Flash Radiation Reprograms Lipid Metabolism and Macrophage Immunity and Sensitizes Medulloblastoma to CAR-T Cell Therapy
Background
Brain tumors, particularly medulloblastoma (MB) in children, are one of the leading causes of cancer-related deaths in pediatric populations. Despite advancements in treatments such as surgical resection, radiotherapy, and chemotherapy, the prognosis for high-risk MB remains poor. In recent years, immunotherapy, especially CAR-T cell therapy, has brought new hope for cancer treatment. However, the immunosuppressive microenvironment of brain tumors severely limits the infiltration and activation of T cells, posing significant challenges to the application of CAR-T cell therapy in brain tumors.
Tumor-associated macrophages (TAMs) are the primary immunosuppressive cells in the tumor microenvironment of brain tumors. They suppress T cell activity by secreting immunosuppressive factors such as IL-10, TGF-β, and arginase 1 (Arg1). Therefore, reprogramming macrophages to reverse tumor immunosuppression has become a key strategy to enhance the efficacy of CAR-T cell therapy.
FLASH radiotherapy is an ultra-high-dose-rate radiation technique that delivers high doses of radiation in an extremely short time (typically milliseconds) while reducing toxicity to normal tissues. However, the impact of FLASH radiotherapy on the tumor immune microenvironment remains unclear. This study aims to explore the effects of FLASH radiotherapy on the immune microenvironment of medulloblastoma, particularly its synergistic effects with CAR-T cell therapy.
Source of the Paper
This research was conducted by a team from the University of Pennsylvania, with key authors including David Kirsch, Gong Yang, and Fanyi Zeng, among others. The paper was published in March 2025 in the journal Nature Cancer, titled “FLASH radiation reprograms lipid metabolism and macrophage immunity and sensitizes medulloblastoma to CAR-T cell therapy.”
Research Process and Results
1. Therapeutic Effects of FLASH Radiotherapy on Medulloblastoma
The research team first used a genetically engineered mouse model (Math1-Cre; SmoM2 mice) to simulate the growth of human medulloblastoma. These mice underwent stereotactic radiotherapy guided by high-resolution computed tomography (CT), receiving either standard radiotherapy (0.7 Gy/s) or FLASH radiotherapy (~100 Gy/s). The results showed that 10 Gy of FLASH radiotherapy and standard radiotherapy both significantly extended the survival of the mice, with comparable tumor control.
2. Impact of FLASH Radiotherapy on the Tumor Immune Microenvironment
Through single-cell transcriptome analysis, the research team found that FLASH radiotherapy significantly increased the infiltration of CD8+ T cells in the tumor and upregulated the expression of pro-inflammatory markers (such as CD80 and CD86) in macrophages, while suppressing immunosuppressive markers (such as CD206 and Arg1). This indicates that FLASH radiotherapy promotes a pro-inflammatory response in the tumor microenvironment and reduces immunosuppression.
3. Effects of FLASH Radiotherapy on Macrophage Polarization
In in vitro experiments, the research team exposed bone marrow-derived macrophages (BMDMs) to FLASH radiotherapy and standard radiotherapy, followed by induction of M1 and M2 polarization using LPS and IL-4, respectively. The results showed that FLASH radiotherapy significantly enhanced M1 macrophage polarization and suppressed M2 macrophage polarization. Additionally, FLASH radiotherapy reduced the expression of PPARγ (peroxisome proliferator-activated receptor gamma) and Arg1 in macrophages, further inhibiting the polarization of immunosuppressive macrophages.
4. Impact of FLASH Radiotherapy on Lipid Metabolism
The research team further explored the effects of FLASH radiotherapy on macrophage lipid metabolism. Through RNA sequencing and real-time PCR analysis, they found that FLASH radiotherapy significantly suppressed the expression of lipid oxidases (such as ALOX12 and MPO) and reduced the generation of oxidized low-density lipoprotein (oxLDL), thereby decreasing PPARγ activity. In contrast, standard radiotherapy promoted the polarization of immunosuppressive macrophages by inducing ROS-dependent PPARγ activation.
5. FLASH Radiotherapy Enhances the Efficacy of CAR-T Cell Therapy
The research team developed GD2-targeted CAR-T cells and tested their efficacy in a medulloblastoma mouse model. The results showed that FLASH radiotherapy significantly enhanced the infiltration of CAR-T cells into the tumor and improved their anti-tumor activity. Compared to standard radiotherapy, the combination of FLASH radiotherapy and CAR-T cell therapy significantly extended the survival of the mice, with 70% of the mice still alive at the end of the experiment.
Conclusions and Significance
This study reveals that FLASH radiotherapy reverses tumor immunosuppression by regulating lipid metabolism and macrophage polarization, thereby enhancing the efficacy of CAR-T cell therapy. FLASH radiotherapy promotes the polarization of pro-inflammatory macrophages by inhibiting PPARγ activity and reducing oxLDL generation, thereby improving T cell infiltration and activation in the tumor microenvironment. This finding provides a theoretical basis for the combined application of FLASH radiotherapy and CAR-T cell therapy, opening new avenues for the treatment of brain tumors and other solid tumors.
Research Highlights
- FLASH Radiotherapy Reprograms the Tumor Immune Microenvironment: FLASH radiotherapy reverses immunosuppression in the tumor microenvironment by regulating macrophage lipid metabolism and polarization.
- Enhances the Efficacy of CAR-T Cell Therapy: FLASH radiotherapy significantly improves the infiltration and anti-tumor activity of CAR-T cells, offering a new strategy for combination therapy.
- Reveals the Key Roles of PPARγ and oxLDL: The study is the first to reveal the molecular mechanism by which FLASH radiotherapy promotes pro-inflammatory macrophage polarization by inhibiting PPARγ and reducing oxLDL generation.
Additional Valuable Information
This study also highlights the advantages of FLASH radiotherapy in reducing toxicity to normal tissues, particularly its potential to protect neurocognitive function. This provides additional support for the application of FLASH radiotherapy in the treatment of pediatric brain tumors.
This research not only provides a scientific basis for the combined application of FLASH radiotherapy and CAR-T cell therapy but also brings new breakthroughs to the field of tumor immunotherapy.