Importantly, chromatin accessibility at Ikzf1 and Pten (or other main drivers, including Notch1 and Mef2c) is similar at different stages of T cell development (that is in the different cell types from which T-ALL subtypes arise; Figure S15), excluding the possibility of integration biases driving the differential distribution or sequentiality of driver gene insertions in T-ALL subtypes. This evidence concerns the gene MEF2C and acute lymphoblastic leukemia.