PRIMITIVE HUMAN HEMATOPOIETIC PROGENITORS ADHERE TO P-SELECTIN (CD62P)

P-selectin was shown to bind committed human hematopoietic progenitors (colony-forming unit-granulocyte-macrophage [CFU-GM] and burst-formin g unit-erythroid [BFU-E]) as identified by their expression of the CD3 4 antigen and by in vitro clonogenic assays. In addition, P-selectin b ound all precursors (pre-CFU) of committed myeloid progenitors assayed by their ability to sustain hematopoiesis in both conventional stroma -containing and stroma-free, cytokine-dependent systems. Binding of CD 34(+) cells to P-selectin was temperature-independent and shear-resist ant, occurred only in the presence of divalent cations, was protease s ensitive, and was completely blocked by anti-P-selectin antibody. Neur aminidase treatment of CD34(+) cells completely abrogated their bindin g to P-selectin, implying a prominent role for sialic acid in the stru cture and function of the P-selectin ligand on hematopoietic progenito rs. Monoclonal antibodies (MoAbs) CSLEX-1 and HECA-452, which identify carbohydrate epitopes involving sialic acid, bound to 33% and 35% of CD34(+) cells, respectively, and included the majority of CFU-GM and p re-CFU. Three-color flow cytometric analysis showed a precise codistri bution of CSLEX-1 and HECA-452 antigens on CD34(+) cells, implying rec ognition of the same glycoprotein antigen by the two MoAbs. Treatment of CD34(+) cells with neuraminidase completely abolished binding of bo th MoAbs. In addition, HECA-452 partially blocked the adhesion of CD34 (+) cells to P-selectin. P-selectin glycoprotein ligand (PSGL-1), rece ntly molecularly cloned from the promyelocytic leukemia cell line HL60 , was expressed by CD34(+) cells as determined by reverse transcriptio n polymerase chain reaction. Combined with the functional and biochemi cal characteristics, these data suggest that PSGL-1 may comprise an im portant P-selectin ligand expressed by primitive hematopoietic cells, but do not preclude the existence of additional P-setectin ligands on these cells. (C) 1995 by The American Society of Hematology.