LEF1-inactivated T-ALL is characterized by developmental arrest at an aberrant cortical stage of T-cell differentiation. (A) Gene set enrichment analysis shows that the published gene expression signature of HOX11-positive T-ALL cases, showing T-cell developmental arrest at an early cortical stage of thymocyte differentiation, closely resembles that of LEF1-inactivated T-ALL. (B) Heatmap depicting the results of the gene set enrichment analysis for the HOX11-positive early cortical signature depicted in Figure 1A. (C-H) Results of flow cytometry to detect T-cell surface markers are shown for all cases in which such data were available. Percent Expression denotes the percentage of blasts that were positive for expression of each immunophenotypic marker. Note that the CD1A antibody does not appear to cross-react with CD1B and CD1E, which were highly expressed in all LEF1-inactivated cases analyzed by expression microarray. Taken together, these data indicate that LEF1-inactivated cases of T-ALL show developmental arrest at an aberrant CD1E/CD1B⁺, CD8⁺, CD34⁻ cortical stage of T-cell development.