When murine fetal liver cells were transduced with either of the human acute myeloid leukemia fusion oncogenes MLL-ENL or MLL-AF9 and then transplanted to irradiated recipient mice, myelomonocyte leukemias rapidly developed from the transplanted cells. Analysis of initial events following transduction showed that both oncogenes immediately induced a wide range of enhanced proliferative states, the most extreme of which could generate continuous lines of cells. Maturation defects accompanied the enhanced proliferative states. At all times, the transformed cells exhibited complete dependency on hematopoietic growth factors, particularly GM-CSF and IL-3. Myelomonocytic leukemic cells from primary or transplanted mice formed colonies in semisolid agar. The large majority were dependent on hematopoietic growth factors, but a low frequency of autonomous colonies was also detected. Unexpectedly, reculture of autonomous leukemic colonies generated large numbers of growth factor-dependent clonogenic progeny. Similarly, transplanted clonal autonomous leukemic cells produced leukemias containing a majority of factor-dependent cells. Conversely, recultures of factor-dependent colonies in vitro always produced small numbers of autonomous colonies among the dependent progeny. The reversible relationship between factor dependency and autonomy is surprising because autonomy would have been presumed to represent the final, irreversible, leukemic state.
Keywords: colony formation; in vitro cultures.