Separate actions of different colony stimulating factors from human placental conditioned medium on human hemopoietic progenitor cell survival and proliferation

More than 20% of human granulocyte‐macrophage and eosinophil colony‐forming cells survived in agar culture for up to 4 days without the addition of exogenous colony stimulating factors (human placental‐conditioned medium, HPCM). Survival was reduced slightly but not significantly, by the removal of adherent cell populations. Significant survival occurred even when only 100 cells enriched for colony‐forming cells (CFCs) were cultured per dish. When individual colonies, initiated by stimulation with HPCM for 5 days, were transferred to dishes without HPCM, subsequent proliferation was significantly reduced compared with control cultures containing HPCM. Using the fluorescence‐activated cell sorter and the fluoresceinated lectin from Lotus tetragonolobus , two populations of marrow cells were obtained, one enriched for day 7 and the other for day 14 colony‐forming cells. Two colony‐stimulating factors fractionated from HPLCM (CSF β and CSF α ) have been shown previously to stimulate the day 7 and day 14 colony‐forming cell populations, respectively. Developing clones from cultures initiated with CSFβ died between the fifth and tenth day of culture after transfer to dishes with CSFα or CSFβ or to dishes with no stimulus. Cells in clusters initiated with CSFα proliferated significantly between the fifth and tenth day of culture when transfered to CSFα or CSFβ but not when transfered to dishes with not stimulus. These studies provide further evidence for the existence of two subtypes of human granulocyte‐macrophage progenitor cells each under the primary control of a specific regulator and indicate that these two regulators can both act on some developing clones of cells.