Modern principles of recombinant vaccines
The principle of creating genetically engineered vaccines is that a gene is built into the structure of weakened viruses, bacteria, yeast or cells of higher organisms, which is responsible for the formation of the antigen of the pathogen against which the vaccine will be directed. At the same time, there is no need to use killed or weakened bacteria and viruses, the safety of workers in vaccine manufacturing enterprises is ensured, there is no toxic or infectious material that often pollutes the microbial antigen obtained from cell cultures, and the ecological situation improves. Antiviral vaccines became the main object of the application for genetic engineering, which is explained by the simplicity of the organization of the viral genomes. The more complex structure of bacterial cells and the relatively low cost of antibiotic vaccines are factors that inhibit the development of genetically engineered work. In perspective, it is proposed to use vectors in which not only genes that control the synthesis of antigens of the pathogen are embedded, but also genes encoding various mediators (proteins) of the immune response (interferons, interleukins, etc.).
Recombinant bacterial vaccine. Bacterial vectors, used in veterinary medicine.
The first among the causative agents of bacterial human infections, the attention of researchers involved in the creation of genetically engineered vaccines, attracted Treponema pallidum - the causative agent of syphilis. And it's not accidental. First, although modern medicine has effective methods of diagnosis and therapy, syphilis has become epidemic in both developed and developing countries; second, obtaining pure cultures of pale treponema presents great difficulties, since it does not grow in an artificial environment; thirdly, it is impossible to obtain a vaccine against it using conventional methods based on the extraction and purification of antigens. Lovett and colleagues (University of California) in 1982, using a bacteriophage as a vector, the DNA of this spirochete was cloned into E. coli cells. Genetic material for the experiment was isolated from the eggs of specially infected rabbits. They obtained an E. coli strain that contained at least seven specific treponema antigens. These studies were designed to develop more specific tests for the diagnosis of syphilis and the production of an effective vaccine (cited by A. Sasson, 1987).
In veterinary medicine, the first genetically engineered antibacterial vaccine, which has found application in practice, is a vaccine against colibacillosis (escherichiosis) of pigs and calves caused by pathogenic strains of E. coli. The developer of this vaccine is the Dutch veterinary pharmaceutical company "Intervet international". In order to isolate the protein in quantities sufficient to produce the vaccine, they cloned the gene responsible for the synthesis of the K88 and K99 colibacillus antigens in E. coli K-12 strain. These antigens in combination with adjuvant were used to produce the vaccine. Immunization of cows and pigs with this vaccine caused the formation of protective antibodies, which were then transferred to newborns with colostrum and milk. Similar vaccines were developed by Cetus in cooperation with Norden Laboratriz (USA) and Tek America Group.
To construct living genetic engineering (recombinant) vaccines, three components are necessary: a bacterial vector, a carrier of heterologous protective antigens, genes for heterologous antigen synthesis, and genetic structures that provide stable and controlled expression of protective antigens that can in turn induce effective protection of the immunized organism.
As bacterial vectors, Salmonella, Escherichia, Mycobacteria, Bacillus, Listeria, Yersinia, Corynebacterium lactobacilli and Franciscella are used. When creating recombinant vaccines for veterinary medicine, vaccine strains of S. typhimurium, S. choleraesuis, S.dublin, S.teritidis, S. abortusovis, Mycobacterium bovis (pc. BCG), Bac.subtilis, Francisella tularensis (E A.Svetochko et al., 2000). Most researchers use genetically characterized Salmonella strains as a bacterial vector, arguing in favor of this: salmonella can be used either orally or parenterally, stimulating local and systemic immunity, including the production of serum antibodies and mucosal secretory antibodies, cell-mediated immunity, and antibody-dependent cytotoxicity.
In GNPTSPM (Russia), problems are actively being developed to study the possibility of using as vaccine vectors vaccine strains of Bac.anthracis. This is primarily due to the following reasons: the principle possibility of secretion of foreign proteins by cells of the vaccine strain of anthrax microbe, the unpretentiousness of the bacillus to nutrient media and, lastly, the high stability of Bac.anthracis spores, which will provide increased storage and stability of the final forms of vaccine preparations.
Antigens providing full protection may include, for example, adhesion antigens and thermolabile enterotoxin of pathogenic Escherichia, O and Vi antigens of salmonella, cholera and diphtheria toxins, toxins of tetanus, botulism, gas gangrene, malignant edema, capsular antigens of plague microbe and others. The development of a combined vaccine against anthrax and brucellosis is especially relevant for veterinary science (Shumilov KV). A genetic construct has been obtained in which the lethal toxin gene of the anthrax microbe and the surface protein protein Brucella abortus with the mol. weight 31kD (AP Pomerantsev). In RosNIPCHI "Microbe" genetically engineered strains with a cloned pag gene, which codes for the synthesis of a protective antigen, the main immunogen of the causative agent of anthrax, were constructed.
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