Abstract B021: A preclinical murine model investigation; Focused ultrasound ablation of osteosarcoma induces local and systemic immunomodulation
Authors: Hay Alayna N , Vickers Elliana , Luong Ny , Lopez Victor , Coutermarsh-Ott Sheryl , Vlaisavljevich Eli , Tuohy Joanne 
Published: October 2024

Abstract
Background: Osteosarcoma (OS) is the most common primary malignant bone tumor in humans primarily occurring in children and adolescents. OS is an aggressive cancer and is typically classified as “immunologically cold” with the primary tumor microenvironment (TME) characterized as an immune desert. In a similar fashion to other cancers, the lack of immune recognition allows the primary disease to progress eventually resulting in metastatic disease. Prognosis for human OS patients without metastatic disease at the time of diagnosis who undergo definitive standard of care is 70% 5-year survival rate. In efforts to improve patient prognosis, more recent research efforts have been geared towards developing therapies to generate an anti-tumor immune response. One major challenge about generating an effective and sustainable immune response with tumor directed therapies is overcoming the immunosuppressive TME. One means of overcoming this challenge is by altering the immune TME through tumor ablation modalities. The overall goal of this study was to investigate the local and systemic immune responses associated with non-thermal focused ultrasound ablation (histotripsy) to determine the potential of histotripsy to serve as a novel immunomodulating treatment modality for OS. We hypothesized that histotripsy ablation of primary OS will result in a reduction in disease burden and stimulate a local and systemic pro-inflammatory immune response. Methods: We utilized a preclinical syngeneic orthotopic OS murine model and evaluated the local and systemic immune response 3-,7-,10-14-, and 21- days post histotripsy (DPH) with immunophenotyping via flow cytometry and immunohistochemistry, and differential gene expression analysis. Tumor ablation was evaluated by ultrasound immediately post ablation and for 2-weeks post ablation via MRI. Results:Tumor ablation was evident on ultrasound and MRI, and we observed a gross reduction in tumor size post ablation. Ablation resulted in significantly greater survival time compared to untreated tumor-bearing mice. Our IHC results revealed greater CD8 and CD4 cells compared to FoxP3 cells on the periphery of histotripsy ablated tumors. Our flow cytometry results indicate that at 3 DPH there was a peak in circulating pro-inflammatory monocytes, a significantly greater population of circulating CD8 T-cells at 14 DPH compared to untreated tumor-bearing mice, and a greater DC population at 14 DPH compared to the 3-and 7- DPH evaluated timepoints. Splenic memory CD4 T cell population increased over time post treatment. Conclusion: Our exciting results are promising and suggest that histotripsy ablation did alter both the local and systemic immune responses as hypothesized. Further investigations are warranted to continue determining the full potential of histotripsy ablation to serve as a novel treatment modality that targets both the primary tumor and induces immunomodulation to potentially mitigate metastatic disease.
Citation Format: Alayna N Hay, Elliana Vickers, Ny Luong, Victor Lopez, Sheryl Coutermarsh-Ott, Eli Vlaisavljevich, Joanne Tuohy. A preclinical murine model investigation; Focused ultrasound ablation of osteosarcoma induces local and systemic immunomodulation [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B021.