| DNA vaccines, also named as nucleic vaccine or genetic vaccine, which carry exogenous genes under the control of eukaryotic promoters, can be used to immunize animals. The direct injection of a naked plasmid DNA vaccine encoding a foreign antigen results in plasmid uptake and protein expression leading to the induction of antigen-specific cellular and humoral immune responses. The ability of DNA vaccine-elicited immune responses to protect against viral and bacterial infections, parasites, cancers, and autoimmune diseases has been well documented in numerous animal models. Phase I human clinical trials have shown that experimental DNA vaccines are safe and well tolerated, however, its immunogenicity are very low. Furthermore, the immunogenicity of DNA vaccines in human is lower than that in mice. These preliminary studies indicate that measures must be taken to improve vaccine immunogenicity. One approach to improve the immunogenicity of DNA vaccines is through the co-delivery of cytokine expression plasmids as genetic adjuvants. The clinical use of recombinant cytokine proteins to modulate in vivo immune responses is well established. It has been widely applied in anti-viruses and anti-tumors. And the source insufficiency of cytokines has been resolved through genetic engineering. However, due to the high cost of purified recombinant cytokines and the systemic toxicity associated with the high doses and multiple injections required to elicit the desired effeciency, new approaches are required. Recently, it was demonstrated that the direct intramuscular injection of a cytokine expressing plasmid DNA in vivo resulted in the production of biologically active cytokine. Moreover, it was shown that expression of the biologically active cytokine persisted for several weeks after DNA inoculation. Therefore, DNA based cytokine expression plasmids, due to their ease of manufacture and their localized cytokine expression, may function as potent genetic adjuvants capable of modulating and augmenting the immune response elicited by DNA vaccination. Studies in a variety of animal models clearly demonstrate that plasmid DNA-encoded immunomodulatory cytokines not only alter the magnitude and direction of the DNA vaccine-elicited immune response, but can also improve vaccine efficacy. These studies suggest that the use of immunomodulatory cytokines with plasmid DNA vaccines may allow clinicians to tailor the resulting immune response to more closely resemble the correlates of protection for a given pathogen.In recent years, it has been proved that bi-cistronic plasmids, including cytokines or co-stimulating molecular genes which can be expressed in the same cells as the foreign protein genes, can enhance the immune response elicited by the foreign protein genes. In bi-cistronic plasmids, two genes are inserted in the downstream of the same promoter so that the expressions of latter genes are always limited. In order to avoid the limitation, we design to construct a co-expression plasmid, which has two promoters. Two genes can be inserted to the downstream of different promoters separately so that separate promoters drive expression of each gene. Furthermore we have evaluated the expression and efficiency of the co-expression DNA vaccine through transfection in vitro and inoculation in vivo. In this study, the antigen was MAGE-A1 (MAGE-1), which is the first to be found and recognized among the MAGE family. The full length of MAGE-1 is 4.5 kb, consisting 3 exons. Full of amino encoding sequence of MAGE-1 lies in the 3rd exon. It has been proved that MAGE-1 is expressed at different levels in melanoma and other malignant tumors but not in normal tissues except for testis and placenta. CTL can recognize an immunogenic segment encoded by open-reading frame contained in the third exon of the MAGE-1 gene. Because of the high homology with other MAGE family numbers, it can be wildly used for immunotherapy for patients with different types of cancers.Mouse IL-18 was selected as genetic adjuvants in our study. Interleukin-18...
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