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
• Mummies
• China/India
Crusaders
• W Europe: fatality rate 25%
• History changed:
Cortes
Louis XIV
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Smallpox
• Variolation
•1% v. 25% mortality
•Life-long immunity: No drift or
shift (proof reading)
• UK: 1700’s
• China 1950
• Pakistan/Afghanistan/Ethiopia
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1970
Smallpox
Vaccination
• Jenner 1796 : Cowpox/Swinepox
• 1800’s Compulsory childhood
vaccination
• 1930’s Last natural UK case
• 1940’s last natural US case
• 1958 WHO program
• October 1977: Last case
(Somalia)
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Smallpox
• No animal reservoir
• Lifelong immunity
• Subclinical cases rare
• Infectivity does
not precede overt symptoms
• One Variola serotype
• Effective vaccine
• Major commitment by governments
Polio Vaccine
Small RNA virus
Some drift…but not too far as non-viable
US: Sabin attenuated vaccine ~ 10 cases vaccine-associated disease
per year
• 50% vaccinees
feces
• 50% contacts
• Vaccine-associated cases: revertants
• 1 in 4,000,000 vaccine infections
paralytic polio
• 1 in 100 of wt infections
Scandinavia: Salk dead vaccine
• No gut immunity
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• Cannot wipe out wt virus
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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 VaccineAssociated 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 crosswww.freelivedoctor.com
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
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patients)
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)
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• 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
• Recombinant DNA
•Single gene (subunit)
S-antigen mRNA
Hepatitis B
vaccine
cDNA
raised in yeast
Express plasmid
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S-antigen mRNA
protein
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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
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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
Antibody
with epitope
binding site
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Anti-idiotype vaccine cont
Antiidiotype
antibody
antibody
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
Anti-idiotype
antibody
Use as vaccine
Binds and
neutralizes virus
Anti-anti-idiotype
antibody
Anti-anti-idiotype
antibody
Antibody to anti-idiotype
antibody
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Anti-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
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Due to differences in circulating viral serotypes
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
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New Methods
Second Generation Jennerian Vaccines
Rotavirus
11 segments of double strand RNA
Two encode:
• VP4 (hemagglutinin)
• VP7 (glycoprotein)
Co-infect tissue culture cells
Elicit neutralizing
antibodies
reassortment
•10 segments from monkey rotavirus
• 1 segment outer capsid protein of each of four major rotavirus strains
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Efficacy >80%
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Vaccines
• 1796 Jenner: wild type animal-adapted
virus
• 1800’s Pasteur: Attenuated virus
• 1996 DNA vaccines
The third vaccine revolution
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DNA Vaccines
Gene for
antigen
Muscle cell
plasmid
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Muscle cell expresses
protein - antibody made
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CTL response
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) 41
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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
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non-responsiveness to www.freelivedoctor.com
that antigen)
DNA Vaccines
DNA vaccines produce a situation that reproduces a virallyinfected 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
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with different
hemagglutinins
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
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How does
HIV kill cells anyway?
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Towards an anti-HIV Vaccine
What should vaccine elicit?
Humoral response
Cellular response
neutralizing antibody
kill infected cells
kill free virus
problem of cell-cell
infection
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Towards an anti-HIV Vaccine
Early faith in neutralizing antibodies backed by chimpanzee
experiments
HIV
high levels of neutralizing antibody
Can resist subsequent challenge by virus injected I.V. !!!!
But not via rectum or vagina
But chimps do not get AIDS
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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
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HIV-exposed but not infected people shows signs of a cell-mediated response
Towards an anti-HIV Vaccine
Since 1986: > 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 (antiMHC)
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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
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•Blood brain barrier
•Oncogenicity