To investigate the effect of GADD45A in the development of CML, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45a null myeloid progenitors transduced with a retroviral vector expressing the 210-kD BCR-ABL fusion oncoprotein. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.