| HBV infection is serious threat to the human being's health. Not only the HBV infection is prevelant, but also the disease is prone to become chronic and deteriorated. According to the statistics, there are about 350 million involved in HBV chronic in the whole world today, and China is one of the countries most affected. The number of infectious HBV is about 120 million, and about 3 million individuals are chronic hepatitis or liver cirrhosis. There are about 300 to 500 thousand patients who are died of all kinds of terminal liver diseases (cirrhosis, hepatocellular carcinoma) and fulminant liver failure caused by HBV. Until now there are only few therapeutic medicines that are specific and effective against chronic HBV infection. So it is a challenge and an urgent task to explore new therapeutic methods and strategise for the prevention and therapy against chronic hepatitis B.Gene immunization, i.e. nucleic acid immunization or DNA immunization is a novel approach in which an eukaryotic expression plasmid encoding exogenous protein is introduced directly into mammalian tissue to induce specific immuneresponse to the expressed antigen. Compared with traditional protein an inactive vaccines, DNA vaccine is cheaper, easier to get and can induce cellular immune response especially cytotoxic T lymphocyte activity which is considered to be essential for eradicating virus-infected cells as well as humoral immune response. Many researches against infectious agents, such as HBV, HIV, HCV, influenza virus, have been carried out. DNA immunization has been shown to be a potential approach to protect and treat infectious diseases.The pathogenesis of hepatitis B has not yet been elucidated. It is recognized that HBV does not attack hepatocytes directly, that is to say, the replication of HBV in liver cells does not affect the physiologic functions of the cells. But its sustained replication and thereby immune responses to HBV infection results in the impairment of the cells. In addition, HBV chronic infection is usually led to the immune tolerance and high level virus loading is vivo. So we should take priority to eradicate HBV and break down the immune tolerance except the conventional therapy for immune response of liver function. Therefore, we should take two steps which combining antiviral method with enhancing immune response of individuals to eradicate viruses. Interferon a is the first option currently in clinical therapy, but its therapeutic effect is far from satisfied and the longterm effect is only 10 to 20 percent. HBV belongs to hepada viridae. Its genome (about 3.2Kb) consists of four open reading frames that encode the viral envelope, nucleocapsid, polymerase and X protein. The envelope protein consists of HBsAg, preSlAg and preS2Ag. And S gene encodes the major neutralizing antigen. It has shown that some important T cell epitopes which locate in preSl and preS2 protein can enhancethe immunogenicity of S gene. PreS2 protein has the activity of poly human serum albumin receptor (PHSA-R). With the PHSA, that HBV can bind with the PHSA-R is the major mechanism that HBV is hepatotropic belongs to hepada virus. We applied molecular cloning technologies to construct recombinant eukaryotic expression plasmid bearing HBVpreS2S/IFN- a fusion gene and intent to get completely antiviral effect through this fusion gene. In addition, we can convey the fusion protein to the target organ, liver, with the help of PHSA-R. Results and conclusion:1. A recombinant eukaryotic expression plasmid was constructed by linking IFN- a gene which was obtained by cleaving plasmid pDO-NEO 239 using restriction enzymes with linear vector pcDNA3.2. According to genetic sequences of substyle HBV-adr (Chinese strain) and IFN-a 13 four primers were synthesized. Applying technique of splicing by overlap extension(SOE) and two times PCR S2S/IFN- a fusion gene fragment was obtained and it was cloned into pcDNA3.1 V5/His TOPO TA cloning vector directly to get recombinant eukaryotic expression plasmid pcDNA3...
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