Virus Recombinant Vaccines Flashcards
Goals of vaccination against viruses
Induce immunity in individual hosts that…
Prevent or eliminates viral disease
Causes no or minimal associated morbidity or mortality.
Induce “herd” immunity that …
Greatly restricts virus circulation in a given community
Protects vulnerable members of the community for whom the vaccine is proscribed
Virus eradication
How do vaccines work?
Vaccine antigen introduced to body (Mucosal or Parenteral) -> Viral antigen taken up by APCs -> present antigen to B and T cells in correct conformation in LNs -> Clonal expansion of epiptope-specific memory B and T cells -> Accelerated response to virus upon infection -> protection from disease due to Tc cells and neutralising Abs
Primary and memory Ig responses - basis of vaccination
1st infection/vaccination - 1º response
2nd exposure - anamnestic response
What are epitopes?
Antigenic determinants of molecules that are bound by:
Antibodies (B cell epitopes) - Peptides, polysaccharides, lipids
T cell receptors (T cell epitopes) = Peptides
Dominant epitopes = Elicit strongest immune responses
Subdominant epitopes = Less immunogenic than dominant epitopes
Viruses direct immune system to dominant epitopes but AREN’T essential and there can be subdominant epitopes = essential (eg part of receptor binding site)
B cell Epitopes can be
Linear peptides
Contiguous chain of amino acids within a protein
Antibodies can recognise primary structures
Conformational peptides
Non-contiguous chains of amino acids within a protein (3º structure)
Antibody recognition dependent of tertiary folding of protein
Peptide scanning (pepscans) for linear B cell epitopes
Synthase overlapping peptides with 1 more peptide at end and 1 less at start. Add to wells and add antibodies to identify which peptides contain the epitope
Examples of T cell Epitopes
T helper cells (CD4+)
- Linear peptides
- Presented by MHC class II
Cytotoxic T cells (CD8+)
- Linear peptides
- Presented by MHC class I
T regulatory cells (CD4+CD25+)
- dampen down response
Antigen-Specific T and B cell maturation and function
Cytokines and chemokines induced following infection
APC interacts with Th0 cell to produce IL-2 - Th2 response - drives towards Th response
Th1 - drives towards t cytotoxic cell
Current recombinant viral vaccine strategies
Live attenuated viruses
Recombinant subunit vaccines
Virus vectors expressing viral vaccine antigens
DNA vaccines
Edible plants expressing viral vaccine antigens
Strategy and rationale of live attenuated viruses
Cold adapted, temperature sensitive:
Multiple passages at progressively lower temps
Restricted growth at 37ºC
Mucosal administration - Mucosal and systemic antibody and T cell responses
Restrict virus replication to upper respiratory tract
- Eliminate virus pathogenesis for lower respiratory tract by restricting growth at 37ºc
Eg Influenza virus and RSV
Edible vaccines
Genetically modified plants expressing viral vaccine antigens
Consumption induces immune responses in intestine = mucosal immunity
- Processing of antigens through M cells
Do edible vaccines work? 🥔
Potato expressing hepatitis B surface antigen (HBsAg)
Double blind placebo controlled trial
- Consumption by previously vaccinated individuals
-Recombinant potatoes expressing HBsAg
-Recombinant potatoes with no antigen - Detection of boosts in anti-HBsAg titres in serum following vaccination.
-Surrogate of protective immunity
Conclusions:
- consumption of HBsAg potatoe increases antibody titres
- edible vaccines have potential in humans
Why continue research on influenza virus vaccines?
Current split/subunit vaccine
Limited heterosubtypic immunity
Vaccine efficacy based on antibody responses
- Antigenic drift = new vaccines required each year
- Antigenic shift may eliminate vaccine efficacy
Rationale:
Search for novel influenza vaccine antigens that
- Induce strong heterosubtypic immunity
- Both B and T cell based
- Reduce/eliminate necessity to change vaccine yearly
Principle of DNA vaccines
Viral antigen expression from DNA plasmids delivered directly to host
Precision plasmid can be generated eg:
- vaccine antigen
- specific promoters
- codon optimisation
- immune enhancing genes
-cytokines/chemokines
5 considerations(steps) in production of a DNA vaccine
Plasmid optimisation
Gene optimisation
Formulation adjuvants
Immune plasma adjuvants
Delivery
