Analysis in serum-free culture of the targets of recombinant human hemopoietic growth factors: interleukin 3 and granulocyte/macrophage-colony-stimulating factor are specific for early developmental stages.

We have used a serum-free culture system for enriched human hemopoietic progenitors to analyze the developmental stages and lineage specificities of the human hemopoietic colony-stimulating factors. None of the individual factors alone efficiently supported hemopoietic colony formation. Neither interleukin 3 nor granulocyte/macrophage-colony-stimulating factor alone or in combination effectively supported proliferation of progenitor cells. However, when combined with granulocyte-colony-stimulating factor or erythropoietin, these factors yielded neutrophil colonies or erythroid bursts, respectively. Serial observations of interleukin 3-supported cultures revealed sequential emergence and subsequent degeneration of clusters of cells. These observations suggest that the primary targets of interleukin 3 and granulocyte/macrophage-colony-stimulating factor are multipotent progenitors at the early stages of development rather than cells in the terminal process of maturation.