Manganese Capture-and-Release Vesicles for Cancer Immunotherapy

Manganese activates the stimulator of interferon genes (STING) pathway, and its sequestration by the TssS micropeptide of Yersinia pseudotuberculosis is an immune evasion tactic. Inspired by this, we developed MnCARS, Mn CApture-and-Release vesicles with STING adjuvant MSA-2, which capture endogenous manganese ions and release them in cancer cells. Constructed from engineered E. Coli outer membrane vesicles (OMVs), the system integrates surface-displayed TssS to accumulate endogenous Mn²⁺, with a von Hippel-Lindau (VHL) PROTAC degradation motif that triggers Mn²⁺ release via ubiquitin-proteasome-mediated cleavage of TssS upon cellular uptake, rather than non-specific degradation by lysosomal proteases. The surface-anchored STING agonist MSA-2 synergizes with the released Mn²⁺ to potentiate cGAS-STING activation and reverse the immunosuppressive tumor microenvironment. In vitro, MnCARS enriched Mn²⁺ and triggered dendritic cell maturation. In vivo, they elicited antitumor immunity, inhibiting the growth of subcutaneous CT26 tumors and improving survival in an orthotopic pancreatic cancer model. To demonstrate platform versatility and enable tumor targeting, a tumor-tropic Peptide was inserted in CAR instead of MSA-2, yielding MnCARP that enables monitoring Mn²⁺ release and STING activation with contrast-enhanced magnetic resonance imaging (MRI). Overall, MnCARs represent a versatile biological nanoplatform to redirect endogenous metal ions for cancer therapy with inherent imaging capabilities.