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The tumor microenvironment is an area of intense interaction between normal and malignant cells. Factors and cell types within this environment can play a crucial role in the progression or regression of the tumor. Of primary interest are tumor-infiltrating T lymphocytes, which have been shown to have a key role in modifying the dynamics of the tumor microenvironment to promote or prevent tumor growth. While there is much in vitro and in vivo evidence for a modification of the tumor infiltrating T cell population toward a pro-tumor environment, what induces these changes within the tumor microenvironment has remained elusive. Our lab previously identified a role for the Inhibitor of Apoptosis protein Survivin as a secreted protein in the extracellular milieu, where it is capable of entering malignant cells and inducing a more aggressive phenotype. We hypothesized that tumorsecreted Survivin could be responsible for modulation of T lymphocytes in the tumor microenvironment. We first isolated tumor released Survivin and confirmed its ability to be taken up by T cells as it is by malignant cells by confocal microscopy, flow cytometry and Western blotting. Subsequently, we evaluated Survivin’s affect on T cell proliferation and found that tumor-released Survivin impairs T cell expansion, but does not alter its activation after exposure to appropriate stimuli. Assessment of phenotypic changes within the cytotoxic and helper T lymphocyte populations showed an increase in anti-inflammatory type 2 T cells and a reduction in type 1 T cells, which
correlates to what has been observed in cancer patients. Although often modified in the tumor microenvironment in patients, we did not observe any changes in regulatory T cells or Th17 cells in the presence of Survivin. The results of this study provide evidence of Survivin’s role as an extracellular mediator of the tumor microenvironment, specifically its role in inducing a pro-tumor type 2 T cell population.
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