They hypothesized that B-ALL did not occur in rag2:hTEL-AML1 fish because TEL-AML1 was needed in less-mature stem/progenitor cells that do not yet express rag2. In fish with global expression of TEL-AML1, gene expression profiles showed deregulation of anti-apoptotic genes, such as bcl2, bcl-xl, and bax, which inhibit apoptosis and/or promote cell cycle arrest in HSC. Here, BCL2 is linked to precursor B-cell acute lymphoblastic leukemia.