Previous large scale studies have focused on murine gamma-retrovirus and vector integration in normal and malignant cells and it was noted anecdotally that many vector insertions in normal CD34 cells were at ‘dangerous’ sites with regard to the risk of malignancy, including the LMO2 locus which has featured as a frequent target of vector integration in gene therapy associated leukaemias [3,4]. This evidence concerns the gene CD34 and leukemia.