Abstract

s Background Bacteria-mediated cancer therapy leverages bacteria to modulate the tumor immune microenvironment and deliver therapeutics. However, its clinical application is limited by toxicity, off-target effects, and uncontrolled drug release. Improving tumor targeting and precise payload delivery through rational bacterial engineering is essential for increasing efficacy and safety. Methods An attenuated Salmonella Δ htrA :: luxI -VNP20009 strain expressing OmpA-SpyTag (AISI-ST) was constructed for the modular surface conjugation of SpyCatcherΔ (SC)-fused quadruple arginine-glycine-aspartic acid (RGD) peptides (named AISI-ST/SC-RGD×4) and for building biointerfaces for enhanced tumor adhesion via RGD-mediated integrin αvβ3 interactions. The tumor-bearing mice received intravenous injections of AISI-ST/SC-RGD×4, and their biodistribution was analyzed using bioluminescence imaging and colony-forming unit (CFU) counts. Quorum-sensing (QS)-regulated high-temperature requirement A (HtrA) and anti-programmed cell death protein 1 (anti-PD1) nanobody expression based on the LuxI promoter in strains was validated by Western blotting. Immune responses were assessed using flow cytometry. Results The incubation of the fused proteins with the AISI-ST strain for 1   h was sufficient to form a stable biological interface. The quadruple RGD-modified bacteria (AISI-ST/SC-RGD×4) exhibited greater enrichment in various solid tumors and lung metastases with reduced off-target accumulation. QS induced the expression of the HtrA protein within tumors, resulting in enhanced extracellular polysaccharide-mediated immunogenicity to activate immune cells. Further expression of anti-PD1 nanobodies synergistically enhanced antitumor immunity, increasing the percentage of M1 macrophages (MACS) and CD8 + T cell proliferation while suppressing M2 MACS and regulatory T cells (Tregs). This approach achieves potent tumor suppression via targeted immune remodeling. Conclusions This study pres