Retrovirus carrying a gain-of-function NOTCH1 mutant, the constitutively activated BCR-ABL1 kinase, or the fusion MLL-AF9 are used to induce T-cell acute lymphoblastic leukemia (T-ALL, chronic myeloid leukemia (CML), or acute myeloid leukemia (AML), respectively. The gene discussed is MLLT3; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.