Interleukin-3 and granulocyte colony-stimulating factor as survival factors in murine hemopoietic stem cells in vitro

We examined the role of various hemopoietic factors in the survival of hemopoietic stem cells in methylcellulose culture. Bone marrow cells from 5-fluorouracil (5-FU)-treated mice were cultured without hemopoietic factors. Several days later, a mixture of colony-stimulating factors (CSF interleukin-3 (IL-3), interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), and erythropoietin (Ep)) was added to the culture (delayed addition of CSF) to induce the maximal colony growth in surviving progenitors. In this system few colonies grew, suggesting that some hemopoietic factors are required for the survival of hemopoietic stem cells in vitro. In a further series of experiments, similar cultures were initiated with single known hemopoietic factors or with a mixture of CSF, followed by the addition of CSF 7 days later. Although IL-3 and G-CSF, as single factors, supported colony growth, the other factors did not. In this experiment, while the total number of colonies in cultures initiated with IL-3 or G-CSF was less than that observed in cultures initiated with a mixture of CSF, the number of multipotential GEMM (granulocyte-erythrocyte-macrophage-megakaryocyte) colonies remained constant. We concluded that IL-3 and G-CSF played important roles as single factors in the survival of murine dormant hemopoietic stem cells in vitro.