Platelet‐derived growth factor stimulates growth of highly enriched multipotent haemopoietic progenitors

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Abstract
Platelet-derived growth factor (PDGF) has been shown to stimulate growth of normal and malignant fibroblasts, glial cells and smooth muscle cells. A growth promoting effect on human haemopoietic precursors has also been described, but the interpretation of this haemopoietic proliferative response to PDGF has been hampered by the lack of purity of the target population. In this study we show that PDGF promotes growth of early bone marrow haemopoietic progenitors depleted of either monocytes or T lymphocytes which are known to influence haemopoiesis. Moreover, the action of PDGF is even increased on a highly enriched BI-3C5 early bone marrow population. BI-3C5 is a novel monoclonal antibody which recognizes an antigen present on all multilineage colony-forming cells (CFU-mix) (Tindle et al, 1985). BI-3C5 positively and negatively sorted fractions were obtained by fluorescence activated cell sorting (FACS) and PDGF was found to stimulate growth of CFU-mix in the BI-3C5-positive fraction (consisting of only 4-6% of the marrow population), the effect being more marked than that on unsorted bone marrow. The results suggest that the product of the cellular proto-oncogene c-sis (the putative structural gene for the .beta. chain of PDGF) may play a regulatory role in the in vivo proliferation and multipotent haemopoietic progenitors.