Flashcards in Vaccine Control Deck (12):
What are the aims of vaccines?
To elicit an immune response that will prevent or limit disease upon encounter with the target organism/antigen.
- Prevention of disease
- Prevention of transmission
- Eradication of disease
What are examples of successful vaccines?
- Polio (salk-inactivated virus, sabin-attenuated virus)
- Diphtheria (toxoid - inactivated toxin)
What is the difference between passive and active immunisation?
Passive or active immunisation?
• Passive immunisation
• Transfer of immune sera/cells to provide protection
• Protection is immediate but short term
• Example: Rabies immune globulin- given to individuals who have been scratched/bitten/licked by rabies-infected animals
• Maternal antibodies transferred to newborn
• Transplancental transfer of IgG (acts systemically)
• Wanes by 6-9 months
• De Novo IgG production evident between 3-6 months
IgA from sucking (probably only acts in gut)
• The introduction of foreign material into a host to stimulate an adaptive immune response
• Typically involves
• The administration of a preparation that contains one or more microbial antigens
• The administration of a vector that directs the expression of one or more microbial antigens
You need a good immune response to have an effective vaccine:
• T cells
• B cells
Innate immunity (dendritic cells)
What does a good vaccine typically need?
- Something to stimulate the innate immune system
- T cell epitopes
- B cell epitopes
• Live attenuated vaccines are usually more potent than subunit or inactivated immunogens
• Pathogen replication creates strong innate immune signals
• Diverse range of antigens expressed
• Higher antigen loads
Better T cell responses
What is an attenuated vaccine?
- Attenuation of pathogens tends to be more potent
- In can be achieved through in vitro passage (humans- monkey - human)
- Attenuation of pathogens can be achieved through targeted deletion of virulence genes/determinants
- Resulting virus is viable but avirulent and so it can be used as a vaccine
What is a subunit vaccine?
- Immunise with components of pathogens rather than the whole organism
- Hepatitis B vaccine is an example of this
What are toxoid vaccines?
- Immunisation with inactive forms of toxins (diphtheria/tetanus)
- Antibodies bind to native toxin and block activity
What are conjugate vaccines?
- Consist of an antigen coupled to a carrier (can't stimulate a T cell response and so it needs to be coupled to a protein which is termed carrier)
Eg. Neissera meningitis -> bacterial meningitis coupled to diphtheria toxoid
DNA vaccines in the form of plasmids can also be used
Features of effective vaccines
• Safe -> vaccine must not itself cause illness or death
• Protective -> vaccine must protect against illness resulting from exposure to live pathogen
• Gives sustained protection -> protection against illness must last for several years
• Induces neutralising antibody -> some pathogens infect cells that cannot be replaced - neutralising antibody is essential to prevent infection of such cells
• Induces protective T cells -> some pathogens, particularly intracellular, are more effectively dealt with by cell-mediated responses
Practical considerations -> low cost per does - biological stability - ease of administration - few side effects
What is the process of sub-cloning?
• Sometimes it is not possible to directly clone your gene of choice into the appropriate expression vector
• Maybe due to size limitation
• Due to additional restriction sites within your gene and those used for cloning
• Or simply just technical issues associated with cloning
• To facilitate this process we can use an intermediate or shuttle plasmid in a process termed sub-cloning
• Shuttle plasmids are generally quite small
Have a greater range of restriction sites