SUMMARY Acute myeloid leukemia (AML) is an aggressive and lethal blood cancer maintained by rare populations of leukemia stem cells (LSCs). Selective targeting of LSCs is a promising approach for treating AML and preventing relapse following chemotherapy, and developing such therapeutic modalities is a key priority. Here, we show that targeting telomerase activity eradicates AML LSCs. Genetic deletion of the telomerase subunit Terc in a retroviral mouse AML model induces cell cycle arrest and apoptosis of LSCs, and depletion of telomerase-deficient LSCs is partially rescued by p53 knockdown. Murine Terc−/− LSCs express a specific gene expression signature that can be identified in human AML patient cohorts and is positively correlated with patient survival following chemotherapy. In xenografts of primary human AML, genetic or pharmacological inhibition of telomerase targets LSCs, impairs leukemia progression, and delays relapse following chemotherapy. Together, these results establish telomerase inhibition as an effective strategy for eliminating AML LSCs.

Abstract Myeloproliferative neoplasms (MPNs) are a group of blood cancers that arise following the sequential acquisition of genetic lesions in hematopoietic stem and progenitor cells (HSPCs). We identify mutational cooperation between Jak2V617F expression and Dnmt3a loss that drives progression from early-stage polycythemia vera to advanced myelofibrosis. Using in vivo, clustered regularly interspaced short palindromic repeats (CRISPR) with CRISPR-associated protein 9 (Cas9) disruption of Dnmt3a in Jak2V617F knockin HSPC, we show that Dnmt3a loss blocks the accumulation of erythroid elements and causes fibrotic infiltration within the bone marrow and spleen. Transcriptional analysis and integration with human data sets identified a core DNMT3A-driven gene-expression program shared across multiple models and contexts of Dnmt3a loss. Aberrant self-renewal and inflammatory signaling were seen in Dnmt3a−/− Jak2V617F HSPC, driven by increased chromatin accessibility at enhancer elements. These findings identify oncogenic cooperativity between Jak2V617F-driven MPN and Dnmt3a loss, leading to activation of HSPC enhancer–driven inflammatory signaling.

The caudal-related homeobox transcription factor CDX2 is expressed in leukemic cells but not during normal blood formation. Retroviral overexpression of Cdx2 induces AML in mice, however the developmental stage at which CDX2 exerts its effect is unknown. We developed a conditionally inducible Cdx2 mouse model to determine the effects of in vivo, inducible Cdx2 expression in hematopoietic stem and progenitor cells (HSPCs). Cdx2-transgenic mice develop myelodysplastic syndrome with progression to acute leukemia associated with acquisition of additional driver mutations. Cdx2-expressing HSPCs demonstrate enrichment of hematopoietic-specific enhancers associated with pro-differentiation transcription factors. Furthermore, treatment of Cdx2 AML with azacitidine decreases leukemic burden. Extended scheduling of low-dose azacitidine shows greater efficacy in comparison to intermittent higher-dose azacitidine, linked to more specific epigenetic modulation. Conditional Cdx2 expression in HSPCs is an inducible model of de novo leukemic transformation and can be used to optimize treatment in high-risk AML.

Earlier invasive fungal infections (IFI) put recipients of hematopoietic SCT (HSCT) at a high risk of IFI-related mortality. We retrospectively assessed the feasibility of HSCT for patients with a history of IFI and the efficacy of secondary prophylaxis. From January 2001 to December 2007, 49 patients with a history of IFI underwent HSCT and most of them received broadspectrum antifungal agents as secondary prophylaxis. After a median follow-up of 355 days (15-967), nine patients experienced failure of IFI prophylaxis, including three cases of IFI-related death, leading to a 2-year cumulative incidence of 18.4 and 6.1%, respectively. Four risk factors for the failure of prophylaxis were found, namely time interval from the diagnosis of IFI to transplantation, residual diseases before transplantation, infection with CMV and use of corticosteroid for the treatment of GVHD. A similar outcome can be achieved in recipients of Auto-and Auto-HSCT. Despite a higher risk of post-transplant progression, residual features of IFI did not affect the overall outcome of HSCT. In conclusion, a history of IFI and residual features are not contraindications to HSCT and secondary prophylaxis by broad-spectrum antifungal agents can protect patients from relapse or progression of an earlier infection.