A smart all-in-one strategy based on hybrid bacteria with targeting drug delivery and spatiotemporal drug release to boost the synergistic therapeutic efficacy against TNBC

Combining immunotherapy with photodynamic therapy (PDT) can optimize their synergistic therapeutic efficacy against triple-negative breast cancer (TNBC), but the limited accumulation of photosensitizers at the tumor site and the off-target binding of PD-L1 antibody with hematopoietic cells and normal tissues severely reduce the therapeutic efficacy and increase the systemic toxicity, leading to failure in the clinical treatment. Therefore, engineered <i>Escherichia coli</i> Rosetta(DE3) expressing PD-L1 nanobody (Rosetta(pPD-L1nb)) are constructed and covalently conjugated with a photosensitizer, chlorin e6 (Ce6), to develop hybrid bacteria (CeRosetta(pPD-L1nb)). As a facultative anaerobe, CeRosetta(pPD-L1nb) can targetedly accumulate and colonize at the hypoxic and hypernutrient microenvironment of tumor, consistently synthesize PD-L1nb and compete for nutrition consumption with tumor cells to inhibit tumor growth. Under light irradiation, CeRosetta(pPD-L1nb) can not only generate reactive oxygen species (ROS) to directly eliminate tumor cells and induce the infiltration of immune cells into tumors and the immunogenic cell death (ICD) to activate adaptive immune responses, but also spatiotemporally release PD-L1nb due to the PDT-induced lysis in the tumor site to reverse the immunosuppressive tumor microenvironment and activate the systemic antitumor immune response, therefore exert synergistic antitumor effects of anti-PD-L1 therapy and PDT. Altogether, the hybrid bacteria CeRosetta(pPD-L1nb) can serve as an all-in-one strategy for optimizing the synergistic therapeutic efficacy in the combination therapy of TNBC.