In another clinical trial to correct the X-linked chronic granulomatous disease (X-CGD) immunodeficiency, gamma-retroviral vector integration caused activation of MDS1-EVI1, resulting in myelodysplastic syndrome (MDS) with transition to acute myeloid leukemia (AML) and development of monosomy 7 [14,15]. Here, MECOM is linked to acute myeloid leukemia.