Pleiotropic Immunomodulatory Functions of Radioactive Inactivated Bacterial Vectors for Enhanced Cancer Radio-immunotherapy

Biomaterial-based pleiotropic immune activation may effectively improve the response rate of immunotherapy and enhance the therapeutic effect of the tumor. Bacteria as a natural carrier have demonstrated great advantages in tumor targeted delivery and immune activation of the body. Herein, we construct an inactivated bacteria vector with 125I/131I labeling (125I-VNP/131I-VNP), which could retain radioiodine at the tumor site for a long time and deliver it into tumor cells and a tumor-associated macrophage (TAM), thus achieving efficient internal radioisotope therapy (IRT) of the primary tumor with good biosafety. More importantly, 131I-VNP-mediated local IRT could further stimulate robust systemic antitumor immune responses via activation of the cGAS-STING pathway of innate immunity and promotion of the maturation of DC cells for T-cell-dominated adaptive immunity. After combination with systemic checkpoint blockade therapy (αPD-L1), 131I-VNP, which induces the up-regulation of PD-L1 expression in the distant tumor, could lead to the inhibition of in situ colon cancer and protection against tumor rechallenge. Our strategy pioneers the use of an inactivated bacteria vector as a bridge to cleverly connect radiotherapy and immunotherapy and provide an enlightening idea for radio-immunotherapy mediated by pleiotropic immune activation functions of bacterial vectors.