In accordance, Irf8 mRNA level was greatly decreased in the APL progenitors compared to all the potential cells of origin of APL including CMP, GMP, promyelocyte and immature c-Kit+CD11b−Gr−1lo BM myeloid cells that immunophenotypically resembled c-Kit+ APL progenitors (Figure 3d).32 To test a possible repressing effect of PML/RARα on Irf8 expression, we transduced PML/RARα into normal c-Kit+ BM cells via retrovirus infection, and revealed an immediate suppressive effect of PML/RARα on the mRNA level of Irf8 (Figure 3e). This evidence concerns the gene IRF8 and acute promyelocytic leukemia.