In thinking about vaccines, recall that there are two arms of the adaptive immune response

1
In thinking about vaccines, recall that there are
two arms of the adaptive immune response

• Cellular (Cytotoxic T Lymphocyte or CTL) response
  -- works well for controlling (most) viral
  infections because viruses replicate
  intracellularly. Less adapted for controlling
  extracellular pathogens such as bacteria or
  protozoa.
• Humoral (antibody-mediated) response -- works
  well for controlling extracellular pathogens.
• Passive transfer of antibodies alone (e.g.,
  mother to offspring) can protect against viral
  infection.
• Neutralizing antibodies can prevent reinfection
  by some viruses (e.g., influenza).

2
Vaccination

• For most viruses, you are immune to reinfection
  by the same virus (e.g., chicken pox).
• Immunization or vaccination Process by which one
  is exposed to a live or inactivated virus, or to
  components of the virus, in order to establish a
  state of immunity.
• Immunizations against smallpox introduced gt1000
  years ago. Variolation introduce dried smallpox
  scabs into nose of an uninfected person, who then
  contracted a mild form of the disease but was
  immune to smallpox.
• 1-2 died after variolation compared with 30
  after smallpox.
• Vaccination against smallpox introduced by Edward
  Jenner in 1796. Jenner infected a boy with cowpox
  (a live-attenuated virus), then exposed him to
  smallpox, which he failed to contract.
• Jenner later experimented on other children,
  including his son. These sorts of experiments are
  illegal today.

3
Clicker question

• Most vaccines today are given in the form of
  whole-killed virus or live-attenuated
  virus.Whole-killed virus vaccines induce _____
  immunity. Live-attenuated virus vaccines
  induce ____ immunity.

• cellular and humoral cellular and humoral
• cellular cellular
• humoral humoral
• cellular cellular and humoral
• humoral cellular and humoral

4
Polio vaccine has been very successful in the US

• Polio epidemics in 1950s affected gt50,000 people
  in US.
• Salk vaccine is an inactivated virus given in a
  series of injections. The vaccine induces
  circulating antibodies, but no cellular immunity.
  Prevents spread of virus from gastrointestinal
  tract to the central nervous system, but doesnt
  prevent infection of the gastrointestinal tract
  by the virus.
• Sabin vaccine is a live-attenuated virus given
  orally. Produces cellular immunity and
  circulating antibodies and prevents subsequent
  infection by wild-type virus. Worldwide use of
  Sabin vaccine has eradicated polio in the US and
  Americas.
• We will discuss both of these methodologies
  (whole-killed virus and live-attenuated virus
  approaches) as potential ways to make an HIV
  vaccine.

5
Clicker question

• What chemical did Jonas Salk use to inactivate
  poliovirus to make the famous vaccine?
• Formaldehyde
• Polyethylene Glycol
• Methanol
• Ammonia

6
Clicker question
What chemical did Jonas Salk use to inactivate
poliovirus to make the famous vaccine? 1) Formald
ehyde 2) Polyethylene Glycol (in many things,
including in Dr. Pepper prevents
over-foaming) 3) Methanol 4) Ammonia
7

• Clicker question
• How many American children contracted polio in
  1955 because of an incompletely inactivated batch
  of poliovirus vaccine produced by Cutter
  Laboratories?
• 1) 10
• 2) 100
• 3) 20000
• 4) 40000

Source Offit, PA (2005) The Cutter Incident, 50
years later. New England Journal of Medicine
8

• Clicker question
• How many American children contracted polio in
  1955 because of an incompletely inactivated batch
  of poliovirus vaccine produced by Cutter
  Laboratories?
• 1) 10
• 2) 100
• 3) 20000
• 4) 40000 120,000 doses contained live virus,
  resulting in 40,000 cases of abortive polio
  (headache, stiff neck, fever, muscle
  weakness). 51 children were permanently
  paralyzed, 5 died 113 family members were
  paralyzed, 5 died.

Source Offit, PA (2005) The Cutter Incident, 50
years later. New England Journal of Medicine
9
Cases of polio per year in US
From Morbidity and Mortality Weekly Report
(MMWR), Vol. 46, p. 79 (1997)
10
Flu vaccines

• WHO specifies the contents of the vaccine each
  year to contain the most likely strains of
  viruses that will attack the next year.
• Annually updated trivalent flu vaccine for
  2008-2009 season consisted of H3N2, H1N1 and B
  influenza viruses. (But the vaccine H1N1 strain
  doesnt confer protection to H1N1 swine flu.)
• Viruses are grown in hens eggs.
• Inactivated viruses are injected or live
  attenuated viruses are given as a nasal spray
  (not currently approved in children younger than
  5).

World Health Organization
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Why we need an HIV vaccine Anti-retroviral
therapy hasnt eradicated HIV

• Anti-retroviral treatment regimens are complex,
  expensive, and can result in serious side
  effects.
• Developing safe, effective and affordable
  vaccines that can prevent HIV infection in
  uninfected people is the best hope for
  controlling and/or ending the AIDS epidemic.
• In 1984, Margaret Heckler (President Reagans
  Secretary of the Department of Health and Human
  Services) announced that the virus responsible
  for causing AIDS had been identified, and that a
  vaccine would be ready for testing within two
  years.
• We still dont have a vaccine. Why?

12
CD4 means CD4 T cells CTL means CD8
cytotoxic T lymphocytes VLP means virus-like
particle
Pantello and Koup, 2004, Nature Medicine 10
806-810
13
Pantello and Koup, 2004, Nature Medicine 10
806-810
14
Traditional approach to an HIV vaccine
whole-killed virus

• Problems
• Safety issues are the viruses really dead?
• Production of strain-specific responses would
  need to inject a mixture of MANY different killed
  HIVs.
• A big problem gp120 is shed from HIV, so what
  is being injected isnt a form to which the host
  will make effective neutralizing antibodies.
• Another big problem where do you get the HIV to
  kill and then inject? Answer grow in cells in
  the lab, but laboratory strains are antigenically
  different than primary HIV isolates.

http//www.niaid.nih.gov/hivvaccines/whole.htm
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Future research needs (from http//www.niaid.nih.
gov/hivvaccines/whole.htm)

• Identify HIV isolate(s) that retain sufficient
  envelope glycoprotein to effectively mimic
  wild-type HIV and generate a strong, protective
  immune response.
• Develop and test inactivation procedures that
  will retain antigenic integrity of the envelope
  glycoprotein.
• Develop cells and culture methods that will
  permit large-scale production of primary HIV
  isolates.
• Develop alternative methods that can circumvent
  some of the safety and technical concerns posed
  by manufacturing and then inactivating infectious
  HIV virions.

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Live-attenuated virus approach to making an HIV
vaccine

• Initial optimism because live SIV with a
  deletion in the Nef gene caused no disease in
  macaques and protected against initial infection
  by wild-type SIV.
• However, Nef-deletion mutants only slow disease
  progression, but dont abrogate it completely
• Adult macaques eventually showed immune
  dysfunction and 18 developed AIDS.
• This vaccine shows limited or no cross
  protection against infection by other strains of
  SIV.
• Live-attenuated HIV vaccines have not been
  tested in humans due to safety concerns.
• Long-term growth of live-attenuated viruses
  would be done in culture, but laboratory strains
  of HIV are antigenically different than primary
  isolates.

Nef down-regulates surface expression class I
MHC molecules and CD4 Wild-type A normal,
non-mutant form of a macromolecule, cell or
organism
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Possible vaccine approaches

• Induction of antibodies by injection with
  whole-killed virus or viral proteins.
• Induction of antibodies and cellular immunity
  using live-attenuated virus.
• Induction of only cellular immunity (cytotoxic T
  lymphocyte (CTL) responses) by inducing
  expression of viral proteins.
• DNA vaccines -- injection of purified DNA,
  usually into muscle, results in transient
  expression of proteins encoded by introduced
  genes. Peptides derived from these proteins are
  presented by MHC class I proteins to CD8 CTLs.
• Note that these sorts of vaccines can never
  prevent infection because T cells do not
  recognize or kill free viruses. A strong anti-HIV
  CTL response, however, has the potential to
  reduce or eliminate virally-infected cells and
  therefore greatly reduce viral load.

DNA vaccines http//people.ku.edu/jbrown/dnavac.
htm
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Possible HIV Vaccine Strategies

• Peptide vaccines
• Recombinant subunit protein vaccines
• gp120, gp41, or gp160 produced by genetic
  engineering
• Live vector vaccines
• non-HIV viruses engineered to carry HIV genes
• Virus-like particle vaccines
• non-infectious HIV containing one or more HIV
  genes
• DNA vaccines
• HIV genes inserted into plasmids
• Combinations of vaccines
• Prime-boost regimens (e.g., DNA vaccine followed
  by injection of recombinant protein)
• Current HIV Vaccine trials
• www.hvtn.org/science/trials.html

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Mercks HIV vaccine

• Merck V520 ad5 vaccine -- a live attenuated
  virus designed to produce cellular and humoral
  immunity
• Three stretches of HIV genome (from HIV gag, pol
  and nef genes)
• Note HIV genes derived from only one HIV strain
• Shell from adenovirus type 5 (normally causes
  cold symptoms)
• Virus was replication incompetent -- could
  infect cells, but couldnt produce more virus --
  Vaccine cannot cause HIV infection.

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STEP trial

• 1500 volunteers (high-risk for HIV infection) in
  Americas and Australia recruited in December
  2004. 3000 volunteers by March 2007.
• 62 male, Average age 29
• Trial stopped in September 2007.
• Vaccine conferred no protective effects against
  HIV infection and no effect on course of
  infection.
• More infections in vaccine recipients (49) than
  placebo (33).
• Much analysis now to figure out what went wrong.
• Is difference in infection rates significant?
• Did adenovirus immunity increase infection risk?

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Is there any hope for an antibody-based
therapeutic approach against HIV given that
people dont normally make broadly neutralizing
antibodies against HIV?

• HIV rapidly mutates so that antibodies are no
  longer effective.

• HIV spike proteins are covered with
  carbohydrates, which are poorly or
  non-immunogenic.

• Antibodies are too big to access some regions of
  the HIV spike.

Burton, Dennis R. et al. (2005) Proc. Natl.
Acad. Sci. USA 102, 14943-14948