Aid svaccine 2012

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

This formidable array of defense mechanismsAllows HIV to avoid being suppressed by our immune system

How can we helpthe body fight back?

Antigenic escape


Downregulating MHC



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

•


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


Rep

ort

ed c

ases

per

100

000

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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


Modern molecular biologyhas offered new approaches

to make vaccines


to make vaccines

1. Clone gene from virus or bacteriaand express this protein antigenin yeast, bacteria or mammalian cells in culture


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

•Poor T cell 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



The vaccine must be able to target conservedand essential parts of the viruses machinery

Antigenic escape


+ existence of many viral strains

Molecular Biology of the Cell Alberts et al



The vaccine must act early in the processBefore the virus becomes firmly established

And destroys the immune system



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?



Neutralizing antibodies

to kill free virus




to kill free virus

T cell response to

kill infected cells

OR




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 viewed as a failure, with only minor effects seen

that were interpretedas statistically insignificant

NY Times

Or was it a failure?A variant on the same vaccine was

tried in Thailand combination of two vaccines:

Patients were primed with ALVAC® HIV vaccine = live canarypox vector expressing gp120

and boosted with the recombinant gp120 protein VacGen AIDSVAX® B/E

The vaccine combination was based on HIV strains common in Thailand.

Or was it a failure?A variant on the same vaccine was

tried in Thailand combination of two vaccines:

Canarypox virus (CNPV) is an Canarypox is an avipoxvirus and the etiologic agent of canarypox, a

disease of wild and captive birds that can cause significant losses. Canarypox can enter human cells,

but it cannot survive and multiply

No thanks!

The results suggested it was partially effective!!

Data suggest the effect dependedon generating antibodies to a variable

loop on gp120

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

However trials continue, but with more focus

on the details of how they affect immunity

Aid svaccine 2012

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