Purpose/Objective: T-cell specific deregulation of Notch3 in transgenicmice (N3-tg), induces the development of a T-cell acute lymphoblastic leukemia (T-ALL), sustained by the constitutive activation of NF-kB canonical pathway. Besides, Notch signalling modulation in bone-marrow stromal cells or in hematopoietic stem cells, has been related to alterations in differentiation/proliferation processes of myeloid cells. To clarify the Notch/NF-kB relationships in the progression of T-ALL and the effects of a T-cell specific deregulation of Notch on myeloid compartment, we decided to delete NF-kB canonical pathway in N3-tg mice. Materials and methods: We generated N3-tg/p50-/- mice, deleted of the NF-kB/p50 subunit in a Notch3 transgenic background. The follow-up of double mutant versus N3-tg mice versus relative controls was conducted and immunophenotyping of hematopoietic cell subsets was performed at different age and in multiple tissues from the indicated animals by flow-cytometry tecniques. Total RNA and protein extract samples, derived from sorted T- or myeloid-cells of our mice models, were processed for RT-qPCR and Western blotting analysis, respectively, to test the expression of Notch-related molecules. Results: The progression of T-ALL, as defined by the peripheral expansion of immature CD4+ CD8+ T cells, was strongly inhibited in N3-tg/p50-/- versus N3-tg mice. However, the double mutant mice succumb earlier than N3-tg counterparts displaying a dramatic increase of Mac1+ Gr1+ myeloid cells in both spleen and blood, as well as of granulocyte/monocyte progenitors in the bone marrow. The expansion of myeloid subsets was detectable at a lower extent also in N3-tg versus wild-type mice. Preliminary data indicate that Mac1+ Gr1+ cells do not express Notch3, suggesting that this receptor may influence the equilibrium of the myeloid compartment mainly in trans, possibly through its interaction with the Jagged-1 ligand. Conclusions: Our results suggest that the NF-kB canonical pathway deletion inhibits the T-ALL progression, thus unveiling the influence of Notch signalling modulation on the behaviour of myeloid cells. We provide a useful model to extend our understanding of Notch/NF-kB interplay in driving the relationships between lymphoid and myeloid compartments in the context of hematological malignancy.