Bacterial Metabolism-Initiated Nanocatalytic Tumor Immunotherapy

The low immunogenicity of tumors remains one of the major limitations of cancer immunotherapy.Herein,we report a bacterial metabolisminitiated and photothermal-enhanced nanocatalytic therapy strategy to completely eradicate primary tumor by triggering highly effective antitumor immune responses.Briefly,a microbiotic nanomedicine,designated as Cu_(2)O@ΔSt,has been constructed by conjugating PEGylated Cu_(2)O nanoparticles on the surface of an engineered Salmonella typhimurium strain(ΔSt).Owing to the natural hypoxia tropism ofΔSt,Cu_(2)O@ΔSt could selectively colonize hypoxic solid tumors,thus minimizing the adverse effects of the bacteria on normal tis-sues.Upon bacterial metabolism within the tumor,Cu_(2)O@ΔSt generates H_(2)S gas and other acidic substances in the tumor microenvironment(TME),which will in situ trigger the sulfidation of Cu_(2)O to form CuS facilitating tumor-specific photothermal therapy(PTT)under local NIR laser irradiation on the one hand.Meanwhile,the dissolved Cu+ions from Cu_(2)O into the acidified TME enables the nanocatalytic tumor therapy by catalyzing the Fenton-like reaction of decom-posing endogenous H_(2)O_(2) into cytotoxic hydroxyl radicals(·OH)on the other hand.Such a bacterial metabolism-triggered PTT-enhanced nanocatalytic treatment could effectively destroy tumor cells and induce a massive release of tumor antigens and damage-associated molecular patterns,thereby sensitizing tumors to checkpoint blockade(ICB)therapy.The combined nanocatalytic and ICB therapy results in the much-inhibited growth of distant and metastatic tumors,and more importantly,induces a powerful immunological memory effect after the primary tumor ablation.

The emerging role of recombineering in microbiology

Recombineering is a valuable technique for generating recombinant DNA in vivo,primarily in bacterial cells,and is based on homologous recombination using phage-encoded homologous recombinases,such as Red βγ from the lambda phage and RecET from the Rac prophage.The recombineering technique can efficiently mediate homol-ogous recombination using short homologous arms(∼50 bp)and is unlimited by the size of the DNA molecules or positions of restriction sites.In this review,we summarize characteristics of recombinases,mechanism of recombineering,and advances in recombineering for DNA manipulation in Escherichia coli and other bacteria.Furthermore,the broad applications of recombineering for mining new bioactive microbial natural products,and for viral mutagenesis,phage genome engineering,and understanding bacterial metabolism are also reviewed.