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ILT3 (LILRB4) Promotes the Immunosuppressive Function of Tumor-Educated Human Monocytic Myeloid-Derived Suppressor Cells

ABSTRACT: Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that accumulate in the tumor microenvironment (TME). MDSCs have been shown to dampen anti-tumor immune responses and promote tumor growth; however, the mechanisms of MDSC induction and their role in promoting immune suppression in cancer remain poorly understood. Here, we characterized the phenotype and function of monocytic MDSCs (M-MDSCs) generated by co-culture of human peripheral blood mononuclear cells with SK-MEL-5 cancer cells in vitro. We selected the SK-MEL-5 human melanoma cell line to generate M-MDSCs because these cells form subcutaneous tumors rich in myeloid cells in humanized mice. M-MDSCs generated via SK-MEL-5 co-culture expressed low levels of human leukocyte antigen (HLA)-DR, high levels of CD33 and CD11b and suppressed both CD8+ T cell proliferation and IFN-γ secretion. M-MDSCs also expressed higher levels of immunoglobulin-like transcript 3 (ILT3, also known as LILRB4) and immunoglobulin-like transcript 4 (ILT4, also known as LILRB2) on the cell surface compared to monocytes. We, therefore, investigated how ILT3 targeting could modulate M-MDSC cell function. Treatment with an anti-ILT3 antibody impaired the acquisition of the M-MDSC suppressor phenotype and reduced the capacity of M-MDSCs to cause T cell suppression. Finally, in combination with anti-programmed cell death protein 1 (PD1), ILT3 blockade enhanced T cell activation as assessed by IFN-γ secretion. These results suggest that ILT3 expressed on M-MDSCs has a role in inducing immunosuppression in cancer and that antagonism of ILT3 may be useful to reverse the immunosuppressive function of M-MDSCs and enhance the efficacy of immune checkpoint inhibitors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE160401 | GEO | 2021/01/29

REPOSITORIES: GEO

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Project description:Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that accumulate in the tumor microenvironment of most cancer patients. There MDSCs suppress both adaptive and innate immune responses, hindering immunotherapies. Moreover, many cancers are accompanied by inflammation, a processes that further intensifies MDSC suppressive activity, causing aggressive tumor progression and metastasis. MDSCs collected from tumor-bearing mice profusely release nano-scale membrane-bound extracellular vesicles, called exosomes, which carry biologically active proteins between cells and contribute directly to the immune suppressive functions of MDSC. Many studies on other cell types have shown that exosomes may also carry microRNAs (miRNAs) and messenger RNAs (mRNAs) which can also be transferred to surrounding and distant cells. However, to the best of our knowledge, the miRNA and mRNA cargo of MDSC-derived exosomes has not yet been interrogated. This study aims to identify and quantify the cargo of MDSC and their immunosuppressive exosomes to gather knowledge that can offer insights on the mechanisms by which MDSCs contribute to immune suppression, focusing on the role of exosomes as intercellular communication mediators in the tumor microenvironment. In order to achieve our objective a well-established mouse model based on a conventional mammary carcinoma (4T1 cells) and heightened inflammation (4T1 transduced to express the cytokine interleukin-1b) was used. We provide evidence that MDSC-derived exosomes carry proteins, mRNAs and miRNAs. Relative quantitation demonstrated quantitative differences between the exosome cargo and the cargo of their parental cells, supporting the hypothesis that selective loading into the exosomes is possible. Additionally, quantitative and functional analyses of the exosome cargo generated under conventional and heightened inflammation conditions are consistent with clinical observations that inflammation is linked to cancer development.

Project description:The gene expression of murine splenic myeloid derived suppressor cells treated with Tff2 is characterized. The motivation of the study originates in the fact that Gr1+Cd11b+ myeloid-derived suppressor cells (MDSCs), which resemble immature myeloid cells (IMCs), expand during cancer in response to inflammatory cytokines and accumulate in the spleen. MDSCs promote neoplastic progression through their suppression of anti-tumourigenic cytotoxic T-cells. MDSCs are also rapidly expanded following acute insults, but in cancer as opposed to acute inflammation, MDSCs persist. It is now recognized that a vagally-mediated, anti-inflammatory reflex arc promoting acetylcholine secretion by Cd4+ (Cd44hiSelllo) T cells, is necessary for a return to homeostasis after an acute insult. Failure of this restorative neural circuit might contribute to unabated procarcinogenic inflammation, with the chronic expansion of MDSCs driving carcinogenesis. Trefoil factor 2 (Tff2) is a secreted anti-inflammatory peptide produced by both epithelial cells and a small subset of splenic T cell. In this study, we show that splenic Tff2 is induced in vagally-modulated memory T cells to suppress the expansion of MDSCs in response to chemical and carcinogenic injury. Deletion of Tff2 interrupts this anti-inflammatory neural arc and leads to expanded MDSCs and a dramatically increased incidence of colorectal cancer. Tff2 directly suppresses proliferation of myeloid progenitors, in a large part through upregulation of cell-bound Apolipoprotein E (ApoE), which has previously been shown to suppress proliferation of haematopoietic stem and progenitor cells. The predisposition to inflammation-associated cancer can be rescued through transgenic overexpression of splenic Tff2, adenoviral transfer of Tff2 expression or transplantation of Tff2-expressing haematopoietic cells. Thus, Tff2 production in memory T cells, is regulated by the vagus nerve, plays a central role in arresting procarcinogenic MDSC proliferation, and offers a novel approach to the prevention and treatment. A. Gr1+Cd11b+ splenic cells from Tff2-/- mice treated with Csf2 (n=4). B. Gr1+Cd11b+ splenic cells from Tff2-/- mice treated with Tff2 and Csf2 (n=4).

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ILT3 (LILRB4) Promotes the Immunosuppressive Function of Tumor-Educated Human Monocytic Myeloid-Derived Suppressor Cells

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