To test the effect of MEK inhibition in T-ALL, human T-ALL cell samples were co-cultured with MS5 or MS5-DL1 stromal cells directly after isolation from patients or after injection in immunodeficient mice (see Supplementary Table S2 for a description of the 26 T-ALL samples used in this study) in the presence of a MEKi (U0126, PD98059 or PD184352). Here, MAP2K7 is linked to acute lymphoblastic leukemia.