HPV

Question 1

HPV

Answer 1

Small non-enveloped dsDNA circular genome of approximately 8kb

Greater than 100 different genotypes:
– Defined by differences in their major capsid protein
– Each genotype has a specific region that it infects in the human body
– At least 13 are oncogenic (16 and 18 together cause 70% of all CC)
– Low risk genotypes 6 and 11 cause genital warts

Question 2

Transmission of HPV

Answer 2

• Physical contact
• One of the most commonly sexually transmitted diseases

Question 3

Where is HPV found?

Answer 3

– 20 million in the US are currently infected
– Worldwide approximately 500,000 new cases of cervical cancer are diagnosed each year, with 250,000 deaths from CC each year
– 80% of deaths occur in the developing world

Question 4

How does HPV enter into its target cells?

Answer 4

• As the infected cells move
  upwards, normally they would stop proliferating, but viral proteins bind cellular proteins to enhance DNA replication.
• E7 – binds pRB and promotes DNA replication
• E6 – binds p53 and prevents the cell detecting abnormal replication and apoptosis
• Virions are shed from the
  top layers of the muscoal
  surface

Only ~50 viral genomes are
made per cell and no capsid
proteins or viral particles are
made

Question 5

HPV genome organization

Answer 5

• has early genes and late genes
• URR, up stream regulator reigon (promoter and enhancer elements and the viral ORI)
• Late proteins make up the viral capsid. These are the antigens that will be seen by the immune system

Question 6

L1 and viral entry

Answer 6

L1 binds heparin
sulfate residues on
cell surface
This changes the
conformational
change of L1 to be
able to bind to an
unknown receptor
and initiate
endocytosis

Question 7

HPV replication and translation

Answer 7

• After entry, the capsid is partially removed (L1 is removed but L2 remains)
• Replicated genome in the nucleus of the cell (6/8 genes are expressed early after infection)
• Late genes encode proteins used to construct new viral capsids (L1 and L2)
• Host cell polymerase synthesizes all mRNA from
  single DNA strand – which remains episomal

Question 8

DNA viruses (transcription, translation and synthesis)

Answer 8

• Genome acts as template for host cell polymerases to make (+) sense RNA
• viral proteins are made immediately in nucleus mediated by host cell enzymes from one strand of
  DNA
• Avoids transcription of overlapping genes and creation of dsRNA
• Viral genome is immediately coated in protein capsid, and the new virus leaves the nucleus and exits the cell

Question 9

HPV disease presentations

Answer 9

• Genital warts: Flat lesions, small cauliflower-like bumps or tiny stem-like protrusions. Genital warts rarely cause discomfort or pain, though they may itch.
• Common warts. Appear as rough, raised bumps and usually occur on the hands, fingers or elbows. In most cases, common warts are simply unsightly, but they can also be painful or susceptible to injury or bleeding.
• Plantar warts. Plantar warts are hard, grainy growths that usually appear on the heels or balls of your feet. These warts might cause discomfort.
• Flat warts. Flat warts are flat-topped, slightly raised lesions darker than your skin. They can appear anywhere, but children usually get them on the face and men tend to get them in the beard area. Women tend to get them on the legs.

Question 10

HPV and cancer

Answer 10

• Long-lasting infections with high-risk HPVs can cause cancer in parts of the body where HPV infects cells
• HPV infects the squamous cells that line the inner surfaces of these organs. For this reason, most HPV-related cancers are a type of cancer called squamous cell carcinoma. Some cervical cancers come from HPV infection of gland cells in the
  cervix and are called aden

Question 11

Clearance of HPV

Answer 11

• Most HPV infections are cleared within a year
• Because the DNA is episomal and basal cells are continually proliferating; there is no appropriation of viral DNA into each daughter cell as there is for chromosomes
• Result is that one daughter cell may receive all the viral
  DNA and the other none.
• Overtime, the viral genome is lost from the basal cell layer (Transient infections)
• Once detected the immune system is very good at clearing the virus (but Killer T cells are genotype specific)

Question 12

Explain the quiet lifecycle of HPV

Answer 12

• By infecting a basal layer of cells with very little viral replication and protein production, HPV ensures that its genome will be maintained (Many immune cells reside at the basal level)
• Ramping up the replication after cells differentiate ensures exit from the top layer of cells and makes the immune system “fight” the
  virus away from the initial (and continual) infectious origin (Location, location, location)

Question 13

HPV Resistance

Answer 13

• Capsid is highly resistant to environmental stresses
• Capsid can withstand detergents in condoms
  that can destroy HIV/HSV

Question 14

HPV vaccine development

Answer 14

• Initial animal model studies showed papillomaviruses induced a protective immune response against homologous virus challenge (Not good substrates for vaccine development b/c don’t grow easily in tissue culture)
• Expression of L1 led to the production of virus-like particles (VLPs) which
  morphologically resemble the authentic HPV virions but contain no viral DNA
• VLPs protected against high dose experimental infection by homologous virus
• Because denatured particles do make neutralizing antibodies – neutralizing epitopes must be conformation-dependent

Question 15

Avalible HPV Vaccines

Answer 15

• Two prophylactic HPV vaccines have been available since 2006.
• Both vaccines are prepared from virus-like particles (VLPs) produced by recombinant technology.
• Purified L1 protein self-assembles to form empty shells that resemble HPV VLPs. These vaccines do not contain viral genetic material or live biological product, so they cannot multiply and are
  not infectious. These two vaccines are:
• Bivalent: Protect against HPV types 16 and 18 protein
• Tetravalent: Protects against HPV types 6, 11, 16 and 18
• Nonavalent: HPV-6, 11, 16, 18, 31, 33, 45, 52, 58
• All vaccines induced high levels of serum antibodies against all vaccine-related types in more than 99% of females aged 9–45 years
  (quadrivalent vaccine) or 10–55 years (bivalent vaccine).

Question 16

HPV diagnosis

Answer 16

• Traditional: pap smear, test for HPV DNA then Colpo
• Reverse: HPV DNA, the papsmear and then Colpo

Question 17

The ATHENA Trial

Answer 17

• The ATHENA trial demonstrated that one in four women who are HPV 16 positive will have cervical disease within three years and that nearly 1 in 7 women with normal Pap cytology who were HPV 16 positive actually had high-grade cervical disease that was missed by cytology
• Comparison of a HPV DNA test screening strategy to alternative strategies using Pap cytology and HPV testing. HPV DNA test to identify women testing positive for HPV 16 or 18, and using cervical cytology (Pap) as a triage, follow-up test, would allow clinicians to detect more disease without referring a significantly
  greater number of women to unnecessary follow-up
• In 2014, based on ATHENA trial data, the U.S. FDA approved for the first time the use of the Roche cobas® HPV test for first-line primary
  screening in women 25 and older.