IRF8 and chronic myelogenous leukemia, BCR-ABL1 positive: Irf8-/- mice manifest symptoms akin to human chronic myeloid leukemia (CML).174 Irf8 gene deletion leads to an increased progenitor cell population that is hypersensitive to granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF).