Yiran Si,1 Jian Yue,2 Zhaoyang Liu,3 Mo Li,3 Feng Du,4 Xue Wang,2 Zhong Dai,5 Nanlin Hu,1 Jie Ju,1 Songlin Gao,1 Xiaobing Wang,3 Peng Yuan2 1Department of Medical Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, People’s Republic of China; 2Department of VIP Medical Services, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, People’s Republic of China; 3State Key Laboratory of Molecular Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, People’s Republic of China; 4China Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), The VIPII Gastrointestinal Cancer Division of Medical Department, Peking University Cancer Hospital and Institute, Beijing, 100142, People’s Republic of China; 5Department of Medical Oncology, Cancer Hospital of Huanxing Chaoyang District, Beijing, 100005, People’s Republic of ChinaCorrespondence: Peng YuanDepartment of VIP Medical Services, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, #17 Pan Jia Yuan Nan Li, Chao Yang District, Beijing, 100021, People’s Republic of ChinaTel +86 10-87787245Email yuanpeng01@hotmail.comXiaobing WangState Key Laboratory of Molecular Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, #17 Pan Jia Yuan Nan Li, Chao Yang District, Beijing, 100021, People’s Republic of ChinaTel +86 10-87788430Email wangxb@cicams.ac.cnPurpose: Immunologically quiescent of breast cancer cells has been recognized as the key impediment for the breast cancer immunotherapy. In this study, we aimed to investigate the role of nanoparticle-mediated sonodynamic therapy (SDT) in promoting anti-tumor immune of breast cancer cells and its potential immune mechanisms.Materials and Methods: The phase-transformation nanoparticles (LIP-PFH nanoparticles) were in-house prepared and its physiochemical characters were detected. The CCK-8 assay, apoptosis analysis and Balb/c tumor model establishment were used to explore the anti-tumor effect of LIP-PFH nanoparticles triggered by low-intensity focused ultrasound (LIFU) both in vitro and in vivo. Flow cytometry and immunohistochemistry of CD4+T, CD8+T, CD8+PD-1+T in blood, spleen and tumor tissue were performed to represent the change of immune response. Detection of immunogenic cell death (ICD) markers was examined to study the potential mechanisms.Results: LIP-PFH nanoparticles triggered by LIFU could inhibit the proliferation and promote the apoptosis of 4T1 cells both in vitro and in vivo. CD4+T and CD8+T cell subsets were significantly increased in blood, spleen and tumor tissue, meanwhile CD8+PD-1+T cells were reduced, indicating enhancement of anti-tumor immune response of breast cancer cells in the nanoparticle-mediated SDT group. Detection of ICD markers (ATP, high-mobility group box B1, and calreticulin) and flow cytometric analysis of dendritic cell (DC) maturity further showed that the nanoparticle-mediated SDT can promote DC maturation to increase the proportion of cytotoxic T cells by inducing ICD of breast cancer cells.Conclusion: The therapy of nanoparticles-mediated SDT can effectively enhance anti-tumor immune response of breast cancer.Keywords: breast cancer, immune response, phase-transformation nanoparticles, immunogenic cell death, DC maturation