To test whether tumors from Tg(rag2:jdp2) zebrafish harbor leukemia-initiating cells, we exploited a recently developed immune-compromised zebrafish line with a rag2E450fs hypomorphic allele, which is permissive of adoptive transfer of allogeneic zebrafish cells (Tang et al., 2014). The gene discussed is RAG2; the disease is leukemia.