Sodium-ion-responsive injectable supramolecular hydrogel delivers engineered Salmonella for safer and enhanced tumor immunotherapy.

Live bacterial therapeutics (LBTs) based on attenuated Salmonella Typhimurium VNP20009 (VNP) show great promise for refractory cancer treatment. However, improvements in antitumor efficacy are often accompanied by increased systemic toxicity. To address this critical challenge of achieving both potent efficacy and acceptable safety, this study developed a sodium-ion-responsive, injectable supramolecular hydrogel suitable for VNP delivery, isosteviol-1,6-diester sodium sulfonate (1,6-DAS). By encapsulating engineered VNP (VNP-TNF-α nanobody [nb]) within this hydrogel for intraperitoneal delivery in murine melanoma models, not only was 78.8% of bacteria-induced body weight loss alleviated and VNP-associated hepatosplenomegaly, necrosis, tissue damage, and immune dysregulation completely prevented, but antitumor immune responses were also further enhanced. The findings indicate that the 1,6-DAS hydrogel achieves comprehensive attenuation of VNP through a dual mechanism whereby slow release lowers acute bacterial burden in the liver and spleen and binding of 1,6-DAS molecules to VNP flagellin attenuates its immunogenicity. In addition, delivery of the VNP-TNF-α nb via the 1,6-DAS hydrogel further enhances antitumor immunity by upregulating and activating dendritic cells (DCs) and CD8+ T cells in the tumor microenvironment. Overall, the 1,6-DAS hydrogel provides a promising approach to address the core challenge of balancing efficacy and safety in VNP-based therapies, with substantial potential to propel microbiome-driven cancer immunotherapy forward.