Lecture 23 - Viral Vaccines

Question 1

Features of smallpox that allowed for eradication
1)
2)
3)
4)
5)
6)
7)
8)

Answer 1

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

Question 2

Child vaccination programs
1)
2)
3)
4)
5)

Answer 2

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

Question 3

Polio vaccine from an inactivated virus

Answer 3

Sabin

Question 4

Derivation of Sabin inactivated type 3 poliovirus
1)
2)
3)
4)
5)
6)

Answer 4

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)

Question 5

Determinants of attenuation in type 1 Sabin strain
1)
2)
3)
4)

Answer 5

1) 5’ UTR
2) VP1
3) VP3
4) VP4

Question 6

Determinants of attenuation in type 2 Sabin strain
1)
2)

Answer 6

1) 5’ UTR

2) VP1

Question 7

Determinants of attenuation in type 3 Sabin strain
1)
2)

Answer 7

1) 5’ UTR

2) VP3

Question 8

Sabin strain that can revert to virulence at low frequency

Answer 8

Sabin type 3

Question 9

Side effects of Sabin type 3 strain

Answer 9

1/2.5 million vaccinees develop paralysis

Question 10

When was measles vaccine introduced?

Answer 10

1963

Question 11

Effects of measles disease
1)
2)
3)
4)

Answer 11

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

Question 12

Effects of measles vaccination

Answer 12

1/1 million develop encephalitis

Question 13

Effects of polio disease

Answer 13

1/20 hospitalised patients die.

1/2 survivors permanently paralysed

Question 14

Effects of mumps disease
1)
2)

Answer 14

1) 1/200 develop mild encephalitis

2) 1/5 post-puberty males develop orchitis

Question 15

Effects of mumps vaccine

Answer 15

1/3 million develop mild encephalitis

Question 16

Effect of rubella disease
1)
2)

Answer 16

1) 1/6000 develop mild encephalitis

2) Congenital rubella syndrome is a danger

Question 17

Pros of live attenuated vaccines
1)
2)
3)

Answer 17

1) Fewer doses required
2) Longer-lasting immunity
3) Similar type of immune response elicited as pathogen

Question 18

Cons of live attenuated vaccines
1)
2)
3)
4)

Answer 18

1) Inappropriate for immunocompromised patients
2) Need booster doses
3) Shed into the environment
4) Potential reversion to virulence

Question 19

Widely-studied potential viral vaccine vector

Answer 19

Vaccinia

Large genome, causes very mild disease, quite safe

Question 20

Construciton of a vaccinia viral vector
1)
2)
3)
4)
5)

Answer 20

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.

Question 21

Example of successful viral vaccines

Answer 21

Oral vaccinia recombinant rabies vaccine. Delivered in baited pellets for raccoons, foxes in the USA, Europe.

Question 22

Are viral vaccine used in humans?

Answer 22

Not yet.

Question 23

Advantages of viral vaccines
1)
2)
3)
4)

Answer 23

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

Question 24

Disadvantages of viral vaccines
1)
2)

Answer 24

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

Question 25

DNA vaccines
1)
2)
3)

Answer 25

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

Question 26

New ways to target vaccines

Answer 26

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

Question 27

VLPs
1)
2)

Answer 27

1) Some viral capsid proteins can self-assemble into empty particles.
2) These are highly-immunogenic, are taken up effectively by APCs

Question 28

Example of current vaccine that might produce VLPs

Answer 28

Hep B vaccine.

HBsAg might form VLPs

Question 29

Example of a possible VLP vaccine
1)
2)
3)
4)

Answer 29

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

Question 30

What can HPV16 lead to?

Answer 30

Cervical intraepithelial neoplasia, which can lead to cervical cancer

Question 31

Gardasil vaccine

Answer 31

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

Question 32

Novel way to make live-attenuated vaccines

Answer 32

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

Question 33

Example of a vaccine produced by reassortment

Answer 33

Co-infect a chicken egg with a highly egg-adapted influenza strain and the latest human influenza strain.

Question 34

Flumist reassortment viral vaccines
1)
2)
3)

Answer 34

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.