Lecture 10 - Vaccines I

Question 1

What were some of the problems and limitations off the wakefield study?

Answer 1

No controls included.
Autism would occur in 25 non-immunised children/month based on probability
No experimental evidence for the hypothesis that MMR peptides were translocated to the brain

Question 2

What are the 4 main types of vaccine?

Answer 2

Live vaccines - Living but cannot cause disease

Killed vaccines - Killed by heating or exposure to chemicals

Subunit vaccines - Fragments of the microorganism e.g. proteins or polysaccharides, which then elicit an immune response

Naked DNA vaccines - DNA that makes proteins after injection

Question 3

What is the mechanism of a sub unit vaccine?

Answer 3

Isolated components of a microorganism such as individual coat proteins or polysaccharides (components generally found on the infective cell’s surface).
The presence of this protein then almost always induces an antibody mediated response

Question 4

In what type of patient is the use of live vaccines less favourable and why?

Answer 4

Less favourable in immunosuppressed patients, as the living pathogen is injected and in theory could overcome a more suppressed immune system in order to cause disease

Question 5

What is the role of agglutination?

Answer 5

Enhances phagocytosis and reduces number of infection until to be dealt with as they get ‘clumped together’.

Question 6

Name the protective mechanisms involved in binding of antibodies to antigens

Answer 6

Agglutination
Activation of complement
Opsonisation
Inflammation
Neutralisation
Antibody dependant cell mediated cytotoxicity (ADCC)

Question 7

What is the role of opsonisation?

Answer 7

Coating antigen with antibody enhances phagocytosis

Question 8

What is the role of ADCC?

Answer 8

Antibodies attached to target cell cause destruction by non specific immune system cells

Question 9

What type of toxoid is the diphtheria vaccine?

Answer 9

Formaldehyde toxin

Question 10

How are formaldehyde toxins produced?

Answer 10

Formaldehyde toxin works by cross linking proteins to form -CH2- linkages that don’t naturally occur.
This physically changes the structure of the protein preventing it from being active but allowing the structure to still remain preserved enough to be recognised by the body and elicit an immune response.

Question 11

What are some of the problems with formaldehyde detoxification in production of a vaccine?

Answer 11

Must balance cross-linking with retention of antigenic structure
Batch to batch variation
Reversion
Requires pure toxin as the starting point
Need to grow pathogen, meaning you need to purify and handle the toxin

Question 12

What method other than formaldehyde detoxification can be used to alter viral proteins and produce subunit vaccines?

Answer 12

Genetic toxoids can be produced through modification of a toxin using genetic engineering so that it is non toxic but immunogenicity is retained

Question 13

How is the genetic toxin for diphtheria produced?

Answer 13

Mutations in specific subunits such as the part with catalytic activity, preventing the toxin from being able to have such activity. It will however still look the same so will still elicit an immunogenic effect.

Question 14

What are the advantages of a genetic toxoid over a formaldehyde toxin?

Answer 14

Don’t have issues with reversion

No batch to batch variation

Question 15

How does the NetB toxin cause necrotic enteritis?

Answer 15

7 subunits form a pore that inserts itself into the gut cell membrane, meaning that it is unable to regulate its own osmotic balance. If we could neutralise the toxin, we would be able to protect against disease.

Question 16

What are the advantages of genetic toxoids?

Answer 16

Produced in harmless bacteria
High yields, due to ease of purification
Molecular structure more similar to active toxin than those formed by formaldehyde detoxification
Reproducible properties minimises variation between batches
No risk of reversion

Question 17

What are the roles of the two proteins identified as important for disease progression and therefore targets for the production of a subunit vaccine?

Answer 17

F1 antigen forms capsule around bacterium that prevents phagocytosis by macrophages etc

V antigen is part of the type III secretion system (needle tip). T3 secretion systems are molecular syringes that poke out of the surface of the bacterial cell and inject toxic proteins into the host

Question 18

What is reverse vaccinology?

Answer 18

Taking a genome sequence of a microorganism and trying to predict from this sequence which proteins would be effective as a vaccine.
This can be achieved by trying to predict from the genome which components of the cell are going to be displayed on the surface, as this is usually where the most important components lie.
Look for signatures in the AA sequence that direct the components translation to the cell membrane.