Epigenetic activation of plasmacytoid DC drives IFNAR-dependent therapeutic differentiation of AML [RNAseq DC]

Pharmacological inhibition of epigenetic enzymes can have therapeutic benefit against hematological malignancies. Apart from affecting tumor cell growth and proliferation, these epigenetic agents may mediate anti-tumor immunity. Here we discovered a novel immuno-regulatory mechanism through inhibition of histone deacetylases (HDACs). In models of AML, leukemia cell differentiation and therapeutic benefit mediated by the HDAC inhibitor panobinostat required activation of the type I interferon (IFN) pathway. Plasmacytoid dendritic cells (pDCs) produced type I IFN after panobinostat treatment, through transcriptional activation of IFN genes concomitant with increased H3K27 acetylation at these loci. Depletion of pDCs abrogated panobinostat-mediated activation of type I IFN signaling in leukemia cells and impaired therapeutic efficacy, while combined treatment of panobinostat and IFN improved outcomes in mouse and human models. These discoveries offer a new therapeutic approach for AML and demonstrate that epigenetic rewiring of pDCs enhances anti-tumor immunity, opening the possibility of exploiting this population for immunotherapies. profiling by high throughput sequencing. Following two days of treatment with panobinostat or vehicle, plasmacytoid dendritic cells (pDCs) and conventional DCs (cDCs) were sorted from leukemia-bearing mice (2 biological replicates per group; pool of 3-6 mice per sample).