chapter 5 Flashcards
Smallpox Virology
Caused by a smallpox virus Poxviridae family
– ~ cowpox virus
– Large dsDNA genome: NCLDVs
– set up ‘second nucleus” in the cell cytoplasm
– enveloped (Golgi membrane-derived)
Edward Jenner
Vaccination
• Observed that milkmaids infected with cowpox were immune to smallpox
inserted pus, taken from a cowpox pustule, into an incision on child’s arm
– James Phipps later exposed to smallpox
à protected
Attenuated Vaccine example
Rabies, = virus weakened (mild or no disease)
Louis Pasteur did
Infected rabbits with rabies isolated from infected dogs
The ultimate goal of vaccines is to
induce memory immune response without causing diseases
Preventative Vaccine
- Administered to an organism free of the targeted infection
- Prepare the body (immune system) to possible infections
Therapeutic Vaccine
Administered to an organism already afflicted with an infection, against which natural (antiviral) immune responses are ineffective
Slow down and impede infections
Therapeutic Vaccination does
moderate effects of an existing pathogen
Therapeutic Vaccination is useful for?
Infections that can’t be cleared
Slow infections where symptoms develop a long time after infections
Vaccine used to boost immunity
Monoclonal antibody
1) Produce by ONE B cell population
2) Recognize ONE AND ONLY ONE antigen/epitope on the same molecule
3) very expensive to produce
4) no or low batch to batch variability
Polyclonal Antibody
1)Produced by different B cell populations
2)Can recognize multiple antigens/epitopes on the same
molecule
3) Relatively less expensive to produce
4) can have batch to batch variability
what does Therapeutic mAbs do?
it is monospecific
reduce the mouse ab immunogenicity
mab need to be re- engineered to become
chimeric ab (-ximab) humanized ab (-zumab)
Active Immunity (long term)
Natural: random/unintended exposure to infectious microbes
Artificial: Vaccination
Both humoral and cell-mediated immunity
Memory response
Passive Immunity (short term)
Natural: maternal antibodies
Artificial: from other sources
Only humoral immunity
No memory cells
what is Fetal/Neonatal Immunity
Only IgG can cross the placenta from mom to fetus.
Antibody production in newborns is very inefficient.
Maternal IgGs help protect them during the first 6 months of life.
Baby starts to produce its own IgG after 6 months.
What makes vaccines “good vaccines”?
- effective
- safe
- affordable
- stable with long shelf life
- easy to administer
what are Features of Smallpox that Enable Its Eradication
DNA virus
No intermediate host
Long incubation time
No persistent/latent infection
Easily diagnosed
Vaccine is safe, stable and inexpensive
what are obstacles for making a good vaccine?
Vectors, host intermediates and other susceptible
host species
multiple strains
Highly mutation rate
Varied genetic differences of the host Maternal antibodies (???)
4 Types of Vaccines Used Today
Attenuated, live viruses
Whole, inactivated (killed) viruses
Capsid and subunit vaccines
DNA vaccines and
recombinant virus vaccines
- Attenuated Live Vaccines
Propagating the virus in semi-permissive cells/hosts or under altered conditions (low temperature) to produce virus particles which are able to replicate but at a reduced level (blind attenuation)
Pastorian approach
Louis Pasteur
Jennerian vaccine
Vaccine derived from a virus different from the one it protects against
Now vaccinia virus is used as a smallpox vaccine (Edward Jenner)
Attenuated viruses are often
often selected for by phenotype, with little to no knowledge of the changes in genotype.
Passages continue until a desired attenuation level is achieved, no matter how many passages take or how many mutations arise.
FluMist:
is a live, attenuated flue virus with 4 strains
Attenuated Live Vaccines – Pros
Live vaccines are generally highly immunogenic.
Activate both humoral (via MHC-II) and cell- mediated (via MHC-I) arms of the immune system
Need less exposures for immunity
Establish memory that lasts for years
No adjuvant
Attenuated Live Vaccines - Cons
- Chance of reversion to virulent strain
- Not appropriate for immuno-suppressed individuals (ex. AIDS patients, very young and very old, cancer patients)
- Virus must remain ‘alive’ during distribution and delivery
- Adventitious contamination
Back mutation
attenuated viruses acquire ‘rescue’ mutations in individuals being immunized, picking up pieces of genome from the host, or recombination with similar viruses or types/strains
Oral Polio Vaccine (OPV)
- Polio virus (Picornaviridae) ssRNA (+) genome
- 1963 OPV (mixture of three polio serotypes: 1, 2, 3) was licensed.
- Showed evidence of reversion
what is Defined Attenuation
Genetically manipulate viruses
Introduce defined mutations
Inactivated Vaccines
Most successful form of vaccination in the early part of this century
Inactivated Vaccines pros
No chance of reversion to live strain
Easier to store, refrigeration not necessary
Virus is not able to replicate, this has consequences on how it is able to stimulate the immune system
Inactivated Vaccines cons
- Require higher dosing and additional boosts to generate useful levels of immunity
- Cannot stimulate an MHC-I response
Capsid and Subunit Vaccines
- Immunogenic viral proteins or whole capsids
- Made by purifying the viral protein from a virus preparation or by recombinant DNA cloning and expression of the viral protein in a suitable host cell
Capsid and Subunit Vaccines: PROs
-No chance for reversion – Not a complete virus being introduced -Stable storage -Fast to produce -Much easier to receive approval -Able to manipulate and optimize protein immunogenicity -Able to develop vaccines against
Capsid and subunit vaccines: CONs
- Not nearly as immunogenic as live or attenuated vaccines
- Proteins are expressed by recombinant DNA technology may not be of correct structure
- Does not induce a cell-mediated response
- Requires a strong adjuvant
- High mutation rates mean chimeric peptides or capsid vaccines are better than single protein vaccines
Hepatitis B Vaccines
Used to isolate virus particles from the blood of infected individuals and hepatitis B surface antigen (HBsAg) was purified
-does not grow well in culture
HPV Vaccine
- Virus associated with cervical carcinomas
- Whole capsid vaccine
- Four serotypes of human papilloma virus
- Recombinant HPV major capsid protein L1 from four HPV types mixed
Recombinant Virus Vaccines
Introducing the genes for immunogenic viral proteins into the genome of another, avirulent, virus
Recombinant Virus Vaccines Pros
carrier’ virus would be alive, allowing for a full repertoire of immune responses against ‘passenger’ protein
‘carrier’ virus could be modified to ensure absolute avirulency
Candidate ‘carrier’ viruses poxviruses, herpesviruses, adenoviruses (vaccinia used mostly)
Recombinant Virus Vaccines cons
Not clear whether the same level of immunity or repertoire of immune responses can be evoked from the expression of a ‘passenger’ protein
‘carrier’ virus can only be used once
Some ‘carrier’ viruses considered have high preexisting immunity in the human population
No vaccines against human diseases using this method are currently in production
Newcastle disease in chickens
DNA Vaccines
- DNA coding for viral proteins under the control of a powerful promoter (IE-CMV)
- Injected into muscle, induce the full range of immune responses
DNA Vaccines pros
Low risk, no virus particle present
Easily manipulated, made, scaled up
Easy to deliver and store
dsDNA stimulates innate immune response
DNA Vaccines cons
- DNA is degraded quickly in the extracellular space
- ‘natural’ transfection rates are very low
Adjuvant 4 functions
Associates antigen with a particle, easier uptake by APCs
Stimulates the immune response
Localizes antigen at site of injection (depot effect)
Can target antigens to particular pathways
MF59-Squalene pros
Stronger immunogenicity
MF59 facilitates introduction of viral proteins into the cytoplasm of cells
MHC-I antigen presentation!
Cell mediated and antibody mediated immunity
MF59-Squalene cons
US veterans’ claims of autoimmune side effects
Later refuted, but stigma attached
Liposome vs Virosome
l: manufactured lipid bilayer, delivery system for transfecting proteins into cells
v: liposome with virus proteins inserted, viral proteins into the cell cytoplasm
Insert DNA vaccine plasmid with eukaryotic promoters into
a bacteriophage
The virus would be taken up by APCs where the insert DNA could be expressed
DNA Vaccines pros
Bacteriophage DNA cannot be expressed in eukaryotic cells = safe
DNA protected within a protein shell
Induce innate immunity
Alternative Delivery Systems (3)
Oral administration
Mucosal immunity
Slow release
Herd Immunity
- When vaccination of a significant portion of the population (herd) provides a measure of protection for susceptible individuals
- The greater the proportion of resistant individuals = smaller probability that a susceptible individual will come in contact with an infectious individual
