The KOR-SA3544 antigen predominantly expressed on the surface of Philadelphia chromosome-positive acute lymphoblastic leukemia cells is nonspecific cross-reacting antigen-50/90 (CD66c) and invariably expressed in cytoplasm of human leukemia cells

We previously reported a novel monoclonal antibody KOR-SA3544 which predomi nantly reacted with a surface antigen (sSA3544) expressed on Philadelphia c hromosome (Phl)-positive acute lymphoblastic leukemia (ALL). In the present study, we demonstrate that the antibody specifically recognized nonspecifi c cross-reacting antigen (NCA)-50/90 (CD66c), one of the carcinoembryonic a ntigen (CEA)-related glycoproteins encoded by a member of the CEA gene fami ly. In addition, we show that the SA3544 antigen (NCA-50/90) was invariably expressed in cytoplasm of all of the human leukemic cell lines examined (s SA3544-positive B-lymphoid two, sSA3544-negative T or B-lymphoid and non-ly mphoid 24) regardless of the presence or absence of surface expression of t his antigen. Immunoelectromicroscopic examination revealed that the cytopla smic antigen was mainly present in granules in sSA3544-positive leukemia ce lls, whereas it was diffusely present in cytosol in sSA3544-negative leukem ia cells. Thus, among members of the CEA family, NCA-50/90 was first demons trated to be expressed not only on the surface of some leukemia cells, but also in cytoplasm of various types of leukemia cells.