DOUBLE KNOCKOUT OF THE ALL-1 GENE BLOCKS HEMATOPOIETIC DIFFERENTIATION IN-VITRO

The ALL-1 gene is involved in translocations with many partner genes i n different types of acute leukemias, but it is not clear whether it a cts as an oncogene or whether the fusion proteins resulting from the t ranslocations have dominant negative effects. To distinguish between t hese two possibilities, we analyzed the ability of wild-type AB2.1 emb ryonal stem (ES) cells and of single or double ALL-1 gene knockout cel ls derived from them to differentiate along hematopoietic lineages aft er withdrawal of leukemia inhibitory factor, using in vitro colony for mation assays. ALL-1 double knockout ES cells formed a significantly g reater number of colonies with faster kinetics than wild-type and ALL- 1 single knockout ES cells. Parental ES cells formed lineage-restricte d colonies, whereas single and double knockout ES cells developed, at high frequency, immature and/or ''biphenotypic'' colonies, mimicking t he aberrant hematopoiesis typical of leukemic patients. These data are consistent with the possibility that loss of function of the ALL-1 ge ne is important in leukemogenesis.