Abstract 2760: Therapeutic ultrasound increases CD8+ lymphocyte infiltration of pancreatic tumors

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Abstract Objectives: The clinical benefit of immunotherapy has not yet been realized in pancreatic cancer, which is characterized by a low antigenicity and dense stroma profile. Focused ultrasound can be used in the treatment of solid tumors, either by inducing necrosis (using ablative temperatures), or by creating cavitation which results in mechanical disruption of the stroma surrounding cancer cells. Both processes may increase the immunogenicity of tumors, and there is anecdotal clinical evidence to that effect. In a pre-clinical study, orthotopic pancreatic tumors have been subjected to a number of different ultrasound exposure regimes (both thermal & cavitational) to explore whether increased T cell infiltration and immune cell activity in the tumor can be induced. Methods: Syngeneic orthotopic pancreatic KPC tumors (KrasLSL.G12D/+; p53R172H/+; PdxCre tg/+) were grown in murine C57BL/6 subjects (> 12 weeks old). Tumor growth was monitored using imaging ultrasound. Tumors were exposed to ultrasound using the Alpinion VIFU 2000 Therapeutic Ultrasound system, with exposure parameters designed to result in either heating (power = 65 W, exposure duration = 2 seconds, duty cycle = 100 %, 6 repeats) or cavitation (power = 200 W, duty cycle = 1 %, pulse repetition frequency = 1, 60 repeats) in the target tissue. Cavitation was detected using a passive, weakly focused, broadband (0.1 to 20 MHz) sensor. The effect of ultrasound on the viability of tumor cells, and their extracellular matrix, was investigated using histology of formalin-fixed, paraffin-embedded control and treated tumors. Immunohistochemical analysis of CD4+ and CD8+ cells in the tumor, and flow cytometry of the blood and spleen, were used. Results: Therapeutic ultrasound treatments resulted in cell and collagen depleted regions inside the tumor. Significant broadband signal (suggestive of cavitation) was seen only in the ‘cavitation' ultrasound exposures. Skin damage, where seen, was limited. Within a week of therapeutic ultrasound exposures a) an increase in the infiltration of CD8+ cells in the tumor volume, b) an increase in the percentage of the tumor area covered by CD8+ cells, c) an increase in the ratio of the percentage of the tumor area covered by CD8+ cells to that covered by CD4+ cells, and d) a decrease in the percentage of the tumor area covered by CD4+ cells were seen. Immune system regulation was also evident in the blood and spleen of treated subjects. Conclusions: Therapeutic ultrasound exposure parameters that could regulate the immune response of subjects carrying orthotopic pancreatic tumors have been identified. These results provide a rationale for the use of Therapeutic ultrasound in combination with current immunotherapeutic approaches to improve the control of pancreatic tumor growth. Citation Format: Petros Mouratidis, Gail ter Haar. Therapeutic ultrasound increases CD8+ lymphocyte infiltration of pancreatic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2760.