Abstract 5861: Characterizing an immune synapse between plasmacytoid dendritic cells and cancer cells that drives cancer cytotoxicity

Abstract Background: Plasmacytoid dendritic cells (pDCs), a unique type of innate immune cells, are known to play an important role in fighting viral infections, especially due to their capacity to sense DNA/RNA nucleic acids by TLR7/-9, and production of type-I interferons. The role of pDCs in driving immunological effects in cancer development and mounting antitumoral responses remains to be elucidated, though few studies describe opposing outcomes in patients based on tumor infiltrating pDCs. These observations come with little evidence explaining the immunosuppressive or tumorigenic state of pDCs. Methods: To study fundamental anti-tumoral functions of pDCs we utilized a robust and validated in vitro stem-cell derived human pDC model. Importantly, this model permits genetic manipulation prior to pDC differentiation and enables large-scale co-culture studies with various cancer types. Using this model, we recently employed a CRISPR library screening approach to identify factors that aid the cytotoxic mechanisms of pDCs following co-culture with tumor cell lines. Results: Initially, using co-culture assays consisting of hematological, lung, or breast cancer cell lines in combination with in vitro generated pDCs, we demonstrated a time-dependent cytotoxic effect using Incucyte live imaging. Importantly, cytotoxic effects were elevated when pDCs had been stimulated with TLR9 agonists. We demonstrated that a direct cell-to-cell interaction was essential for pDC cytotoxicity, and that promoting stronger cell-to-cell interaction, by genetically modifying pDCs to express scFv targeting a tumor antigen, increased the killing effects. CRISPR knock-out of Granzyme B in pDCs did not remove the cytotoxic capabilities of pDCs. We are currently conducting a genetic screen to identify universal factors vital for pDC interactions and cytotoxicity effects in cancer settings. This preliminary data will be presented at the AACR meeting. Conclusion: Using in vitro-generated pDCs we explore an important anti-tumoral function of pDCs. If successful, our work can open for potential new therapeutics and prognostic possibilities in cancer treatment, harnessing the cytotoxic effects of pDCs. Citation Format: Tobias Wang Bjerg, Ian Helstrup Nielsen, Sabina Sanchez Hernandez, Anders Laustsen, Isabella Barbutti, Shuli Svetitsky, James Lee, Rasmus Bak, Martin Jakobsen. Characterizing an immune synapse between plasmacytoid dendritic cells and cancer cells that drives cancer cytotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5861.