Induction of proliferation of purified human myeloid progenitor cells: a rapid assay for granulocyte colony-stimulating factors

The proliferation and differentiation of granulocyte and monocyte progenitor cells (CFU-C) in vitro is dependent on the presence of a group of closely related glycoproteins termed colony-stimulating factors (CSF). In order to investigate the interaction of these factors with CFU-C, we purified CFU-C from the peripheral blood of chronic myeloid leukemia patients with an immune rosette technique using specific monoclonal antibodies (mean 74-fold enrichment, 45% cloning efficiency). Colony formation by purified CFU-C demonstrated an absolute dependence on an exogenous source of CSF. Liquid culture of small aliquots of enriched CFU-C with CSF-containing medium resulted in a rapid, time- and concentration-dependent induction of DNA synthesis as measured by 3H-thymidine incorporation. This specific CSF induction of DNA synthesis by enriched CFU-C was used to develop a microassay system for CSF activity. CSF activity could be reproducibly quantitated in 24–48 hr. The proliferating cells in this assay system were shown to be myeloid progenitor cells by examining the morphology of their progeny and by determining the surface antigen phenotype of the responding cells (Ia+, T3-, B1-, Mo1-). This microassay provides a quantitative assessment of CSF activity that may be useful in the purification of human CSF and in the generation of monoclonal antibodies to CFU-C surface structures.