pfwatsonshefacuk Vaccines Theory and Practice Learning goals History of Vaccination Importance of Vaccination in Healthcare Strategy Theory of vaccination Nature of pathogen and vaccine choice ID: 774972
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Slide1
Phase 1B2015Phil Watsonp.f.watson@shef.ac.uk
Vaccines Theory and Practice
Slide2Learning goals
–
History of Vaccination
Importance of Vaccination
in Healthcare Strategy
Theory of vaccination
Nature of pathogen and vaccine choice
Passive and Active Immunisation
Adjuvants
Different forms of vaccine agent
Live-attenuated
Inactivated
Subunit
Peptides
DNA vaccines
Recombinant vectors
Qualities of an Ideal Vaccine
Slide3Vaccines Theory and Practice
Vaccination is one of the most effective weapons in the medicinal armouryWhy?Because it is successful and cost effective (compared to pharmaceuticals)Since the discovery and development of vaccination a number of formerly major afflictions have been controlled or the frequency hugely reduced
Smallpox
Diptheria
Mumps
Tetanus
Pertussis (whooping cough)
Poliomyelitis
Last natural case – 1977 - It is now eradicated
Slide4Vaccines work !
Pre-VaccineAnnual MorbidityPercent DecreaseCurrent LevelsDiptheria21,000100%0Mumps162,00099%982Rubella50,00099%4Smallpox29,000100%0Polio16,000100%0
(typical US population data)
Slide5Poliomyelitis
Slide6Poliomyelitis
Slide7Today there is a pressing need for new vaccines
HIV-1 – approximately 16,000 new infections per day
Substantial economic impact of HIV/AIDS
Now a pandemic
Destruction of economies and human capital
No really effective current
vaccine
Treatment – not cure
Anti-
retrovirals
- AZT
Treatments consume the majority of household budget
High numbers of orphans
Breakdown in family structures
S.A. Reported that approximately 20% teachers are living with HIV
Slide8Ebola
Highly contagiousNew strains can emerge at any timeDeath rates from 20-90%Modern transport hubs mean that we arenever more than 5 hours from an outbreakin a large population centerBioterrorism
Slide9Origins of Vaccination
VariolationObserved in ancient times that infection with a particular disease renders the individual resistant to infection with the same diseaseAncient Greece Thucydides 429 BCChina 900ADSmallpox – Was a worldwide scourgeFatality – 20%Survivors scarred
Infection with a mild case protected the individual from subsequent serious infection
Scratches on the arm inoculated with pus from a pustule -
variolation
Slide10Origins of Vaccination
VariolationEdward Jenner –Based on the observation that milkmaids (who often suffered from cowpox) were resistant to infection by smallpoxInfected people deliberately with pus from cowpox lesionThe result was a resistance to smallpoxTested on a boy James Phipps 8 yo
1749-1823
Edward Jenner
Slide11Development of Immunological Theory
The
concept of microorganisms as source of disease
Infection
Robert Koch (1843-1910) – the association of particular diseases with a specific variety of microorganism
Slide12Louis Pasteur (1822-1895)The idea of generating weakened pathogens to artificially infect subjects – concepts still used todayMost famously developed a vaccine for rabies
Development of Immunological Theory
Slide13Immunological Theory
Infection with an organism lead to the generation of protective substances in the serum
This protection persisted "memory"
Could be transferred to other subjects
By late 19th century - protective substance identified as circulating globulin
Could neutralise and kill bacteria and other pathogens
Antibodies
Slide14Modern Concept of Immunisation and Vaccines
Manipulating the immune system to generate a persistent protective response against pathogens Immunisation with a vaccine that can trigger an immune response and safely mimic natural infectionMobilise the appropriate arms of the immune system and generate immunological memory
(Active immunisation
)
Slide15Passive vs Active Immunization
Passive Immunisation
Transfer of preformed antibodies to the circulation
Can be natural or artificial
Natural Passive Immunity
This occurs naturally by the transfer of maternal antibodies across the placenta to the developing foetus
Provides protection against:
Diptheria
Tetanus
Streptococcus
Rubella
Mumps
Poliovirus
Slide16Passive Immunisation
Indications for use of artificial passive immunity
Individuals with
agammaglobulinaemias
– B cell defects – inborn or acquired
Treated with pooled normal human IgG
Exposure to a disease that could cause complications –
eg
. immune compromised patient exposed to measles or other pathogen
Or - when there is no time for active immunization to give protection
ie
. a pathogen with a short incubation time
Acute danger of infection
Slide17Anti-toxins and Anti-veninsPrior to the introduction of vaccines and antibiotics, passive immunization was the major treatment for a range of infectious diseasesUsually horse serum – despite the risks These antisera were frequently used to neutralise toxinsWith some pathogens the main hazard is not the primary infection itself Which can be eliminated by the immune systemRather it is the effects of very potent toxins released by the bacteriaTwo common examples are Tetanus Clostridium tetaniandBotulinum Clostridium botulinum
Passive Immunisation
Slide18Natural immunity to these toxins is difficult to achieveGiven the lethal dose of botulinum toxin is approximately 1.5 ng/kg intravenousExposure to sufficient toxin to stimulate the immune system would be lethalDeactivated toxin derivatives (toxiods) can be used as vaccines to produce immunity and this will be covered in the section dealing with Active ImmunisationMost commonly used is tetanus toxoid
Passive Immunisation
Slide19Passive Immunisation
A painting by Sir Charles Bell dating from the Napoleonic War period. It shows a patient with tetanus resulting from a gunshot wound.
Slide20Uses of Passive Immunization
Routinely used for people infected or exposed to BotulismTetanusDiptheriaHepatitisMeaslesRabies
Also – exposure to venom Snake bite InsectsJellyfish
Anti-toxins
Used
prophylactically
to reduced the chance of establishing infection after exposure
Anti-
venins
SUMMARY
Slide21Drawbacks of Passive Immunisation
Does not activate immunological memory
No long term protection
Possibility of reaction to anti-sera
Slide22Challenging the subjects immune system to induce a state of immunityThe production of high affinity protective antibodies against the immunogenThe induction of immunological memory
Also known as “vaccination” – derived from the Greek word for cow and based on the historical work of Jenner on smallpox
Not to be confused with “inoculation” - which strictly speaking refers to the introduction of viable microorganisms into the subject.
Active Immunisation
Slide23Aims of a “perfect” vaccineTo achieve long term protection (ideally from a small number of immunisations) To stimulate both B and T cellsTo induce memory B and T cellsTo stimulate protective high affinity IgG production (possibly IgA too!)The aim of vaccination depends on the nature of the targeted pathogen and the natural history of the diseaseInduction of Immune ResponseMemorySelection of Appropriate Immune ResponseThe importance of the memory B cell response depends on the nature of the pathogen!
Active Immunisation
Slide24Typical Primary and Secondary Antibody Response to Antigen
Initial response –
Relies on “innate” immune systemIgM predominatesLow affinityEssentially germline repertoire
Secondary response Rapid and LargeHigh Affinity IgGSomatic HypermutationT cell helpDoes not rely on innate immune system
The goal of immunisation is to achieve this initial exposure –
without the risks of actual infection!!
Slide25Slide26Typical Primary and Secondary Antibody Response to Antigen
Second exposure can be years later
During this phase memory T and B cells are generated and circulate for years
Second response is
prompt and powerful
High levels of IgG
High affinity IgG
Somatic hypermutation
T cell help!
Slide27Immunological Memory and Pathogens
Influenza – has a rapid onset – Infection can become established before immunological memory can be activated Infection of tissues is blocked by antibodyTherefore it is important to maintain high levels of neutralising antibody by repeated (annual) immunizationCirculating antibodies need to be regularly boostedAlso - annual "escape" variants require the generation of new vaccines
Contrast this with
Polio
– where it takes 3 days to establish infection in the nervous system
This lag provides an opportunity for for memory to be activated and the production of neutralising antibodies
Slide28Aim To achieve long term protection (ideally from a small number of inoculations) To induce memory B and T cellsTo stimulate protective IgG production (or IgA)Some pathogens infect primarily through mucous membranes!
Active Immunisation
Slide29Active Immunisation
The first stage of any immunisation is to engage the Innate Immune System
Elicit “danger” signals that activate the immune systemtriggers such as molecular fingerprints of infection – PAMPs (pathogen-associated molecular patterns) etc..Engage TLR receptors
Activate specialist antigen presenting cells – eg. follicular dendritic cells
Engage the Adaptive Immune System
Generate memory T and B cells
Activate T cell help
Slide30Whole OrganismLive attenuated pathogenKilled, inactivated pathogenSubunitToxoidsAntigenic ExtractsRecombinant proteinsPeptidesDNA VaccinesEngineered Virus
Active Immunisation
Pros and Cons !
Different Vaccine Types
Slide31Examples of Common Vaccines
Whole Organism
Bacterial CellsAnthrax InactivatedCholera InactivatedPertussis InactivatedTuberculosis Live Attenuated (BCG)Typhoid Live Attenuated
Viral Particles
Hepatitis A Inactivated
Influenza Inactivated
Measles Live Attenuated
Mumps Live Attenuated
Polio Sabin Live Attenuated
Polio Salk Inactivated
Slide32Live Attenuated VaccinesMethods of Attenuating Pathogens
Tuberculosis – BCGBacillus Calmette-Guerin (BCG)Mycobacterium bovis – grown for 13 years on medium containing bileBecame adapted and had reduced virulence
Polio Sabin
Polio virus grown on monkey kidney epithelial cells
Prolonged culture leads to adaptation and a strain that has reduced virulence in humans
Other methods can include chemical treatments
Slide33Live Attenuated VaccinesAdvantages
Attenuated pathogen sets up a transient infectionActivation of full natural immune responseProlonged contact with the immune systemThe stimulation of a memory response in the T and B cell compartmentsResulting in prolonged and comprehensive protection
Often only a single immunization is required – advantages in the Third World
Slide34Live AttenuatedDisadvantages
Immunocompromised patients (or other rare individuals) may become infected as a result of immunizationComplications !For example – live measles vaccine1 per 1,000,000 - post-infectious encephalomyelitis(0.5 – 1.0 per 1000 with natural disease)
Occasionally the attenuated organism can revert to a virulent form
For example –
Polio Sabin
Approximately 1 case in 2,400,000 doses
In areas with poor sanitation this can lead to a serious outbreak – so Polio Salk is the preferred vaccine in the Third World
Slide35Live AttenuatedDisadvantages
Refrigeration and Transport!
Typically live organisms need to be refrigerated for stable storage
This can be an issue in remote areas of the world
This is an important issue for any vaccine
Can it be used without extensive technology?
Is it stable?
Slide36Correct Vaccine Preparation is Critical with Live Attenuated Organisms
Salk Polio vaccine is prepared by inactivation of viral particles by formaldehyde treatment1950s - A series of outbreaks were caused by improper chemical treatment
It is important that the treatment does not reduce the immunogenicity of the pathogen – to ensure a correct response
Heat treatment is not preferred as it can alter conformation of target antigens
Modern approaches can exploit recombinant DNA technology to remove genes that control virulence but leave intact the genes for infection
Slide37Whole Inactivated Pathogen
No risk of infectionStorage less criticalA wide range of different antigenic components are present so a good immune response is possible
Advantages
Slide38Whole Inactivated Pathogen
Disadvantages
Tend to just activate
humoral
responses
Lack of T cell involvement
Without transient infection the immune response can be quite weak
Repeated booster vaccinations required
Patient compliance can be an issue
Slide39Examples of Inactivated Vaccines
BacterialAnthraxCholeraPertussisPlagueVirusesHepatitis AInfluenzaPolio (Salk)RabiesRubella
Not as effective as live attenuated in producing cell-mediated immunity
ie
. they are less effective at activating T cell immunity
Typically, repeated doses are necessary to provide protection
Slide40Subunit Vaccines
Theoretically safer than handling live or inactivated pathogensNo risk of infectionPurify molecular components as immunogenic agent
Currently 3 major types of such vaccines are in use –
Inactivated
exotoxins
(
toxoids
)
Capsular polysaccharides
Recombinant microbial antigens
Peptide vaccines
Slide41Bacterial Exotoxins
A number of important pathogens produce the symptoms of disease as a result of exotoxinsFor example diptheria and tetanus
Diptheria toxin inactivates mammalian elongation factor EF2So it is an inhibitor of translationLethal dose – approx 100 ng/kg - Necrosis of the heart and liver
Tetanus toxin – neurotoxinUncontrolled contraction of voluntary muscles
Toxoid
– heat treated or chemically modified to eliminate toxicity
Slide42Capsular PSs are highly polar, hydrophilic cell surface polymers consisting of oligosaccharide repeating units. These molecules are the main antigens involved in the protective immunity to encapsulated bacteria. Capsular PSs interfere with bacterial interactions with phagocytes by blocking opsonization. Opsonization is the coating of the organisms by specific antibodies and complement, which enables host phagocytes to ingest and destroy invading bacteria.
Capsular Polysaccharides
Slide43Subunit Vaccines
Purified Proteins
Cultivation of pathogen and subsequent processing to purify single component
(
toxoids
are an example)
Recombinant Proteins (since
1970s
)
Cloning and expression of single gene in recombinant host
Examples include subunit vaccine comprised of Hepatitis B surface proteins (expressed in yeast)
Gardasil
– a recombinant vaccine for human
papilloma
virus
Virus coat proteins expressed in yeast
Spontaneously assemble in virus like particles
Slide44DifficultiesIt is now clear that knowledge of HLA presentation of peptides is essentialPeptides can be stimulatory OR suppressive !Most B cell epitopes are conformational
Synthetic Peptides as VaccinesDespite initial promise – the field has advanced slowlyAim – to produce a peptide that includes immunodominant B cell epitopes and can stimulate memory T cell development
B cell
T cell
APC
Slide45Subunit Vaccines
AdvantagesSafetyOnly portions of pathogen are usedNo risk of infectionMay be easier to store and preserve
Disadvantages
Immune response is less powerful than to live attenuated vaccines
Repeat vaccinations needed and
adjuvants
Subunits have to chosen that elicit a response in the widest range of subjects (HLA differences?)
Slide46Adjuvants
Essentially any substance added to vaccine to stimulate the immune system
Can include:
Whole killed organisms
Toxoids
Proteins (as in conjugate vaccines)
Chemicals
Aluminium salts
Paraffin oil
Slide47Adjuvants
The mechanisms can vary:
Aluminium salts may extend the half-life of immunogen in the site of injection (depot effect)
Chemicals can cause irritation and inflammation
Toxoids
and killed organisms trigger the immune system and send out “danger signals”
Slide48Aim – to transiently express genes from pathogens in host cells. Generates immune response similar to natural infection Leading to T and B cell memory responses
Expression vector
Transfected
into muscle cells
Expression from
episomal
form or DNA may integrate into chromosome
Other cell types may also take-up DNA – such as antigen presenting cells (follicular dendritic cells)
DNA Vaccines
Slide49DNA Vaccines
As proof of the principle of DNA vaccination, immune responses in animals have been obtained using genes from a variety of infectious agents, including Influenza virus,Hepatitis B virusHIV,Rabies virus
In some cases protective responses have resulted
Still too little is known about how DNA immunisation leads to immune response
What
adjuvants
could be useful?
Possible side effects?
Slide50Advantages:DNA vaccines do not require complex storage and transportationDelivery can be simple and adaptable to widespread vaccination programs – “DNA gun”
DNA Vaccines
Disadvantages:
As with “killed” vaccines, and subunit vaccines, there is
no transient infection
DNA
vaccination is likely to produce a mild immune response and require subsequent boosting
Slide51Recombinant Vector VaccinesAim – to imitate the effects of transient infection with pathogen but using a non-pathogenic organismGenes for major pathogen antigens are introduced into a non-pathogenic or attenuated microorganism and introduced into the hostViral or BacterialVaccinia virusCanarypoxAttenuated poliovirusAttenuated strains of SalmonellaBCG strain of Mycobacterium bovis
Canarypox
ALVAC
-HIV
Slide52Recombinant Viral
Vaccines
Adenovirus
Strains that can infect humans
Vesicular Stomatitis Virus
relative of rabies virus
Advantages
Create ideal stimulus to immune system
Produce immunological memory
Flexible - different components can be engineered in
Safe - relative to live attenuated pathogen
Potential drawbacks:
Require refrigeration for transport
Can cause illness in compromised individuals
Immune response to virus in subjects can negate effectiveness
Slide53The ideal vaccine
Safe!
this could mean attenuated live if suitable or subunit if the pathogen is lethal for example
Should
induce a suitable immune response
for example - mucosal if pathogen uses this route
high antibody titer if antibody most useful protective agent
Generate T and B cell memory
Stable and easy
to transport
for use in remote areas
Should not require
repeated boosting
patient compliance