Leukemia Research Vol. 15, No. 6, pp. 457~161.1991. 0145-2126/91 $3.00 + .00 Printed in Great Britain. Pergamon Press plc CD9 ANTIGEN ON ACUTE NON-LYMPHOID LEUKEMIA CELLS: PREFERENTIAL EXPRESSION BY PROMYELOCYTIC (M3) SUBTYPE DARIO FERRERO, NADIA CARLESSO, EUGENIO GALLO, PATRIZIA PREGNO, PAOLO DE FABRITIIS,* MARIA CONCEqTA PETI'I* and FRANCO MANDELLI* Cattedra di Ematologia, Universita' di Torino, Italy and *Cattedra di Ematologia, Universita' "La Sapienza" Roma, Italy (Received 6 August 1990. Revision accepted 17 November 1990) Abstract-- A monoclonal antibody (S17-12), previously described to recognize subsets of myelo- monocytic cells, is demonstrated to bind CD9 antigen, a surface marker of B-cell precursors, platelets and several non-hematopoietic tissues. The proportion of S17-12, CD9-positive leukemic cells was determined in 102 patients with acute non-lymphocytic leukemia. It was found to be above 75% in 14/22 M3 cases (including 3/3 of microgranular variant) and only in 1/80 cases of different FAB subtype. Complete reactivity (>95%) of leukemic cionogenic cells with CD9 MoAB was restricted to 4/18 M3 cases. Therefore, a high proportion of CD9-positive cells seems to be peculiar to M3 cases. This may help in the diagnosis of cases that lack typical morphological features. Key words: Acute promyelocytic leukemia, monoclonal antibody, CD9, CFU-L. INTRODUCTION IN THE past ten years, the use of monoclonal anti- bodies (MoAbs) has greatly enhanced the possibility to characterize the lineage and the differentiation level of hematological malignancies [1]. Several MoABs, however, firstly regarded as specific for a defined subset of normal and neoplastic cells, have been subsequently found to react with elements of different hematopoietic lineages and/or non-hem- atopoietic tissues [2, 3]. CD9 MoAbs bind to a 24kD m.w. surface protein (P24) [2], originally described as a marker of 'common' acute lymphoblastic leukemia (c-ALL) and normal B-cell precursors [4, 5]. CD9 antigen, however, was also found to be highly expressed by platelets [6], that undergo activation and aggregation after binding to most CD9 MoAbs [7, 8]. Other hemotopoietic cells (monocytes, granulo- cytes, peripheral blood T and non-T lymphocytes, acute myelo-monocytic and monocytic leukemia cells) were subsequently found to react in variable proportions to some [2, 7, 8] but not all [5, 6] CD9 Abbreviations: ANLL, acute non-lymphocytic leukemia; ALL, acute lymphoid leukemia; MoAb, mono- clonal antibody; BM, bone marrow; PB, peripheral blood; FBS, fetal bovine serum; C', complement. Correspondence to: Dr Dario Ferrero, Cattedra di Ema- tologia, Ospedale Maggiore S. Giovanni, via Genova 3, 10126 Torino, Italy. MoAbs. Evidence was reported of at least three epitopes on CD9 P24 molecules that are recognized by different MoAbs [8] and can be variably expressed by hematopoietic cells. Finally, CD9 antigen was also detected by immunohystological studies in several non-hemato- poietic tissues: brain, liver, kidney, heart, smooth muscle, various epithelia, fibroblasts and endothelial ceils [5, 7]. A MoAb ($17-12), previously reported to recog- nize subpopulations of myeloid cells and to immuno- precipitate a 23 kD m.w. protein [9, 10], is here identified, by its reactivity pattern and by competition experiments, as a CD9 MoAb. This reagent has been tested in 102 cases of ANLL and evidence has been provided of a highly preferential expression of CD9 antigen by acute promyelocytic leukemia (APL) cells. 457 MATERIALS AND METHODS Monoclonal antibodies CD9 MoAb Tec-Cellsl was purchased from Tech- nogenetics. This MoAb is the product of FMC VIII hybridoma, described by Zola et al. [11]. $17-12 hybridoma, kindly provided by Dr G. Rovera (The Wistar Institute, Philadelphia, PA), was obtained by mouse immunization with the BV 173 cell line, derived from a patient with chronic myelogenous leukemia in lymphoid-like blast crisis [12].