Patients with acute myeloid leukaemia (AML) often achieve remission after therapy, but subsequently die of relapse1 that is driven by chemotherapy-resistant leukaemic stem cells (LSCs)2,3. LSCs are defined by their capacity to initiate leukaemia in immunocompromised mice4. However, this precludes analyses of their interaction with lymphocytes as components of anti-tumour immunity5, which LSCs must escape to induce cancer. Here we demonstrate that stemness and immune evasion are closely intertwined in AML. Using xenografts of human AML as well as syngeneic mouse models of leukaemia, we show that ligands of the danger detector NKG2D—a critical mediator of anti-tumour immunity by cytotoxic lymphocytes, such as NK cells6–9—are generally expressed on bulk AML cells but not on LSCs. AML cells with LSC properties can be isolated by their lack of expression of NKG2D ligands (NKG2DLs) in both CD34-expressing and non-CD34-expressing cases of AML. AML cells that express NKG2DLs are cleared by NK cells, whereas NKG2DL-negative leukaemic cells isolated from the same individual escape cell killing by NK cells. These NKG2DL-negative AML cells show an immature morphology, display molecular and functional stemness characteristics, and can initiate serially re-transplantable leukaemia and survive chemotherapy in patient-derived xenotransplant models. Mechanistically, poly-ADP-ribose polymerase 1 (PARP1) represses expression of NKG2DLs. Genetic or pharmacologic inhibition of PARP1 induces NKG2DLs on the LSC surface but not on healthy or pre-leukaemic cells. Treatment with PARP1 inhibitors, followed by transfer of polyclonal NK cells, suppresses leukaemogenesis in patient-derived xenotransplant models. In summary, our data link the LSC concept to immune escape and provide a strong rationale for targeting therapy-resistant LSCs by PARP1 inhibition, which renders them amenable to control by NK cells in vivo.
Bibliographical noteFunding Information:
Acknowledgements This study was supported by grants from the Deutsche Forschungsgemeinschaft (LE 2483/7-1 to C.L.; SA1360/9-1, SA1360/7-3 to H.R.S.; and SFB873, FOR2674 and FOR2033 to A.T.), the Swiss National Science Foundation (179239) and the Foundation for Fight Against Cancer (Zürich) to C.L., Germany’s Excellence Strategy (EXC 2180/1), the Wilhelm Sander-Stiftung (2007.115.3 to H.R.S. and 2019.042.1 to C.L.), the Deutsche Krebshilfe (111828, 70112914) to H.R.S., the SyTASC consortium (Deutsche Krebshilfe), the Swiss Bridge Foundation and the Dietmar Hopp Foundation to A.T. We thank Amgen for the NKG2D antibody clone 6H7; U. Kohlhofer, A. Jauch, M. M. Martinez and Z. Gu for experimental assistance; and the Animal and Flow Cytometry Facilities in Basel, Heidelberg, Tübingen and the Genomics & Proteomics Core Facility (DKFZ) for support.
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PubMed: MeSH publication types
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- Research Support, Non-U.S. Gov't