The XSCID background is known to be a predisposing factor to vector-induced T cell leukemia [32], [35], [36], potentially due to the potent clonal selection and expansion associated with corrected lymphocyte progenitors and alterations in the biologic status of target cells in the XSCID bone marrow [32], [37], and the possibility that arrested T cell progenitors may accumulate collaborating mutations associated with Lmo2-induced transformation [13], . Here, LMO2 is linked to T-cell leukemia.