Very recently, Lin et al [6] fused human MLL to murine Af4, resulting in a human-mouse chimeric fusion gene that produced high-titer retrovirus facilitating efficient transduction of human CD34+ cells, thereby generating the first “faithful” model of t(4;11) pro-B ALL recapitulating key immunophenotypic/molecular aspects of the disease. Here, AFF1 is linked to acute lymphoblastic leukemia.