Compared with traditional vaccines, genetic vaccines have the following obvious advantages:
1, plasmid DNA is very stable, easy to store, transport and use. But also has simple preparation, easy mass production and low cost. For viruses with high toxicity and high risk, and vaccines that are difficult to extract antigens, the preparation of genetic vaccines is relatively safe and much easier.
2. Plasmid DNA can exist in the host for a long time, and the antigen gene continues to express in the body to produce antigen protein, which constantly stimulates the immune system to produce long-term immunity, and the immune effect is reliable.
3. Gene vaccine can not only produce humoral immune response, but also lead to the activation of cytotoxic T lymphocytes and induce cellular immunity. However, traditional vaccines can only induce cellular immunity with live vaccines, but there is a danger that the virulence of live vaccines will rise again.
4. The gene vaccine prepared with the conserved DNA sequence of the core protein can produce immune response to all variants (bacteria or viruses) of pathogens, thus avoiding the immune evasion problem caused by pathogen variation.
5. A plasmid vector can clone multiple antigen genes to form a multivalent vaccine, so that a gene vaccine can prevent many diseases.
6. Plasmid DNA has no immunogenicity, and it will not induce an autoimmune reaction against the vector like recombination vaccines, at least no anti-DNA antibody has been detected yet. In addition, the genetic vaccine will not be affected by the existing antibodies in the human body. As a new vaccine, there are still many problems that need further study:
1. safety: plasmid DNA is generally not integrated into the genome of the host cell, and there is no evidence of insertion mutation at present. However, the possibility of mutation caused by inserting a few plasmid DNA into chromosomes cannot be completely ruled out. Once integrated into the genome, it may activate cytooncogenes or inactivate tumor suppressor genes.
2. Protection efficiency: Up to now, the immune efficiency of gene vaccine is difficult to reach 100%, and there are obvious species and individual differences, which may be related to different animal cells needing different promoters, antigen genes, administration methods and doses.
3. Immune tolerance: The sustained expression of antigen protein in gene vaccine may break the immune balance of the body and trigger immune tolerance. (Note: 8)
Seven, the application of gene vaccine vaccine
DNA vaccine has a wide range of applications. So far, it has been used in experiments to prevent at least ten infectious diseases, including various types of microorganisms such as viruses, bacteria and protozoa. Some people also use DNA vaccines to treat some infectious diseases. In addition, it is also used to prevent or treat some cancers.
(1) HBV DNA vaccine is one of the most detailed DNA vaccines studied at present. At present, the composition of hepatitis B vaccine is S antigen synthesized by genetic engineering technology. On the whole, the effect of this vaccine is quite wrong. However, less than 5% of young people with normal immunity still cannot produce enough antibodies. Intramuscular injection of HBV DNA vaccine can produce good immune protection: it can produce anti-HBV antibody and cytotoxic T cell reaction at the same time. For some individuals who can not produce enough protection after receiving traditional vaccine injection, DNA vaccine also has error effect [34]. CpG structural fragment is a good immunostimulant in hepatitis B virus DNA vaccine. It strengthens the immune response of HBV DNA vaccine [35]. However, experiments on chimpanzees show that the effect of hepatitis B virus DNA vaccine depends on a large amount of DNA, and it must be injected repeatedly to maintain long-term immunity. In addition to preventing hepatitis B virus infection, some people also use hepatitis B virus DNA vaccine to treat hepatitis B. In the study of a transgenic mouse carrying hepatitis B virus, hepatitis B virus DNA vaccine successfully induced hepatitis B virus surface antibody, but after removing hepatitis B virus surface antigen from blood, hepatitis B virus mRNA in liver cells disappeared, which will also cause harm to liver cells themselves, indicating that T cells with hepatitis B virus specificity also reacted with it. In addition to animal experiments, human experiments of hepatitis B virus DNA vaccine were carried out, including its application in prevention and treatment. The result is still quite exciting. (Note: 2)
(2) influenza virus. An important feature of influenza virus is that it will break mutation, mainly because its hemagglutinin and neuraminidase surface protein will break, and new virus strains will appear, leading to large-scale infection. Now, the injection of inactivated vaccine must predict the possible virus strains and then enter vaccine manufacturing. Once there is a prediction error or a new virus strain appears, the existing vaccine may fail. The nucleoprotein (NP) of influenza virus will change relatively, which may have a cross-virus protection effect. Unfortunately, under natural infection, nucleoprotein itself is not enough to generate enough immunity to protect the host from infection. With regard to the DNA vaccine experiment of influenza virus, it was first successfully used the hemagglutinin (H7) gene of influenza virus to produce protective effect on chickens. In addition, in order to solve the problem that influenza virus will constantly mutate, some people use DNA vaccine containing influenza virus nucleoprotein gene to induce protection against influenza A virus in mice. This result proves that it can be applied to human body and will be a very important breakthrough in preventing influenza. (Note
(3) Human immunodeficiency virus (HIV) HIV infection will lead to the collapse of the immune system, resulting in the so-called acquired immunodeficiency syndrome (AIDS), also known as AIDS. Although, with the development of anti-AIDS drugs, AIDS treatment has made a lot of progress. However, antiviral drugs have great side effects; Human immunodeficiency virus will mutate repeatedly and appear drug resistance; Moreover, once the drug is stopped, the virus will multiply in large numbers and even cause illness; In addition, the cost of drugs is very expensive, which is beyond the reach of most AIDS-endemic countries. Together, these factors make AIDS still an incurable disease. Therefore, in the face of AIDS prevention and treatment, it is obviously worthwhile and the most possible direction to develop an effective AIDS vaccine. (Note: 4)
(4) Tuberculosis is still one of the most important infectious diseases in the world, especially after the number of patients with AIDS and other immunodeficiency diseases has increased, the importance of tuberculosis has gradually increased. The emergence and prevalence of drug-resistant tuberculosis also makes it more and more important to prevent tuberculosis infection. BCG is the only vaccine that can be used to prevent tuberculosis at present, but its effect is limited. In the chronic infection of tuberculosis, Mycobacterium tuberculosis usually shows some protein peculiar to the late stage of infection. These antigens can cause strong immune response and may be the main components of DNA vaccine. Animal experiments have confirmed that the DNA vaccine containing heat shock protein 65 can reduce infection after being injected into mice. (Note: 5)
(5) Hepatitis C DNA vaccine 1996, Major et al. fused the major antigenic determinant gene encoding HBV core protein with the major HBV protein gene to construct a recombinant HCV DNA vaccine. After immunizing mice, they successfully induced immune responses against these two antigens and detected antibodies against these two viruses. In the same year, Tobushige K and others immunized BALB/C mice with DNA to produce immune response to the core protein.
(6) Herpes simplex virus DNA vaccine Recently, Kriesel et al. immunized BALB/c mice with HSV-2 gD2 and pRSVnt. After 13 days, all the mice in the control group died one after another, indicating that the herpes simplex virus DNA vaccine has a protective effect on animals.
(7) Plasmid DNA constructed by malaria DNA vaccine 1994 Sedegah. Contains the gene encoding the cyclosporin (PyCSP) of Plasmodium yoelii. Compared with the vaccine (irradiated sporozoite) in the current experiment, the vaccine can induce higher levels of anti-PyCSP antibody and CTL, and make 9 mice immunized with 16 obtain the defense effect against plasmodium infection. Recent research shows that malaria gene vaccine may become the earliest gene vaccine used in humans.