Vaccines
description
Transcript of Vaccines
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VaccinesVaccines
• Successes of the Past
• Possibilities for the Future
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VaccinesImmunity 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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VaccinesMinor 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 1970
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SmallpoxVaccination
• 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
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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
• Cannot wipe out wt virus
Polio Vaccine
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Rep
ort
ed c
ases
per
100
000
po
pu
lati
on
100
10
1
0.1
0.001
0.01
1950 1960 1970 1980 1990
Inactivated (Salk) vaccine
Oral vaccine
Cases per 100,000 population United States
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10000
1000
100
10
10
Rep
ort
ed c
ases
1950 1955 1960 1965 1970 1975
Killed (Salk) vaccine
Total casesSweden and Finland
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Rec
ipro
cal v
irus
antib
ody
titer
512
128
32
8
2
1
Serum IgGSerum IgG
Serum IgM Serum IgM
Nasal and duodenal IgA
Nasal IgA
Serum IgA
Serum IgA
Duodenal IgA
DaysVaccination Vaccination
48 4896 96
Killed (Salk) Vaccine
Live (Sabin) Vaccine
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Sabin Polio VaccineAttenuation 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 VaccineNew 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 RecommendationsTo 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
• 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
Advantages of Attenuated Vaccines I
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Vaccines
• 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
Advantages of Attenuated Vaccines II
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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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VaccinesAdvantages 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 MethodsSelection 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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PB2PB1PA
HANANP
MNS
PB2PB1PA
HANANP
MNS
PB2PB1PA
HANANP
MNS
Attenuated Donor Master Strain
New Virulent Antigenic Variant Strain
X
Attenuated Vaccine Strain: Coat of Virulent strain with Virulence Characteristics of Attenuated 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
cDNA
Express plasmid
S-antigen mRNA
protein
Hepatitis B vaccine
raised in yeast
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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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antibody
New methodsAnti-idiotype vaccine
epitope
Antibody with epitope binding site
Virus
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antibody
Anti-idiotype vaccine cont
Make antibody against antibody idiotype
Anti-idiotypeantibody
Anti-idiotype antibody mimics the epitope
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Anti-anti-idiotypeantibody
Anti-idiotype antibody cont 2
Use anti-idiotype antibody as injectable vaccine
Antibody to anti-idiotype antibody
Binds and neutralizes virus
Anti-idiotypeantibody
Anti-anti-idiotypeantibody
Anti-anti-idiotypeantibody
Use as vaccine
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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 MethodsNew 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 MethodsSecond Generation Jennerian Vaccines
Rotavirus
11 segments of double strand RNA
Two encode:
• VP4 (hemagglutinin)
• VP7 (glycoprotein)
Co-infect tissue culture cells reassortment
•10 segments from monkey rotavirus
• 1 segment outer capsid protein of each of four major rotavirus strains
Efficacy >80%
Elicit neutralizing antibodies
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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
plasmidMuscle cell
Gene for antigen
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 VaccineQuestions:
• 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 VaccineWhat should vaccine elicit?
Humoral response
neutralizing antibody
kill free virus
Cellular response
kill infected cells
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 VaccineChimp 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 VaccineSince 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 VaccineLive 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 VaccineInactivated:
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 VaccineSummary 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