Comparison of the biological activity of two sources of colony-stimulating factor (CSF)

Two possible standard sources of colony-stimulating factor (CSF) have been available commercially; one is GCT-conditioned medium (GCT-CM) and the other is T3M-5A-CSF. To clarify their biological activity and determine whether they can provide a stimulus identical with leukocyte feeders, the number and the morphology of colonies stimulated by them were compared. A dose-response study and a mixing experiment between them suggested the presence of inhibitor(s) in GCT-CM but not in T3M-5A-CSF. Both types of CSF stimulated mainly granulocytic colonies at day 7. T3M-5A-CSF caused a dose-dependent increase in macrophagic colonies at day 14. The number of colonies stimulated by GCT-CM and T3M-5A-CSF did not differ from that of leukocyte feeders, but the morphology of colonies differed significantly. These results indicate that there is a qualitative difference in the effect of GCT-CM and T3M-5A-CSF on human bone marrow cells, and that they do not supply a stimulus identical with leukocyte feeders. Though GCT-CM and T3M-5A-CSF are expected to serve as useful tools in the standard CFU-C assay, we should observe their characteristics and accumulate more information about their behavior on normal as well as on patient bone marrow cells.