VACCINES

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VACCINES

• Introduction
• The Immune System
• Subunit Peptide Vaccines
• Attenuated Vaccines
• Vector Vaccines
• Bacterial Antigen delivery systems

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VACCINES

• Immunization a procedure designed to increase
  concentrations of antibodies and/or effector
  T-cells which are reactive against infection (or
  cancer).
• Immunization procedure called vaccination and the
  immunizing agent called vaccine (or serum in
  historical references)

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Discovery of Vaccination
VACCINES
Introduction

• Discovered in 1796 by
• Dr. Edward Jenner
• Tested empirical knowledge mild cattle disease
  cowpox protects against deadly human disease
  smallpox
• scratching liquid from cowpox sores into the
  boy's skin -gt full protection against smallpox

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VACCINES
The Immune system
Interactions between the two systems
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Innate versus Adaptive Immunity
VACCINES
The Immune system

• No time lag

• A lag period

• Not antigen specific

• Antigen specific

• Development of memory

• No memory

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VACCINES
The Immune system
Innate Immune System
First-line defense physical and chemical
barrier The first-line defense includes barriers
to infection, such as skin and mucus coating of
the gut and airways. Second-line defense
Phagocytic cells phagocytic cells (Myeloid
cells) (macrophages and neutrophil granulocytes)
can destroy (phagocytose) foreign substances.
Phagocytosis involves digestion of the bacterium
by using enzymes. Anti-microbial
proteins Anti-microbial proteins are activated if
a pathogen passes through the barrier offered by
skin. There are several classes of antimicrobial
proteins, such as acute phase proteins (for
example, proteins that enhance phagocytosis),
lysozyme, and the complement system. The
complement system is a very complex group of
serum proteins, which is activated in a cascade
fashion. Three different pathways are involved in
complement activation A cascade of protein
activity follows complement activation -gt
destruction of the pathogen and
inflammation Interferons are also anti-microbial
proteins. -gt secreted by virus-infected cells
-gt diffuse rapidly to neighboring cells -gt
inhibit the spread of the viral infection.
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VACCINES
The Immune system
Adaptive Immune System
The adaptive immune system, also called the
"acquired immune system", ensures that most
mammals that survive an initial infection by a
pathogen are generally immune to further illness
caused by that same pathogen. The adaptive
immune system is based on dedicated immune cells
termed leukocytes (white blood cells) that are
produced by stem cells in the bone marrow, and
mature in the thymus and/or lymph nodes. It is
in the lymph nodes where antigen is usually
presented to the immune system.
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Cells of the Immune System
VACCINES
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Development of the Immune System
VACCINES
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The Immune System
VACCINES
What Happens during an infection?

• Innate Immunity activated
• macrophages slip between cells extravasation to
  arrive
• cytokine chemicals attract other troops
  chemotaxis
• histamine chemicals dilate blood vessels for
  easier access to injury vasodilatation

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The Immune System
VACCINES
Macrophages (The big eaters)

• Phagocytic cells -
• able to ingest small foreign invaders
• neutrophils
• monocyte
• they release cytokines that enhance the immune
  response

• Mast cells /basophils
• release histamine that dilates blood vessels
• causes redness erythrema, swelling edema, and
  heat fever

• Call for help from the ADAPTIVE IMMUNE System
• -gt results in a coordinated successful
  defense !
• Major players . . . the B lymphocytes

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The Immune System
VACCINES
The Adaptive Immune system

• Humoral immune system -gt acts against bacteria
  and viruses using immunoglobulins (also known as
  antibodies) -gt produced by B cells.
• 2. Cellular immune system -gt destroys
  intracellular pathogens (such as virus-infected
  cells and mycobacteria causing tuberculosis)
  using T cells (also called "T lymphocytes" "T"
  means they develop in the thymus).
• There are two major types of T cells
• Cytotoxic T cells (TC cells) -gt recognize
  infected cells by using T cell receptors to probe
  cell surfaces (-gt Major Histocompatability
  Complex MHC) . If they recognize an infected
  cell, they release granzymes (proteases) to
  trigger that cell to become apoptotic ("commit
  suicide")
• Helper T cells (TH cells) -gt activate
  macrophages and also produce cytokines
  (interleukins) that induce the proliferation of B
  and T cells.
• -gt recognize infected cells of the immune
  system by using HelperT cell receptors to probe
  cell surfaces (-gt Major Histocompatability
  Complex MHC)

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The Immune System
VACCINES
The Adaptive Immune system
Activated B cells differentiate into . . .

• Antibody producing cells attack mode
• Memory cells remembers future protection

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Principle of Vaccination
VACCINES

• A vaccine renders the recipient resistant to
  infection.
• During vaccination a vaccine is injected or given
  orally.
• The host produces antibodies for a particular
  pathogen.
• Upon further exposure the pathogen is inactivated
  by the antibodies and disease state prevented.
• Generally to produce a vaccine the pathogen is
  grown in culture and inactivated or nonvirulent
  forms are used for vaccination.

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Immunization
VACCINES
Principle of Vaccination

• When performed before exposure to an infectious
  agent (or soon after exposure in certain cases),
  it is called immunoprophylaxis,
• intended to prevent the infection.
• When performed during an active infection (or
  existing cancer), it is called immunotherapy,
  intending to cure the infection (or cancer)

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Types of Immunity
VACCINES
Principle of Vaccination

• -gt Two mechanisms by which immunization can be
  achieved
• Passive immunization
• Protective Abs --gt non immune recipient
• No immunological memory
• Active immunization
• Induction of adaptive immune response, with
  protection and memory.

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Passive versus active immunization
VACCINES
Principle of Vaccination
-gt TYPE ACQUIRED THROUGH Passive Immunization
-gt Natural maternal serum/milk
-gt Artificial immune serum
-gt Type ACQURIED THROUGH Active Immunization
-gt Natural infection -gt
Artificial infection Attenuated
organisms (live) inactivated organisms
(dead) Cloned genes of microbiological
antigens Purified microbial
macromolecules Synthetic peptides
DNA Artificial refers to steps involving human
intervention
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Mechanism of Vaccination
VACCINES
Principle of Vaccination
Establish resistance to virus/pathological
organism by evoking an immune response 1. Give
host a foreign organism/protein in non-infectious
form -gt active immunization 2. Antibodies are
generated Ab binds to surface proteins of
organism -gt passive immunization
Other vaccination components

• Adjuvant chemicals in the vaccine solution that
  enhance the immune response
• Alum Ag in the vaccine clumps with the alum
  such that the Ag is released
• slowly, like a time-release capsule
• gives more time for memory cells to form

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Principle of Vaccination
VACCINES

• Traditional Vaccines
• Grow in animals (vaccinia in calves for smallpox
  rabbit brains for rabies)
• Simple bacterial culture (Cholera vibrio) then
  inactivation
• Grow in eggs (influenza, vaccinia) then
  inactivate

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Principle of Vaccination
VACCINES
Limitations To Traditional Vaccines
-gt cant grow all organisms in culture -gt safety
to lab personnel -gt Expense -gt insufficient
attentuation (living agent altered to become
harmless or less virulent) -gt reversion to
infectious state -gt need refrigeration -gt do
not work for all infectious agents -gt
infants/children receive them immature immunity
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Principle of Vaccination
VACCINES
New Generation of Vaccines

• Recombinant DNA technology is being used to
  produce a new generation of vaccines.
• Virulence genes are deleted and organism is still
  able to stimulate an immune response.
• Live nonpathogenic strains can carry antigenic
  determinants from pathogenic strains.
• If the agent cannot be maintained in culture,
  genes of proteins for antigenic determinants can
  be cloned and expressed in an alternative host
  e.g. E. coli.

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Principle of Vaccination
VACCINES
Recombinant Vaccines

• 1. Subunit Vaccines
• peptide vaccines
• Genetic immunization
• 2. Attenuated Vaccines
• 3. Vector Vaccines
• Bacterial Antigen Delivery Systems
• -gt ghosts -gt delivery systems (next
  semester)

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Principle of Vaccination
VACCINES
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Subunit/Peptide Vaccines
VACCINES

• Do NOT use entire virus or bacteria (pathogenic
  agent)
• Use components of pathogenic organism instead of
  whole organism
• Advantage no extraneous pathogenic particles
  i.e. DNA
• Disadvantage Is protein the same as in situ?
  -gt Cost?

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Subunit/Peptide Vaccines
VACCINES
Development of Subunit vaccines based on the
following observation

• It has been showed that the capsid or envelope
  proteins are enough to cause an immune response
• Herpes simplex virus envelop glycoprotein O.
• Foot and mouth disease virus capsid protein (VP1)
• Extracellular proteins produced by Mycobacterium
  tuberculosis.
• Subunit Vaccines
• Antibodies usually bind to surface proteins of
  the pathogen or proteins generated after the
  disruption of the pathogen.
• Binding of antibodies to these proteins will
  stimulate an immune response.
• Therefore proteins can be use to stimulate an
  immune response.

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Subunit/Peptide Vaccines
VACCINES
Example for a subunit vaccine -gt Tuberculosis

• Tuberculosis is caused by Mycobacterium
  tuberculosis.
• The bacterium forms lessions in the tissues and
  organs -gt causing cell death. Often the lung is
  affected.
• About 2 billion people are infected and there are
  3 million deaths/year.
• Currently tuberculosis is controlled by a vaccine
  called BCG (Bacillus Calmette-Guerin) which is a
  strain of M. bovis.
• M. bovis often responds to diagnostic test for M.
  tuberculosis.

• Six extracellular proteins of M. tuberculosis
  were purified.
• Separately and in combinations these proteins
  were used to immunized guinea pigs.
• These animals were then challenged with M.
  tuberculosis.
• After 9-10 weeks examination showed that some
  combinations of the purified proteins provided
  the same level of protection as the BCG vaccine.

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Subunit/Peptide Vaccines
VACCINES
Selection delivery of vaccine peptides
Use discrete portion (domain) of a surface
protein as Vaccine These domains are epitopes
(antigenic determinants) -gt are recognized by
antibodies
CARRIER PROTEINS Problem -gt Small Peptides are
often Digested -gt no strong immune
response -gt Carrier Proteins Make more Stable
stronger immune response Make fusion protein of
carrier vaccine peptide -gt inert carrier or
highly immunogenic carrier (hepatitis B core
protein)
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Attenuated Vaccines
VACCINES

• Attenuated vaccines often consists of a
  pathogenic strains in which the virulent genes
  are deleted or modified.
• Live vaccines are more effective than a killed or
  subunit (protein) vaccines.

Example -gt Vaccine against Cholera

• cholera is caused by infection withVibrio
  cholerae and is transmitted through contaminated
  water.
• V. cholerae produces a enterotoxin with an A1
  subunit and 5 B subunits -gt causes disease
• Presently the cholera vaccine consist of a
  phenol-killed V. cholerae and it only last 3-6
  months.
• A live vaccine would be more effective.

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Attenuated Vaccines
VACCINES
Example -gt Vaccine against Cholera
550 bases deleted of A1 peptide
The final result is V. cholerae with a 550 bp of
the A peptide deleted. -gt Currently being tested.
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Vector Vaccines
VACCINES
Virus as Antigen Gene Delivery System !!!

• Vaccinia good candidate for a live recombinant
  viral vaccine
• benign virus
• replicate in cytoplasm (viral replication genes)
• easy to store

-gt The vaccinia virus is generally nonpathogenic.

• The procedure involves
• The DNA sequence for the specific antigen is
  inserted into a plasmid beside the vaccinia virus
  promoter in the middle of a non-essential gene
  e.g. thymidine kinase.

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Vector Vaccines
VACCINES
The procedure involves

• The plasmid is used to transform thymdine kinase
  negative cells which were previously infected
  with the vaccinia virus.
• Recombination between the plasmid and vaccinia
  virus chromosomal DNA results in transfer of
  antigen gene from the recombinant plasmid to the
  vaccinia virus.
• Thus virus can now be used as a vaccine for the
  specific antigen.
• -gt Recombinant Virus

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Vector Vaccines
VACCINES

• A number of antigen genes have been inserted into
  the vaccinia virus genome e.g.
• Rabies virus G protein
• Hepatitis B surface antigen
• Influenza virus NP and HA proteins.
• A recombinant vaccinia virus vaccine for rabies
  is able to elicit neutralizing antibodies in
  foxes which is a major carrier of the disease.

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Vector Vaccines
VACCINES
Control of Viral Vaccines Post Innoculation

• Vaccinia virus is resistant to interferon -gt due
  to presence of K3L protein
• Use an interferon-sensitive strain of vaccinia
  virus -gt delete K3L gene to create mutant

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Bacterial Antigen Delivery Systems
VACCINES

• -gt Use live nonpathogenic bacterium which
  contains antigen (Salmonella or epitope from
  cholera)
• Insert antigen gene into flagellin gene
• Epitope is expressed on the flagellum surface
• -gt Flagellin-engineered bacteria is VACCINE
• Advantage - Oral Administration

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Vaccine Approval
VACCINES

• Done by CBER (Center for Biologics Evaluation and
  Research), an arm of the FDA
• Generally same clinical trial evaluation as other
  biologics and drugs
• Site to learn more about vaccines
• http//www.fda.gov/cber/vaccine/vacappr.htm