The early development of T-ALL requires Prdm14 expression in a stem/progenitor compartment, because breeding R26PR to Mx1-cre (+pIpC), which is expressed in hematopoietic stem cells, rapidly induces disease, whereas dLck-cre, which is expressed at late (DP) stages of thymocyte development, did not induce disease by 8 months of age. Here, MX1 is linked to acute lymphoblastic leukemia.