Single-cell genomics details the maturation block in BCP-ALL and identifies therapeutic vulnerabilities in DUX4-r cases

B cell progenitor acute lymphoblastic leukemia (BCP-ALL) is the most common childhood malignancy, driven by multiple genetic alterations that cause maturation arrest and accumulation of abnormal progenitor B cells. Current treatment protocols with chemotherapy have led to favorable outcomes but are associated with significant toxicity and risk of side effects, highlighting the necessity for highly effective, less toxic, targeted drugs, even in subtypes with a favorable outcome. Here, we used multimodal single-cell Sequencing to delineate the transcriptional, epigenetic, and immunophenotypic characteristics of 23 childhood BCP-ALLs, belonging to the BCR::ABL1-positive, ETV6::RUNX1-positive, high hyperdiploid, and recently discovered DUX4-rearranged (DUX4-r) subtypes. Projection of the ALL cells along the normal hematopoietic differentiation axis revealed a diversity in the maturation pattern between the different BCP-ALL subtypes. Whereas the BCR::ABL1-, ETV6::RUNX1-positive, and high hyperdiploidy cells mainly showed similarities to normal pro-B cells, the DUX4-r ALL cells also displayed transcriptional signatures resembling mature B cells. Focusing on the DUX4-r subtype, we found that the blast population displayed multilineage priming toward non-hematopoietic cells, myeloid, and T cell lineages, but also an activation of PI3K/Akt signaling that sensitized the cells to PI3K inhibition in vivo. Given the multilineage priming of the DUX4-r blasts with aberrant expression of the myeloid marker CD371 (CLL-1), we generated chimeric antigen receptor T cells, which effectively eliminated DUX4-r ALL cells in vivo. These results provide a detailed characterization of BCP-ALL at the single-cell level and reveal therapeutic vulnerabilities in the DUX4-r subtype with implications for the understanding of ALL biology and new therapeutic strategies.