Human papillomavirus vaccines: The knowns and the still unknowns

1
Title

• Human papillomavirus vaccines The knowns and the
  (still) unknowns
• FEAM Conference, Lisboa, 15 December 2007
• Marc P Girard
• Lyon, France

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Papillomaviruses

• Papillomaviruses are animal viruses which affect
  man and animals. They typically are the agents of
  warts
• Among animal viruses, one finds
• The Shope cotton tail rabbit virus
• The agent of canine oral papillomatosis
• The agent of oesophagal papillomatosis of calves

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Human Papillomaviruses

• More than 100 HPV types have been identified
• that affect humans.
• They all are small icosahedral viruses,
• with a circular double-stranded DNA genome
• and a strong epithelial tropism.
• About 40 HPV genotypes spread through
• sexual contact and infect the ano-genital
  mucosae.
• HPV infection is one of the most, if not the most
  frequent sexually transmitted infection (STI) in
  humans.

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The HPV Genome

• Six early genes E1, E2, E4, E5, E6
  and E7
• E1 E2 proteins viral replication
• E6 E7 oncoproteins responsible for
  transformation of infected cells (induction of
  premalignant alterations) and directly contribute
  to malignant progression
• Two late genes L1 and L2
• L1 L2 capsid proteins

HPV genomic organization
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Prevalence of genital HPV infections

• Prevalence of genital HPV in the female
  population varies from 2- 44 in different
  studies.
• In a study on 474 young female students in the
  USA, the cumulative risk of HPV infection after
  onset of sexual activity was 45 over 2 years
• Prevalence of genital HPV infection among female
  college students in the USA was estimated to be
  20-30.

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Infection can be multiple

• Multiple genital infections (several types of HPV
  together) can also be observed.
• Thus, of 3578 female volunteers recruited for a
  vaccine study in the USA
• 23.7 were infected by one HPV of genotype 16,
  18, 6 or 11
• 4.8 were infected by two of the 4 genotypes
• 1 were infected by three of the four genotypes
• And 0.1 carried the four genotypes together

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HPVs at the Root of Cervical Cancer

• Fifteen HPV genotypes (high-risk HPVs) are
  recognized as the major cause of cervical cancer.
• Of these, HPV 16 represents 57 of cases, and HPV
  18 14
• Altogether, five specific high-risk HPV (HPV 16,
  18, 31, 33 and 45) cause more than 80 of the
  cervical cancers diagnosed worldwide.
• Over 99 of cervical cancer biopsies contain HPV
  DNA

Bosch et al. J Clin Pathol. 2002
Apr55(4)244-65 Walboomers at al. J Pathol.199
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Burden of HPV-related cancers

• High-risk HPVs, especially HPV 16 and 18, were
  estimated to cause 100 of the almost 260,000
  deaths from cervical cancer worldwide in 2005.
• They also caused 60-65 of cancers of the vagina,
  20-50 of cancers of the vulva, 85-95 of
  cancers of the anus and 12-36 of cancers of the
  oropharynx.
• Altogether, cancer cases attributed to HPVs in
  2002 were estimated to number about 450,000 in
  developing countries and 110,000 in
  industrialized countries.

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Disease burden

• Cervical cancer is the second most frequent
  cancer in women worldwide
• In developing countries, cervical cancer is the
  leading cause of cancer deaths in women

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Low-risk HPVs

• Low-risk genital HPVs are responsible for
  genital warts (condyloma acuminata) which grow on
  the cervix, vagina, vulva or anus in women and
  penis, scrotum or anus in men.
• HPV genotypes most frequently responsible for
  genital warts are HPV 6 and HPV 11.
• HPVs also cause epithelial growths over the vocal
  cords of children and adults that require
  surgical intervention (recurrent juvenile
  respiratory papillomatosis)?

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The outcome of HPV infection

• Most genital HPV infections are asymptomatic and
  more than 90 of detected infections are
  spontaneously cleared within two years.
• Persisting infection leads to integration of the
  viral genome into human DNA, which translates
  into lesions called squamous intraepithelial
  lesions (SIL) or cervical intraepithelial lesions
  (CIN) of low then high grade.
• If untreated, moderate (CIN2) or severe (CIN3)
  lesions (often grouped together as CIN 2/3) lead
  to cancer.

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CIN2/3 Screening / Diagnostic
Suspected on cytology HSIL on screening Pap
smear Visualized by colposcopy ? directed
biopsy of acidophil lesion CIN2/3 diagnosis
based on histology epithelial hyperplasia,
atypical mitoses, marked nuclear abnormalities,
etc.
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Treatment of CIN2/3

• CIN2/3 indication for the removal of the entire
  extent of the suspicious area
• Outpatient technique known as the loop
  electrosurgical excision procedure (LEEP).
• More aggressive procedure called conization
  (cone biopsy).
• Treatment efficacy gt90
• Relapse after conization (disease present more
  than 6 months after treatment) can reach a rate
  of 15
• Safety conization is associated with a low rate
  of significant hemorrhage and may have
  consequences in terms of fertility

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The need for preventive vaccines

• Routine screening of 25-65 years-old women has
  been estimated to prevent the occurrence of 90
  of cervical cancers (Europ Union Recommendations,
  Vienna 1999).
• However, neither routine screening for
  precancerous lesions nor their eventual treatment
  are done in developing countries.
• The need for a preventive vaccine is therefore
  both obvious and urgent

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Size of the problem

• The population of less than 15 years-old girls
  worldwide is about 80 million today.
• It is projected to be 300 million by 2040.
• The 493,000 cases of cervical cancer in 2002 is
  projected to become 702,000 by 2020

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Vaccine Positioning
HPV Infection
Persistent Infection
CIN 2/3
Therapeutic Vaccine
GlaxoSmithKline - Cervarix Merck - Gardasil
Average age 35 years
Invasive cancer
Prevention
years
40
45
35
30
25
20
15
10
5
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HPV VLPs

• HPV vaccines are prepared from empty viral
  protein shells called pseudo-virions, or
  virus-like particles (VLPs), that spontaneously
  assemble from the L1 viral capsid protein
  produced by recombinant technology in yeast or
  insect cells.
• They do not contain any DNA, so they are not
  infectious.
• They elicit the production of high-titer
  neutralizing antibodies (IgG) that diffuse by
  transudation into the mucosal ano-genital tissues
  where they can block incoming HPV particles of
  the cognate genotype and prevent infection

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The two HPV vaccines

• Two HPV vaccines have been developed
• ? Gardasil TM, a quadrivalent vaccine made of
  VLPs produced in yeast and corresponding to HPV
  16, 18, 6 and 11 Merck aluminium adjuvant
• ? Cervarix TM, a bivalent vaccine made of VLPs
  produced in insect cells and corresponding to
  HPV 16 and 18 GSK AS04 adjuvant (oil-in-water
  emulsion with Al(OH)3 and monophosphoryl lipid
  A)?
• One month after the third dose of vaccine, nearly
  100 of women in trials of either of the vaccines
  developed neutralizing antibodies to each of the
  HPV genotype in the vaccine at titers 10-100 fold
  higher than in natural infection.

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Major properties of VLP vaccines

• VLP vaccines are prophylactic vaccines that work
  remarkably well only if administered prior to
  infection 100 efficacy proven over 36 months
  against HPV vaccine types infection in
  perprotocol phase III study of GardasilTM
• But only 45 efficacy in intention-to-treat
  protocol (women who were infected at time of
  first vaccination).
• Protection is HPV genotype-specific, although
  evidence has been gathered for partial
  cross-protection against HPV 45 and 31.
• They induce a long-term neutralizing antibody
  response (gt5 years) in vaccinated women.

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The unknowns -1-

• Duration of protection
• Persistence of neutralizing antibodies after 5
  years?
• Minimum protective antibody threshold for disease
  proptection?
• Need for eventual booster injections?
• Target age group pre-adolescent girls (age 9-12
  years)?
• Effectivness of the vaccine given at an earlier
  age?(school-age)?
• Problem of limited efficacy in already infected
  young women
• Safety and efficacy in developing countries?
• Especially in populations of high HIV prevalence
• Gender effect efficacy in men?

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The unknowns -2-

• HPV vaccination will reduce, but not eliminate
  the risk of cancer.
• Screening programmes will therefore remain
  necessary for cervical cancer prevention even
  after the vaccines are introduced.
• A combination of HPV vaccination and screening
  1-3 times per lifetime might turned out to be
  cost-effective
• But much will depend on the cost of the vaccine
  in the different settings

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A complementary approach Therapeutic vaccination

• There is a high rate of spontaneous regression
  involving immune mechanisms
• A therapeutic vaccination that would improve HPV
  antigens presentation immunogenicity should
  further enhance this mechanism
• CIN2/3 are lesions which slowly evolves into
  invasion
• Although conization leads to immediate cure of
  the CIN lesions, there is time, without raising
  safety concern, to implement an immune response
  through therapeutic vaccination
• E6 and E7 HPV antigen involvement in cervical
  cells transformation is clearly defined
• They are the ideal candidate vaccine antigens for
  a therapeutic vaccination

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Therapeutic vaccination in CIN2/3 medical
rationale

• In the context of CIN2/3 pathology and compared
  to current treatment methods, therapeutic
  vaccines would present several advantages
• Non-invasive, safe procedure avoiding surgery and
  its complications
• Easy procedure vaccination during visit at
  gynecologist, no need for out-patient
  hospitalization
• No relapse, due to eradication of the viral
  cause. The vaccine should induce an HPV-specific
  immune response able not only to cure CIN2/3
  lesions but also, on a long-term basis, to reduce
  the rate of recurrent disease, even though
  booster immunizations may be needed

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Therapeutic Vaccines postulated mechanism of
action
MVA-Antigen
Dendritic cells
Antigen-specific CD8 T cells killing a cancer cell
Migration
T cells
www.cancer-info.com