BSCI-25. THE ROLE OF THE IFNγ PATHWAY IN BREAST CANCER BRAIN METASTASIS FORMATION

In previous work, we showed the prominence of the T cell response in the formation of brain metastases of primary ER-negative breast cancers. We also showed that prior co-cultured breast cancer cells with stimulated T lymphocytes bear an overexpression of Guanylate-binding protein 1 (GBP1) and possess an increased trespassing ability through an in vitro blood-brain barrier (BBB) model. In addition, we demonstrated a predilection for metastasizing to the brain of breast cancer cells that were co-cultured with activated T cells in a mouse model. In the present work, we show that activated CD8+ cytotoxic T lymphocytes, rather than CD4+ lymphocytes, are the main cause of increasing the ability of breast cancer cells to cross the BBB. While synthetic IFNγ does not change the ability of breast cancer cells to cross the BBB, this study shows that the T lymphocyte-secreted IFNγ activates the STAT1-dependent IFNγ pathway in breast cancer cells, enabling them to cross the in vitro BBB. Direct inhibition of soluble IFNγ or blocking of the IFNγ-specific receptor in breast cancer cells significantly decreases their ability to cross the BBB. The results illustrate that IFNγ signaling pathway is one of the crucial pathways in the formation of brain metastasis of ER- breast cancer. The interference with the IFNγ pathway will develop preventive strategies against the formation of brain metastases of breast cancer.