To evaluate if eliminating the Notch pathway in Tg8 T cells would stop T-ALL, we infected Tg8 hematopoietic stem cells (HSC) with a retroviral construct harboring a short hairpin (sh) against Dll4 (shDll4), and reconstituted irradiated RAG1-/- mice with HSC infected with either shDll4 or the empty vector. This evidence concerns the gene DLL4 and acute lymphoblastic leukemia.