Activated T cells polarize mesenchymal stromal cells (MSCs) to a proinflammatory Th1 phenotype which likely has an important role in amplifying the immune response in the tumor microenvironment. We investigated the role of interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), two factors produced by activated T cells, in MSC polarization. Gene expression and culture supernatant analysis showed that TNF-α and IFN-γ stimulated MSCs expressed distinct sets of proinflammatory factors. The combination of IFN-γ and TNF-α was synergistic and induced a transcriptome most similar to that found in MSCs stimulated with activated T cells and similar to that found in the inflamed tumor microenvironment; a Th1 phenotype with the expression of the immunosuppressive factors IL-4, IL-10, CD274/PD-L1 and indoleamine 2,3 dioxygenase (IDO). Single cell qRT-PCR analysis showed that the combination of IFN-γ and TNF-α polarized uniformly to this phenotype. The combination of IFN-γ and TNF-α results in the synergist uniform polarization of MSCs toward a primarily Th1 phenotype. The stimulation of MSCs by IFN-γ and TNF-α released from activated tumor infiltrating T cells is likely responsible for the production of many factors that characterize the tumor microenvironment.
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