IRF8-deficient mice (Irf8−/− mice), in which macrophages and microglia are defective in functions, including cytokine production, are known as an animal model for human chronic myeloid leukemia, in which granulocytes (neutrophils) are systemically increased (Holtschke et al., 1996); these mice are recognized as a vital tool for studying the immunological events related to the disease. This evidence concerns the gene IRF8 and chronic myelogenous leukemia, BCR-ABL1 positive.