Acid-responsive engineered bacteria with aberrant In-Situ anti-PD-1 expression for post-ablation immunotherapy of hepatocellular carcinoma

Local thermal ablation (TA) can not only reduce the tumor burden of hepatocellular carcinoma (HCC) but also stimulate the host anti-tumor immune response, offering a promising avenue for combination with immune checkpoint blockade (ICB). However, tumor recurrence and ICB resistance are associated with residual tumor masses caused by incomplete TA treatment. Thus, adjuvant therapy that can accurately eliminate residual HCC tumors post-TA is expected to improve prognosis. Bacteria-mediated tumor therapy has showed promising potential for tumor-targeting ability and in situ therapeutic proteins expression in the tumor. Here, we presented a kind of nonpathogenic engineered bacteria (named PD-1@EcM) for the potent tumor-targeting and acidic-controlled production of fusion protein comprising a mouse-derived anti-PD-1 single-chain variable fragment (scFv). A single injection of this engineered bacteria demonstrated a significantly tumor inhibition and extended survival in advanced murine primary and metastatic post-TA treatment HCC model. We observed that this engineered bacteria elicited an enhanced antitumour immune response resulting in an extensive priming of activated CD8⁺ T cells and polarization of tumor-associated macrophage from M2 phenotype to M1 phenotype. Taken together, this work provides a novel strategy to address major challenges in TA therapy and expand the current applications of bacteria-based platforms for precision therapy.