Safe Induction of Acute Inflammation with Enhanced Antitumor Immunity by Hydrogel‐Mediated Outer Membrane Vesicle Delivery

Abstract Acute inflammation has the potential for the recruitment of immune cells, inhibiting tumor angiogenesis, metastasis, and drug resistance thereby overcoming the tumor immunosuppressive microenvironment caused by chronic inflammation. Here, an acute inflammation inducer using bacteria outer membrane vesicles (OMVs) loaded in thermal‐sensitive hydrogel (named OMVs‐gel) for localized and controlled release of OMVs in tumor sites is proposed. OMVs trigger neutrophil recruitment and amplify acute inflammation inside tumor tissues. The hydrogel ensures drastic inflammation is confined within the tumor, addressing biosafety concerns that the direct administration of free OMVs may cause fatal effects. This strategy eradicated solid tumors safely and rapidly. The study further elucidates one of the possible immune mechanisms of OMVs‐gel therapy, which involves the assembly of antitumor neutrophils and elastase release for selective tumor killing. Additionally, tumor vascular destruction induced by OMVs‐gel results in tumor darkening, allowing for combinational photothermal therapy. The findings suggest that the use of OMVs‐gel can safely induce acute inflammation and enhance antitumor immunity, representing a promising strategy to promote acute inflammation application in tumor immunotherapy.