Although there is controversy about the contribution of the therapeutic IL2RG gene in the leukemogenesis [6,7,19], if the activation of only two genes, LMO2 and the IL2RG, were enough to induce leukemia, more of the patients would have developed leukemia in light of our estimation for the integration frequency and the reports that there are hotspots in the LMO2 locus [14,21]. The gene discussed is LMO2; the disease is leukemia.