To determine whether Bcl-2 expression plays a role in HoxA9-dependent leukemias in vivo, hematopoietic progenitor cells from C57BL6/Ly5.2 Bcl-2+/+(wt) or Bcl-2−/− embryos were transduced with retrovirus expressing HoxA9/Meis1, MLL-AF9 or GFP and then transplanted into irradiated C57BL6/Ly5.1 recipients. This evidence concerns the gene MLLT3 and leukemia.