Vaccines and Type of Vaccines

This presentation talks about vaccines, currently being used in medicinal processes and therapeutics and their types. It elaborates the importance of the different types of vaccines along with their examples and their mechanism of action. The mode of production of all the types of vaccines is also discussed in the presentation including recent developments made for the production of mRNA vaccine against SARS-CoV-2

1. PRESENTATION BY TATHAGAT SAH BTech . Biotechnology URN – 1901181

2. VACCINES Table of Contents Vaccine and Vaccination Immunization and Immunity Types of Vaccines Live-attenuated vaccines Inactivated vaccines Messenger RNA (mRNA) vaccines Subunit Vaccines – Toxoid, Polysaccharide and Recombinant Conjugate vaccines DNA vaccines Recombinant Vector vaccines

3. Vaccine and Vaccination Vaccine is a biological product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease. Vaccines are usually administered through needle injections, but can also be administered by mouth or sprayed into the nose. Vaccination refers to the act of introducing a vaccine into the body to produce immunity to a specific disease. Immunization and Immunity Immunization is the process of being made immune or resistant to an infectious disease, typically by the administration of a vaccine. It implies that a person had an immune response . Immunity refers to protection against a disease. There are two types of immunity, passive and active. Immunity is indicated by the presence of antibodies in the blood and can usually be determined with a laboratory test.

4. Types of Vaccines There are several different types of vaccines. Each type is designed to teach the immune system how to fight off certain kinds of germs and the serious diseases they cause. When scientists create vaccines, they consider: How the immune system responds to the germ Who needs to be vaccinated against the germ The best technology or approach to create the vaccine Based on a number of these factors, scientists decide which type of vaccine they will make. There are several types of vaccines, including: Live-attenuated vaccines Inactivated vaccines Messenger RNA (mRNA) vaccines Subunit Vaccines – Toxoid, Polysaccharide and Recombinant Conjugate vaccines DNA vaccines Recombinant Vector vaccines

5. Live-Attenuated Vaccines Live vaccines use a weakened (or attenuated) form of the germ that causes a disease. Attenuation can often be achieved by growing a pathogenic bacterium or virus for prolonged periods under abnormal culture conditions. This selects mutants that are better suited for growth in the abnormal culture conditions than in the natural host. For example, an attenuated strain of Mycobacterium bovis called Bacillus Calmette-Guérin (BCG) was developed by growing M. bovis on a medium containing increasing concentrations of bile. Diseases against which LVA vaccines are used include: Measles, Mumps and Rubella ( MMR Vaccine ) Polio ( Sabin vaccine ) Rotavirus ( Rotarix , Rota Teq , Rotavac , Rotavin-M1 ) Tuberculosis ( BCG Vaccine ) Varicella ( Varivax , Varilrix ) Yellow fever ( YF- Vax , Stamaril )

6. Advantages of Live-Attenuated Vaccines Because of their capacity for transient growth, such vaccines provide prolonged immune system exposure to the individual epitopes on the attenuated organisms and more closely mimic the growth patterns of the “real” pathogen, resulting in increased immunogenicity and efficient production of memory cells . Thus, these vaccines often require only a single immunization . Just 1 or 2 doses of most live vaccines can induce a lifetime of protection against an antigen and the disease it causes. Disadvantages of Live-Attenuated Vaccines The live forms may mutate and revert to virulent forms in vivo, resulting in paralytic disease in the vaccinated individual and serving as a source of pathogen transmission. They need to be kept cool, so they don’t travel well. This means that they can’t be used in countries with limited access to refrigerators.

7. Development of a poliovirus type 2 vaccine strain ( nOPV2 ) that is genetically more stable and less likely to regain virulence than the original Sabin2 strain. Modifications were introduced at the 5′ un-translated region of the Sabin2 genome to stabilize attenuation determinants , 2C coding region to prevent recombination , and 3D polymerase to limit viral adaptability.

8. Inactivated Vaccines Inactivated vaccines use the killed version of the germ that causes a disease. The pathogen is generally treated with heat or chemicals to achieve this. Chemical inactivation with formaldehyde or various alkylating agents has been successful. The Salk polio vaccine is produced by formaldehyde inactivation of the poliovirus. Inactivated vaccines are used to protect against: Cholera ( Dukoral ®, Shanchol ™ and Euvichol ® ) Influenza Hepatitis A ( Havrix , Vaqta ) Plague Polio ( Salk vaccine ) Rabies ( HDCV vaccine ( Imovax , Sanofi Pasteur), PCECV vaccine ( RabAvert , Novartis ))

9. Advantages of Inactivated Vaccines Stable Safer than live vaccines Refrigerated storage not required Disadvantages of Inactivated Vaccines Killed vaccines often require repeated boosters to achieve a protective immune status. Because they do not replicate in the host, killed vaccines typically induce a predominantly humoral antibody response and are less effective than attenuated vaccines in inducing cell-mediated immunity or in eliciting a secretory IgA response. Even though the pathogens they contain are killed, inactivated whole-organism vaccines still carry certain risks. A serious complication with the first Salk vaccines arose when formaldehyde failed to kill all the virus, leading to paralytic polio in a high percentage of recipients. Risk is also encountered in the manufacture of the inactivated vaccines. Large quantities of infectious agents must be handled safely

10. Messenger RNA (mRNA) Vaccines mRNA vaccines make proteins in order to trigger an immune response and this technology is used to make some of the COVID-19 vaccines. COVID-19 mRNA vaccines give instructions for our cells to make a harmless piece of what is called the “spike protein”. The spike protein is found on the surface of the virus that causes COVID-19. First , COVID-19 mRNA vaccines are given in the upper arm muscle. Once the instructions (mRNA) are inside the immune cells, the cells use them to make the protein piece. After the protein piece is made, the cell breaks down the instructions and gets rid of them. Next , the cell displays the protein piece on its surface. Our immune systems recognize that the protein doesn’t belong there and begin building an immune response and making antibodies, like what happens in natural infection against COVID-19. At the end of the process , our bodies have learned how to protect against future infection.

11. Facts about COVID-19 mRNA Vaccines: They cannot give someone COVID-19 mRNA vaccines do not use the live virus that causes COVID-19. They do not affect or interact with our DNA in any way. mRNA never enters the nucleus of the cell, which is where our DNA is present. The cell breaks down and gets rid of the mRNA soon after it is finished using the instructions. Advantages of mRNA Vaccines mRNA vaccines have several benefits compared to other types of vaccines, including shorter manufacturing times and, because they do not contain a live virus, no risk of causing disease in the person getting vaccinated.

12. Subunit – Toxoid, Polysaccharide and Recombinant Subunit vaccines use only specific, purified macromolecules derived from the pathogen. The three most common applications of this strategy are, inactivated exotoxins or toxoids, capsular polysaccharides or surface glycoproteins, and key recombinant protein antigens. Toxoid Some bacterial pathogens, including those that cause diphtheria and tetanus, produce exotoxins that account for all or most of the disease symptoms resulting from infection. Diphtheria and tetanus vaccines have been made by purifying the bacterial exotoxin and then inactivating it with formaldehyde to form a toxoid. Vaccination with the toxoid induces anti-toxoid antibodies, which are capable of binding to the toxin and neutralizing its effects. Conditions for the production of toxoid vaccines must be closely controlled and balanced to avoid excessive modification of the epitope structure while also accomplishing complete detoxification.

13. Polysaccharide The virulence of some pathogenic bacteria depends primarily on the anti-phagocytic properties of their hydrophilic polysaccharide capsule. Coating the capsule with antibodies and/or complement greatly increases the ability of macrophages and neutrophils to phagocytose such pathogens. These findings provide the rationale for vaccines consisting of purified capsular polysaccharides. The vaccine for Streptococcus pneumoniae (the organism which causes pneumococcal pneumonia) consists of 13 antigenically distinct capsular polysaccharides (PCV13). The vaccine for Neisseria meningitidis , a common cause of bacterial meningitis, also consists of purified capsular polysaccharides. Some viruses carry surface glycoproteins that have been tested for use in antiviral vaccines, with little success. Glycoprotein-D from HSV-2 has been shown to prevent genital herpes in clinical trials of some vaccines, therefore this may be the approach for some antiviral vaccines as well.

14. Recombinant Theoretically, the gene encoding any immunogenic protein can be cloned and expressed in cultured cells using recombinant DNA technology, and this technique has been applied widely in the design of many types of subunit vaccines. A number of genes encoding surface antigens from viral, bacterial, and protozoan pathogens have been successfully cloned into cellular expression systems for use in vaccine development. The first such recombinant antigen vaccine approved for human use is the hepatitis B vaccine, developed by cloning the gene for the major hepatitis B surface antigen ( HBsAg ) and expressing it in yeast cells . The recombinant yeast cells are grown in large fermenters, allowing HBsAg to accumulate in the cells. The yeast cells are harvested and disrupted, releasing the recombinant HBsAg , which is then purified by conventional biochemical techniques. Recombinant hepatitis B vaccine induces the production of protective antibodies.

15. Therefore subunit vaccines are used to protect against: Hepatitis B Pertussis Diphtheria and Tetanus Advantages and Disadvantages of Subunit Vaccines Because these vaccines use only specific pieces of the germ, they give a very strong immune response that’s targeted to key parts of the antigen. They can also be used on almost everyone who needs them, including people with weakened immune systems and long-term health problems. One limitation of some subunit vaccines, especially polysaccharide vaccines, is their inability to activate T H cells. Instead, they activate B cells in a thymus- independent type 2 (TI-2) manner, resulting in IgM production but little class switching, no affinity maturation, and little, if any, development of memory cells. However, vaccines that conjugate a polysaccharide antigen to a protein carrier can alleviate this problem by inducing T H cell responses.

16. Conjugate or Multivalent Vaccines These types of vaccines employ the fusing of a highly immunogenic protein to a weak vaccine immunogen (a conjugate) or mixing in extraneous proteins (multivalent) to enhance or supplement immunity to the pathogen. Although this type of vaccine can induce memory B cells, it cannot induce memory T cells specific for the pathogen. The vaccine against Haemophilus influenzae type b ( Hib ) , a major cause of bacterial meningitis and infection-induced deafness in children, is a conjugate formulation consisting of type b capsular polysaccharide covalently linked to a protein carrier, tetanus toxoid . MCV4 vaccine is a multivalent vaccine consisting of individual capsular Neisseria polysaccharide antigens joined to the highly immunogenic diphtheria toxoid protein.

17. One common means of producing a multivalent vaccine that can deliver many copies of the antigen into cells is to incorporate antigens into protein micelles, lipid vesicles (liposomes), or immuno -stimulating complexes. Protein-containing liposomes are prepared by mixing the proteins with a suspension of phospholipids under conditions that form lipid bilayer vesicles; the proteins are incorporated into the bilayer with the hydrophilic residues exposed. Immuno -stimulating complexes (ISCOMs) are lipid carriers prepared by mixing protein with detergent and a glycoside called Quil A , an adjuvant. Membrane proteins from various pathogens, including influenza virus, measles virus, hepatitis B virus, and HIV, have been incorporated into micelles, liposomes, and ISCOMs and are being assessed as potential vaccines. In addition to their increased immunogenicity, liposomes and ISCOMs appear to fuse with the plasma membrane to deliver the antigen intra- cellularly , where it can be processed by the endogenous pathway, leading to CTL responses.

18. (T)A conjugate vaccine is prepared by conjugating the surface polysaccharide to a protein molecule, making the vaccine more immunogenic than either alone. (R) ISCOMs and liposomes can deliver agents inside cells, so they mimic endogenous antigens. Subsequent processing by the endogenous pathway and presentation with class I MHC molecules induces a cell-mediated response.

19. DNA Vaccines These utilize plasmid DNA encoding antigenic proteins that are injected directly into the muscle of the recipient. This strategy relies on the host cells to take up the DNA and produce the immunogenic protein in vivo, thus directing the antigen through endogenous MHC class I presentation pathways, helping to activate better CTL responses. The DNA appears either to integrate into the chromosomal DNA or to be maintained for long periods in an episomal form, and is often taken up by dendritic cells or muscle cells in the injection area. DNA vaccines are able to induce protective immunity against a number of pathogens, including influenza and rabies viruses. The addition of a follow-up booster shot with protein antigen (called a DNA prime and protein boost strategy), or inclusion of supplementary DNA sequences in the vector, may enhance the immune response. One sequence that has been added to some vaccines is the common CpG DNA motif found in some pathogens.

20. Comparative Analysis of Vector DNA and mRNA vaccines. It can be seen that the process of transcription occurs when vector DNA vaccine is administered, which produces mRNA which is then translated into viral spike proteins. In mRNA vaccines, the host cell directly translates the mRNA strand into spike proteins.

21. Advantages of DNA Vaccines DNA vaccines offer some potential advantages over many of the existing vaccine approaches: Since the encoded protein is expressed in the host in its natural form—there is no denaturation or modification —the immune response is directed to the antigen exactly as it is expressed by the pathogen, inducing both humoral and cell-mediated immunity. DNA vaccines also induce prolonged expression of the antigen , enhancing the induction of immunological memory. No refrigeration of the plasmid DNA is required, eliminating long term storage challenges. In addition, the same plasmid vector can be custom tailored to insert DNA encoding a variety of proteins, which allows the simultaneous manufacture of a variety of DNA vaccines for different pathogens, saving time and money.

22. Recombinant Vector Vaccines Individual genes that encode key antigens of especially virulent pathogens can be introduced into attenuated viruses or bacteria. The attenuated organism serves as a vector, replicating within the vaccinated host and expressing the gene product of the pathogen . However, since most of the genome of the pathogen is missing, reversion potential is virtually eliminated. Recombinant vector vaccines have been prepared utilizing existing licensed live, attenuated vaccines and adding to them genes encoding antigens present on newly emerging pathogens. Yellow fever vaccine – engineered to express antigens of WNV. A number of organisms have been used as the vector in RVV preparations, including vaccinia virus , the canarypox 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.

23. Production of vaccine using a recombinant vaccinia vector. (T) The gene that encodes the desired antigen (orange) is inserted into a plasmid vector adjacent to a vaccinia promoter (pink) and flanked on either side by the vaccinia thymidine kinase ( TK ) gene (green). (R)When tissue culture cells are incubated simultaneously with vaccinia virus and the recombinant plasmid, the antigen gene and promoter are inserted into the vaccinia virus genome by homologous recombination at the site of the nonessential TK gene, resulting in a TK - recombinant virus. Cells containing the recombinant vaccinia virus are selected by addition of bromodeoxyuridine ( BrdU ), which kills TK + cells.

24. Examples and Advantages of RVV Vaccinia virus, the attenuated vaccine used to eradicate smallpox, has been widely employed as a vector for the design of new vaccines. This large, complex virus, with a genome of about 200 genes, can be engineered to carry several dozen foreign genes without impairing its capacity to infect host cells and replicate . The genetically engineered vaccinia expresses high levels of the inserted gene product, which can then serve as a potent immunogen in an inoculated host. A relative of vaccinia , the canarypox virus, can also be engineered to carry multiple genes. Unlike vaccinia , it does not appear to be virulent, even in individuals with severe immune suppression. Another possible vector is an attenuated strain of Salmonella typhimurium , which has been engineered with genes from the bacterium that causes cholera ( Vibrio cholerae ) . Recombinant vectors maintain the advantages of live attenuated vaccines while avoiding the risk of reverting to pathogenic forms.

25. SUMMARY

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