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Introduction to vaccine types and differences (part two)

3. Live-attenuated vaccine
This type of viral vaccine has more than 90% efficacy and its protection usually lasts for many years. Its outstanding advantage is that the pathogen produces an antigenic stimulus in the host replication, the amount, nature and location of the antigen are similar to the natural infection, so the immunogenicity is generally strong, and even does not require booster immunity. This outstanding advantage is also potentially dangerous: infection can be triggered in individuals with poor immunity; mutations may restore virulence. The latter can be more rationally attenuated with the understanding of the molecular basis of the pathogenic virulence, which may make it more effective to attenuate the virulence.
4. Inactivated vaccine
Compared with live attenuated vaccines, inactivated vaccines used non-replicating antigens (dead vaccines). Therefore, they are safe, but their immunogenicity is also weakened, and it is often necessary to boost immunity. It should be noted that not all pathogens can be highly effective vaccines after inactivation: some of these vaccines are highly effective, such as the polio vaccine (IPV) or hepatitis A vaccine for injection; others are inefficient, Short-lived vaccines, such as inactivated cholera vaccines, have almost been abandoned; there are some partially inactivated vaccines that are less effective and need to increase their protection rates and duration of immunization, such as traditional inactivated influenza and typhoid vaccine.
5. Vector vaccine
The vector vaccine introduces an antigenic gene into the body through a vector that is harmless to induce an immune response. It is characterized by a combination of strong immunogenicity of live attenuated vaccines and the accuracy of subunit vaccines. A significant benefit of this live vector vaccine is that it can effectively induce cellular immunity in vivo, which is currently not good enough to induce cellular immunity, and cellular immunity is promising in the context of some diseases that are particularly important. Important vectors used in the assay are variants of vaccinia virus, poliovirus, fowlpox virus, adenovirus, herpes virus, salmonella, Shigella, and the like. It is also possible to construct one or more cytokine genes at the same time, which can enhance the immune response or change the direction of the immune response.
The polysaccharide protein conjugate vaccine chemically binds the polysaccharide antigen to the carrier protein, and the antigen type changes from TIA to Thymus Dependent Antigen (TDA), which can stimulate children under 2 years old, the elderly and immunodeficiency produces an effective immune response and produces immune memory. The induced protective antibody is mainly immunoglobulin G, which is more effective than the polysaccharide vaccine-induced IgM (which can also stimulate IgG2 in human body) and can last for a long time with the incomparable advantages of polysaccharide vaccine
Hapten antigen, a small molecule, which alone does not induce an immune response, is not immunogenic, but is immunogenic when it is cross-linked or bound to a carrier such as a macromolecular protein or a non-antigenic polysine that induces an immune response. These small molecular substances can bind to the response effect product and are antigenic. They are only immunoreactive and not immunogenic, also called incomplete antigen. Most polysaccharides and all lipids are haptens. If the hapten is chemically combined with a molecule (carrier) of a pure protein, the pure protein will acquire new immunogenicity and stimulate the animal to produce the corresponding antibody. Once a hapten binds to a pure protein, it constitutes an antigenic cluster of the protein. Some chemically active group substances (such as penicillin, sulfonamides, etc.) which have a smaller molecular weight than the general hapten but have a specific structure are called simple haptens. When a simple hapten enters an allergic body, it binds to tissue proteins in the body. Become a complete antigen, this complete antigen can cause hypersensitivity reactions. In general, B lymphocytes recognize hapten determinants, and T lymphocytes recognize vector antigenic determinants.
6. Toxoid vaccine
Toxoid vaccines have great significance when pathological changes in the disease are mainly caused by strong exotoxin or enterotoxin, such as tetanus and diphtheria vaccines. In general, the toxoid of enterotoxin is rarely successful. However, the heat-stable enterotoxin (LT) of enterotoxin-type Escherichia coli has a genetically engineered detoxified allosteric construct that promises to be an effective traveler diarrhea vaccine. Mutations corresponding to cholera toxin (CT) may become a more important vaccine. These two toxin variants can even induce good mucosal immunity and are promising mucosal immune adjuvants. Most of the currently used toxoid vaccines are manufactured using conventional techniques. These vaccines, such as diphtheria and tetanus vaccines, contain many impure components, and the formaldehyde treatment of toxins into toxoids also results in cross-linking with bovine-derived polypeptides from the culture medium, ultimately producing unnecessary antigens. Therefore, the study of a mutant, non-toxic pure molecule as a new vaccine can improve the quality and efficacy of these vaccines, such as the replacement of diphtheria toxin 52 at the glutamate to glycine, can lead to loss of toxicity, and can cross-react with diphtheria toxin.
Virus-like particles (VLPs) are assembled from viral structural proteins with self-assembly characteristics, and are similar in morphology to pathogens. VLPs do not contain viral nucleic acid substances, are not infectious, and cannot replicate autonomously; VLPs can repeated high-density expression of antigenic epitopes, resulting in a strong immune response, so VLPs are an ideal form of vaccine for a variety of diseases.  Enveloped virus-like particles (eVLPs) has the same size and structure as enveloped viruses and present antigens in their natural state for an improved immune response. Compared to non-enveloped VLPs, the former is relatively complex in structure, contain a host cell membrane, and the host cell membrane (envelope) is cross-linked to the target antigen displayed on the outer surface. Envelope VLPs can integrate multiple antigens of homologous or heterologous pathogens, producing envelope VLPs. Some structural proteins that require co-expression of the virus are assembled into granules that are released from the cell membrane in the form of budding. A variety of cell matrices can be used to produce enveloped VLPs, including: yeast cells, insect cells, mammalian cells, plant cells, and the like; in addition, chimeric envelope VLPs can also be prepared in vitro as virosomes.
The immunogenicity of VLPs can be enhanced by immunostimulating adhesion molecules and cytokines. CD40L is expressed on the surface of HIV VLPs and interacts with CD40-CD40L to localize and activate DCs, enhancing CD4+, CD8+ T cell responses. The virus-like particles can be used as an antigen carrier and an adjuvant delivery system, and the partial amino acid sequence of the hemagglutinin and neuraminidase of the influenza virus is inserted into the double-layer lipid globule membrane in a targeted manner, so that the two molecules can be combined with the host. The receptor-bound group on the surface of the immune cell is exposed on the surface, and the antigen or DNA encoding the antigen is encapsulated inside, which has the advantage of facilitating the directional transport of the antigen or drug molecule.
The discovery of vaccines is a landmark event in the history of human development. Because in a sense, the history of human reproduction is the history of human beings constantly fighting diseases and natural disasters. The most important means of controlling infectious diseases is prevention, and vaccination is considered to be the most effective measure. And it turns out that the variola virus that threatens humans for hundreds of years has been completely eliminated after the emergence of vaccinia vaccine, ushered in the first victory of human vaccines against the virus, and more firmly believes that vaccines control and eliminate infectious diseases. Since then, the vaccine family has expanded and developed over the past 200 years, and there are currently more than 20 vaccines for human disease prevention and treatment.
Reference
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publié le jeudi 15 août à 13:34

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