BCL2 and precursor B-cell acute lymphoblastic leukemia: The murine Myc/Bcl-2 model, like human B-ALL, does not appear to be characterized by a stem cell hierarchy [50], so expansion of B-cell precursors downstream of the LMPP and expressing Bcl-2 would be expected to promote initiation of disease in combination with Eμ-Myc expression (2nd hit).