A pro B cell population forms the apex of the leukemic hierarchy in Hoxa9/Meis1-dependent AML

Relapse is a major challenge to therapeutic success in acute myeloid leukemia (AML) and can be partly associated with heterogeneous leukemic stem cell (LSC) properties. In the murine Hoxa9/Meis1-dependent (H9M) AML model, LSC potential lies in three defined immunophenotypes, including Lin^-cKit⁺ progenitor cells (Lin^-), Gr1⁺CD11b⁺cKit⁺ myeloid cells, and lymphoid cells (Lym⁺). Previous reports demonstrated their interconversion and distinct drug sensitivities. In contrast, we here show that H9M AML is hierarchically organized. We, therefore, tracked the developmental potential of LSC phenotypes. This unexpectedly revealed a substantial fraction of Lin^- LSCs that failed to regenerate Lym⁺ LSCs, and that harbored reduced leukemogenic potential. However, Lin^- LSCs capable of producing Lym⁺ LSCs as well as Lym⁺ LSCs triggered rapid disease development suggestive of their high relapse-driving potential. Transcriptional analyses revealed that B lymphoid master regulators, including Sox4 and Bach2, correlated with Lym⁺ LSC development and presumably aggressive disease. Lentiviral overexpression of Sox4 and Bach2 induced dedifferentiation of H9M cells towards a lineage-negative state in vitro as the first step of lineage conversion. This work suggests that the potency to initiate a partial B lymphoid primed transcriptional program as present in infant AML correlates with aggressive disease and governs the H9M LSC hierarchy.