. Previously, we serially transplanted tumors that produced colony-stimulating factor (CSF) into nude mice, who developed marked granulocytosis along with tumor growth; their leukocyte counts reaching approximately one million per cu mm. The numbers of CFU-GM, CFU-E, CFU-Meg, CFU-S and BFU-E were increased in nude mice bearing CSF-producing tumor. We here report that tumor-conditioned medium (TCM) derived from the CSF-producing tumors had colony-stimulating activity (CSA) and burst-promoting activity (BPA) when normal murine spleen cells as well as normal human bone marrow cells were the target cells. The activity of TCM supported multilineage colony formation in 5-fluorouracil (5-FU)-treated mouse spleen cells, in which only the primitive population of stem cells was reserved. No interleukin-3 (IL-3) activity was detected in TCM when assayed using the IL-3 dependent cell lines. We conclude that the factor in TCM acts on pluripo-tent stem cells and on the early progenitor stage of various cell lineages. It is distinct from IL-3.
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