so tell me, this physician of whom you were just speaking, is he a money maker, an earner of fees,...
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So tell me, this physician of whom you were just speaking,Is he a money maker, an earner of fees, or a healer of the sick?
Plato, The Republic
Antigenic escape
Inaccessible epitopes
Downregulating MHC
Destruction of CD4+ T cells
Integration and latency
Blocking Cytosine Deamination
This formidable array of defense mechanismsAllows HIV to avoid being suppressed by our immune system
How can we helpthe body fight back?
Antigenic escape
Inaccessible epitopes
Downregulating MHC
Destruction of CD4+ T cells
Integration and latency
Blocking Cytosine Deamination
This formidable array of defense mechanismsAllows HIV to avoid being suppressed by our immune system
How about anAIDS vaccine?
Even 2,500 Years Ago, People Knew Immunity Worked.
• Greek physicians noticed that people who survived smallpox never got it again.
• The insight: Becoming infected by certain diseases gives immunity.
Vaccination
• Edward Jenner 1796 : Cowpox/Swinepox
• 1800’s Compulsory childhood vaccination
Fast forward 2300 years
Smallpox
•1% v. 25% mortality
•Life-long immunity
• UK: 1700’s
• China 1950
• Pakistan/Afghanistan/Ethiopia 1970
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
Variolation was a huge advance
Smallpox• No animal reservoir
• Lifelong immunity
• Subclinical cases rare
• Infectivity does not precede overt symptoms
• One Variola serotype
•
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
Smallpox presented many advantages that made this possible
SmallpoxAs a result, after a world-wide effort
Smallpox was eliminated as a human disease in 1979
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
Rep
ort
ed c
ases
per
100
000
po
pu
lati
on
100
10
1
0.1
0.001
0.01
1950 1960 1970 1980 1990
Inactivated (Salk) vaccine
Oral vaccine
Cases per 100,000 population United States
Other vaccines have followed,making once feared diseases a thing of the past
How does vaccination work?
• A live or inactivated substance (e.g., protein, polysaccharide) derived from a pathogen (e.g bacteria or virus) capable of producing an immune response
Expose the patient to an Antigen
• A live or inactivated substance (e.g., protein, polysaccharide) derived from a pathogen (e.g bacteria or virus)capable of producing an immune response
Expose the patient to an Antigen
If the patient is subsequently exposed to infectious agent carrying this Antigen they will mount a faster immune response
How does vaccination work?
Molecular Biology of the Cell Alberts et al
Patient exposed to pathogenCarrying antigens A and B
It works like this
Vaccines can be divided into two types
• Live attenuated
• Inactivated
Inactivated Vaccines fall into different categories
• viruses• bacteria
• Individual proteins from pathogen• Pathogen specific complex sugars
Whole
Fractional
Live Attenuated Vaccineshave several advantages
• Attenuated (weakened) form of the "wild" virus or bacterium
• Can replicate themselves so the immune response is more similar to natural infection
• Usually effective with one dose
Live Attenuated Vaccinesalso have several
disadvantages• Severe reactions possible
especially in
immune compromised
patients
• Worry about recreating
a wild-type pathogen
that can cause disease
• Fragile – must be
stored carefully
MMWR, CDC
A number of the vaccines you receivedwere live Attenuated Vaccines
• Viral measles, mumps,rubella, vaccinia,
varicella/zoster, yellow fever,
rotavirus, intranasal influenza, oral polio
• Bacterial BCG (TB), oral typhoid
Inactivated Vaccines are the other option
• No chance of recreating live pathogen
• Less interference from circulating antibody than live vaccines
Pluses
Inactivated Vaccines are the other option
• Cannot replicate and thus generally not as effective as live vaccines
• Usually require 3-5 doses
• Immune response mostly antibody based
Minuses
Inactivated Vaccines are alsoa common approach today
• Viral polio, hepatitis A, rabies, influenza*
• Bacterial pertussis*, typhoid*cholera*, plague*
Whole-cell vaccines
*not used in the United States
Other Inactivated Vaccinesnow contain purified proteins
rather than whole bacteria/viruses
• Proteins hepatitis B, influenza,acellular pertussis,
human papillomavirus, anthrax, Lyme
• Toxins diphtheria, tetanus
Sabin Polio VaccineAttenuated by passage in foreign host (monkey kidney cells)
Selection to grow in new host makes virus
less suited to original host
Sabin Polio VaccineAttenuated by passage in foreign host (monkey kidney cells)
Selection to grow in new host makes virus
less suited to original host
• Grows in epithelial cells
• Does not grow in nerves
• No paralysis
•Local gut immunity (IgA)
Salk Polio Vaccine
• Formaldehyde-fixed
• No reversion
US: Sabin attenuated vaccine
~ 10 cases vaccine-associated polio per year =
1 in 4,000,000 vaccine infections
Scandinavia: Salk dead vaccine
• No gut immunity
• Cannot wipe out wt virus
Polio Vaccine illustrates the pluses and minuses of live vaccines
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
Rec
ipro
cal v
irus
antib
ody
titer
512
128
32
8
2
1
Serum IgG
Serum IgG
Serum IgM Serum IgM
Nasal and duodenal IgA
Nasal IgASerum
IgA
Serum IgA
Duodenal IgA
DaysVaccination Vaccination
48
4896 96
Killed (Salk) Vaccine
Live (Sabin) Vaccine
Live virus generates a more complete immune response
Modern molecular biologyhas offered new approaches
to make vaccines
Modern molecular biologyhas offered new approaches
to make vaccines
1. Clone gene from virus or bacteriaand express this protein antigenin yeast, bacteria or mammalian cells in culture
Modern molecular biologyhas offered new approaches
to make vaccines
2. Clone gene from virus or bacteriaInto genome of another virus (adenovirus, canary pox, vaccinia)And use this live virus as vaccine
Cloned protein antigenshave pluses and minuses
Pluses
•Easily manufactured and often relatively stable
•Cannot “revert” to recreate pathogen
Minuses
• Poorly immunogenic
• Post-translational modifications
• Poor CTL response
Viral vectors have pluses and minuses
Pluses
• Infects human cells but some do not replicate
• Better presentation of antigen
• Generate T cell response
Minuses
•Can cause bad reactions
•Can be problems with pre-exisiting immunity to virus
•Often can only accommodate one or two antigens
Given that introduction, should we search for a
vaccine against HIV and how would we do so?
30 million deaths caused by HIV
33 million living with HIV/AIDS
2.7 million new infections in 2008
An effective vaccine could have a MAJORImpact on the future prognosis
iavi.org
This allows T cells to recognize HIV infected cells,for example, and even internal proteins
like reverse transcriptase can serve as antigens
An effective vaccine must get around the strategies HIV uses to evade the immune system
This allows T cells to recognize HIV infected cells,for example, and even internal proteins
like reverse transcriptase can serve as antigens
The vaccine must be able to target conservedand essential parts of the viruses machinery
Antigenic escape
Inaccessible epitopes
+ existence of many viral strains
Molecular Biology of the Cell Alberts et al
This allows T cells to recognize HIV infected cells,for example, and even internal proteins
like reverse transcriptase can serve as antigens
The vaccine must act early in the processBefore the virus becomes firmly established
And destroys the immune system
Destruction of CD4+ T cells
Integration and latency
There are many possible HIV Vaccine Approaches
Protein subunit
Synthetic peptide
Naked DNA
Inactivated Virus
Live-attenuated Virus
Live-vectored Vaccine
Ramil Sapinoro, University of Rochester Medical Center
To begin we need to ask some key questions
What should vaccine elicit?
To begin we need to ask some key questions
What should vaccine elicit?
Neutralizing antibodies
to kill free virus
To begin we need to ask some key questions
What should vaccine elicit?
Neutralizing antibodies
to kill free virus
T cell response to
kill infected cells
OR
To begin we need to ask some key questions
What should vaccine elicit?
Neutralizing antibodies
to kill free virus
T cell response to
kill infected cells
OR
OR BOTH?
The biology of HIV provides some clues
Remember the long term non-progressorsInfected with a Nef mutant virus?
This would generate both an antibody and a T cell response
Could this be used to generate a vaccine?
This prompted an experimentthat demonstrated
the feasibility of a vaccine
This prompted an experimentthat demonstrated
the feasibility of a vaccine
December 1992: Live attenuated SIV vaccine
Lacking the gene Nef
protected all monkeys for 2 years against massive dose of virus
• All controls died
• cell mediated immunity was key
However, this approach is still viewed as too risky to try on human
subjects
December 1992: Live attenuated SIV vaccine
Lacking the gene Nef
protected all monkeys for 2 years against massive dose of virus
• All controls died
• cell mediated immunity was key
Another effort attempted touse recombinant viral proteins as antigens
in an effort to generate neutralizing antibodies
VaxGen made two different formsof gp120 from different HIV strains
and began human trials after chimp testing
Human vaccine trials are large and very expensive
The trial was a failure, with only minor effects seen
that were viewed as statistically insignificant
NY Times
The next approach involved usingviral vectors to try to
also boost the T cell response
Many different viral vectors are being investigated but this trial used the human cold virus called adenovirus
They actually used three adenoviruses carrying three different viral proteins
Gag
Pol
Nef
Early results suggested the immune system was being stimulated
The hotly awaited results were released at the 2007 AIDS Meeting
You be the judge—what happened?
This stunning failure led to a re-thinking
of the approach
“DNA” vaccines are a novel approach
The field has decided in part togo back to the basics:
how does HIV workand how can we assess vaccine success?
Questions:
• For a vaccine what are the measures of protection?
• Can we overcome polymorphism?
• What are the key antigens?
• Attenuated or killed or neither?
• Is Mucosal immunity critical?
• Should it Prevent infection or prevent disease?
• What are the best Animal models
How does HIV kill cells anyway?
However trials continue, but with more focus
on the details of how they affect immunity