IMMU-21. LOW-INTENSITY PULSED ULTRASOUND PROMOTES THE PRESENTATION OF BRAIN-DERIVED ANTIGENS THROUGH ENHANCED TRAFFICKING OF ANTIGEN-PRESENTING CELLS FROM THE BRAIN INTO THE PERIPHERY

Abstract

Abstract The central nervous system, immunologically unique due to specialized lymphatics and anatomical barriers, often conceals brain neoplasm from the peripheral immune system. Low-intensity pulsed ultrasound with microbubbles (LIPU/MB) enables transient opening of the BBB, allowing drug transport and immune cell trafficking into brain tumors. However, it remains unclear whether BBB opening promotes immune cell trafficking from the brain to the periphery. To investigate this, we performed intravital imaging of Colony-stimulating factor receptor 1 (CSFR1) and CX3CR1 reporter mice to visualize antigen-presenting cell locomotion in the brain before and immediately after LIPU/MB using two-photon microscopy. Within one hour after LIPU/MB, we observed the exiting of CSFR1+ and CX3CR1+ immune cells from the brain parenchyma and perivascular space into the bloodstream, a phenomenon we did not observe prior to LIPU/MB treatment. To further evaluate the immunological effects of LIPU/MB on brain antigen presentation, we performed LIPU/MB in novel transgenic mice that express a minigene encoding for 4 immunogenic peptides under the glial fibrillary acidic protein (GFAP) promotor. We observed significant proliferation of naïve antigen-specific CD8 T cells targeting one of the peptides in the cervical lymph nodes one week after LIPU/MB treatment, but not in the animals that received T cells but did not undergo LIPU/MB. These data indicate that LIPU/MB facilitates the presentation of brain-localized antigens to antigen-reactive T cells in the systemic circulation. In 3 out of 5 GBM patients that underwent LIPU/MB plus doxorubicin and anti-PD-1 blocking antibodies, we observed CD11b+CD14+P2YR12+ microglia in blood samples collected after sonication. This increase was present in cycles 3-6 of this treatment. We did not observe the presence of this immune cell population in blood samples from healthy donors. Taken together, our results indicate that LIPU/MB could be a novel approach to enhance brain-antigen presentation in the periphery.