Week 9 Part 2 - Vaccine Development Flashcards
What was Smallpox Caused By?
Virus called variola
From Poxviridae family
Genus orthopoxviruses
How to Generate Live Attenuated Vaccines
Pathogenic virus isolated from patient and grown in human cultured cells
Cultured virus used to infect monkey cells
Virus acquires many mutations that allow it to grow well in monkey cells
Virus no longer grows well in human cells (attenuated) and can be used for vaccines
Vaccine Generation and Examples - Live Attentuated
Pathogen adapts to new growth conditions
Less infectious to the original host
E.g. measles, mumps and rubella vaccine
Vaccine Generation and Examples - Toxoid
Toxins cause disease
Toxin inactivated
Antibodies block the toxin
E.g. Tetanus and diphtheria
Vaccine Generation and Examples - Subunit
Defined antigens
Purified or recombinant
Excellent safety
Not as immunogenic as whole organism
Need a strong adjuvant
E.g. HPV vaccine
Vaccine Generation and Examples - Conjugate Vaccines
Bacteria protected by polysaccharide coat
Poorly immunogenic
Synthesise polysaccharides conjugated to immunogenic protein
E.g. HiB, meningitis C and pneumococcal vaccines
DNA and RNA Vaccines
Used for gene therapy
Can contain multiple antigens, cheap and quick to develop
Vectored Vaccines
Antigens vectored into host cells by replication deficient viruses
E.g. Adenovirus
Reverse Vaccinology
Use genome sequencing to select immunogenic antigens
Coronavirus Structure
Medium-sized virus
Largest mRNA genome
mRNA encased in nucleocapsid
Lipid bilayer (soap disrupts this)
Corona = Crowns for Spikes
- Glycoprotein Spike (S)
- enable attachment to tissues by ACE-2 Receptors
ACE-2 Receptor Tissue Expression
Type 2 alveolar cells
Bronchial epithelia
Tongue > buccal epithelia
Upper Intestinal epithelia
Myocardial cells
Kidney proximal tubule cells
Bladder urothelial cells
What are Nanoparticles
Small objects that behave as a whole unit in terms of transport and properties
Dimensions are 1-100 nanometres = 8,000th of a human hair in width
Occur naturally in clay, volcanic ash, ocean spray, milk, etc.
Can be manufactured
How are Nanoparticles used in Vaccines?
As antigen delivery systems
As immune adjuvants
Nanoparticles can be entrapped with antigens such as:
- proteins
- peptides
- DNA, RNA, etc
= Control the release of vaccine antigens
Can optimise the immune response by selective targeting of the antigen to antigen presenting cells
Possible to target specific APCs, in particular dendritic cells (DCs)
Induce a CD4+ and CD8+ T cell response plus a B cell (antibody) response
What Biodegradable and Biocompatible Polymers can Prepare Nanoparticles?
Poly(lactide-co glycolide) (PLGA)
Poly(amino acid)s
Polysaccharides
Liposomes
Closed lipid bilayer vesicles that spontaneously form in water = a fatty capsule
Consist of a phospholipid bilayer shell with an aqueous core
Can be:
1. Unilameller - single phospholipid bilayer
2. Multilameller - several concentric phospholipid shells separated by layers of water
Can be tailored to incorporate:
- hydrophilic molecules (e.g. antigens) into the aqueous core
- hydrophobic molecules within the phospholipid bilayers
Disadvantages of Liposomes
Short circulation time in blood stream
Unstable in human body
Lack selective targeting
Disadvantages of Liposomes and it’s Solution - Short Circulation Time in Blood Stream
Solution: Improve longevity by coating the surface with biocompatible inert polymers such as PEG
- should be undetected
- but some people experience severe allergic reactions to PEG
Disadvantage of Liposomes and it’s Solution - Unstable in the Human Body
Solution: Develop stimuli responsive liposomes e.g. sensitive to to temperature and pH
Disadvantages of Liposomes and it’s Solution - Lack Selective Targeting
Solution: Can place antibodies on the surface of the liposome
Advantage of Liposomes
Good platform to deliver DNA and RNA
RNA, mRNA, siRNA and DNA difficult to deliver directly due to:
1. Negatively charged and hydrophilic
2. Prevents passive diffusion across plasma membranes
3. Susceptible to nuclease degradation - free mRNA breaks down quickly in the body
Solution: Use nanoparticles with synthetic positively charged (cationic) lipid
- nucleic acids are now more stable and resistant to nuclease degradation.
Pfizer, Moderna and CureVac Vaccines - Overview
Liposomes with mRNA coding for the coronavirus spike protein
Pfizer and Moderna = 2 doses >90% successful at reducing infection and disease severity – a variant
CureVac = 47% effective at preventing disease = failure, must be > 50%
Similarities between Pfizer and Moderna
Ionizable cationic lipid
PEGylated lipid
Cholesterol
Phospholipid distearoylphosphatidylcholine (DSPC)
Modified RNA = incorporate pseudouridine in place of uridine
- may help avoid inflammatory reactions to foreign mRNA
Pfizer = 30 micrograms of vaccine
Moderna = 100 micrograms of vaccine
CureVac Vaccine
Dose & side effect problems
Uses normal uridine
- altered the mRNA sequence - does not affect the protein it codes for
- aimed to help the mRNA evade immune detection
- structural differences in the non-coding regions of the CureVac sequence
Higher storage temperature = might accelerate breakdown of mRNA
How do RNA Vaccines Work?
- mRNA enters the cell
- Cell starts spike protein production
- Spike protein is recognised by the immune system
- Antibody production
- Immune response + cytotoxic T cell response
