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Identification of monocyte-like precursors of granulocytes as a mechanism for accumulation of PMN-MDSC in cancer

ABSTRACT: Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) inhibit immune responses in cancer, limit the effects of therapies and promote tumor cell metastasis. Here, we have identified a new precursor that differentiates into granulocytes in vitro and in vivo yet belong to the monocytic lineage. We have termed these cells monocyte-like precursors of granulocytes (MLPG). Under steady state conditions MLPG were absent in the spleen and barely detectable in the bone marrow (BM). In contrast, these cells significantly expanded in tumor-bearing mice. Selective depletion of monocytic cells had no effect on the number of granulocytes present in naïve mice but decreased the population of PMN-MDSC in tumor-bearing mice by 50%. The expansion of MLPG was found to be controlled by the down-regulation of the protein Rb1 and not the IRF8 transcription factor that is known to regulate the expansion of PMN-MDSC from classical granulocytes precursors. In cancer patients, putative MLPG were found within the population of CD15 CD14+HLA-DR-/lo M-MDSC. CXCR1+CD15 CD14+HLA-DR-/lo cells lacked immune suppressive activity but had potential to differentiate to neutrophils in contrast to monocytes and CXCR1- suppressive M-MDSC. These findings describe a mechanism of abnormal myelopoiesis in cancer and suggest potential new approaches for selective targeting of MDSC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE131552 | GEO | 2019/05/30

REPOSITORIES: GEO

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Project description:Myeloid-derived suppressor cells (MDSCs) are key players in immune evasion, tumor progression and metastasis. MDSCs accumulate under various pathological states, and fall into two functionally and phenotypically distinct subsets: polymorphonuclear (PMN)-MDSCs and monocytic (M)-MDSCs. These subsets have been studied extensively in humans and mice, yet to date no study has identified MDSC subsets in dogs with spontaneous tumors. As dogs are an excellent model for human tumor development and progression, we set out to identify PMN-MDSCs and M-MDSCs in clinical canine oncology patients. We identified MDSCs as hypodense MHC class II-CD5-CD21-CD11b+ cells and show for the first time that they can also be subdivided into polymorphonuclear (CADO48A+CD14-) and monocytic (CADO48A-CD14+) subsets. The transcriptomic signatures of PMN-MDSCs and M-MDSCs are distinct from each other and from those of conventional polymorphonuclear (PMN) and monocytic cells, respectively. Notably, bioinformatic analyses reveal a statistically significant similarity between canine and previously published human MDSC gene expression patterns. As in humans, peripheral blood frequencies of canine PMN-MDSCs and M-MDSCs are significantly different in dogs with cancer compared to healthy control dogs (PMN-MDSCs: p < .001; M-MDSCs: p < .01). Furthermore, a comparison of our canine MDSC RNA-seq data with transcriptomic results previously published for human and murine MDSCs highlights five commonly upregulated genes in PMN-MDSCs in all species, suggesting that these genes are evolutionarily conserved and functionally important. Interestingly, one gene has previously been implicated in PMN-MDSC function (MMP8), but four genes (LTF, LCN2, CAMP, EBP41L3) are novel in the context of PMN-MDSCs. Our findings therefore demonstrate for the first time that dogs have two distinct populations of MDSCs, characterized by specific phenotypic and transcriptomic signatures that share key features of human MDSC subsets. Importantly, by leveraging the power of evolution, we have identified additional conserved genes in PMN-MDSCs of multiple species which may play a role in MDSC function. Our findings therefore validate the dog as a model for studying MDSCs in the context of cancer.

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Identification of monocyte-like precursors of granulocytes as a mechanism for accumulation of PMN-MDSC in cancer

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