Lecture 23 - Viral Vaccines Flashcards
Features of smallpox that allowed for eradication 1) 2) 3) 4) 5) 6) 7) 8)
1) No secondary hosts. Grows only in humans,
2) Long incubation period
3) Infectious only after incubation period
4) Low communicability
5) No persistent infection
6) Subclinical infections are not a cause of spread
7) Easily diagnosed
8) Only one viable serotype, infection confers long-term immunity
Child vaccination programs 1) 2) 3) 4) 5)
1) Birth: Hep B
2) 2, 4, 6 months: Hep B, inactivated polio, rotavirus
3) 12 months: MMR
4) 18 months: MMR, varicella
5) 4 years: Inactivated polio, MMR, if MMRV wasn’t given at 18 months
Polio vaccine from an inactivated virus
Sabin
Derivation of Sabin inactivated type 3 poliovirus 1) 2) 3) 4) 5) 6)
1) Isolated strain from a fatal paralytic case
2) 21 passages in vivo (intracerebrally in monkeys)
3) 8 passages in vitro (monkey testicular cultures)
4) 39 passages in vitro (monkey kidney cultures)
5) 3 plaque purifications (monkey kidney culture)
6) 3 passages in vitro (monkey kidney cultures)
Determinants of attenuation in type 1 Sabin strain 1) 2) 3) 4)
1) 5’ UTR
2) VP1
3) VP3
4) VP4
Determinants of attenuation in type 2 Sabin strain
1)
2)
1) 5’ UTR
2) VP1
Determinants of attenuation in type 3 Sabin strain
1)
2)
1) 5’ UTR
2) VP3
Sabin strain that can revert to virulence at low frequency
Sabin type 3
Side effects of Sabin type 3 strain
1/2.5 million vaccinees develop paralysis
When was measles vaccine introduced?
1963
Effects of measles disease 1) 2) 3) 4)
1) 1/1000 develop encephalitis
2) 20% encephalitis cases fatal
3) 1/3 encephalitis survivors have permanent brain damage
4) 1/1 million develop subacute sclerosing panencephalitis
Effects of measles vaccination
1/1 million develop encephalitis
Effects of polio disease
1/20 hospitalised patients die.
1/2 survivors permanently paralysed
Effects of mumps disease
1)
2)
1) 1/200 develop mild encephalitis
2) 1/5 post-puberty males develop orchitis
Effects of mumps vaccine
1/3 million develop mild encephalitis
Effect of rubella disease
1)
2)
1) 1/6000 develop mild encephalitis
2) Congenital rubella syndrome is a danger
Pros of live attenuated vaccines
1)
2)
3)
1) Fewer doses required
2) Longer-lasting immunity
3) Similar type of immune response elicited as pathogen
Cons of live attenuated vaccines 1) 2) 3) 4)
1) Inappropriate for immunocompromised patients
2) Need booster doses
3) Shed into the environment
4) Potential reversion to virulence
Widely-studied potential viral vaccine vector
Vaccinia
Large genome, causes very mild disease, quite safe
Construciton of a vaccinia viral vector 1) 2) 3) 4) 5)
1) Thymidine kinase is a gene which is not necessary for vaccinia replication, but vaccinia grows very poorly in its absence
2) Make a bacterial plasmid vector with TK gene, disrupted by vaccine antigen gene (insert gene into middle of TK gene). Gene is inserted downstream of early gene promoter.
3) Transfect tissue culture cells with plasmid. Also infect with wild type vaccinia.
4) Because of homology of viral gene segment in plasmid and viral genome, can get insertion of mutated gene into viral genome by homologous recombination,
5) Cells are plaqued in the presence of BUdr, which kills TK+ cells. TK-, vaccine antigen+ viruses are selected for.
Example of successful viral vaccines
Oral vaccinia recombinant rabies vaccine. Delivered in baited pellets for raccoons, foxes in the USA, Europe.
Are viral vaccine used in humans?
Not yet.
Advantages of viral vaccines 1) 2) 3) 4)
1) High levels of antigen expressed
2) Can be delivered via mucosal route
3) Can elicit CTL and AB responses
4) Vaccine antigen correctly processed and folded by host
Disadvantages of viral vaccines
1)
2)
1) Can’t be used in immunocompromised patients (Except for abortive infection, eg: avipox, or extremely-attenuated viral vector)
2) Immune response against vector. Problems with reusing vector in the same patient
DNA vaccines
1)
2)
3)
1) Produce DNA plasmid.
2) Plasmid has bacterial origin, gene of interest with a eukaryotic promoter (EG: CMV promoter), antibiotic resistance gene
3) Plasmid is amplified in bacteria, delivered via gene gun into vaccinee
New ways to target vaccines
Vaccine can include a TLR ligand to target vaccine to DCs. This can improve uptake of viral antigen. Some of these systems (EG: TLR2 ligands. TLR2 is an endocytic receptor) can trigger DC maturation as well
VLPs
1)
2)
1) Some viral capsid proteins can self-assemble into empty particles.
2) These are highly-immunogenic, are taken up effectively by APCs
Example of current vaccine that might produce VLPs
Hep B vaccine.
HBsAg might form VLPs
Example of a possible VLP vaccine 1) 2) 3) 4)
1) HPV vaccine.
2) Recombinant L1 capsid protein self-assembles in insect cells
3) VLPs enter host cells like virions.
4) Protect against HPV in dogs, cattle, cottontail rabbits
What can HPV16 lead to?
Cervical intraepithelial neoplasia, which can lead to cervical cancer
Gardasil vaccine
1) VLP vaccine based on L1 expressed in yeast
2) Has HPV16, 18, which cause 70% of cases of cervical cancer
3) Has HPV6, 11, which cause 90% of cases of genital warts
4) 99.5% seroconversion in those that have 3 doses
Novel way to make live-attenuated vaccines
1) Genetic reassortment. Only possible for viruses with segmented genomes.
2) Co-infect a cell with viral strain with antigens of interest, and viral strain that is very weakly-pathogenic
3) Select for strain expressing antigens of interest, that is also highly-attenuated
Example of a vaccine produced by reassortment
Co-infect a chicken egg with a highly egg-adapted influenza strain and the latest human influenza strain.
Flumist reassortment viral vaccines
1)
2)
3)
1) Reassort influenza HA and NA genes of interest with 6 other genes from a cold-adapted strain
2) Effect is a virus that only grows at the lower temperatures of URT.
3) Can be used in children, can be delivered intranasally, so induces mucosal immunity.
