Placenta as Detected by a Monoclonal Antibody Factor by a Myeloid Leukemia Cell Line (KPB-M15) and Production of Human Hematopoietic Survival and Growth

Fifty-five hematopoietic cell lines, including 19 T-, 16 B-, S pre-B-, 5 non-T non-B-, 1 erythroid, and 9 myeloid-monocytoidcells, were screened for production of human hematopoietic survival and stem cell growth factor (SCGF) by enzyme immunoassay using anti-SCGF monoclonal antibody. The KPB-M15 myeloid cell line constitutionally secreted a considerable quantity of SCGF, while other Tor myeloid-monocytoid cell lines did not secrete SCGF. Other biomaterials investigated were fetal calf, horse, and human serum; granulocyte-macrophage colonystimulating factor and erythropoietin preparations;human placental con ditioned medium; lectin (phytohemagglutinin, concanavalin A, and pokeweed mitogen); and mixed leukocyte reaction-stimulated leukocyte-con ditioned medium.SCGF was detected only in humanplacental conditioned medium. SCGF produced by the KPB-M15 cells was a protein with a molecular weight of 20,000. The molecule, highly purified by immunoadsorbent affinity chromatography, retained SCGF activity in vitro, e.g., erythroid burst-promoting activity and granulocyte-macrophage-colony potentiation. With the availability of purified SCGF, it is now possible to study in detail the mechanisms regulating hematopoietic stem cells.