Low-Dose ¹²⁵I-Irradiation Enhances PRC1-Targeted NIS-CAR-T Cell Cytotoxicity Against Breast Cancer Cells

The efficacy of chimeric antigen receptor (CAR)-T therapy in solid tumors is limited by the immunosuppressive microenvironment and poor T-cell infiltration. Radiotherapy offers immunomodulatory potential, yet its synergy with CAR-T via targeted internal radionuclides remains unexplored. Here, we identified protein regulator of cytokinesis 1 (PRC1) as a novel immunotherapeutic target. Through bioinformatic analysis, we engineered PRC1-specific CAR-T cells coexpressing the sodium iodide symporter (NIS) and an shRNA targeting SLC26A4, enabling enhanced iodide uptake and retention. These NIS-CAR-T cells demonstrated potent, antigen-restricted cytotoxicity and cytokine secretion upon co-culture with breast cancer cells. Low-dose ¹²⁵I selectively induced cytolysis in tumor cells without impairing CAR-T function. At low effector-to-target ratios mimicking poorly infiltrated "cold" tumors, internal irradiation via ¹²⁵I significantly boosted CAR-T killing, even against low-antigen tumors. This study introduces a multifunctional CAR-T platform that integrates internal radiotherapy to overcome key barriers in solid tumors, thereby offering a radiosensitized cellular therapy designed for the hostile tumor microenvironment.