Abstract 6648: Low-intensity pulsed ultrasound enhances the presentation of brain-derived antigens by facilitating the migration of antigen-presenting cells from the brain to the periphery

Abstract Gliomas, the most common primary brain tumors, remain largely incurable despite advancements in surgical and adjuvant therapies. While immunotherapies offer promising avenues, their efficacy has been limited by formidable anatomical barriers, such as the blood-brain barrier (BBB), which restricts the migration of immune cells into the brain and impedes the efficient drainage of brain-derived antigens, establishing an immune-privileged environment. Consequently, neoplastic formations within the brain often escape detection by the peripheral immune system, complicating therapeutic interventions. The application of low-intensity pulsed ultrasound with microbubbles (LIPU/MB) has emerged as a potential solution, enabling the transient opening of the BBB. This facilitates drug transport and immune cell trafficking, including Chimeric Antigen Receptor (CAR) T cells, into brain tumors. However, challenges such as antigen-loss escape persist with CAR T cells. One proposed solution involves promoting antigen/epitope spreading by inducing the presentation of brain (tumor) antigens to the systemic immune system. To investigate this, we conducted intravital imaging using Colony-stimulating factor receptor 1 (CSFR1) and CX3CR1 reporter mice, visualizing antigen-presenting cell locomotion in the brain before and after LIPU/MB treatment using two-photon microscopy. Within one hour after LIPU/MB, we observed the migration of CSFR1+ and CX3CR1+ immune cells from the brain parenchyma and perivascular space into the bloodstream, a phenomenon absent prior to LIPU/MB treatment. Beyond that, flow cytometry identified CD45intermediateCD11b+-CX3CR1+-TMEM119+-P2RY12+microglia-like' cells in the blood. To further assess the immunological effects of LIPU/MB on brain antigen presentation, we utilized transgenic mice expressing a minigene encoding four immunogenic peptides under the glial fibrillary acidic protein (GFAP) promoter. LIPU/MB treatment was associated with increased proliferation and priming of adoptively transferred CNS antigen-specific naïve T cells in cervical lymph nodes, ultimately homing into the CNS, indicating enhanced antigen presentation. Furthermore, in a subset of glioblastoma (GBM) patients undergoing LIPU/MB combined with doxorubicin and anti-PD-1 blocking antibodies, CD11b+CD14+P2YR12+ microglia were detected in blood samples during cycles 3-6 of treatment. This increase was absent in blood samples from healthy donors. Collectively, our findings suggest that LIPU/MB represents a novel approach to augment brain-antigen presentation in the periphery, holding potential implications for improving the immunotherapeutic management of gliomas. M. G. , V. A. A. , A. M. S. , and H. O. contributed equally to this work. Citation Format: Marco Gallus, Victor Andres Arrieta, Atsuro Saijo, Pavlina Chuntova, Akane Yamamichi, Jeffrey Haegelin, Su Phyu, Lan Phung, Shayan A. Amir-Kabirian, Senthilnath Lakshmanachetty, Li Chen, Karl Habashy, Andrew Gould, Christina Amidei, Catalina Lee Chang, Roger Stupp, Michael Canney, Hideho Okada. Low-intensity pulsed ultrasound enhances the presentation of brain-derived antigens by facilitating the migration of antigen-presenting cells from the brain to the periphery abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6648.