Initiation in DNA synthesis by colony-stimulating factors in subsets of human CD34+ marrow cells

Initiation of DNA synthesis by recombinant colony-stimulating factors (CSFs) was assessed in normal human marrow blast cells isolated by expression of CD34 antigen (tritiated thymidine incorporation). Continuous exposure to CSF was required. A mild increase in DNA synthesis was initiated by granulocyte CSF (G-CSF; ≥1 ng/ml), to approximately 1.5 times control levels. A greater increase was initiated by granulocyte-macrophage CSF (GM-CSF), with a threshold of approximately 0.1 ng/ml and a plateau increment 2.5 times control levels. CD34⁺ cells were stimulated by interleukin 3 (IL-3) over a wide concentration range: two times control at 0.1/ml, three times control at 1 ng/ml, and four times control at 10 ng/ml. Overlap between responding populations was analyzed. G-CSF plus GM-CSF induced DNA synthesis greater than GM-CSF alone and supported the growth of much larger granulocyte-monocyte colonies. At saturating IL-3 concentrations, neither G-CSF nor GM-CSF induced additional DNA synthesis; at lower concentrations of IL-3, however, GM-CVSF recruited additional cells into DNA synthesis. Using CD10 and CD19 antibodies to separate B-lineage cells, the CD34⁺ cells responding to CSF were observed to be in the non-B-lineage subset. Therefore 1) the response of CD34⁺ cell subsets CSFs is IL-3 > GM-CSF > G-CSF, and the IL-3-responsive population is heterogeneous for dose requirement; 2) a CD34⁺ subpopulation responding to concurrent G-CSF and GM-CSF includes increased proliferative potential cells; 3) IL-3-responsive cells include GM-CSF and G-CSF-responsive cells, but cells responding to lower IL-3 concentration do not respond to GM-CSF; and 4) B-cell precursors do not respond to GM-CSF or IL-3 in this assay.