Vaccines

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Vaccines

• Successes of the Past
• Possibilities for the Future

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Vaccines

• Immunity to viral infections usually depends on
  the development of an immune response to
• Antigens on the virus surface
• Antigens on the virus-infected cell
• In most cases response to internal proteins has
  little effect on humoral immunity to infection
• Humoral antibodies can be important
  diagnostically (HIV)

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Vaccines

• Minor role for internal proteins can be seen in
  influenza pandemics
• New flu viral strain contains a novel
  glycoprotein
• Pandemic virus contains internal proteins to
  which the population has already been exposed
• Nevertheless the CTL response to internal
  proteins is important

Surface glycoprotein protective immunogen which
must be identified for a logical vaccine
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Vaccines

• Some viruses have more than one surface protein
• Influenza (Orthomyxovirus)
• Hemagglutinin - attaches virus to cell receptor
• Neuraminidase - involved in release of virus
  from cell
• Hemagglutinin is major target stimulates
  neutralizing antibody

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Vaccines

• Neutralization may result from
• Binding of antibody to site on virus surface -
  block interaction with receptor
• Aggregation of virus by polyvalent antibody
• Complement-mediated lysis

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Vaccines
Addition points to note Site in body at which
virus replicates Three major sites for viral
replication
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Three major sites for viral replication

• Mucosal surfaces of respiratory tract and GI
  tract. Rhino myxo corona parainfluenza
  respiratory syncytial rota
• Infection at mucosal surfaces followed by spread
  systemically via blood and/or neurones to target
  organs picorna measles mumps HSV varicella
  hepatitis A and B
• Direct infection of blood stream via needle or
  bites and then spread to target organs hepatitis
  B alpha flavi bunya rhabdo
• Local immunity via IgA very important in 1 and 2.

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There is little point in having a good
neutralizing humoral antibody in the circulation
when the virus replicates, for example, in the
upper respiratory tract. Clearly, here secreted
antibodies are important. Although in the case of
influenza serum antibodies may be important
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Vaccines - Problems

• Different viruses may cause similar
  disease--e.g. common cold
• Antigenic drift and shift -- especially true of
  RNA viruses and those with segmented genomes
• Shift reassortment of segmented genomes (flu
  A but not rota or flu B)
• Drift rapid mutation - retroviruses
• Large animal reservoirs - Reinfection may occur

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Vaccines - Problems

• Integration of viral DNA. Vaccines will not work
  on latent virions unless they express antigens on
  cell surface. In addition, if vaccine virus
  integrates it may cause problems
• Transmission from cell to cell via syncytia
• Recombination of the virulent strain or of the
  vaccine virus

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Smallpox
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Smallpox
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Smallpox
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Smallpox
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Polio Vaccine
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100
Inactivated (Salk) vaccine
Cases per 100,000 population United States
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Oral vaccine
1
Reported cases per 100000 population
0.1
0.01
0.001
1950
1960
1990
1970
1980
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Total casesSweden and Finland
10000
Killed (Salk) vaccine
1000
Reported cases
100
10
1
0
1950
1955
1960
1965
1970
1975
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Sabin Polio Vaccine

• Attenuation by passage in foreign host
• More suited to foreign environment and less
  suited to original host
• Grows less well in original host
• Polio
• Monkey kidney cells
• Grows in epithelial cells
• Does not grow in nerves
• No paralysis
• Local gut immunity (IgA)
• Pasteur rabies vaccine also attenuated

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Salk Polio Vaccine

• Formaldehyde-fixed
• No reversion

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Polio Vaccine

• Why use the Sabin vaccine?
• Local immunity Vaccine virus just like natural
  infection
• Stopping replication in G.I. Tract stops viral
  replication TOTALLY
• Dead Salk vaccine virus has no effect on gut
  replication
• No problem with selective inactivation
• Greater cross reaction as vaccine virus also has
  antigenic drift
• Life-long immunity

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Polio Vaccine

• New CDC Guidelines
• Last US natural (non-vaccine associated) case was
  15 years ago
• 2 does injectable (Salk) vaccine
• 2 doses oral
• Vaccine cases 1 in 3 million does
• New strategy will prevent about 5 of the 10
  vaccine-associated cases (the five found in
  vaccinees)
• Cost 20 million
• Savings from eradication 230 million

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New Recommendations
To eliminate the risk for Vaccine-Associated
Paralytic Poliomyelitis, the ACIP recommended an
all-inactivated poliovirus vaccine (IPV) schedule
for routine childhood polio vaccination in the
United States. As of January 1, 2000, all
children should receive four doses of IPV at ages
2 months, 4 months, 6-18 months, and 4-6 years.
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Vaccines
Advantages of Attenuated Vaccines I

• Activates all phases of immune system. Can get
  humoral IgG and local IgA
• Raises immune response to all protective
  antigens. Inactivation may alter antigenicity.
• More durable immunity more cross-reactive

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Vaccines
Advantages of Attenuated Vaccines II

• Low cost
• Quick immunity in majority of vaccinees
• In case of polio and adeno vaccines, easy
  administration
• Easy transport in field
• Can lead to elimination of wild type virus from
  the community

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Vaccines

• Disadvantages of Live Attenuated Vaccine
• Mutation reversion to virulence (often
  frequent)
• Spread to contacts of vaccinee who have not
  consented to be vaccinated (could also be an
  advantage in communities where vaccination is not
  100)
• Spread vaccine not standardized--may be
  back-mutated
• Poor "take" in tropics
• Problem in immunodeficiency disease (may spread
  to these patients)

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Vaccines

• Advantages of inactivated vaccines
• Gives sufficient humoral immunity if boosters
  given
• No mutation or reversion
• Can be used with immuno-deficient patients
• Sometimes better in tropics
• Disadvantages of inactivated vaccines
• Many vaccinees do not raise immunity
• Boosters needed
• No local immunity (important)
• Higher cost
• Shortage of monkeys (polio)
• Failure in inactivation and immunization with
  virulent virus

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New Methods

• Selection of attenuated virus strain
• Varicella
• Hepatitis A
• Use monoclonal antibodies to select for virus
  with altered surface receptor
• Rabies
• Reo
• Use mutagen and grow virus at 32 degrees. Selects
  for temperature-sensitive virus. Grows in upper
  respiratory tract but not lower
• flu (new vaccine)
• respiratory syncytial virus

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New Methods
Recent flu vaccine from Aviron Passage
progressively at cold temperatures TS mutant in
internal proteins Can be re-assorted to so that
coat is the strain that is this years flu strain
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New Methods

• Deletion mutants
• Suppression unlikely (but caution in HIV)
• Viable but growth restrictions
• Problems
• Oncogenicity in some cases (adeno, retro)

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New Methods
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Single gene (subunit) - problems

• Surface glycoprotein poorly soluble - deletion?
• Poorly immunogenic
• Post-translational modifications
• Poor CTL response

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Single gene (subunit) in expression vector

• Vaccinate with live virus
• Canary Pox
• Infects human cells but does not replicate
• Better presentation
• CTL response
• Vaccinia
• Attenuated Polio
• Being developed for anti-HIV vaccine

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New Methods

• Chemically synthesized peptide
• malaria
• poorly immunogenic

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New methods
Anti-idiotype vaccine
Virus
epitope
Antibody with epitope binding site
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Anti-idiotype vaccine cont
Make antibody against antibody idiotype
Anti-idiotype antibody mimics the epitope
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Anti-idiotype antibody cont 2
Use anti-idiotype antibody as injectable vaccine
Use as vaccine
Binds and neutralizes virus
Antibody to anti-idiotype antibody
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New Methods

• New Jennerian Vaccines
• Live vaccines derived from animal strains of
  similar viruses
• Naturally attenuated for humans
• Rotavirus Monkey Rota
• 80 effective in some human populations
• Ineffective in others
• Due to differences in circulating viral serotypes

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New Methods

• New Jennerian Vaccines
• Bovine parainfluenza Type 3
• Bovine virus is
• Infectious to humans
• Immunogenic (61 of children get good response)
• Poorly transmissable
• Phenotypicaly stable

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New Methods
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Vaccines

• 1796 Jenner wild type animal-adapted virus
• 1800s Pasteur Attenuated virus
• 1996 DNA vaccines
• The third vaccine revolution

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DNA Vaccines
Gene for antigen
Muscle cell
plasmid
Muscle cell expresses protein - antibody made CTL
response
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DNA Vaccines

• Plasmids are easily manufactured in large
  amounts
• DNA is very stable
• DNA resists temperature extremes so storage and
  transport are straight forward
• DNA sequence can be changed easily in the
  laboratory. This means that we can respond to
  changes in the infectious agent
• By using the plasmid in the vaccinee to code for
  antigen synthesis, the antigenic protein(s) that
  are produced are processed (post-translationally
  modified) in the same way as the proteins of the
  virus against which protection is to be produced.
  This makes a far better antigen than purifying
  that protein and using it as an immunogen.

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DNA Vaccines

• Mixtures of plasmids could be used that encode
  many protein fragments from a virus/viruses so
  that a broad spectrum vaccine could be produced
• The plasmid does not replicate and encodes only
  the proteins of interest
• No protein component so there will be no immune
  response against the vector itself
• Because of the way the antigen is presented,
  there is a CTL response that may be directed
  against any antigen in the pathogen. A CTL
  response also offers protection against diseases
  caused by certain obligate intracellular
  pathogens (e.g. Mycobacterium tuberculosis)

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DNA Vaccines

• Possible Problems
• Potential integration of plasmid into host
  genome leading to insertional mutagenesis
• Induction of autoimmune responses (e.g.
  pathogenic anti-DNA antibodies)
• Induction of immunologic tolerance (e.g. where
  the expression of the antigen in the host may
  lead to specific non-responsiveness to that
  antigen)

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DNA Vaccines

• DNA vaccines produce a situation that reproduces
  a virally-infected cell
• Gives
• Broad based immune response
• Long lasting CTL response
• Advantage of new DNA vaccine for flu
• CTL response can be against internal protein
• In mice a nucleoprotein DNA vaccine is effective
  against a range of viruses with different
  hemagglutinins

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Towards an anti-HIV Vaccine

• Questions
• For a vaccine what are the measures of
  protection?
• Can we overcome polymorphism?
• What are the key antigens?
• Attenuated or killed or neither?
• Mucosal immunity critical?
• Prevent infection or prevent disease?
• Animal models
• How does HIV kill cells anyway?

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Towards an anti-HIV Vaccine
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Towards an anti-HIV Vaccine
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Towards an anti-HIV Vaccine

• Chimp studies designed for success
• Animals challenged with small doses of virus at
  moment that antibody levels high (virus --not
  infected cells!)
• Challenge virus same strain as that used to
  induce antibody
• No vaccine made from one virus strain has
  protected chimps from another virus strain
• Protection in man may not result from
  neutralizing antibodies at all
• Ability to raise neutralizing antibodies in
  monkeys does not correlate with protection
• Cell-mediated immunity is the key
• This is also key in humans
• HIV-exposed but not infected people shows signs
  of a cell-mediated response

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Towards an anti-HIV Vaccine
Since 1986 gt 15 SUBUNIT VACCINES Based on
gp160/gp120 All safe None effective Low levels
of strain-specific antibodies that quickly
disappear Only ephemeral effects of
cell-mediated immunity All done with gp160/gp120
of syncytium-inducing virus None tested on large
groups of high risk people
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Towards an anti-HIV Vaccine

• A Classical Approach?
• December 1992 Live attenuated SIV vaccine
  protected all monkeys for 2 years against massive
  dose of virus
• All controls died
• cell mediated immunity was key

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Towards an anti-HIV Vaccine
Humans NEF deletion mutant
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Towards an anti-HIV Vaccine

• Live attenuated
• Pro
• SIV with NEF deletion protects after ONE
  immunization
• Long lived cell-mediated and humoral immunity
• Possible herd immunity
• Con
• Safety in immunodeficient people
• LTR
• Reversion
• Need multiple strains polymorphism

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Towards an anti-HIV Vaccine

• Inactivated
• Pro Simple
• Mimics natural infection
• Protects against systemic and rectal challenge
• No reversion
• Con
• Polymorphism
• LTR
• Inactivation failure

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Towards an anti-HIV Vaccine

• Subunit vaccine
• Pro
• Safety
• Con
• Ephemeral humoral response
• Little cell mediated response

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Towards an anti-HIV Vaccine

• Subunit in vector
• Pro
• Potent cell-mediated immunity

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Towards an anti-HIV Vaccine

• Problems for all vaccines
• Enhancing antibody
• Vaccine may be immunosuppressive (anti-MHC)

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Towards an anti-HIV Vaccine

• Summary of problems
• Virus can hide in cells
• Cell-cell transmission
• Ethical problems
• Lack of animal models
• Immuno-silent sugars
• Polymorphism/hypervariability DRIFT
• Activation of same cells that virus infects
• Useless if T4 cells are depleted
• Blood brain barrier
• Oncogenicity