Abstract P61: Turning Back TIME: Leveraging an Improved Humanized Mouse Model to Dissect the Tumor Immune Microenvironment and Guide Immunotherapy in Soft Tissue Sarcoma

Abstract

Humanized mouse models are critical for studying cancer immunology, but traditional models often fail to fully recapitulate human immune complexity, particularly underrepresenting natural killer (NK) cells. To address this, we developed a humanized mouse model with improved NK cell reconstitution using human IL-15, enabling a more accurate representation of human anti-tumor immune responses. We applied this improved model to study soft tissue sarcoma (STS), a cancer with a highly immunosuppressive tumor immune microenvironment (TIME) that limits immunotherapy efficacy. Immunodeficient mice were engrafted with human hematopoietic stem cells partially HLA-A matched to the SK-UT1 STS cell line, followed by hIL-15 administration, and then inoculated with tumor cells to establish a physiologically relevant TIME. Tumor-infiltrating lymphocytes (TILs), splenocytes, and peripheral blood immune cells were analyzed using flow cytometry and single-cell RNA sequencing to assess immune infiltration, activation status, and exhaustion phenotypes. Our model demonstrated robust infiltration of CD4+ and CD8+ T cells, as well as CD56+ NK cells, within the tumor. Compared to their peripheral counterparts, TILs expressed significantly higher levels of exhaustion markers and upregulation of immune evasion pathways, indicating a dysfunctional immune state within the tumor. This gradient of exhaustion highlights the TIME’s role in suppressing anti-tumor immunity and driving therapeutic resistance, while also guiding the design of strategies to reinvigorate exhausted immune cells. This improved model offers a robust and translational tool to investigate human specific immune-tumor interactions and develop targeted therapies for STS. Current efforts focus on testing immunotherapy combinations designed to overcome resistance by reactivating exhausted immune cells. By modeling critical features of human immunity and reversing immunosuppressive mechanisms within the TIME, this platform lays the foundation for more effective treatment strategies in STS.