Salmonella has demonstrated considerable potential as a vaccine vector,exhibiting robust immunogenicity,ease of oral administration,and cost-effective production.Live attenuated Salmo-nella carrying heterologous antigens can induce both localized mucosal immunity and systemic a-daptive immune responses in hosts after successfully reaching the intestinal tract via oral delivery.Recent advances such as permanent deletion of virulence genes,regulated-delayed attenuation and lysis systems,have initially achieved a balance between the safety and immunogenicity of these vaccine platforms.Nevertheless,practical applications of such vaccine vectors remain constrained by challenges related to gastrointestinal barrier obstruction,inefficient antigen delivery,and im-mune tolerance.With the rapid advancement of multidisciplinary technologies,these limitations are anticipated to be progressively addressed.This review presented a comprehensive summary and dis-cussion of the immune mechanisms,development strategies,current applications,advantages,and challenges associated with oral live attenuated Salmonella vaccine vectors.It also delineated the fu-ture direction of research and development,with a view to providing theoretical references for re-lated research.

Salmonella has demonstrated considerable potential as a vaccine vector,exhibiting robust immunogenicity,ease of oral administration,and cost-effective production.Live attenuated Salmo-nella carrying heterologous antigens can induce both localized mucosal immunity and systemic a-daptive immune responses in hosts after successfully reaching the intestinal tract via oral delivery.Recent advances such as permanent deletion of virulence genes,regulated-delayed attenuation and lysis systems,have initially achieved a balance between the safety and immunogenicity of these vaccine platforms.Nevertheless,practical applications of such vaccine vectors remain constrained by challenges related to gastrointestinal barrier obstruction,inefficient antigen delivery,and im-mune tolerance.With the rapid advancement of multidisciplinary technologies,these limitations are anticipated to be progressively addressed.This review presented a comprehensive summary and dis-cussion of the immune mechanisms,development strategies,current applications,advantages,and challenges associated with oral live attenuated Salmonella vaccine vectors.It also delineated the fu-ture direction of research and development,with a view to providing theoretical references for re-lated research.

The enterobacterial common antigen (ECA) is a polysaccharide composed of polysaccharide repeats that are located in the outer membrane of almost all Enterobacteriaceae bacteria and has diverse biological functions. ECA is synthesized by the synergistic action of multiple genes that are present in clusters on the genome of Enterobacteriaceae bacteria, forming the ECA antigen gene cluster, an important virulence factor that plays a role in host invasion and survival of Enterobacteriaceae in vivo. ECA also plays an important role in the maintenance of the bacterial outer membrane permeability barrier, flagella gene expression, swarming motility, and bile salts resistance. In addition, ECALPS, anchored in the core region of bacterial lipopolysaccharide, is an important surface antigen for bacteria, stimulating high levels of antibody production in the host and could be a target for vaccine research. This review summarizes ECA purification, genes involved in ECA biosynthesis, its immunological characteristics, biological functions and clinical applications.
Antigens, Bacterial/genetics* ; Enterobacteriaceae/genetics* ; Lipopolysaccharides ; Polysaccharides

Recombinant bacterial vector vaccines have been widely used as carriers for the delivery of protective antigens and nucleic acid vaccines to prevent certain infectious diseases because of their ability to induce mucosal immunity, humoral immunity and cellular immunity. However, protective antigens and nucleic acids recombined into bacterial vector vaccines are difficult to be released into host cells because of the presence of bacterial cell wall. Vaccine strains that are residual in animals or livestock products may also cause environmental contamination and spread of the vaccine strains. The effective solution for these problems is to construct an auto-lysis system that can regulate the vaccine strains to grow normally in vitro while lysis in vivo. The lysis systems that have been applied in germs mainly include: the lysis system based on regulated delayed peptidoglycan synthesis, the lysis system based on the regulation of bacteriophage lysis protein and the lysis system based on the toxin-antitoxin system. In addition, a potential lysis system based on bacterial Type Ⅵ Secretion System (T6SS) is also expected to be a new method for the construction of auto-lysis strains. This review will focus on the regulatory mechanisms of these bacterial lysis systems.
Animals ; Antigens, Bacterial ; Bacterial Vaccines ; Vaccines, Attenuated ; Vaccines, DNA

Cancer is one of the most important diseases threatening human health. Frequently-used traditional cancer treatment methods, like radiotherapy, chemotherapy and surgery, have serious toxic side effects and limitations. The widely-used drug delivery carriers (liposomes, nanoparticles, etc.) have also possessed many issues such as drug leakage and incomplete loading in the late clinical stage. Currently, using tumor-targeting vectors to deliver anti-tumor drugs or small molecules is one of the promising strategies for mediating safe and effective tumor therapy. In recent years, bacterial-derived non-replicating minicells, which are nanoscale non-nucleated cells produced during abnormal bacterial division, have got more and more attention. With a diameter of 200-400 nm, minicells have a large drug loading capacity. Meanwhile, the surface of minicells are able to be modified to load the assembly of antibodies/ligands that bind to tumor cell surface specific antigens or receptors, which can significantly improve tumor targeting of minicells. This tumor-targeting nanomaterials of minicells not only are used to deliver anti-tumor chemotherapeutic drugs, functional nucleic acids or plasmids encoding functional small molecules to mammalian cells, but also greatly increase drug loading and reduce drug penetration. Thus, the use of minicells combining with chemical therapy could help reduce the toxicity and maximize the effectiveness of the drug in the body. This paper summarizes the research and development of production purification, drug loading, tumor cells targeting, and internalization process of minicells, as well as its use in the delivery of anti-tumor drugs, to provide some information for the development and utilization of minicell carriers.
Animals ; Drug Carriers ; Drug Delivery Systems ; Humans ; Nanoparticles ; Neoplasms ; Plasmids

Tumor is a neoplasm formed by the abnormal proliferation of local tissue cells under the effects of different tumorigenic factors. Tumor-therapy has always been a difficult clinical issue, while regular cancer treatments, such as radiotherapy, chemotherapy and surgery, have obvious limitations. Earlier studies have shown that some obligate anaerobes or facultative anaerobes have anti-tumor effects, for example, Salmonella typhymurium as facultative anaerobic bacteria can selectively colonize tumors and inhibit their growth. Besides, Salmonella has many advantages in tumor-therapy. In the past decade or two, many researchers have carried out genetic manipulation to attenuate the virulence of Salmonella, to improve their specificity of tumor colonization and specially to use attenuated Salmonella as carriers to deliver a variety of anti-tumor therapeutic molecules, and these genetically modified Salmonella have shown good anti-tumor effects in many animal experiments. Along with further research of Salmonella-mediated antitumor treatment, applications of genetically modified Salmonella for more effective tumor-therapy are promising. We reviewed the anti-tumor mechanisms of Salmonella, the research progress in tumor-therapy using genetically modified Salmonella, and current problems and possible solutions.
Animals ; Humans ; Microorganisms, Genetically-Modified ; Neoplasms ; therapy ; Salmonella ; genetics ; Virulence