CD66C ANTIGEN EXPRESSION IS MYELOID RESTRICTED IN NORMAL BONE-MARROW BUT IS A COMMON FEATURE OF CD10(-B-CELL MALIGNANCIES() EARLY)

CD66c is a surface (and intracellular) molecule bound to the membrane by a glycosyl-phosphatidylinositol anchor. While its expression on per ipheral granulocytes is well recognized, less is known about its distr ibution in early steps of normal and neoplastic hematopoiesis. We anal yzed by flow cytometry cell surface expression of CD66c on bone marrow cells from 4 healthy subjects and on bone marrow or peripheral blood cells from 127 patients with newly diagnosed hematologic malignancies: 70 de novo acute myeloid leukemias (AML), 6 refractory anemias with e xcess of blasts in transformation, 3 myeloid and 3 lymphoid blastic ph ases of chronic myelogenous leukemia 33 B-lineage and 6 T-lineage acut e lymphoblastic leukemias (B- and T-ALL), and 3 B-cell and 3 T-cell no n-Hodgkin's lymphomas in the leukemic phase. We found that in normal b one marrow CD66c expression was myeloid restricted, reaching its highe st level on promyelocytes. As for de novo AML, slight expression of CD 66c was found on 6/25 (24%) AML-M4 and only occasionally in other subg roups. In 9 out of 10 cases of acute promyelocytic leukemia, CD66c was totally absent, but antigen expression was easily detectable followin g in vitro exposure to all-trans retinoic acid. Among lymphoid maligna ncies, CD10<SUP>+</SUP> early-B-ALL consistently expressed the molecul e (20/23 cases, or 87%) whereas both CD10<SUP>-</SUP> early-B ALL and SmIg<SUP>+</SUP> B-ALL completely lacked it. Finally, dual staining wi th CD66c and CD10 proved to be a suitable tool for distinguishing even low percentages of residual leukemic cells (CD10<SUP>+</SUP>/CD66c<SU P>+</SUP><INF></INF>) from normal regenerating early-B cells (CD10<SUP >+</SUP>/CD66c<SUP>-</SUP>) in CD10<SUP>+</SUP> early-B-ALL induced in to remission.