Abstract A048: PITPα-mediated tumor signaling shapes NK cell phenotypes and promotes breast cancer metastasis

Abstract Metastatic disease is the leading cause of breast cancer-related deaths, with more than 42,000 patients predicted to die from breast cancer this year. Immunotherapies, which reengage the immune system to fight cancer cells, have shown only modest success in metastatic triple negative breast cancer (TNBC), and a deeper understanding of the anti-tumor immune response is essential to expand the scope of immunotherapy in this disease context. Though T cells have maintained a spotlight in immunotherapy, NK cells are the first responders to metastatic sites, and my data demonstrate a critical role for cytotoxic NK cells in controlling metastatic outgrowth. However, tumor cells develop various mechanisms to evade NK cells, and a comprehensive understanding of NK-cancer cell crosstalk is lacking. To address this gap in knowledge, we conducted a novel, in vivo CRISPR/Cas9 screen in NK cell-competent and -depleted models using a single guide RNA library designed identify druggable genes that have known inhibitors and promote breast cancer metastasis in an NK cell-dependent manner. Top hits from this screen included the protein Phosphatidyl-inositol Transfer Protein Alpha (PITPα; gene name Pitpna), which facilitates the transfer of phosphatidylinositol lipids between membrane. To better understand the role of PITPα in TNBC, we knocked down Pitpna in the murine TNBC cell line E0771, which is syngeneic to C57BL/6 mice, and tested the consequences of Pitpna knockdown in vivo. We observed that Pitpna knockdown reduces both early metastasis and primary tumor growth, suggesting that targeting PITPα could impact both metastatic and primary disease. Intriguingly, Pitpna knockdown had no effects on cancer cell growth in vitro, suggesting that the effects of Pitpna knockdown are dependent on effects from the tumor microenvironment. To interrogate this further, we performed flow cytometry analysis on metastatic lungs and primary tumors with and without Pitpna knockdown and evaluated the presence and phenotypes of immune cell subsets. We observed that Pitpna knockdown is associated with a shift in NK cell maturation state from regulatory to cytotoxic, and increased levels of degranulating NK cells. Altogether, this study identifies PITPα as a novel druggable target that promotes resistance to cytotoxic NK cells and contributes to TNBC metastasis. Citation Format: Sheera Rosenbaum, Erin Citarella, Vadym Zaberezhnyy, Molishree Joshi, James Costello, Michael Verneris, Jill Slansky, Heide Ford. PITPα-mediated tumor signaling shapes NK cell phenotypes and promotes breast cancer metastasis [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr A048.