To make it possible to carry out a direct experimental test of the in vivo impact of the ablation of SOS1 and SOS2 GEFs on the development of CML in mice, we generated a mouse colony resulting from cross-mating a transgenic strain expressing p210BCR/ABL under the control of the promoter of the mouse Tec gene [33,34], which starts developing full-blown CML symptoms between 5 and 8 months of age with our TAM-inducible SOS1/2-KO system, allowing us to produce the individual or combined ablation of SOS1 and/or SOS2 in mice [26,35] (Figure 1). Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.