Papillomaviruses (HPV)- vaccination and treatment

Question 1

More conventional vaccines such as Poliovirus vaccines have proved very effective (cases reduced by 99% and only two countries still have cases-Afghanistan and Pakistan). What are the two vaccines given for such a virus?

Answer 1

OPV- mutant virus
IPV- inactivated virus (chemicals kill the active virus for this vaccine)

Both produced from live virus. Hela cells are grown in large vats and these are full of virus particles.

Question 2

HPV does not grow in cell culture/ liquid culture like the poliovirus due to its lifecycle being mirrored to the cycle of epithelium cells. Rafts are used in labs but the yield is very small so is not used for vaccines. So how is this overcome?

Answer 2

Only parts/subunits of the virus is used; often using a protein from the capsid (L1). So all vaccines are made from virus-like particles of L1. These are all non-infectious due to absence of viral genome

Question 3

Which two vaccines are in commercial use at the moment?

Answer 3

Gardasil- tetravalent- targets HPV 16/18/6/11

Cervarix- bivalent- targets HPV 16/18

Question 4

What shape are viral capsids?

Answer 4

Icosahedra (20 sided shape)- only one copy of each protein so is economic for the virus (no need to produce many elements)

Question 5

How can a virus build a larger capsid compared to that of a icosahedra?

Answer 5

Each protein can code for many copies/many triangles instead of just one so to make the capsid larger

Question 6

As the capsid gets larger, what happens to the symmetry of the capsid?

Answer 6

Not all proteins are in equivalent position so perfect symmetry is broken. Proteins will cluster into fives or sixes (pentamers and hexamers)

Question 7

HPV breaks the capsid symmetrical/pattern rule, how?

Answer 7

It has no hexamers at all. It produces a T=7 capsid with only pentamers

Question 8

BPV structure is used to study the structure due to ease of getting it as it grows on cow skin. Why is it not possible to get a crystal structure of HPV?

Answer 8

Is not possible to get enough to form a high resolution whole structure but BPV supports that this virus uses only pentamers and no hexamers

Question 9

Which virus is similar in capsid structure to HPV?

Answer 9

SV40 (was once classified under papillomavirus family) due to its pentameric pattern

Question 10

What is meant by the pentamers making hexameric interactions?

Answer 10

Pentamers make interactions with six other pentamers in the capsid structure- this makes it a stable network

Question 11

L1 alone can be heterogeneous (sizes and shapes are different). What can be done to make them more homogeneous?

Answer 11

Disassemble and re-assemble these virus-like particles to get rid of any extraneous nucleic acid. This is actually part of one of the vaccine purification processes

Question 12

Why is it important for a vaccine capsid to have a homogeneous structure?

Answer 12

The immune system prefers a regular pattern so it will induce a better immune response, In addition, less material is lost so the product will be cheaper and it is easier to get through regulations which question the purity of the material

Question 13

Are there more human or animal papillomaviruses?

Answer 13

More human ones known but most likely there are more animal ones

Question 14

What are the structural differences between low-risk and high-risk HPVs? How does this affect protection against different types of HPV?

Answer 14

E6 and E7 sequence and affinity for binding partners (pRB, p53 etc)

L1 sequences are variable so it is also hard to tell if there will be any cross over of vaccination/protection against other types of HPV than the one you’ve been vaccinated for

Question 15

How was the Cervarix vaccine made?

Answer 15

Made from truncated L1 proteins in insect cells with recombinant baculovirus. Truncated L1 use meant that they did not have to undergo many purification processes that Gardasil did. A proprietary adjuvant ASO4, alum + TLR4 ligand, MPL was used to boost the innate immune response (adjuvants are tightly regulated but the most common one is alum)

Question 16

How was the Gardasil vaccine made?

Answer 16

Through particles being dis-assembled and reassembled again and using yeast and Alum-based adjuvants

Question 17

HPV vaccines are very expensive, which foundation helps subsidise them in some countries?

Answer 17

The Gates Foundation ($5/dose) to encourage vaccination. The price most countries can afford is $1/dose but this is a high ask as it has to include needle, safe storage, the actual vaccine etc.

Question 18

Who was Ian Frazer?

Answer 18

He worked on the development of VLPs and then on the idea of vaccine

Question 19

In the 1990s, what was the vaccine tested on? What was tested in the 2000s?

Answer 19

Cottontail rabbits in the 1990s, then young women that were HPV 16/18 negative who were then monitored for two years

Question 20

Why were HPV 6 and 11 in Gardasil useful?

Answer 20

Both these are low-risk genital wart producing HPVs but they have a large economic burden and may last a life time so finding a way of preventing it is beneficial. Also a shorter monitoring time is needed to see a decrease compared to cervical cancer

Question 21

What is the current vaccination programs that girls undergo for Cervarix?

Answer 21

Used to be 3 injections over 6-12 months but now it has gone down to 2 and switched to Gardasil as the results of this were very good and had added benefits of protection against HPV 6 and 11

Question 22

Why do we only vaccinate girls in this country?

Answer 22

Purely financial reasons- it is actually more effective to vaccinate men. Some countries are changing and are now vaccinating boys and now offered to gay men in the UK

Question 23

Is it possible to eradicate HPV?

Answer 23

There are many different types so it is very difficult and also benefits of vaccination is not seen for a long time

Question 24

What sort of HPV screening test is being used?

Answer 24

PCR-based screening tests are being used and there has been 60% drop in cases of CIN 2/3 in uk over the last 30 years due to this

Question 25

Cervical cancer is the number 2 cancer killer of women under 35 world wide. It is much harder in countries outside the west to get screening tests for it. Describe a way that’s being used to screen for HPV in these countries.

Answer 25

Putting vinegar on the cervix and looking for colour change which indicates lesions and therefore that treatment is needed

Question 26

Why are head and neck cancers hard to diagnose?

Answer 26

Due to the difficulty of performing biopsies on the oropharynx and nasopharynx

Question 27

CIN2/3 and cervical cancer often involves surgery. What is conisation?

Answer 27

Excision of a cone-shaped or cylindrical wedge from the cervix including the transformation zone and part of the endocervical canal
A relatively high risk of recurrence.
Scarring may result in functional problems (e.g. in pregnancy)

Question 28

What is bad about anticancer agents/drugs such as Imiquimod?

Answer 28

Incredibly good whilst taking the drugs but as soon as the person stops taking them then the cancer comes back