Vaccinology - Vaccine formulations Flashcards
Which types of vaccine are considered ‘classic’? (3)
Vaccines that are based on the modification of a wild-type pathogen
1. Live-attenuated vaccines
2. Inactivated vaccines
3. Subunit vaccines
Which type of vaccine are considered ‘novel’? (5)
Vaccines that rely on recombinant DNA technologies
1. DNA vaccines
2. Vector-based vaccines
3. Virus-like particles
4. Antigen-loading of autologous DCs
5. RNA/mRNA vaccines
What are examples of current live-attenuated vaccines? (5)
- Measles, mumps, rubella (MMR/BMR)
- Varicella zoster virus (VZV)
- Yellow fever (YFV)
- Influenza
- BCG
Which two production strategies can be used to produce live attenuated vaccines?
- Taking an animal pathogen similar to the human pathogen to generate cross-protection
- Adapt the virus to conditions very dissimilar in humans, ensuring that it can no longer effectively replicate in humans
What are requirements of animal viruses being used to induce cross-protectivity against human viruses? (2)
- It must generate strong cross-protection
- The animal pathogen must have some replication in humans to induce an immune response, but not so much that it causes disease
What is an example of a succesful case of an animal virus being used to generate cross-protectivity against the human virus?
Cowpox being used for smallpox eradication
What is an example of a virus that was passaged in conditions dissimilar to humans, making int unable to replicate efficiently in humans? Under which conditions was it adapted?
Rubella -> passaged in embryonated chicken eggs at reduced temperature
What are the advantages of live attenuated vaccines? (2)
- Immune responses resemble natural immunity
- Often induce long-lasting protection after a single dose
Why do live attenuated vaccines strongly mimic natural immunity?
Viral replication & antigen production within host cells leads to presentation on MHCI and MHCII, inducing a strong B- and T-cell (both CD4+ and CD8+) response
What are the disadvantages of live attenuated vaccines? (3)
- Safety risk in immunocompromised
- Possibility to revert to wildtype
- Interference by maternal antibodies
What are two reasons live attenuated vaccines cannot be given during the first few months of children’s life?
- Maternal antibodies neutralize the virus before it has a chance to trigger the immune system
- Immunodeficiencies have not always been diagnosed at a very young age -> live attenuated viruses could cause severe illness
From how many months onwards are children typically vaccinated with live attenuated vaccines?
> 14 months
What is the advantage of inactivated vaccines over live attenuated vaccines?
Infectivity & replication eliminated (no chance of spread or disease) while maintaining immunogenicity
What are examples of current inactivated vaccines? (4)
- Influenza (being replaced by subunit vaccines)
- Polio
- Hepatitis A
- Bordetella pertussis
What are strategies to inactivate a virus for vaccines? (3)
- Chemicals (formalin)
- Heat (mild)
- Radiation
What are important characteristics for possible inactivation methods to produce an inactivated vaccine? (2)
- Antigenicity should be retained
- Immunogenicity should be retained
What is the main advantage of inactivated vaccines?
Safety
Why do inactivated vaccines induce poor CD8+ T-cell responses?
No endogenous production of proteins -> no presentation on MHCI
What are the disadvantages of inactivated vaccines? (3)
- Usually multiple doses required
- Short-lasting immunity
- Poor induction of CD8+ T-cells
In which settings is the lack of CD8+ T-cells induction by a vaccine problematic, and in which cases isn’t it?
Problematic in case of intracellular pathogens, but not a problem in case of extracellular pathogens
What is an additional rare disadvantages of inactivated vaccines? In which virus families does it occur?
Risk of priming for advanced disease in paramyxoviruses & feline coronavirus
What are the two manufacturing options to manufacture subunit vaccines? Are they both in use?
- Non-recombinant: fractionation of pathogen & purification of proteins
- Recombinant: express gene of interest in yeasts/bacteria/cells & purification of proteins
Nearly all subunit vaccines are produced using recombinant techniques
What are examples of current subunit vaccines? (3)
- Influenza
- Hepatitis B (HBV)
- Tetanus
Which antigens are typically used in subunit vaccines?
Capsid- or membrane proteins
What are the advantages of subunit vaccines? (3)
- Safe
- Selection of subunits facilitates a targeted immune response
- Can be used as a marker vaccine to differentiate infected from vaccinated animals
What are disadvantages of subunit vaccines? (3)
- Poorly immunogenic
- Short-lasting immunity
- Poor induction of CD8+ T-cell responses
Why do subunit vaccines induce poor CD8+ T-cell responses?
No endogenous production of proteins -> no presentation on MHCI
What are solutions for the poor immunogenicity of subunit vaccines? (2)
- Multiple doses
- Addition of adjuvants
What is DIVA?
Differentiating vaccinated from infected animals though analyzing their immune response -> if it is only specific to vaccine components, the animal was not infected
What is a virus-like particle?
Essentially a subunit vaccine, modified in such a way that the presentation of the subunits is virus-like -> virus-like capsid structure
By which mechanism do virus-like particles deliver antigens to cells?
They can infect cells, much like viruses can (they just lack the genetic material)
What are examples of virus-like particle vaccines? (3)
- Hepatitis B virus (HBV)
- Human papilloma virus (HPV)
- Hepatitis E virus (HEV)
What are the advantages of virus-like particle vaccines? (4)
- Safe
- Structural similarity to viruses
- Selection of subunit facilitates targeted immune response
- Can be used as a marker vaccine to differentiate infected from vaccinated animals
What are disadvantages of virus-like particle vaccines? (4)
- Poorly immunogenic
- Short-lasting immunity
- Poor induction of CD8+ T-cell responses
- Pre-existing immunity to VLP vector
Why do virus-like particle vaccines induce poor CD8+ T-cell responses?
No endogenous production of proteins -> no presentation on MHCI
Why is pre-existing immunity to VLP-vectors a problem for virus-like particle vaccines?
Immunity to the vector could neutralize the particles before they have a change to deliver their antigens
In what configuration is the DNA in DNA vaccines stored?
Bacterial plasmid DNA
What is the mechanism of action of DNA vaccines?
DNA gets taken up by host cells and causes transient expression of encoded genes & proteins
True or false: DNA vaccines are currently used in humans
False; they have proven poorly immunogenic in humans
In which settings can DNA vaccines sometimes be effective in humans?
In heterologous prime-boost settings
In which settings have DNA vaccines proven to be effective on their own?
For vaccination of small laboratory animals
What is the major challenge of DNA vaccines?
Administration
What are currently explored administration methods for DNA vaccines? (4)
- Gene gun
- Microneedles
- Gas injectors
- In vivo electroporation
What is ‘gene gun’ administration?
Intradermal administration of DNA-coated gold particles
What are the advantages of DNA vaccines? (5)
- Easy to produce
- Induction of humoral immune responses
- Induction of CD4+ and CD8+ responses
- Very stable -> can be stored at room temperature
- Can encompass large inserts
Why do DNA viruses induce CD8+ T-cells?
They lead to endogenous production of antigens, which are presented on MHCI
What are disadvantages of DNA vacciness? (2)
- Often poor protection
- Perceived risk of genome integration by the public
Which two types of RNA vaccines can be distinguished?
- Non-replicating mRNA
- Viral-derived self-amplifying mRNA (SAM)
What is the configuration of RNA in non-replicating mRNA vaccines?
Replicates human mRNA: gene of interest, flanking untranslated regions, 5’-cap and poly(A)-tail
What is the configuration of RNA in viral-derived self-amplifying (SAM) mRNA vacciness?
Alphavirus mRNA structures added to region of interest, allowing for replication of mRNA
What is the advantage of viral-derived self-amplifying mRNA vaccines (SAM) over standard mRNA vaccines?
Large amount of antigen production from an extremely small dose of vaccine
How is RNA in RNA vaccines delivered intracellularly?
With lipid nanoparticles
What are the advantages of RNA vaccines? (5)
- Safe
- Good induction of cellular immune responses, including CD8+
- Good induction of humoral immune response
- Can be administered repeatedly without immunity to administration mechanism
- Scalable
What is the main disadvantage of all RNA vaccines?
Stability -> require cold-chain
What are disadvantages specific to self-amplifying viral-mRNA (SAM) vaccines? (2)
- Size constraints
- dsRNA formation
Why is dsRNA formation in self-amplifying viral-mRNA (SAM) vaccines disadvantageous?
dsRNA = potent TLR trgger -> can cause side effects
Sidenote: this can also be beneficial to inuce a strong immune response
True or false: DC vaccines are currently being used to vaccinate against rare infectious diseases
False: DC vaccination is fully experimental
What is the process of DC vaccine manufacturing? (4)
- Isolate PBMCs
- Select monocytes & culture into DCs
- Maturate DCs & expose them to antigen
- Re-infuse loaded DCs
What are advantages of DC vaccines? (2)
- Good induction of cellular immune responses, including CD8+
- Individual, tailor-made vaccines
What is the main disadvantage of DC vaccines? Why? (2)
Individual, tailor-made vaccine
1. Labour-intensive
2. Expensive
What is a viral vector?
Tool used by molecular biologists to deliver genetic material into cells/hosts
What is a viral vector-based vaccine?
Use of vectors to carry selected genes from another pathogen for immunization purposes
What is the immunological advantage of vector-based vaccines?
They form their own adjuvant & induce a natural type of immune response
For which disease are vector-based vaccines currently in use?
Covid-19 (Johnson & Johnson, University of Oxford-Astrazeneca)
For which disease are RNA vaccines currently in use?
Covid-19 (Moderna, Pfizer-BioNTech)
What are the advantages of vector-based vaccines? (4)
- Safe
- Intrinsic adjuvant
- Induction of natural immunity, including CD8+
- Can be used as marker vaccine to differentiate infected from vaccinated animals
What are the disadvantages of vector-based vaccines? (2)
- Usually multiple doses required
- Pre-existing immunity against the vector
What is the problem with repeated adminstration of vector-based vaccines?
Can lead to immunity against the vector, rather than the target of the vaccine
What is an adjuvant?
Pharmacologica/immunological agent that enhances the immune response to a vaccine
What are mechanisms of action of adjuvants? (4)
- Antigen stabilization and/or delayed release
- Enhanced antigen uptake in macrophages
- Activation of co-stimulatory molecules
- Improved delivery of antigens to the cytosol -> increased cross-presentation
What are examples of adjuvants? (6)
- Aluminium salts
- Mineral oils
- Bacterial products
- Detergents
- ISCOMS
- Cytokines
What are bacterial products that are frequently used as adjuvants? (2)
- Pertussis
- Freund’s adjuvant
What is the disadvantage of using adenoviruses as a vector for vaccines?
Adenoviruses are common in humans -> there is a lot of pre-existing immunity against adenovirus
What are workarounds of the high pre-existing immunity to adenoviruses when using them as vaccine vectors? (2)
- Picking a serotype taht is uncommon in humans
- Use a non-human adenovirus
What are the currently approved SARS-CoV-2 vaccine platforms? (4)
- Inactivated virus
- mRNA
- Viral vector
- Protein subunit
Which SARS-CoV-2 vaccines make use of inactivated virus? (3)
- Sinovac
- Sinopharm
- Bharat
Which SARS-CoV-2 vaccines make use of mRNA? (2)
- Pfizer-BioNTech
- Moderna
Which SARS-CoV-2 vaccines make use of viral vectors? (2)
- University of Oxford-AstraZeneca
- Johnson & Johnson
Which SARS-CoV-2 vaccine makes use of protein subunits?
Sputnik V
What is the common target antigen of all SARS-CoV-2 vaccines?
Spike protein
What is “vaccine effectiveness”? (definition)
Ability to protect an individual or population from an infectious disease
What is “vaccine efficacy”? (definition)
Protection offered by vaccines in ideal-world settings (=clinical trials)
When comparing mRNA and vector-based vaccines for SARS-CoV-2, which has higher efficacy?
mRNA has higher efficacy
How can the lower efficacy of vector-based SARS-CoV-2 (when compared to mRNA) be offset?
By boosting
Which groups of vectors influence vaccine effectiveness? (5)
- Host factors
- Demographic factors
- Vaccine access factors
- Immune factors
- Viral variant factors
Which host factors can positively/negatively/both affect vaccine effectiveness? (5)
Positively: previous infection
Negatively:
-Old age
-Immune compromised
-Underlying health conditions
Both: genetic polymorphisms
Which demographic can positively/negatively/both affect vaccine effectiveness? (4)
Positively:
-High levels of vaccine uptake
-High levels of herd immunity
Negatively:
-High levels of circulating virus
-Close proximity of people living together
Which vaccine access factors can positively/negatively/both affect vaccine effectiveness? (6)
Negatively:
-Limited access to vaccines
Both:
-Type of vaccine used
-Number of doses
-Timing between doses
-Heterologous prime-boost
-Cost-benefit decision by national vaccine bodies
Which immune factors can positively/negatively/both affect vaccine effectiveness? (3)
Positively:
-High antibody titres
-High quality of antibodies (neutralization)
Both: T-cell response
Which viral variant factors can positively/negatively/both affect vaccine effectiveness? (2)
Negatively:
-Antigenic mismatch with vaccine
-Increased transmissibility
What is “immunogenicity” of a vaccine? (definition)
The ability of a vaccine to stimulate an immune response to the vaccine product
Why are immunogenicity studies of vaccines important? (3)
- Easy & high-throughput read-out in smaller numbers of patients (compared to clinical trials)
- Improving vaccine formulations when the immune response is not as desired
- Adaptation of vaccination policies
What is a correlate of protection? (definition)
Immune response a vaccine/natural infection needs to induce protection from the infectious disease in the future
What is the most frequent assay to test correlates of protection?
Neutralization assays using antibodies
What is the new strategy to study correlates of protection?
Establishing immune profiles of protection -> trying to correlate a broad set of immunological characteristics to protection against disease
Which immunological factors can be analysed to obtain immune profiles of protection? (8)
Humoral immunity:
1. Virus neutralization
2. Macrophage phagocytosis (Fc-mediated)
3. Neutrophil activation (Fc-mediated)
4. Complement deposition (Fc-mediated)
5. Antibody-dependent cellular cytotoxicity (Fc-mediated)
Cellular immunity:
6. CD4 T-cell regulation of the immune response
7. CD4 T-cell capacity to activate & induce class switch in B-cells
8. CD8 T-cell capacity to lyse virus-infected cells
True of false: the difference in antibody titres between mRNA and adeno-based SARS-CoV-2 vaccines directly correlates to the difference in efficacy
False: while the adeno-based vaccines had lower antibody titres, their efficacy was relatively comparable with mRNA-based vaccines
What are the differences between mRNA and adeno-based SARS-CoV-2 vaccines when it comes to:
1. Antibody titres
2. T-cell responses
Antibody titres: mRNA vaccines have higher titres & longer persistence of antibodies
T-cell responses: mRNA vaccines induce a higher number of spike-specific T-cells
Does the humoral or cellular response suffer more from antigenic variation of viruses?
Humoral response
Why does the humoral response suffer more from antigenic variation than cellular responses?
Antibodies recognize 3D structures -> more sensitive to antigenic variation
T-cell recognize nonamers/decamers -> less sensitive to antigenic variation
What is a possible solution to antigenic variation?
Bivalent vaccination -> include multiple variants in vaccines
What is the downside of bivalent vaccination?
Leads to a disproportionate boosting of the original vaccine, but does not lead to a substantial response to the new variant
What is a problem of the current method of measuring correlates of protection of vaccines?
They are measured in circulation -> not representative for location where pathogens are encountered
What is a strategy to induce local immune responses that is currently being explored for SARS-CoV-2?
Step 1: induce systemic immunity with intramuscular injectoin
Step 2: boost with mucosal vaccine to attract immune cells to pathogen entry sites
What is the advantage of heterologous prime-boosting for SARS-CoV-2?
Leads to superior boosting of antibody and T-cell responses compared with homologous boosting
Prior SARS-CoV-2 infection gives a [weaker/stronger] vaccination response
(Far) stronger
What is the influence of age on mRNA SARS-CoV-2 vaccines?
No strong influence
What is the influence of age on inactivated/adeno-based SARS-CoV-2 vaccines?
Less effective in elderly
