Abstract 5714: SPADE identification of novel MDSC subsets

Abstract

Abstract Myeloid derived suppressor cells (MDSC's) are a heterogeneous population of myeloid cells at varying stages of differentiation that occur in increased numbers in the blood of cancer patients. The phenotypes of MDSC's, are controversial but are generally subdivided into three phenotypes: macrophage (M-), granulocytic (G-) and immature (i-) MDSC's. Our studies used a single staining tube with antibodies to linage markers (CD3, CD19 and CD56), HLA-DR, CD11b, CD14, CD15, CD16, CD33, CD34, CD45, PD-L1 and lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1). Mobilized apharesis products from lymphoma patients provided a product with a high frequency of MDSCs compared to normal donor blood samples. A total MDSC population (Lin-HLA-DR-CD11b+CD14+ and Lin-HLA-DR-CD11b+CD14-CD33+) was exported from FlowJo to Spanning tree progression analysis of density normalized events (Spade) in Matlab. This analysis identified nine MDSC sub-populations as nodes. Impressively, cells from the non-MDSC populations, including monocytes and granulocytes did not occur within these nodes. The SPADE analysis identified four M-MDSC nodes, four G-MDSC nodes and one iMDSC node. LOX-1 expression was limited to two G-MDSC and one M-MDSC subset. The nodes were differentiated based on CD14, CD15, CD33, CD16, LOX-1, and CD34 expression. The total populations were SPADE analyzed by overlaying non-MDSCs populations onto MDSCs and monocytes and granulocytes subset to nodes independent of MDSC nodes. The assessment of MDSC function used intracellular arginase-1 and nitric oxide synthetase-2 expression with the expected differential expression consistent with the M and G-MDSC subsets. The proportions of the different MDSC nodes varied between cancer patients and were generally at least a log higher than in the blood of normal donors. In summary, a SPADE analysis can cleanly identify MDSCs from monocytes and granulocytes and provide insight into novel MDSC subsets. Citation Format: Kathryn Cole, Holly Britton, Phyllis Warkentin, James E. Talmadge. SPADE identification of novel MDSC subsets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5714.