Extracellular vesicles released by cancer-associated fibroblast-induced myeloid-derived suppressor cells inhibit T-cell function

ABSTRACT

Myeloid cells are known to play a crucial role in creating a tumor-promoting and immune suppressive microenvironment. Our previous study demonstrated that primary human monocytes can be polarized into immunosuppressive myeloid-derived suppressor cells (MDSCs) by cancer-associated fibroblasts (CAFs) in a 3D co-culture system. However, the molecular mechanisms underlying the immunosuppressive function of MDSCs, especially CAF-induced MDSCs, remain poorly understood. Using mass spectrometry-based proteomics, we compared cell surface protein changes among monocytes, in vitro differentiated CAF-induced MDSCs, M1/M2 macrophages, and dendritic cells, and identified an extracellular vesicle (EV)-mediated secretory phenotype of MDSCs. Functional assays using an MDSC/T-cell co-culture system revealed that blocking EV generation in CAF-induced MDSCs reversed their ability to suppress T-cell proliferation, while EVs isolated from CAF-induced MDSCs directly inhibited T-cell function. Furthermore, we identified fructose bisphosphatase 1 (FBP1) as a cargo protein that is highly enriched in EVs isolated from CAF-induced MDSCs, and pharmacological inhibition of FBP1 partially reversed the suppressive phenotype of MDSCs. Our findings provide valuable insights into the cell surface proteome of different monocyte-derived myeloid subsets and uncover a novel mechanism underlying the interplay between CAFs and myeloid cells in shaping a tumor-permissive microenvironment.

KEYWORDS:

• Cancer-associated fibroblasts (CAF)
• extracellular vesicles (EV)
• myeloid-derived suppressor cells (MDSC)
• proteomics

Acknowledgments

This work was supported by the Merck & Co., Inc., Rahway, NJ, USA Research Laboratories Postdoctoral Research Program.

Disclosure statement

All authors are current or previous employees of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA and shareholders of Merck & Co., Inc., Rahway, NJ, USA.

Author contributions

C.P. Ramil and A. Chi conceptualized the study; C.P. Ramil, H. Xiang, J. Hai, and B. Ruprecht, designed the experiments, C.P. Ramil, H. Xiang, L. Cabral, P. Zhang, and A. Cronin performed the assays, co-culture, EV and proteomics experiments; C.P. Ramil, L. Cabral, and Z. Yin performed the EV characterization; C.P. Ramil, J. Hai, H. Xiang, D. Sun, Y. Jia, and H. Chen sourced and cultured cells from patient tissues; C.P. Ramil, H. Xiang and H. Wang identified and selected tool compounds for the assays; A. Chi supervised the study; C.P. Ramil wrote the manuscript with input from all authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/2162402X.2023.2300882.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.