Vaccine
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Vaccines work by stimulating the immune system to recognize and destroy pathogens like bacteria and viruses. There are several types of vaccines including whole organism vaccines using live attenuated or killed pathogens, purified components like exotoxins or capsular polysaccharides, recombinant vector vaccines using attenuated viruses expressing pathogen genes, experimental DNA vaccines, and multivalent subunit vaccines combining multiple antigens. Adjuvants are often included in vaccines to boost the immune response.
Vaccine
- 1. VACCINE by Dr.Reena ,MD,Asst Prof
- 2. Vaccine is a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from causative agent of a disease, its product or a synthetic substitute, treated to act as an antigen without inducing the disease. The term vaccine is derived from Variolae vaccinae (smallpox of the cow), the term devised by Edward Jenner to denote cowpox.
- 3. A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe. The agent stimulates the body's immune system to recognize the agent as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters.
- 4. TYPES OF VACCINE 1. Whole organism vaccines 2. Purified macromolecules as vaccine 3. Recombinant vector vaccines 4. DNA vaccines 5. Multivalent subunit vaccines
- 5. 1. Whole organism vaccines: Many of the common vaccines currently in use consists of inactivated (killed) or live but attenuated (avirulent) bacterial cells or viral particles. Live attenuated vaccine: An Attenuated Vaccine contain micro-organisms that can be attenuated so that they lose their ability to cause significant disease (pathogenicity) but retain their capacity for transient growth within an inoculated host. Attenuation often can be achieved by growing a pathogenic bacterium or virus for prolonged periods under abnormal culture conditions.
- 6. For example, Bacillus Calmette-Guerin is a vaccine against tuberculosis, developed in 1921, caused by attenuation of the Mycobacterium bovis strain on a medium containing increasing concentration of bile. Advantage of attenuated vaccine is that such vaccines provide prolonged immune-system exposure to the individual epitopes on the attenuated organisms, resulting in increased immunogenicity and production of memory cells. These vaccines require only a single immunization, eliminating the need for repeated
- 7. A major disadvantage of attenuated vaccines is the possibility that they will revert to a virulent form. Attenuated vaccines may also be associated with complications similar to those seen in the natural disease. Genetic engineering is the other technique that provide a way to attenuate a virus irreversibly by selectively removing genes that are necessary for virulence.
- 8. Examples of live attenuated vaccine are: BCG vaccine Measles vaccine Mumps vaccine Sabin polio vaccine
- 9. Inactivated/killed vaccine: An Inactivated vaccine can be produced by inactivation of the pathogen by heat or by chemical means so that it is no longer capable of replication in the host. It is critically important to maintain the structure of epitopes on surface antigens during inactivation.
- 10. Examples of inactivated vaccines: Salk polio vaccine Rubella vaccine Rabies vaccine Influenza vaccine Hepatitis vaccine Pertusis vaccine
- 12. 2. Purified macromolecules as vaccines: These vaccine are Created from specific purified immunogenic macromolecules. They Eliminate some risk of attenuated or killed vaccines. There are three general forms of such vaccines. a) Inactivated exotoxins b) Capsular polysaccharides c) Recombinant microbial antigens
- 13. a) Inactivated exotoxins: Toxoids are vaccines which consist of exotoxins that have been inactivated, either by heat or chemicals. These vaccines are intended to build immunity against the toxins. Some examples are botulinum antitoxin and diphtheria antitoxin. b) Capsular polysaccharides: Protective immunity to encapsulated bacteria involves an antibody response to polysaccharide antigen, interaction with T and B lymphocytes and host defence mechanism.
- 14. Polysaccharide vaccines, such as those developed against Neisseria meningitidis, Streptococcus pneumoniae and Salmonella typhi, prevent infection by inducing an immune response against specific capsular polysaccharides. Limitation of polysaccharide vaccines is that they activate B cells in thymus-independent manner so that THcells are not activated. They produce IgM, little IgG, and limited if any immune memory.
- 15. c) Recombinant antigen vaccine: DNA encoding the surface antigens is isolated and cloned. Introduced into bacteria or yeast to induce expression of antigens. Allows for increased production of surface antigen. Ex: Hepatitis B vaccine- Genes for HBsAg(major surface antigen of HBV) is cloned in yeast cells and purified.
- 16. 3. Recombinant vector vaccines: Genes that encode major antigens of especially virulent pathogens can be introduced into attenuated viruses or bacteria. The attenuated virus or bacteria serves as a vector, replicating within the host and expressing the gene product of the pathogen. A number of organisms have been used for vector vaccines, including vaccinia virus, attenuated poliovirus, adenoviruses, attenuated strains of Salmonella, the BCG strain of Mycobacterium bovis, and certain strains of streptococcus that normally exist in the oral cavity.
- 18. 4. DNA vaccines: These vaccines are still in experimental stage. Like recombinant vaccines, genes for the desired antigens are located and cloned. The DNA encoding antigenic proteins is injected into the muscle of the recipient being vaccinated, usually with a "gene gun“ that uses compressed gas to blow the DNA into the muscle cells. DNA can be introduced into tissues by bombarding the skin with DNA-coated gold particles.
- 19. DNA vaccines advantages: The encoded protein is expressed in the host in its natural form therefore the immune response directed to the antigen is expressed in the same way as it is expressed by the pathogen. They induce both humoral and cell mediated immunnity. They cause prolonged expression of the antigen, which generates significant immunological memory.
- 20. The major disadvantage of DNA vaccine is integration of DNA into host genome leading to mutation. There are human trials underway with several different DNA vaccines including those for malaria, AIDS, influenza and herpes virus.
- 21. 5. Multivalent subunit vaccines: There are two approaches to develop multivalent subunit vaccine. One approach is to prepare solid matrix– antibody antigen (SMAA) complexes by attaching monoclonal antibodies to particulate solid matrices and then saturating the antibody with the desired antigen. Another approach of producing a multivalent vaccine is to use detergent to incorporate protein antigens into protein micelles, lipid vesicles
- 22. ADJUVANTS Adjuvants (from Latin adjuvare, to help) are substances that, when mixed with an antigen and injected with it, enhance the immunogenicity of that antigen. Adjuvants are often used to boost the immune response when an antigen has low immunogenicity or when only small amounts of an antigen are available. They are often included in vaccines to enhance the recipient's immune response to a supplied antigen,
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