recombinant vaccines 1

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CONTENTS What is a vaccine? Properties of good vaccine Types of vaccines Advantages of recombinant vaccines over conventional vaccines Recombinant virus vaccines or live recombinant vaccines Recombinant DNA vaccines


WHAT IS A VACCINE? A preparation of killed or weakened microorganism that is given to a person orally or injected in order to prevent disease. Edward Jenner demonstrated that a person inoculated into the skin with cowpox was protected against small pox and he thus developed the principles of vaccination in 1796. In 1881 Louis Pasteur honored Jenner by naming the processing ‘’vaccination’’ and the substance used to vaccinate was a ‘’vaccine’’.

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Principle of a vaccine is to induce a primary response in the vaccinated subject so that following the exposure of a pathogen,a rapid secondary immune response is generated leading to accelerated elimination of the organism and protection from clinical disease. Success depends on the generation of memory T cells and B cells and presence of neutralizing antibody serum .

Properties of a good vaccine:

Properties of a good vaccine Ability to elicit the appropriate immune response for the particular pathogen. Long term protection Safety Stability Inexpensiveness

Types of vaccines:

Types of vaccines Live vaccines Killed or whole organism vaccines Subunit vaccines-purified or recombinant antigen Recombinant vaccines DNA vaccines

Live vaccines:

Live vaccines These vaccines are prepared from attenuated strains that are almost or completely devoid of pathogenicity but are capable of inducing a protective immune response to the body. They multiply in human host and provide continuous antigenic stimulation over a period of time. For example typhoid vaccines.

Killed whole organism vaccines:

Killed whole organism vaccines It is a vaccine that is produced by growing the organism and then killing or inactivating it with heat and/or chemicals. These are used when safe live vaccines are not available For example inactivated polio vaccine Rabies vaccine


SUBUNIT VACCINES Subunit vaccines are defined as those vaccines containing one or more pure or semi-pure antigen. These are of three types, toxoids, recombinant subunit vaccines and non recombinant subunit vaccines .


Toxoids In some diseases like diphtheria and tetanus it is not the growth of the bacterium that is dangerous, but the protein toxin that is liberated by it. Treating the toxin with formaldehyde denatures the protein so that it is no longer dangerous. The inactivated toxin is called as toxoid. For example, DPT vaccine also called as triple vaccine.

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SUBUNIT VACCINES (NON-RECOMBINANT) Constituent proteins of bacteria or virus are isolated and purified Advantages : Defined Composition Various delivery systems available Disadvantages: Antigens must be produced and purified by cultivation of a pathogen Multiple doses typically required Adjuvant needed

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Subunit recombinant vaccines T hese vaccines are those in which genes for desired antigens are inserted into a vector, usually a virus, that has a very low virulence. The vector expressing the antigen may be used as the vaccine, or the antigen may be purified and injected as a subunit vaccine. The only recombinant vaccine currently in use in humans is the Hepatitis B Virus (HBV) vaccine, which is a recombinant subunit vaccine Hepatitis B surface antigen is produced from a gene transfected into yeast cells and purified for injection as a subunit vaccine. This is much safer than using attenuated HBV, which could cause lethal hepatitis or liver cancer if it reverted to its virulent phenotype. Recombinant DNA techniques can also be used to make safer attenuated pathogen vaccines

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Hepatitis B vaccine(HBV ) Originally based on the surface antigen purified from the blood of chronically infected individuals. Due to safety concerns, the HBV vaccine became the first to be produced using recombinant DNA technology (1986) Produced in bakers’ yeast (Saccharomyces cerevisiae ) Virus-like particles (VLPs) Viral proteins that self-assemble to particles with the same size as the native virus. VLP is the basis of a new vaccine against human papilloma virus (HPV)

Vaccine Advantages Drawbacks type:

Vaccine Advantages Drawbacks type Live vaccines or few doses 1.controlled attenuation normally required required 2.Long term protection 2.risk of reversion 3.Both cellular and humoral 3.poorly defined responses composition Killed vaccines 1.No risk of reversion 1.multiple doses 2.No risk of transmission required 2.poorly defined composition Subunit vaccines 1.Defined composition 1.multiple doses (non recombinant) 2.various delivery systems required available 2.adjuvants needed Subunit vaccines risk of pathogenicity 1.multiple doses typically (recombinant) 2.defined composition needed 3.various delivery systems 2.adjuvants needed available 4.large scale production simplified 5.further genetic engineering possible

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Which Vector to be used? Must be compatible with host cell system (prokaryotic vectors for prokaryotic cells, eukaryotic vectors for eukaryotic cells) Needs a good combination of strong promoters ribosome binding sites termination sequences affinity tag or solublization sequences multi-enzyme restriction site

Recombinant vaccines:

Recombinant vaccines Genetic engineering approach Hepatitis B Vaccina or adenovirus alteration

Recombinant virus vaccines or live recombinant vaccines:

Recombinant virus vaccines or live recombinant vaccines A gene coding for an immunogenic protein from one organism into the genome of other, such as vaccinia virus is introduced. The organism expressing that gene is called as recombinant. Following injection into the subject, the recombinant will replicate and express sufficient amounts of the foreign protein to induce a specific immune response to the protein.

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Advantages of viral vector vaccines Elicit strong humoral and cell-mediated immune responses, resulting in immunological memory . • Can be targeted by viral tropisms for particular cells, e.g. intestine, brain, etc., inducing desired immunity. • Can also encode for several antigens from different pathogens, introducing the possibility of a single vaccine for several diseases. • Viral vectors have been found not to interfere with the protection produced by other types of vaccines.. • Vaccines are relatively inexpensive and, for some, easily transportable.

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Disadvantages of viral vector vaccines Since the live virus being used is an attenuated form of a human pathogen, there is always a risk of reversion to virulence. Some of the vectors under consideration, such as adenovirus, have the capability of transforming cells to a cancerous phenotype. While these oncogenes are removed, vector virus could recombine with naturally occurring, pathogenic strains in the environment and form a new hybrid virus with transforming properties. • Immune response to virus-infected cells may cause pathology .

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DNA vaccines Create a recombinant plasmid containing a gene encoding a specific antigen. Engineer in sequences Enabling it to be expressed in humans Passaged through bacteria Introduce it into humans Let the human cells produce the antigen Present it to T-cells Provoke immune response

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Advantages/Disadvantages of DNA vaccines DNA vaccines stimulate both humoral and cell mediated responses. Dendritic cells may play a role. In animal studies, the vaccination produced long-term protection. Such vaccines are heat stable and non virulent. DNA vaccines are easily constructed with available tools of molecular biology. • Concerns over foreign DNA integrating into the cell’s DNA. Such integration could cause the cell to transform and become cancerous. Also thought that DNA vaccines might produce anti-DNA Abs, causing auto-immunity in host, but naked DNA is not very immunogenic in animal studies. It is not know exactly how long the DNA persists in the host cells .

Conventional vs Recombinant DNA Vaccines:

Conventional vs Recombinant DNA Vaccines Conventional vaccines Chemical or physical inactivation(killed) Laboratory induced changes to weaken pathogens(live attenuated) Isolate related and designed attenuated (Live) Recombinant DNA vaccines Recombinant generated subunits or DNA vaccines(killed) Gene deleted pathogens Vector-based organisms to deliver foreign gene products(Live)

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Future Developments • Identification and utilization of better immunogens as new vaccines for diseases for which no currently available vaccines exist. • Better vaccine delivery methods: oral, intranasal, and systems allowing mass vaccinations • Use of immunomodulators in vector-based vaccines: CPG motifs and cytokines. • Expression of foreign proteins in plants and the development of edible vaccines • Vaccines developed for non-infectious agents: control and prevent cancer; vaccines to induce long lasting contraception


conclusions R ecombinant vaccines are in their early phase. There are no DNA vaccines in market at present . But this just the beginning . R ecombinant vaccines are going to be the vaccines of next generation .

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