In order to obtain a deeper mechanistic insight into the functional contribution of SOS1 and/or SOS2 to the process of CML development, here, we isolated the compartment of hematopoietic stem cells (HSPCs) from p210BCR/ABL transgenic animals of the four relevant SOS genotypes (WT, SOS1-KO, SOS2-KO, and SOS1/2-DKO) and compared their functionality using in vitro colony-formation assays under different experimental conditions, including a TAM treatment for SOS1 ablation and/or imatinib treatments (Figure 5). This evidence concerns the gene SOS1 and chronic myelogenous leukemia, BCR-ABL1 positive.