14q32 rearrangements deregulating BCL11Bmark a distinct subgroup of T-lymphoid and myeloid immature acute leukemia

Acute leukemias (ALs) of ambiguous lineage are a heterogeneous group of high-risk leukemias characterized by coexpression of myeloid and lymphoid markers. In this study, we identified a distinct subgroup of immature acute leukemias characterized by a broadly variable phenotype, covering acute myeloid leukemia (AML, M0 or M1), T/myeloid mixed-phenotype acute leukemia (T/M MPAL), and early T-cell precursor acute lymphoblastic leukemia (ETP-ALL). Rearrangements at 14q32/BCL11Bare the cytogenetic hallmark of this entity. In our screening of 915 hematological malignancies, there were 202 AML and 333 T-cell acute lymphoblastic leukemias (T-ALL: 58, ETP; 178, non-ETP; 8, T/M MPAL; 89, not otherwise specified). We identified 20 cases of immature leukemias (4% of AML and 3.6% of T-ALL), harboring 4 types of 14q32/BCL11Btranslocations: t(2,14)(q22.3;q32) (n = 7), t(6;14)(q25.3;q32) (n = 9), t(7;14)(q21.2;q32) (n = 2), and t(8;14)(q24.2;q32) (n = 2). The t(2;14) produced a ZEB2-BCL11Bfusion transcript, whereas the other 3 rearrangements displaced transcriptionally active enhancer sequences close to BCL11Bwithout producing fusion genes. All translocations resulted in the activation of BCL11B, a regulator of T-cell differentiation associated with transcriptional corepressor complexes in mammalian cells. The expression of BCL11Bbehaved as a disease biomarker that was present at diagnosis, but not in remission. Deregulation of BCL11Bco-occurred with variants at FLT3and at epigenetic modulators, most frequently the DNMT3A, TET2, and/or WT1genes. Transcriptome analysis identified a specific expression signature, with significant downregulation of BCL11B targets, and clearly separating BCL11BAL from AML, T-ALL, and ETP-ALL. Remarkably, an ex vivo drug-sensitivity profile identified a panel of compounds with effective antileukemic activity.