Programmable-bacteria-macrophage backpacks for enhanced solid tumor therapy via mechanobiological interplay

Current adoptive cell-based immunotherapies show limited efficacy against solid tumors, largely due to dynamic cellular phenotypic shifts and the immunosuppressive tumor microenvironment (TME). To address these challenges, we engineer therapeutic bacteria controlled by a temperature-actuated genetic switch. Brief exposure to focused ultrasound (US) hyperthermia activates this switch, driving sustained CCL21 release to recruit immune cells. These bacteria are surface-modified for bromelain conjugation and bacterial "backpack" formation on macrophages. Following in vitro co-incubation, bacteria-loaded macrophages are intravenously administered for tumor-targeted delivery. In vivo experiments confirm that system activation promotes macrophage repolarization toward a CD86-expressing phenotype within the TME and enhances immune cell infiltration. Moreover, treatment reduces collagen I deposition, weakens the mechanobiological properties of tumor cells, and mitigates tumor-mediated immune evasion. Collectively, this system remodels the immunosuppressive TME through macrophage-mediated bacterial delivery and US-triggered CCL21 release, facilitating dendritic cell and CD4⁺/CD8⁺ T cell infiltration and improving antitumor immunotherapy.