Thus, although aberrant maintenance of Hoxa gene expression may play an important role in MLL-ENL induced leukemia, the contribution of this pathway to immortalization is critically dependent on the cytokine environment of the immortalized myeloid cells..     ///    The mechanism of hematopoietic progenitor cell immortalization by MLL-ENL..     ///    Immortalized myeloid cell lines can be generated by expression of MLL-ENL in murine hematopoietic progenitors.     ///    "By establishing myeloid cell lines with conditional expression of MLL-ENL, we recently demonstrated that MLL-ENL is necessary to maintain immortalization and sustain the expression of a characteristic pattern of Hox genes. "    ///    "Expression of Hoxa genes is reduced in cells differentiating as a result of MLL-ENL loss, but is maintained in G-CSF treated cells. "    ///    The cell lines can be induced to undergo terminal differentiation by inhibition of MLL-ENL expression or by treatment with G-CSF. 