DNMT3A mutations are founding events in T-ALL and alter DNA methylation. (A) Genomic summary of the T-ALL cohort showing incidence of recurrently mutated genes, engraftment in PDXs, and VAFs. (B) Schematic for flow cytometric purification of HSPC populations from the BM of patients with T-ALL. (C) Summary of human HSPC-derived colony sequencing showing detection of different somatic variants in individual populations. (D) Principle component analysis of DNA methylation profiles of patients with T-ALL by whole-genome bisulfite sequencing. (E) Clustering of T-ALL samples based on differentially methylated regions.