Heptad regulatory regions have dynamic accessibility profiles across normal and leukemic blood development, and accessibility patterns are sufficient to classify normal and leukemic cells. (A) tSNE plot of scRNAseq in normal BM, with cells labeled by inferred identity as determined by Setty et al.⁶ CLP, common lymphoid progenitor; DC, dendritic cell (B) Relative expression of CD34 and heptad genes projected on to the tSNE plot in panel A. (C) The branching hierarchy model of normal blood development showing relationships between the cell populations shown in panel D. (D) ATACseq peaks at heptad regulatory regions over developmental time. Plots show merged data from available replicates. (E) ATACseq peaks at heptad regulatory regions in 1 representative patient with AML, showing pHSCs, LCSs, and leukemic blasts (Blast). (F) Classification of normal cell types using only ATACseq signal at heptad regulatory regions. Heat map shows calculated distance between each sample and the training set. The red box indicates a single MEP replicate that was misclassified as a CMP. (G) Classification of AML nearest normal cell type using only ATACseq signal at heptad regulatory regions. Plots show distance from each normal cell type for preleukemic HSCs, LSCs, and leukemic blasts from 7 patients with AML. (H) Performance of the heptad regulatory region classifier compared with previous classification of these samples using genome wide enhancer (Enh.) cytometry. Panels D and H adapted from Corces et al⁴ with permission. tSNE, t-distributed stochastic neighbor embedding.