Immunity

Specific defensesImmunity

Passive immunityActive immunity

Following clinical infection

Following subclinical infection

Following vaccination Following administration ofImmunoglobulin or antiserum

Transfer of maternal Antibodies Through milk

Transfer of maternal Antibodies Through placenta

natural

acquired

Viral Vaccines

Immunizing agents

Immunizing agents

antiseraimmunuglobulinsvaccines

Vaccination

• Vaccination is a method of giving antigen to stimulate the immune response through active immunization.

• A vaccine is an immuno-biological substance designed to produce specific protection against a given disease.

• A vaccine is “antigenic” but not “pathogenic”.

Let’s go back in time to seehow this strategy works

The time: 500 B.C.The place: Greece

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.

Fast forward 2300 years

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

I had a brilliant idea

Vaccination• Charles Jenner 1796 : Cowpox/Swinepox

• 1800’s Compulsory childhood vaccination

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

• No animal reservoir

• Lifelong immunity

• Subclinical cases rare

• Infectivity does not precede overt symptoms

• One serotype

•

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

Smallpox presented many advantages that made this possible

As a result, after a world-wide effortSmallpox was eliminated as a human disease in 1978

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

Types of vaccines

• Live vaccines• Attenuated live vaccines• Inactivated (killed vaccines)• Toxoids• Polysaccharide and polypeptide (cellular

fraction) vaccines• Surface antigen (recombinant) vaccines.

Live vaccines

• Live vaccines are made from live infectious agents without any amendment.

• The only live vaccine is “Variola” small pox vaccine, made of live vaccinia cow-pox virus (not variola virus) which is not pathogenic but antigenic, giving cross immunity for variola.

Live attenuated (avirulent) vaccines

• Virulent pathogenic organisms are treated to become attenuated and avirulent but antigenic. They have lost their capacity to induce full-blown disease but retain their immunogenicity.

• Live attenuated vaccines should not be administered to persons with suppressed immune response due to:– Leukemia and lymphoma– Other malignancies– Receiving corticosteroids and anti-metabolic agents– Radiation– pregnancy

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 (killed) vaccines

• Organisms are killed or inactivated by heat or chemicals but remain antigenic.

• They are usually safe but less effective than live attenuated vaccines.

• The only absolute contraindication to their administration is a severe local or general reaction to a previous dose.

Inactivated Vaccines

• Cannot replicate and thus generally not as effective as live vaccines

• Usually require 3-5 doses• Immune response mostly antibody based

Minuses

Inactivated Vaccines

• No chance of recreating live pathogen• Less interference from circulating antibody than

live vaccines

Pluses

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

Reci

proc

al v

irus

antib

ody

titer

512

128

32

8

2

1

Serum IgGSerum 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

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

Toxoids

• They are prepared by detoxifying the exotoxins of some bacteria rendering them antigenic but not pathogenic. Adjuvant (e.g. alum precipitation) is used to increase the potency of vaccine.

• The antibodies produces in the body as a consequence of toxoid administration neutralize the toxic moiety produced during infection rather than act upon the organism itself. In general toxoids are highly efficacious and safe immunizing agents.

Polysaccharide and polypeptide (cellular fraction) vaccines

• They are prepared from extracted cellular fractions e.g. meningococcal vaccine from the polysaccharide antigen of the cell wall, the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism, and hepatitis B polypeptide vaccine.

• Their efficacy and safety appear to be high.

Surface antigen (recombinant) vaccines.

• It is prepared by cloning HBsAg gene in yeast cells where it is expressed. HBsAg produced is then used for vaccine preparations.

• Their efficacy and safety also appear to be high.

Types of vaccinesLivevaccines

LiveAttenuated vaccines

KilledInactivated vaccines

Toxoids Cellular fraction vaccines

Recombinant vaccines

•Small pox variola vaccine

•BCG•Typhoid oral•Plague•Oral polio•Yellow fever•Measles•Mumps•Rubella•IntranasalInfluenza•Typhus

•Typhoid•Cholera•Pertussis•Plague•Rabies•Salk polio•Intra-muscular influenza•Japanise encephalitis

•Diphtheria•Tetanus

•Meningococcal polysaccharide vaccine•Pneumococcal polysaccharide vaccine•Hepatitis B polypeptide vaccine

•Hepatitis B vaccine

Routes of administration

• Deep subcutaneous or intramuscular route (most vaccines)

• Oral route (sabine vaccine, oral BCG vaccine)• Intradermal route (BCG vaccine)• Scarification (small pox vaccine)• Intranasal route (live attenuated influenza

vaccine)

Scheme of immunization

• Primary vaccination– One dose vaccines (BCG, variola, measles, mumps,

rubella, yellow fever)– Multiple dose vaccines (polio, DPT, hepatitis B)

• Booster vaccinationTo maintain immunity level after it declines after

some time has elapsed (DT, MMR).

Periods of maintained immunity due to vaccines

• Short period (months): cholera vaccine• Two years: TAB vaccine• Three to five years: DPT vaccine• Five or more years: BCG vaccine• Ten years: yellow fever vaccine• Solid immunity: measles, mumps, and rubella

vaccines.

Levels of effectiveness

• Absolutely protective(100%): yellow fever vaccine• Almost absolutely protective (99%): Variola, measles,

mumps, rubella vaccines, and diphtheria and tetanus toxoids.

• Highly protective (80-95%): polio, BCG, Hepatitis B, and pertussis vaccines.

• Moderately protective (40-60%) TAB, cholera vaccine, and influenza killed vaccine.

HIV Vaccine

Given that introduction, should we search for a vaccine against HIV and how would we do so?

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

Antigenic escape

Inaccessible epitopes

Downregulating MHC

Destruction of CD4+ T cells

Integration and latency

An effective vaccine could have a MAJORImpact on the future prognosis

iavi.org

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

Inaccessible epitopes

+ 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 establishedAnd 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 virusT cell response to

kill infected cellsOR

To begin we need to ask some key questions

What should vaccine elicit?

Neutralizing antibodies

to kill free virusT cell response to

kill infected cellsOR

OR BOTH?

The biology of HIV provides some clues

Long term progressorsInfected with a Nef mutant virus?

This would generate both an antibody and a T cell responseCould this be used to generate 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

The next efforts 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

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