Hematopoietic suppression is one of the serious problems induced by whole body irradiation.
Granulocyte colony-stimulating factor (
G-CSF) stimulates the progenitors of granulocytes and accelerates their recovery from bone marrow suppression induced by cytotoxic
chemotherapy or radiation. On the other hand,
G-CSF stimulates proliferation of
myeloid leukemia cells as well as normal granulocytes in vitro. We designed a method to determine if
G-CSF affects the incidence of
myeloid leukemias induced by irradiation and the types of
leukemias induced according to the French-American-British (FAB) classification in RFM/MsNrs mice. Administration of
G-CSF (2 micrograms/d for 7 days) after a single 3-Gy irradiation significantly increased the number of peripheral blood neutrophils as compared with those in control mice. Even after discontinuation of
G-CSF, both the total leukocyte and neutrophil counts increased to day 10, and their levels remained elevated until day 14. The incidence of
myeloid leukemia in mice exposed to a single 3-Gy irradiation was 18.6% (38 of 204), and treatment with
G-CSF did not increase the incidence (15.7% [32 of 204]). In the mice with
radiation-induced leukemia, those receiving
G-CSF had a mean survival time of 357 days, whereas those not receiving the factor survived for 349 days. There was no significant difference of survivals between the two groups. Most of the
radiation-induced leukemias in the two groups were M1 or M2, according to the FAB classification; no characteristic difference was observed among the types of
leukemias. Although
G-CSF stimulated the
leukemia cells in vitro,
G-CSF administration after irradiation did not increase the occurrence of radiation-induced
myeloid leukemias. Our results show that administration of
G-CSF effectively accelerates neutrophil recovery from irradiation-induced hematopoietic injury and does not enhance the induction of
myeloid leukemia in RFM/MsNrs mice by irradiation.