Inhibition of LSD1 in Myelodysplastic Syndrome Progenitors Restores Differentiation of CD141Hi Conventional Dendritic Cells

Background: Immunotherapeutic approaches for myelodysplastic syndrome (MDS) show promise, but progress is limited by our incomplete understanding of the immunologic milieu. In a recent Phase I trial, we found that MDS patients with higher numbers of CD141Hi conventional dendritic cells (cDCs) were more likely to respond to NY-ESO-1 vaccination. In solid tumor models, the CD141Hi cDC is critical for initiating anti-tumor immune responses but its impact in myeloid malignancies is unknown. In studies of primary human specimens and mouse models, we tested the hypothesis that MDS patients exhibit decreased quantity and quality of CD141Hi cDCs due to impaired myeloid differentiation. Methods: Bone marrow (BM) cells were collected from MDS patients (pre-treatment) and age matched healthy donors (HD; defined as absence of hematologic malignancy). We quantified DC populations, stem, progenitor cells and interferon regulatory factor-8 (IRF-8) expression using flow cytometry and RT-qPCR. Histone modifications were assessed by chromatin immunoprecipitation. To assess DC differentiation of progenitors, human CD34+ and mouse c-kit+ cells were expanded and differentiated in vitro. Results: We found fewer CD141Hi cDCs (p Disclosures Sait: Celgene: Consultancy. Griffiths: Boston Scientific: Consultancy; Boston Scientific: Consultancy; Genentech, Inc.: Research Funding; Persimmune: Consultancy; Persimmune: Consultancy; Abbvie, Inc.: Consultancy; Genentech, Inc.: Research Funding; Novartis Inc.: Consultancy; Celgene, Inc: Consultancy, Research Funding; New Link Genetics: Consultancy; New Link Genetics: Consultancy; Astex Phramaceuticals/Otsuka Pharmaceuticals: Consultancy, Research Funding; Astex Phramaceuticals/Otsuka Pharmaceuticals: Consultancy, Research Funding; Novartis Inc.: Consultancy; Partner Therapeutics: Consultancy; Partner Therapeutics: Consultancy; Appelis Pharmaceuticals: Other: PI on a clinical trial; Onconova Therapeutics: Other: PI on a clinical trial; Appelis Pharmaceuticals: Other: PI on a clinical trial; Onconova Therapeutics: Other: PI on a clinical trial; Celgene, Inc: Consultancy, Research Funding; Abbvie, Inc.: Consultancy, PI on a clinical trial.