The results of our study show that co-culture between primitive CML cells and normal endothelial cells, without any additional factor, generates a microenvironment that allows for the in vitro maintenance of primitive CML cells through their permanence in a quiescent state, their proliferation and differentiation, which seem to be associated with the generation of an inflammatory environment, and their own adhesion abilities that could involve the Notch1–Jagged2 axis. Here, NOTCH1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.