developing parasite vaccines Flashcards
(29 cards)
1
Q
anti-parasitic vaccines
A
- none commercially available for human disease
- some for animals
- giardia in dogs
- tapeworm in pigs
2
Q
malaria vaccine
A
- huge efforts
- massive socio-economic burden ($12 billion yearly in africa alone)
3
Q
features of plasmodium
A
- unicellular eukaryote
- complex multi-host lifecycle
- sporozoite form is transmitted from mosquito to human
- merozoite form infects human RBCs
- gametocytes medaite transmission to mosquitoes
- all potential vaccine targets
4
Q
potential mechanisms of malaria vaccines
A
- prevent infection - liver stage
- prevent disease - blood stage
- prevent transmission - mosquito stage
5
Q
features of an effective vaccine
A
- induction of strong and appropriate immune responses
- durable and broad enough
- safe, well tolerated
- easy to administer and transport
- cost effective
6
Q
potential for plasmodium life cycle intervention
A
- antibody response to sporozoites before liver cell invasion
- CD8+ T cell repsonse against parasite infected liver cells
- antibody/CD4+ mediated destruction of free floating merozoites in blood
- antibody mediated response to sexual stage forms in mosquito
7
Q
vaccine strategies
A
- whole organism approach
- subunit vaccine approach
8
Q
vaccine classes
A
- pre-erythrocytic malaria vaccines (PEV)
- blood-stage vaccines
- transmission blocking vaccines (TBVs)
9
Q
whole organism vaccine approach
A
- make preparations of parasites from infected people/mosquitoes
- attenuate with radiation, chemicals, crispr/cas9 editing
- increased susceptibility to immune response
10
Q
subunit vaccine approach
A
- create recombinant expression of single, relevant antigens
- deliver with adjuvant
- usually stage specific
- difficult to design, make and are expensive
- issues with injecting peopel with recombinant parasite
11
Q
PEVs
A
- aim to stimulate strong T cell responses against liver stage
- and/or antibodies against sporozoites
- prevent blood stage infection and transmission
- some evidence of reduced liver burden
- can ameliorate blood stage clinical disease
12
Q
challenge models
A
- good ones available for PEVs in small animals and humans
- mosquito bite challenge
- 5 infected mosquitoes in cup exposed to person
- after all have bitten, see how person is affected
- expesnive, need volunteers, is 5 enough (different parasite numbers)
- i.v. challenge
- purify sporozoites from salivary glands and inject
- but 95% of parasites dead
13
Q
RTS,S
A
- vaccine nearest clinical release
- PEV
- subunit vaccine
- targets circumsporozoite protein - 60% of surface, liver cell binding
14
Q
structure of RTS,S
A
- recombinant expression of B cell and CD4+ epitopes
- fused to hep B surface antigen
- binds non-conjugated antigens
- RTS = fusion protein
- part of CSP with T/B cell epitopes
- S = HBsAg
- RTS and S spontaneously combine to form virus like particles
15
Q
RTS,S adjuvant
A
- AS01
- liposome-based with MPL
- safe and mdoerately effective
16
Q
RTS,S efficacy
A
- higher in children compared to infants after 12 months
- 56% - 31%
- unknwon why
- efficacy wanes quickly
- almost completely gone after 3 years
17
Q
drawbacks of RTS,S
A
- waning efficacy
- high initial outlay
- could shift disease burden to older children in areas of high transmission
18
Q
irradiated sporozoites
A
- whole organism vaccine, 1960s
- attenuation by irradiation
- mobile sporozoites invade liver cells but don’t develop further
- effective but discontinued in 1970s
- difficult to get enough sporozoites to clinical quality
- advances in subunit techniques
- Sanaria
19
Q
Sanaria vaccine
A
- PfSPZ, whole parasite, 2013
- dissected sporozoites out of mosquitoes for vaccine use
- doesn’t always work but highly effective when it does
- more sporozoites → more effective
- is it feasible?
- iv delivery most effective - difficult
- also liquid N2 storage
20
Q
blood stage vaccines
A
- stimulate T cell and/or antibody responses to blood stage
- antigens on iRBC or parasite surface
- focus on metabolism, cytoadherence and mainly invasion
- reduces pathology - fewer parasites in bloodstream
- high parasite numbers in circulation make it difficult
- also genetic variation
21
Q
blood stage vaccine targets
A
- MSP1 - merozoite surface protein 1
- AMA1 - microneme secreted merozoite surface protein
22
Q
MSP1
A
- secreted to coat surface from micronemes
- GPI anchored
- undergoes proteolysis to form fragments
- essential for attachment to RBC
- successful in mice and primates but not humans
23
Q
AMA1
A
- transported to surface when schizonts rupture
- conserved, interats with RON in RBC
- associated with antibodies in natural immunity
- highly polymorphic
- difficult vaccine design
- no success in humans so far
24
Q
TBVs
A
- prevent mosquitoes getting malaria in the first place
- only 1-5 parasites in msoquito - much easier target
- larger window of opportunity
- extracellular for 24h in mosquito
- highly invariant targets
- no pressure from host immune system
25
successful TBV features
* inhibit parasite development by inducing a circulating antibody
* antibody ingestion via bloodmeal
* 24h IgG and complement window in midgut before IgG degradation
* target antigens on sexual stage surface
* induce high and long enough titres for at least one transmission season (6 months)
26
SMFA
* standard membrane feeding assay for TBVs
* infected human blood with gametocytes
* mix with test antibody and keep warm
* introduce membrane and let females feed
* oocysts in midgut counted
* assess intensity and prevalence
27
TBV antigens
* 5 identified and proven to work
* ookinete surface proteins
* P25 and P28 -reduce transmission to 0.01% in knockouts
* male gamete surface proteins
* P48/45 - fertilisation
* P230 - may hold P48/45 on surface
* HAP2 - fertilisation
* need more for success
* screening proteomes
28
current TBV status
* immunisation of humans and animals has induced antibodies with high efficacy
* can result in eradication in animal lab populations
* coverage? field trials? more antigens? better delivery?
* combination of multiple vaccine classes?
* need to immunise whole population
29
non-falciparum malaria vaccines
* P. vivax another major cause of malaria
* forms dormant heptic hypnozoites
* can lead to relapse years later
* greater global distribution
* lower temperatrues
* restricted by Duffy antigen emergence
* removed receptor of RBC invasion
* neglected but may become problem
