Lineage-ambiguous leukemias are high-risk malignancies of poorly understood genetic basis. Here, we describe a distinct subgroup of acute leukemia with expression of myeloid, T lymphoid, and stem cell markers driven by aberrant allele-specific deregulation of BCL11B, a master transcription factor responsible for thymic T-lineage commitment and specification. Mechanistically, this deregulation was driven by chromosomal rearrangements that juxtapose BCL11B to superenhancers active in hematopoietic progenitors, or focal amplifications that generate a superenhancer from a noncoding element distal to BCL11B. Chromatin conformation analyses demonstrated long-range interactions of rearranged enhancers with the expressed BCL11B allele and association of BCL11B with activated hematopoietic progenitor cell cis-regulatory elements, suggesting BCL11B is aberrantly co-opted into a gene regulatory network that drives transformation by maintaining a progenitor state. These data support a role for ectopic BCL11B expression in primitive hematopoietic cells mediated by enhancer hijacking as an oncogenic driver of human lineage-ambiguous leukemia. SIGNIFICANCE: Lineage-ambiguous leukemias pose significant diagnostic and therapeutic challenges due to a poorly understood molecular and cellular basis. We identify oncogenic deregulation of BCL11B driven by diverse structural alterations, including de novo superenhancer generation, as the driving feature of a subset of lineage-ambiguous leukemias that transcend current diagnostic boundaries.This article is highlighted in the In This Issue feature, p. 2659.
©2021 American Association for Cancer Research.

The aberrant expression of dopamine receptors (DRDs) in acute myeloid leukemia (AML) cells has encouraged the repurposing of DRD antagonists such as thioridazine (TDZ) as anti-leukemic agents. Here, we access patient cells from a Phase I dose escalation trial to resolve the cellular and molecular bases of response to TDZ, and we extend these findings to an additional independent cohort of AML patient samples tested preclinically. We reveal that in DRD2+ AML patients, DRD signaling in leukemic progenitors provides leukemia-exclusive networks of sensitivity that spare healthy hematopoiesis. AML progenitor cell suppression can be increased by the isolation of the positive enantiomer from the racemic TDZ mixture (TDZ+), and this is accompanied by reduced cardiac liability. Our study indicates that the development of DRD-directed therapies provides a targeting strategy for a subset of AML patients and potentially other cancers that acquire DRD expression upon transformation from healthy tissue.
Crown Copyright © 2021.

CBL encodes an E3 ubiquitin ligase and signaling adaptor that acts downstream of cytokine receptors. Recurrent CBL mutations occur in myeloid malignancies, but the mechanism by which these mutations drive oncogenesis remains incompletely understood. Here we performed a series of studies to define the phosphoproteome, CBL interactome and molecular mechanisms of signaling activation in cells expressing an allelic series of CBL mutants. Our analyses revealed that increased LYN activation and interaction with mutant CBL are key drivers of enhanced PIK3R1 recruitment and downstream PI3K/AKT signaling in CBL -mutant cells. Furthermore, we demonstrated in vitro and in vivo efficacy of LYN inhibition by dasatinib in CBL -mutant cell lines and primary chronic myelomonocytic leukemia cells. Overall, our data provide rationale for exploring the therapeutic potential of LYN inhibition in patients with CBL -mutated myeloid malignancies. h4>Statement of Significance/h4> We investigated the oncogenic mechanisms of myeloid malignancy-associated CBL mutations by mass spectrometry-based proteomics and interactomics. Our findings indicate that increased LYN kinase activity in CBL -mutant cells stimulates PI3K/AKT signaling, revealing opportunities for the use of targeted inhibitors in CBL -mutated myeloid malignancies.

Using non-human primates (NHPs), mice, and human primary cells, we found a role for interleukin-10 (IL-10) in the upregulation of the tissue-resident memory T cell (TRM) marker CD103. In NHPs, intravenous, but not subcutaneous, immunization with peptide antigen and an adjuvant combining an agonistic anti-CD40 antibody plus poly(IC:LC) induced high levels of CD103+ TRMs in the lung, which correlated with early plasma IL-10 levels. Blocking IL-10 reduced CD103 expression on human T cells stimulated in vitro with the adjuvant combination as well as diminished CD103 on lung-resident T cells in vivo in mice. Monocyte-produced IL-10 induced the release of surface-bound transforming growth factor β (TGF-β), which in turn upregulated CD103 on T cells. Early TGF-β imprinted increased sensitivity to TGF-β restimulation, indicating an early commitment of the T cell lineage toward TRMs during the priming stage of activation. IL-10-mediated TGF-β signaling may therefore have a critical role in the generation of TRM following vaccination.
Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.