Synergistic interactions between hematopoietic growth factors as detected by in vitro mouse bone marrow colony formation

We have investigated the proliferative effects of several combinations of hematopoietic growth factors in agar cultures of murine bone marrow cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) synergized with granulocyte colony-stimulating factor (G-CSF), while G-CSF also synergized with macrophage colony-stimulating factor (CSF-1) and interleukin 3 (IL3), resulting in colony numbers greater than the sum of the numbers of colonies formed with each factor alone. In addition, these combinations resulted in increased colony sizes, with the formation of day-14 colonies with diameters > 0.5 mm. The combination of GM-CSF plus IL3 showed an increase in numbers of colonies that approximated the sum of that seen with each factor alone, however, the size of the colonies was increased with a number of day-14 and day-21 colonies having diameters > 0.5 mm. These data add to the list of hematopoietic factors known to synergistically stimulate myeloid progenitors and suggest that some of these interactions may be on early progenitor cells with high proliferative potentials.