Bone marrow collected 14 days after in vivo administration of granulocyte colony-stimulating factor and stem cell factor to mice has 10-fold more repopulating ability than untreated bone marrow.

We have examined the repopulating ability of bone marrow and peripheral blood cells collected immediately and at intervals after treatment of donor mice with the combination of granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Using a competitive repopulation assay we showed that the repopulating ability of peripheral blood cells was highest immediately after cytokine treatment and declined to normal levels within 6 weeks of the termination of treatment with G-CSF and SCF. In contrast the repopulating ability of bone marrow cells was low immediately after cytokine treatment and increased to levels that were 10-fold or more greater than marrow from untreated mice by 14 days after termination of treatment with G-CSF and SCF. This high level of repopulating activity declined to normal levels by 6 weeks after termination of treatment with G-CSF and SCF. The high level of repopulating ability was confirmed by injecting cells from G-CSF- and SCF-treated donors into unconditioned recipients. Peripheral blood cells collected immediately after treatment with G-CSF and SCF engrafted into unconditioned mice sevenfold better than an equivalent number of bone marrow cells from untreated mice. Likewise, bone marrow cells collected 14 days after treatment of the donor animal with G-CSF and SCF engrafted at 10-fold higher levels than an equivalent number of bone marrow cells from untreated mice. We conclude that the treatment of donor mice with G-CSF and SCF causes a transient increase in the repopulating ability of peripheral blood and later of bone marrow. These observations may have applications to clinical hematopoietic stem cell transplantation.