Frederic Padilla

Cell-based immunotherapies have emerged as promising strategies for brain tumors, offering the potential for targeted and durable antitumor responses. However, their efficacy has been limited by challenges unique to the central nervous system, including suboptimal delivery routes and an immunosuppressive tumor microenvironment that impairs cell function. Focused ultrasound (FUS) is a noninvasive technology that, when combined with intravenously administered microbubbles, can transiently and reversibly increase blood-brain barrier permeability. FUS has improved drug delivery to brain tumors in clinical trials and offers compelling opportunities to enhance trafficking, activation, and control of therapeutic cells. Despite this potential, critical questions remain regarding the timing and sequencing of FUS with cell therapies, the impact of FUS on the tumor and neuroimmune microenvironments, strategies to mitigate acute and delayed toxicities, and methods to tune potency to maximize tumor specificity while minimizing bystander tissue injury. To address these challenges, the Focused Ultrasound Foundation convened a multidisciplinary roundtable in March 2025. Experts in neuro-oncology, neuroimmunology, cell therapy, neurosurgery, and FUS participated. Discussions focused on cell delivery routes, pharmacokinetics and blood-brain barrier opening, tumor microenvironment and CNS inflammation, FUS-induced immune modulation, clinical trial design, and approaches to safety monitoring and cell control. In this review, we summarize the discussions and key messages from the roundtable, which may serve as a foundation for advancing FUS-enhanced cell therapy for brain tumors in a collaborative manner.

Ablative Focused ultrasound (FUS) therapies are promising non-invasive techniques for localized tumor ablation that may additionally enhance systemic antitumor immunity. However, the spatial distribution of immune responses following these treatments remains limited. This study employs digital spatial transcriptome profiling to compare transcriptional changes in periablative versus distal, untargeted, regions of tumors after FUS treatement. We identified significant gene expression changes in tumors treated with either mechanical or thermal destruction modalities compared to controls, with an emphasis on upregulation of RNA processing and ribosome biogenesis pathways. Surprisingly, minimal transcriptional differences were observed between periablative and distal regions, suggesting that FUS-induced transcriptional regulation isn’t limited to the lesion periphery. Cellular deconvolution analyses revealed increased proportions of Th17 cells, dendritic cells, and CD8+ T cells in FUS-treated tumors, pointing to enhanced immune activation. Our results suggest that both mechanical and thermal FUS elicit widespread tumor transcriptional modulation and highlight the need for further investigation into their systemic and spatial bioeffects.

The radiosensitization potential of focused ultrasound (FUS)-induced mild hyperthermia was assessed in an allogenic subcutaneous C6 glioma tumor model in rats. Mild hyperthermia at 42 °C was induced in tumors using a single-element 350 kHz FUS transducer. Radiation was delivered with a small animal radiation research platform using a single-beam irradiation technique. The combined treatment involved 20 min of FUS hyperthermia immediately before radiation. Tumor growth changes were observed one week post-treatment. A radiation dose of 2 Gy alone showed limited tumor control (30% reduction). However, when combined with FUS hyperthermia, there was a significant reduction in tumor growth compared to other treatments (tumor volumes: control—1174 ± 554 mm³, FUS-HT—1483 ± 702 mm³, 2 Gy—609 ± 300 mm³, FUS-HT + 2 Gy—259 ± 186 mm³; ANOVA p < 0.00001). Immunohistological analysis suggested increased DNA damage as a short-term mechanism for tumor control in the combined treatment. In conclusion, FUS-induced mild hyperthermia can enhance the effectiveness of radiation in a glioma tumor model, potentially improving the outcome of standard radiation treatments for better tumor control.

Focused ultrasound (FUS) is a powerful emerging tool for non-invasive, non-ionizing targeted destruction of tumors. The last two decades have seen a growing body of preclinical and clinical literature supporting the capacity of FUS to increase nascent immune responses to tumors and to potentiate cancer immunotherapies (e.g. checkpoint inhibitors) through a variety of means, including immune modulation and drug delivery. With the rapid acceleration of this field and a multitude of FUS immunotherapy clinical trials having now been deployed worldwide, there is a need to streamline and standardize the methodology for immunological analyses field-wide. Recently, the Focused Ultrasound Foundation and Cancer Research Institute partnered to convene a group of over 85 leaders to discuss the nexus of FUS and immuno-oncology. The guidelines documented herein were assembled in response to recommendations that emerged from this discussion, emphasizing the urgent need for heightened accessibility of immune analysis methods and standardized protocols unique to the field. These guidelines are designated for existing stakeholders in the FUS immuno-oncology domain or those newly entering the field, to provide guidance on collection, storage, and immunological profiling of tissue or blood specimens in the context of FUS immunotherapy studies, and additionally offer templates for standardized deployment of these methods based on collective experience gained within the field to date. These guidelines are tumor-agnostic and provide evidence-based, consensus-based recommendations for both preclinical and clinical immune analysis of tissue and blood specimens.

In transcranial focused ultrasound therapies, such as treating essential tremor via thermal ablation in the thalamus, acoustic energy is focused through the skull using a phased-array transducer. Ray tracing is a computationally efficient method that can correct skull-induced phase aberrations via per-element phase delay calculations using patient-specific computed tomography (CT) data. However, recent studies show that variations in CT-derived Hounsfield unit may account for only 50% of the speed of sound variability in human skull specimens, potentially limiting clinical transcranial ultrasound applications. Therefore, understanding the sensitivity of treatment planning methods to material parameter variations is essential. The present work uses a ray-tracing simulation model to explore how imprecision in model inputs, arising from clinically significant uncertainties in skull properties or considerations of acoustic phenomena, affects acoustic focusing quality through the skull. We propose and validate new methods to optimize ray-tracing skull simulations for clinical treatment planning, relevant for predicting intracranial target's thermal rise, using experimental data from ex-vivo human skulls.

The integration of the CIVA simulation platform with the Insightec ExAblate system requires the conversion of data between software systems that can including: skull ge- ometry, material properties, transducer element layout, element phase information, and sonication parameters. This report details the processes and information required to perform simulation of clinical transcranial ultrasound using input from the Insightec Ex- Ablate system and patient data, with the goal of demonstrating and establishing CIVA as a tool for use in clinical use of transcranial ultrasound.Chapters 2 and 3 in this report provide details on the methods by which the skull may be imported and properly positioned within the CIVA environment, as well as methods for the easy import of transducer element phases and amplitude from the Insightec into CIVA Healthcare. The following chapters then present the methods, results, and analysis from using of the CIVA software and import tools in order to simulate clinical scenarios using real human skull samples. The use of imported phase profiles for transcranial focusing is first verified by simulating acoustic steering in water, without the presence of the skull.

Ultrasound-triggered microbubbles destruction leading to vascular shutdown have resulted in preclinical studies in tumor growth delay or inhibition, lesion formation, radio-sensitization and modulation of the immune micro-environment. Antivascular ultrasound aims to be developed as a focal, targeted, non-invasive, mechanical and non-thermal treatment, alone or in combination with other treatments, and this review positions these treatments among the wider therapeutic ultrasound domain. Antivascular effects have been reported for a wide range of ultrasound exposure conditions, and evidence points to a prominent role of cavitation as the main mechanism. At relatively low peak negative acoustic pressure, predominantly non-inertial cavitation is most likely induced, while higher peak negative pressures lead to inertial cavitation and bubbles collapse. Resulting bioeffects start with inflammation and/or loose opening of the endothelial lining of the vessel. The latter causes vascular access of tissue factor, leading to platelet aggregation, and consequent clotting. Alternatively, endothelium damage exposes subendothelial collagen layer, leading to rapid adhesion and aggregation of platelets and clotting. In a pilot clinical trial, a prevalence of tumor response was observed in patients receiving ultrasound-triggered microbubble destruction along with transarterial radioembolization. Two ongoing clinical trials are assessing the effectiveness of ultrasound-stimulated microbubble treatment to enhance radiation effects in cancer patients. Clinical translation of antivascular ultrasound/microbubble approach may thus be forthcoming.