Vaccines Flashcards
developing a vaccine is not
simple, cheap or quick
how long does it take create a vaccine and get it on the market
10/20 yr cycle
how much does a vaccine cost to develop
1 billion pounds
how many lives a year do vaccines save
2.5 million
how could an additional 2 million lives/yr be saved
by extending vaccine programs to all countries
infectious diseases are
one of the largest causes of mortality worldwide- save morbidity and mortality
there have been few events which have
made us think about cost-benefit analysis
why do some distrust vaccine e.g.
Do vaccines cause autism?
o Study reported by Andrew Wakefield in the Lancet 1998
o Severe trust of MMR
o People stopped immunizing their children- increase in infectious disease
why wasn’t Wakefield’s research valid
No controls included, autism would occur in 25 non-immunised children/month based on probability. No experimental evidence for the hypothesis that MMR peptides wee translocated in the brain.
why was wakefield so harmful
due to his research decreasing trust in vaccines and therefor limiting their uptake- reducing herd immunity
risk-benefit analysis
Shows how the morbidities related to the actual disease are ten times worse than the possible side effects of the reaction to the vaccine
compared to the actual disease itself
the possible and rare side-effects of vaccines are minute
main types of vaccines
live vaccines, killed vaccines, subunit vaccine sand DNA vaccines
Live vaccines e.g.
yellow fever
- in practice can cause disease in immunocompromised patients
what is preferred to a live vaccine
subunit vaccines- a way to reduce probability of side-effects
killed vaccines (attenuated)
by heating or exposure to chemicals
subunit vaccines
fragments of microorganisms e.g. proteins and polysaccharides
Naked DNA vaccines
the purest form - DNA makes proteins after injection using apparatus of the cell
example of a vaccine which had a side affect
H1N1 bird flu vaccine made people develop narcolepsy
- 800 European children developed narcolepsy after receiving H1N1 vaccine
more likely to make the US Olympic team
than suffer a severe allergic reaction
some people will develop
pain and swelling- but goes within a few days
sub-unit vaccines use
isolated components of microorganisms- protein or polysaccharide
- in reality only one or two of these components will work as an effective vaccine
immunity induced by sub-unit vaccines is almost always
triggering of antibodies
protective mechanism of binding antibodies to antigen
- agglutination
- opsonisation
- neutralisation
- activation of complement
- inflammation
- antibody-dependent cell-mediated cytotoxicity
agglutination
enhances phagocytosis and reduces the number of infectious units to be dealt with
opsonization
coating antigen with antibody enhances phagocytosis
neutralisation
blocks adhesion of bacteria and virus to mucosa and blocks active site of toxin
activation of complement
attaches complement to bacteria causing cell lysis
inflammation
disruption of cell by complement/reactive protein attracts phagocytic and other defensive immune system cells
Antibody-dependent cell mediated cytotoxicity
antibodies attached to target cell cause destruction by non-specific immune system cells
example of a single subunit vaccine
diptheria
Corynebacterium diptheria causes pathogenesis by releasing
a potent toxin
diptheria potent toxin
blocks protein synthesis and causes heart failure
since the diptheria vaccine was introduced om 1942
very few deaths
how are vaccines prepared form diptheira toxin treated?
with formaldehyde (tetanus vaccine also uses this )
formaldehyde detoxification
- Formaldehyde cross links amino groups in proteins with other nearby nitrogen atoms in proteins through a CH2 linkage
- Both intramolecular cross-linking and cross-linking between adjacent protein molecules
- Physically changing structure of protein to prevent toxic action, but preserve its shape enough so that the immune system can mount an accurate response
formaldehyde detoxification simple
-causes cross bridges to form, making a complex of toxins unable to cause harmq
why is formaldehyde detoxification not always the best technology
- too much cross linking can change structure too much
- too little may mean it is still toxic
- batch variation
- reversion- cross bridges breaking releasing monomers
- requires pure toxin at the starting point
- need to grow and purify pathogen-dangerous
example of multiple sub-unit vaccines
plague and Yesinia pestis
example pandemics of the plague
- The Justinian plague (AD542-AD570)
- The Black Death (killed a third of European population) (14th-16th century)
- The third pandemic- continues yto be a problem in parts of the world (Mid 19th century)
where is Yersina pestis still rife
N.America, SE Asia, Madagascar
- in these parts of the world diseases are maintained in rodent reservoirs
which are the two key protective components used in vaccines against the plague
F1 antigen and v antigen
F1 antigen
capsule which prevents phagocytosis
V antigen
Type II secretory system- a molecular syringe which are structured in bacterial cell wall and inject toxic proteins into the host cell
hwo ar eF1 anfd V antigens produced
via genetic engineering
- production mediated using antibodies
- transferring antibodies from vaccine mice can protect against disease- proving that antibodies are protective against the plagye
the plague vaccine is in hbuman trial
2 dose schedule- day 1 and 2
- competed phase 1 in humans
F1 or V alone
induces protection against low challenge doses
F1 and V together
induce solid protection
how do we find the protective protein sub-unit
- Decades of research on understating how the pathogen causes disease
- Trial and error
a modern approach to subunit vaccines
- modify the toxin using genetic engineering so that is non-toxic
- genetic toxoids
what is a genetic toxoid
a genetically modified non-toxic toxin
example of a genetic toxoid
diphtheria toxin CRM197
- mutation in catalytic A subunit blocks activity
- glycine to glutamine acid substitution at residue 52
benefits of genetic toxoids
- no issues of reversion
- can be reproduced in a harmless E.coli
- high yields- ease of purification
- molecular structure more similar to active toxin
-reproducible properties
- no batch to batch variation, product always works in the same way- reproducible
- very effective
reverse vaccinology in bacterial virsuses
- You take a genome sequence of a microorganism and try and predict which of the proteins would be effective for inclusion in a vaccine
o Important proteins will be found on surface of the bacteria- for an immune response
o Predict which of the proteins encoded on the genome will end up on the outside of the cell - Use pSORT
o Looks at every open-reading frame and predicts the structure of the protein and looks to see if it has the right features (single features, altered amino acid composition etc), which means its likely to be on the surface.
o Can build a list of proteins likely to be on the surface
Neisseria meningitides B causes how many death globally
1.2 mill invasive disease and causes and 135,000 deaths per year
which approach to produce a vaccine for N.meningitides B
reverse vaccinology
what vaccine produced for N.meningitides
4CMenB - via reverse vaccinology
which strain of neisseria meningitides B cause disease in europe, nz, australia, argentina, canada and japan
serogoup B
traditional vaccinology has failed to
identify a vaccine for Neisseria meningitides B
describe MenB reverse vaccinology
1) MenB genome sequenced (3500 ORFs)
2) 570 ORFs identified encoding putative secreted/ exported proteins
3) express and purify 350 protein
4) Immunise mice and harvet sera
5) confirm surface location
6) test for bactericidal activity
7) 28 candidates for further testing
reverse vaccinology predicts vaccine from
the genome sequence
why does reverse vaccinology focus on surface antigens
due to being what the innate and adaptive immune system use to identify pathogens
what can be used to predict cellular location of proteins found in ORFs
pSORt
4CMenB is a vaccine for
meningococcal strains that cause meningitis B
which proteins are found within a 4CMenB vaccine
H binding protein (fHbp), fused with NA2091 protein, binds human factor H, a negative regulator of the alternative pathway of complement activation.
NadA, major adhesion protein involved in colonization, invasion, and induction of pro-inflammatory cytokines.
NHBA, heparin-binding protein that increases resistance against the bactericidal activity of human serum
PorA 1.4 Porin, A major outer membrane protein and the target for bactericidal antibodies
H binding protein (fHbp), fused with NA2091 protein, binds human factor H,
binds human factor H, a negative regulator of the alternative pathway of complement activation.
NadA
major adhesion protein involved in colonization, invasion, and induction of pro-inflammatory cytokines.
NHBA
eparin-binding protein that increases resistance against the bactericidal activity of human serum
PorA 1.4 Porin
A major outer membrane protein and the target for bactericidal antibodies
