Epithelial-to-Mesenchymal Transition Contributes to Immunosuppression in Breast Carcinomas

Abstract

The epithelial-to-mesenchymal transition (EMT) is a cell biological program that confers mesenchymal traits on carcinoma cells and drives their metastatic dissemination. It is unclear, however, whether the activation of EMT in carcinoma cells can change their susceptibility to immune attack. We demonstrate here that mammary tumor cells arising from more epithelial carcinoma cell lines expressed high levels of MHC-I, low levels of PD-L1, and contained within their stroma CD8⁺ T cells and M1 (antitumor) macrophages. In contrast, tumors arising from more mesenchymal carcinoma cell lines exhibiting EMT markers expressed low levels of MHC-I, high levels of PD-L1, and contained within their stroma regulatory T cells, M2 (protumor) macrophages, and exhausted CD8⁺ T cells. Moreover, the more mesenchymal carcinoma cells within a tumor retained the ability to protect their more epithelial counterparts from immune attack. Finally, epithelial tumors were more susceptible to elimination by immunotherapy than corresponding mesenchymal tumors. Our results identify immune cells and immunomodulatory markers that can be potentially targeted to enhance the susceptibility of immunosuppressive tumors to various therapeutic regimens. Cancer Res; 77(15); 3982-9. ©2017 AACR.

Fig 1. Immunosuppressive cells in tumors arising from mesenchymal cell lines

(A) Western blot for EMT markers expressed by cell lines. Haemotoxylin and Eosin and (B, D) Immunofluorescent staining of tumor sections for the indicated markers (N=5). Scale bar, 100 μm. (B, C) Digested tumors were analyzed for the indicated immune populations by flow cytometry after gating on CD45⁺ cells. Data represent three independent experiments

Fig 2. Immunosuppressive cells in tumors arising from Snail⁺ cells

(A) Western blot for EMT markers. Haemotoxylin and Eosin and (C, D) Immunofluorescent staining of tumor sections for the indicated markers (N=5). Scale bar, 100 μm. (B, C) Digested tumors were analyzed for the indicated immune populations by flow cytometry after gating on CD45⁺ cells. Data represent three independent experiments.

Fig 3. Ability of mesenchymal cells to protect epithelial cells from immune attack

(A, B) Digested tumors were analyzed for the indicated immune populations by flow cytometry after gating on CD45⁺ cells. (C) Haemotoxylin and Eosin and (C, D) Immunofluorescent staining of tumor sections for the indicated markers. (N=5). Scale bar, 100 μm. Data represent three independent experiments.

Fig 4. Response of Epithelial and Mesenchymal tumors to immunotherapy

(A, B, C) Average tumor growth of mice that did or did not receive anti-CTLA4 therapy. Data represent three independent experiments.