that the develop ment of these leukemias occurs at a later stage than the hematopoietic stem cell. Characterization of Thy-1 expression in acute leukemia may eventually provide insights into the origin of the disease. In additi on, separation of leukemic blasts from normal stem cells based on Thy- 1 expression may prove useful in assessing residual disease, as well a s in excluding leukemic blasts from stem cell preparations destined fo r autologous bone marrow or peripheral stem cell transplantation. (C) 1995 by The American Society of Hematology.