If proto-oncogenes are involved, this may result in oncogenic transformation: in two distinct clinical trials for the treatment of inherited immunodeficiencies, patients injected with γ-retrovirus-engineered hematopoietic stem cells developed leukemia as a result of insertional activation of proto-oncogenes LMO2, MDS1-EVI1, PRDM16 and SETBP1 (30, 31). This evidence concerns the gene MECOM and leukemia.