Circulating blast cells from the peripheral blood of acute myeloblastic leukemia patients include a subpopulation capable of colony formation in the presence of phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM). We describe the complete replacement in the blast assay of PHA-LCM by conditioned medium from a human bladder carcinoma cell line, HTB9. Both conditioned media contain a stimulator of blast cell growth that elutes as a single peak from a Sephadex G100 column with an apparent molecular weight of 30,000. It is shown that this leukemic blast growth factor is distinct from erythroid-potentiating activity (EPA) and possibly granulocyte macrophage colony-stimulating factor.

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