Epigenetic activation of plasmacytoid DC drives IFNAR-dependent therapeutic differentiation of AML [scRNAseq 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. Overall design: Following two days of treatment with panobinostat or vehicle, dendritic cells were isolated from leukemia-bearing mice through Optiprep gradient, followed by sorting of GFP- cells and magnetic negative selection using EasySep Mouse Pan-DC Enrichment Kit (Stem Cell Technologies, Cat# 19763). Cells then were incubated with Cell Hashing HTO-conjugated antibodies (Biolegend, TotalSeq™ anti-mouse Hashtag reagents Cat# A0301-A0306) and CITE-seq antibodies (Biolegend, TotalSeq™-A0106 anti-mouse CD11c and A0119 anti-mouse Siglec H). A total of 6 samples (vehicle and pano; leukemia-bearing mice and WT mice) were hashtagged and pooled for a single capture reaction.