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. 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.