Targeting DLK1 improves survival in patient-derived xenograft models of myeloid leukemia associated with Down syndrome

Children with Down syndrome have a markedly increased risk of developing myeloid leukemia (ML-DS). Although having an excellent prognosis, 10-20% develop relapsed or refractory disease with poor survival, highlighting the need for new targeted approaches. The pathogenesis of ML-DS is tightly linked to fetal hematopoiesis and mutations in GATA1, generating the truncated GATA1short(s) isoform. We identified Delta-like non-canonical Notch ligand 1 (DLK1) as a direct GATA1s target. DLK1, a paternally imprinted transmembrane protein, is highly expressed in fetal liver CD34 cells but absent in adult hematopoiesis, making it an attractive immunotherapeutic target. Chromatin profiling revealed GATA1s occupancy at a distal enhancer within the DLK1-DIO3 locus, driving aberrant DLK1 upregulation in ML-DS. Functional studies demonstrated that DLK1 is a leukemia dependency, as its genetic ablation impaired proliferation and engraftment, induced apoptosis, and altered Notch and {beta}-catenin signaling. Therapeutically, a DLK1-directed antibody-drug conjugate (DLK1-ADC) induced selective cytotoxicity, abrogated colony formation, and significantly prolonged survival in refractory ML-DS PDX models, achieving durable remissions at higher doses. These findings establish DLK1 as a leukemia-specific vulnerability and provide preclinical proof-of-concept for DLK1-targeted therapies in ML-DS and other leukemias with fetal-like expression programs. Key PointsO_LIDLK1 is a GATA1s-driven leukemia dependency in ML-DS, linking fetal hematopoietic programs to leukemic stemness and refractory disease. C_LIO_LITherapeutic targeting of DLK1 with an antibody-drug conjugate selectively eradicates leukemia cells and prolongs survival in ML-DS PDX models C_LI