Pharmaceutical Biotechnology (PHA412) Lecture: 16 Topic: Vaccine (continued) Mohammad Abbas Gani Lecturer, Department of Pharmacy, IUB CONVENTIONAL VACCINES • Conventional vaccines originate from viruses or bacteria and can be divided in live attenuated vaccines and non-living vaccines. In addition, three vaccine generations can be distinguished for nonliving vaccines. • First generation vaccines consist of an inactivated suspension of the pathogenic microorganism. Little or no purification is applied. Examples: Influenza vaccine, Cholera vaccine. • For second generation vaccines purification steps are applied, varying from the purification of a pathogenic microorganism (e.g., improved non-living polio vaccine) to the complete purification of the protective component (e.g., polysaccharide vaccines). • Third generation vaccines are either a well-defined combination of protective components (e.g., acellular pertussis vaccine) or the protective component with the desired immunological properties (e.g., polysaccharides conjugated with carrier proteins). CONVENTIONAL VACCINES Live Attenuated Vaccines: • An attenuated vaccine (or a live attenuated vaccine, LAV) is a vaccine created by reducing the virulence of a pathogen, but still keeping it viable (or "live"). • Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent. • Examples: polio vaccine, measles-rubella-mumps (MMR) combination vaccine, and tuberculosis vaccine (BCG vaccine; BCG means Bacillus Calmette-Guerin). • Advantage: few and low doses are required, give long-lasting humoral and cellmediated immunity. • Disadvantage: reversion to a virulent form may occur, immunization of immunodeficient children with live organisms can lead to serious complications. CONVENTIONAL VACCINES Non-Living Vaccines: Whole Organisms • An inactivated vaccine (or killed vaccine) is a vaccine consisting of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy disease-producing capacity. • A number of reagents (e.g., formaldehyde, glutaraldehyde) and heat are commonly used for inactivation. • Examples: pertussis, cholera, typhoid fever, and inactivated polio vaccines. • Advantages: more stable than live pathogens, cannot revert to a virulent form and cause disease. • Disadvantage: little or no CMI is induced, more frequently cause adverse effects as compared to live attenuated vaccines and second and third generation non-living vaccines. CONVENTIONAL VACCINES Non-Living Vaccines: Subunit Vaccines • A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response. • A "subunit" vaccine doesn't contain the whole pathogen but contains only the antigenic parts such as proteins, polysaccharides or peptides. • Advantages: cannot revert to virulence, safe for immunocompromised patients, can withstand changes in conditions (e.g. temperature, light exposure, humidity). • Disadvantages: reduced immunogenicity compared to attenuated vaccines, require adjuvants to improve immunogenicity, often require multiple doses ("booster" doses) to provide long-term immunity, can be difficult to isolate the specific antigen(s) which will invoke the necessary immune response. CONVENTIONAL VACCINES Non-Living Vaccines: Subunit Vaccines (Types) • Toxoid vaccines: A toxoid is an inactivated toxin whose toxicity has been suppressed either by chemical (formalin) or heat treatment, while other properties, typically immunogenicity, are maintained. Toxins are secreted by bacteria, whereas toxoids are altered form of toxins; toxoids are not secreted by bacteria. There are toxoids for prevention of diphtheria, tetanus and botulism. • Protein subunit vaccines: contains isolated proteins from pathogens (virus or bacteria). Examples: hepatitis B, acellular pertussis vaccines. • Polysaccharide vaccines: contains chains of polysaccharides (sugar molecules) found in the pathogen's capsule such as cell walls of some bacteria. Examples: pneumococcal polysaccharide vaccine, meningococcal vaccine. MODERN VACCINE TECHNOLOGIES 1) Genetically Improved Live Vaccines a) Genetically Attenuated Microorganisms: By making multiple deletions the risk of reversion to a virulent state during production or after administration can be virtually eliminated. A prerequisite for attenuation by genetic engineering is that the factors responsible for virulence and the life cycle of the pathogen are known in detail. It is also obvious that the protective antigens must be known: attenuation must not result in reduced immunogenicity. b) Live Vectored Vaccines: A way to improve the safety or efficacy of vaccines is to use live, avirulent or attenuated organisms as a carrier to express protective antigens from a pathogen. Live vectored vaccines are created by recombinant technology, wherein one or more genes of the vector organism are replaced by one or more protective genes from the pathogen. MODERN VACCINE TECHNOLOGIES 2) Genetically Improved Subunit Vaccines a) Genetically Detoxified Proteins: A biotechnological improvement of the acellular pertussis vaccine has been the switch from chemically to genetically inactivated pertussis toxin. Genetic detoxification by site directed mutagenesis warrants the reproducible production of a non-toxic mutant protein that is highly immunogenic because the integrity of immunogenic sites is fully retained. b) Recombinant Peptide Vaccines: After identification of a protective epitope, it is possible to incorporate the corresponding peptide sequence through genetic fusion into a carrier protein, such as HBsAg, hepatitis B core antigen, and bgalactosidase. An example of the recombinant peptide approach is a malaria vaccine. Genetic fusion of peptides with proteins offers the possibility to produce protective epitopes of toxic antigens derived from pathogenic species as part of non-toxic proteins expressed by harmless species. MODERN VACCINE TECHNOLOGIES c) Synthetic Peptide-Based Vaccines: The use of synthetic peptides as vaccine has the following advantages: i. They can be prepared in unlimited quantities using solid-phase technology. ii. They are easily purified by HPLC methods. iii. They do not contain infectious or toxic material. d) Nucleic Acid Vaccines: A revolutionary application of rDNA technology in vaccinology has been the introduction of nucleic acid vaccines. In this approach plasmid DNA or messenger RNA encoding the desired antigen is directly administered into the vaccinee. The foreign protein is then expressed by the host cells and generates an immune response. Plasmid DNA is produced by replication in E. coli or other bacterial cells and purification by established methods (e.g., density gradient centrifugation, ion-exchange chromatography). MODERN VACCINE TECHNOLOGIES Advantages and disadvantages of nucleic acid vaccines: MODERN VACCINE TECHNOLOGIES Reverse Vaccinology: • Nowadays vaccines can be designed based on the information encoded by the genome of a particular pathogen. • The genome sequence of a pathogen provides a complete picture of all proteins that can be produced by the pathogens at any given time. • Using computer algorithms, proteins that are either excreted or expressed on the surface of the pathogen, and thus most likely available for recognition by the host’s immune system, can be identified. • After recombinant production and purification, these vaccine candidates can be screened for immunogenicity in mice. • From these, the best candidates can be selected and used as subunit vaccines. MODERN VACCINE TECHNOLOGIES MODERN VACCINE TECHNOLOGIES • A big advantage of reverse vaccinology is the ease at which novel candidate antigens can be selected without the need to cultivate the pathogen. • Furthermore, by comparing genomes of different strains of a pathogen, conserved antigens can be identified that can serve as a “broad spectrum” vaccine, giving protection against all strains or serotypes of a given pathogen. • One drawback of this approach is that it is limited to the identification of proteinbased antigens. • Reverse vaccinology has been successfully used to identify novel antigens for a variety of pathogens, including Neisseria meningitidis, Bacillus anthracis, Streptococcus pneumoniae, Staphylococcus aureus, Chlamydia pneumoniae and Mycobacterium tuberculosis. TYPES OF VACCINES (Summary)
