PRESENTED BY: Deepti Singh

Ph.D. Biotechnology

FIRST SEMESTER

ENROL. NO. B-1384/14

COLLEGE OF BIOTECHNOLOGY

DUVASU, MATHURA

INTRODUCTION

Vaccines where a live micro-organism (bacteria or virus)

has been modified to express entire genomes or a portion of

foreign RNA or DNA sequences or proteins and where the

replicative competent vector acts as a carrier and may itself

act as a protective immunogen.

Vector/ Recipient:

A replicative competent micro-organism ( bacteria or virus)

into which the genetic sequence of interest will be inserted.

DEFINITION Vector vaccines:

Vector vaccines are liquid or freeze-dried preparations of one or

more types of live micro-organisms (bacteria or viruses) that

are non-pathogenic or have a low pathogenicity for the target

species and in which have been inserted one or more genes

encoding antigens that stimulate an immune response

protective against other micro-organisms

A live vector vaccine is a vaccine that uses a chemically

weakened virus to transport pieces of the virus in order to

stimulate an immune response.

The genes used in this vaccine are usually antigen coding

surface proteins from the pathogenic organism. They are then

inserted into the genome of a non pathogenic organism such

as Adenovirus were they are expressed on the cells surface

and can elicit an immune response.

EXTENSIVELY USED VECTORS

Poxviruses have been extensively studied as potential

vaccine vectors.

Vaccinia virus, used as a vector in many vaccines,

induces strong immuno stimulation at the injection site.

Its large genome can integrate many transducible genes

and it has an excellent safety profile.

Vaccinia has been administered to more than a billion

people since the WHO's 1967 launch of the Global

Smallpox Eradication Program.

VECTOR VACCINES: VIRUS AS

ANTIGEN GENE DELIVERY SYSTEM

Antigen Gene

Virus

Patient

Antigen Protein is Made

Diagram representing the formation of vector vaccine

VACCINIA VECTOR VACCINES

Vaccinia is a good candidate for a live recombinant viral

vaccine because it is:

•benign virus

•replicate in cytoplasm (viral replication genes)

•easy to store

RECOMBINANT LIVE VECTOR

VACCINES

• Recombinant live vector vaccines are preparations of one ormore types of live bacteria or viruses.

• One or more DNA/RNA sequences have been inserted intothese organisms.

• These organisms generally have a stable non or lowpathogenic phenotype for the species the vaccine is intendedfor.

• Recombinant live vector vaccines are expected to beattenuated and genetically defined live vaccines, which havedefined, non-reverting mutations or deletions.

TYPES OF VECTOR

Homologous vector:

When the target species of the vaccine is a natural host for

the vector, this is considered a homologous vector.

Heterologous vector:

When the target species of the vaccine is not one of the

natural hosts for the vector, the vector is classified as a

heterologous vector.

Picture representing the formation of malaria vaccine by using a

vector

BACTERIAL ANTIGEN DELIVERY

SYSTEMS: BACTERIAL VECTORS

Antigen Gene

Bacterium

Antigen Proteins made on Bacterial cell

Vaccinate Patient

BACTERIAL ANTIGEN

DELIVERY SYSTEMS•Use live non pathogenic bacterium which contains antigen

•Insert antigen gene into flagellin gene

•Epitope is expressed on the flagellum surface

***Flagellin-engineered bacteria is VACCINE**

Advantage - Oral Administration

VIRAL VECTORADVANTAGES:

•Infects human cells but some do not replicate

•Better presentation of antigen

•Generate T cell response

DRAWBACKS:

•Can cause bad reactions

•Can be problems with pre-exisiting immunity to virus

•Often can only accommodate one or two antigens

PROCEDURE FOR VACCINE

PREPARATIONGenes that encode major antigens of especially virulent pathogens

can be introduced into attenuated viruses or bacteria.

The attenuated organism 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, 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.

Vaccinia virus, the attenuated vaccine used to eradicate smallpox,has been widely employed as a vector vaccine.

This large, complex virus, with a genome of about 200 genes, canbe engineered to carry several dozen foreign genes withoutimpairing its capacity to infect host cells and replicate.

The procedure for producing a vaccinia vector that carries a foreigngene from a pathogen is outlined as follows:

PRODUCTION OF VACCINIA

VECTOR VACCINE 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).

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 (BUdr), which kills TK cells.

ADVANTAGES OF VECTOR

VACCINE• The genetically engineered vaccinia expresses high levels

of the inserted gene product, which can then serve as a

potent immunogen in an inoculated host.

• Like the smallpox vaccine, genetically engineered vaccinia

vector vaccines can be administered simply by scratching

the skin, causing a localized infection in host cells.

• If the foreign gene product expressed by the vaccinia is a

viral envelope protein, it is inserted into the membrane of

the infected host cell, inducing development of cell-

mediated immunity as well as antibody-mediated

immunity.

ADVANTAGES OF VECTOR

VACCINE• Other attenuated-vector vaccines may prove to be safer than

the vaccinia vaccine. The canarypox virus has recently been

tried as a vector vaccine. Like its relative vaccinia, the

canarypox virus is la genes.

• Unlike vaccinia, the canarypox virus 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 rge and

easily engineered to carry multiple from the bacterium that

causes cholera.

ADVANTAGES OF VECTOR

VACCINE• Salmonella infects cells of the mucosal lining of the gut

and therefore will induce secretory IgA production.

• Effective immunity against a number of diseases, including

cholera and gonorrhea, depends on increased production of

secretory IgA at mucous membrane surfaces.

• Similar strategies using bacteria that are a normal part of

oral flora are in development.

• The strategy would involve introduction of genes encoding

antigens from pathogenic organisms into bacterial strains

that inhabit the oral cavity or respiratory tract.

• Eliciting immunity at the mucosal surface could provide

excellent protection at the portal used by the pathogen.

DISADVANTAGES OF VECTOR

VACCINE

Since the genes for the desired antigens must be located,

cloned, and expressed efficiently in the new vector, the

cost of production is high.

When engineered vaccinia virus is used to vaccinate, care

must be taken to spare immuno deficient individuals.

STILL A SIGNIFICANT NEED

FOR NEW VACCINES

For other diseases: TB

MALARIA

HIV

1. Increase safety of present

vaccine, lower cost, and

dissemination

2. Road to vaccine development is

long and laden with:

Side effects

Exacerbations of disease state

Acquisition of disease state