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Ablation of NLRP3 inflammasome rewires MDSC function and promotes tumor regression

ABSTRACT: Myeloid-derived suppressor cells (MDSCs) are myeloid precursors which exert potent immunosuppressive properties in cancer. Despite the extensive knowledge on mechanisms implicated in mobilization, recruitment and function of MDSCs, still their therapeutic targeting remains an unmet need in cancer immunotherapy suggesting that unappreciated mechanisms of MDSC-mediated suppression exist. Herein, we demonstrate an important role of NLRP3 inflammasome in the functional properties of MDSCs in tumor-bearing hosts. Specifically, Nlrp3-deficient mice exhibited reduced tumor growth compared to wild-type animals and induction of robust anti-tumor immunity, accompanied by re-wiring of the MDSC compartment. Interestingly, both monocytic (M-MDSCs) and granulocytic (G-MDSCs) subsets from Nlrp3-/- mice displayed impaired suppressive activity and demonstrated significant transcriptomic alterations supporting the loss-of-function and associated with metabolic re-programming. Finally, therapeutic targeting of NLRP3 inhibited tumor development and re-programmed the MDSC compartment. These findings propose that targeting NLRP3 in MDSCs could overcome tumor-induced tolerance and may provide new checkpoints of cancer immunotherapy.

ORGANISM(S): Mus musculus

PROVIDER: GSE188973 | GEO | 2022/08/08

REPOSITORIES: GEO

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Project description:Tumor growth is associated with a profound alteration of myelopoiesis, leading to recruitment of immunosuppressive cells known as myeloid-derived suppressor cells (MDSCs). Analyzing the cytokines affecting myelo-monocytic differentiation produced by various experimental tumors, we found that GM-CSF, G-CSF, and IL-6 allowed a rapid generation of MDSCs from precursors present in mouse and human bone marrow (BM). BM-MDSCs induced by GM-CSF+IL-6 possessed the highest tolerogenic activity, as revealed by the ability to impair the priming of IFN- -producing CD8+ T cells upon in vivo adoptive transfer. Moreover, adoptive transfer of syngeneic, GM-CSF+IL-6-conditioned MDSCs to diabetic mice transplanted with allogeneic pancreatic islets resulted in long term acceptance of the allograft and correction of the diabetic status. Cytokines inducing MDSCs acted on a common molecular pathway. Immunoregulatory activity of both tumor-induced and BM-derived MDSCs was entirely dependent on C/EBP transcription factor, a key component of the emergency myelopoiesis triggered by stress and inflammation. Adoptive transfer of tumor antigen-specific CD8+ T lymphocytes resulted in therapy of established tumors only in mice lacking C/EBP in myeloid compartment. These data unveil another link between inflammation and cancer and identify a novel molecular target to control tumor-induced immune suppression. We used gene expression analysis to identify those factors, secreted by tumor-infiltrating MDSC, which could drive emathopoiesis. Moreover we compare gene expression profile of tumor-induced MDSC, obtained from either the spleen and the tumor infiltrate of tumor bearing mice, and in vitro bone marrow-derived MDSC. CD11b+ cells were immunomagnetically enriched from various murine tissue and experimental conditions, and cRNA samples were prepared accordingly to Expression Analysis: Technical Manual. 701021 Rev. 5. Santa Clara, CA, Affymetrix; 2004, and hybridized to the Affymetrix GeneChip MOE430 2.0 array which contains more than 45,000 probe sets, representing more than 34,000 genes. CD11b+ cells obtained from the spleen of healthy BALB/c and C57BL/6 mice were used as reference sample for tumor induced CD11b+ MDSC, enriched from either the spleen and the tumor infiltrate of tumor-bearing mice. Moreover CD11b+ cells enriched from fresh bone marrow were used as reference sample for in vitro bone marrow-differentiated MDSC, obtained with either GM-CSF+IL-6 and GM-CSF+G-CSF 4 days cytokine cocktail treatment.

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.

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Ablation of NLRP3 inflammasome rewires MDSC function and promotes tumor regression

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