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. The gene discussed is RAG1; the disease is acute lymphoblastic leukemia.