text: Enhanced reconstitution of hematopoietic organs in irradiated mice, following their transplantation with bone marrow cells pretreated with recombinant interleukin 3.
  Lethally irradiated C3H/eb mice were injected with syngeneic bone marrow cells that had been exposed for 4 h in vitro to purified bacterially synthesized interleukin 3 (rIL-3). Control mice were injected with cells exposed to incubation medium only. Mice injected with rIL-3-treated cells exhibited, on day 10 after transplantation an 8.2-fold and 2.7-fold increase in number of myeloid progenitors in their spleen and bone marrow, respectively, but the in vitro differentiation pattern of the myeloid progenitors was not affected. There was, however, an increase in the number of cells per individual in vitro myeloid colony (CFU-C) of the rIL-3-treated mice. The latter mice also showed a 1.6-fold increase in the number of splenic colony-forming units (CFU-S), a higher self-renewal capacity of hematopoietic progenitors, and a higher number of leukocytes in the peripheral blood. These results indicate that the injection into lethally irradiated recipients of bone marrow cells briefly pretreated in vitro with rIL-3 significantly enhances the reconstitution of their hematopoietic organs, and suggest that the in vitro pretreatment of bone marrow cells with appropriate stimulating factors could be useful in bone marrow transplantation.