CD1a expression in T-ALL and normal hematopoiesis and thymopoiesis. (A) Immunophenotype of de novo T-ALL samples (n = 38) for the indicated markers. Red and blue circles identify CD1a^+/++ and CD1a^low/+ coT-ALL patients, respectively. Green circles depict non-coTALL patients. (B) Representative FACS dot plot of a patient with coT-ALL. Red cells are CD7⁺CD1a⁺ coT-ALL blasts, and blue cells are normal mature T cells (CD3⁺CD7⁺CD1a^–, either CD4⁺ or CD8⁺) present in the diagnostic (DX) sample. (C) CD1a is retained at relapse (RX) (n = 5 DX-RX coT-ALL pairs). Data shown as CD1a expression in RX samples relative to the DX-matched samples (DX shown as 100% expression). (D) T cells and CD34⁺ HSPCs do not express CD1a across ontogeny. (E) Scheme depicting the phenotype of developing thymic T-cell populations. (F) Representative FACS for precortical (CD34^highCD7⁺⁺CD1a^–) and cortical (CD34⁺CD7⁺⁺CD1a⁺) thymocytes.