Engineering Nonpathogenic Bacteria for Synergistic Tumor-Targeted Protein Degradation and Immunotherapy by Checkpoint-Inhibiting Nanobodies

Abstract

Microbial cell therapies hold considerable promise as programmable and versatile modalities for targeted interventions in complex biological environments. Here, we developed a living bacterial delivery platform that could leverage its endogenous metabolism to synchronize the release of surface-anchored targeted protein degradation (TPD) chimeras and the secretion of immune-modulatory nanobodies (Nbs) for enhanced antitumor efficacy. By means of metabolic labeling coupled with bioorthogonal click chemistry, transferrin (Tf)-CD24 antibody chimeras (TransCACs) were covalently displayed on the surface of nonpathogenic Escherichia coli (E. coli) K12. In parallel, this strain was equipped with a constitutive expression module for the in situ biosynthesis of PD-L1-blocking nanobodies. Capitalizing on the natural tumor tropism of bacteria, our engineered E. coli K12 achieved tumor-targeted CD24 degradation, thereby augmenting macrophage-mediated phagocytosis and synergizing with PD-L1 blockade to elicit robust tumor-specific CD8+ T cell immunity. In vivo administration of engineered microbes led to marked tumor growth inhibition in both subcutaneous breast and orthotopic hepatocellular carcinoma models, along with prolonged animal survival, driven by remodeling of the suppressive tumor microenvironment through coordinated crosstalk between M1-like macrophages and tumor-resident memory (TRM)-like CD8+ T cells. Altogether, this integrated genetic engineering and metabolic labeling of bacteria (InGeM) opens avenues for the development of next-generation microbe-based cancer immunotherapies.