Specific anti-tumor effect inducea by attenuated Salmonella typhimurium vaccine expressing extraceUular region of vascular endothelial growth factor receptor 2

• Published in: Chinese science bulletin 2008, Vol.53 (19), p.3000-3007
• Main Author: YANG Jun DONG Jian PU Ping WANG ZhiQiang HONG Min CHEN MingQing
• Format: Article
• Language: English
• Subjects: 减毒活疫苗; 实验研究; 沙门氏菌属; 血管内皮生长因子
• ISSN: 1001-6538; 1861-9541

The purposes of this research were to study the stable expression of exogenous gene encoding therapeutic protein in attenuated Salmonella typhimurium, observe the metabolism of oral gene vaccine carried by attenuated Salmonella typhimurium in BALB/c mouse, and investigate the feasibility of prevention and treatment of tumors by the recombinant bacteria. Recombinant plasmid pcDNA3.1＋ VEGFR2（n1-7） was transformed into competent attenuated Salmonella typhimuriurn SL3261 to develop oral DNA vaccine SL3261-pcDNA3.1＋VEGFR2（n1-7）. To observe whether the exogenous gene can be expressed in the recombinant bacteria, PCR was performed to amplify the CMV promoter of the eukaryotic expression vector as the proof of stable expression of exogenous protein; transmission elec- tron microscopy （TEM） was applied to observe the morphology of the recombinant bacteria to confirm that the exogenous gene has no impact on the growth of the bacteria, and then BALB/c mice were immunized with the gene vaccine. After inoculation of the gene vaccine, the recombinant bacteria SL3261 could be detected in the tissues such as small intestine, colon, liver and spleen. And then, mice in each group were challenged with tumor cells. The results of animal experiment showed that tumor growth of the mice in experimental group was inhibited and survival time of immunized mice was prolonged compared with control groups. A higher lymphocyte infiltration in tumors from animals treated with DNA vaccine was observed. Immunohistochemical analysis of tumor samples revealed an enhanced accumulation of CD8^＋ cytotoxic T lymphocytes, as well as an increase in CD4^＋ cells in the tumore of animals treated with the oral gene vaccine compared to tumors from control group mice. UI- trestructure of the tumor tissue showed that tumor cells in the samples of the immunized mice were well-differentiated. Our research confirmed that the exogenous gene can be stably expressed in the attenuated Salmonella typhimurium and has no impact on the growth of the recombinant bacteria; the exogenous gene can de delivered to the host by attenuated Salmonella typhimurium to produce anti-tumor effect with no obvious cytotoxify to the host. In this study, it is established that attenuated Salmonella typhlmurlum could be used as a vector for oral gene vaccine, and our study provided a theoretical basis for the body distribution and the metabolism of the recombinant bacteria. This strategy may provide a simple, safe and effective way