RECOMBINANT VACCINES

By-Gautam ParmarIBT Sem -2nd

PREFACE• 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• Future Potential• References

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’’.

• 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

• Ability to elicit the appropriate immune response for the particular pathogen.• Long term protection• Safety• Stability• Inexpensiveness

Types of vaccines• Live vaccines• Killed or whole organism vaccines• Subunit vaccines-purified or

recombinant antigen • Recombinant vaccines• DNA 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

• 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.

• 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

Subunit recombinant vaccines

These 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

Vaccine Advantages Drawbackstype

• Live vaccines 1.one 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 1.no 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

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 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.

Advantages of viral vector vaccines

• Elicit strong humoral and cell-mediated immuneresponses, 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 differentpathogens, introducing the possibility of a singlevaccine 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.

Disadvantages• 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 pathological problems.

Conventional vs Recombinant DNA Vaccines

Conventional vaccines• Chemical or physical

inactivation(killed)• Laboratory induced

changes to weaken pathogens(live attenuated)

• Isolate related anddesigned attenuated (Live)

Recombinant DNA vaccines• Recombinant generated

subunits or DNA vaccines(killed)

• Gene deleted pathogens

• Vector-based organisms to deliver foreign gene products(Live)

Future Developments• Identification and utilization of better immunogens as newvaccines for diseases • Better vaccine delivery methods: oral, intranasal, and systems allowing mass vaccinations• Use of immunomodulators in vector-based vaccines: CPGmotifs and cytokines.• Expression of foreign proteins in plants and the developmentof edible vaccines• Vaccines developed for non-infectious agents: control andprevent cancer; vaccines to induce long lasting contraception

References

• Sciencedirect.com• Academia.com• Animal Agriculture's Future through

Biotechnology- Mark W. Jackwood, Leslie Hickle

• Essentials of Clinical Immunology-A.V Hoffbrand

Thanx a lot