New vaccine development Flashcards
Criteria of a good vaccine
- safe and effective
- generate an appropriate immune response
- delivery method/vaccination schedule (no of doses etc)
- affordable, cheap to manufacture, speed (response to outbreak)
- easy to transport and store
Empiricism vs Rational design
Empiricism: Knowledge obtained by direct or indirect observation or experience
Rational design: Creating new molecules with certain functionality –requires the ability to predict how changes in the molecule’s structure will affect its behaviour
moving towards rational design
Vaccine formula
3 parts
- Antigens
- Adjuvants
- Delivery systems
- Antigens
Empirical approaches include live vaccines, inactivated toxin and killed
Sub-unit/conjugate include glycoconjugate and virus-like particle
Rationally designed include reverse vaccinology, synthetic vaccine and structural vaccinology
Glycoconjugate vaccine
Poor polysaccharides antigens conjugated to carrier protein (e.g. diphtheria toxin) - generates more powerful immune response.
Mechanism: When purified, the polysaccharides are poorly immunogenic, as they are unable to enter the cavity of MHC molecules and therefore they fail to be presented to T cells. In conjugate vaccines, such as those against Haemophilus influenzae type b, pneumococcus, meningococcus and group B streptococcus, polysaccharides are covalently linked to proteins.
The peptides derived from the proteins (blue triangles) enter the cavity of the MHC molecule and engage the T cell receptor directly or function as an anchor for a sugar epitope
Virus-like particles (VLPs)
Virus-like particles resemble viruses but, are non-infectious because they contain no viral genetic material.
Self-assembly of viral structural proteins (e.g. envelope or capsid)
Mimics native virus but do not contain genetic material (safer)
Examples: Hepatitis B vaccine; Human Papilloma Virus 16 and HPV18 (Gardasil, Cervarix)
Like overall virus but lack viral genome. Polymerase, and internal structures. Therefore, cant replicate.
Safer than attenuated vaccine / inactivated.
Examples: Hep B vaccine, gardasil, vervarix.
Reverse vaccinology
Starts with the genome of pathogen, which is sequenced and computer predicts candidate antigens
Proteins purified and used in mouse
e.g. Bexsero vaccine for meningitis serogroup B
Previous technique = epitope discovery starts from identifying which proteins are protective antigens.
Examples: meningococcus serogroup B (Bexsero, GSK), MRSA (pre-clinical)
Reverse vaccinology: benefits and limitations
Most powerful antigen discovery tool currently available
Provides access to the entire antigen repertoire of bacteria and parasites (even those not cultivable under laboratory conditions)
Screen for the most conserved protective antigens
Limitations: Data overload; protein antigens only; antigen in wrong conformation
Can compare across multiple genomes to screen for most conserved protective antigens.
Its limited to protein antigens only as polysaccharides are note coded in genome and can’t be detected using this method.
Not for HIV as protective antigens are known but mutating quickly and for RSV – antigens in wrong conformation.
Structural Vaccinology
It depends on structural biology.
Use atomic-level information about key antigens and their epitopes to rationally modify antigens
Modify antigens to become better immunogens.
3D structure of proteins determined by X-ray crystallography, NMR, electron microscopy
Examples: RSV, HIV
RSV F protein
RSV
F protein
Respiratory syncytial virus - affects lung and breathing passage. No licensed vaccine, infants most vulnerable.
is a syncytial virus that causes respiratory tract infections. It is a major cause of lower respiratory tract infections and hospital visits during infancy and childhood.
F protein – mediates fusion of virus to host cell, allows entry to cytoplasm
Has pre and post fusion conformation (pre-fusion is preferred but less stable, induces higher neutralising antibody titres that existing vaccines that were based on post-fusion).
Synthetic Vaccines
equence viral genome, synthesis gene, make it in mammalian cells. Can be used as seed virus for larger scale manufacture.
Used published sequence of antigens to manufacture vaccine subunit
No need for cultivation of actual virus, shipping; can manipulate DNA before production
Accelerate vaccine availability in pandemics
Examples: H7N9 avian influenza virus (without virus even having to leave country of origin)
Benefits: can make tweaks in DNA before production, accelerates vaccine availability in pandemIcs.
Plasmid DNA (pDNA) Vaccine
First amplify /synthesis gene of interest e.g. antigenic / immunoadjuvant genes.
Put it into plasmid. Purified then delivered muscularly or subcutaneously.
This hijacks the host’s cellular machinary.
Targeting 2 cells; muscle cells (myocytes) and APCs
In muscle – transcribe and translate the plasmid and protein folded, modified post translationally. Antigen may shed or stay within muscle cells as it apoptosis. It will be internalised and processed by APC and presented as MHC2. OR cross presented on MHC1.
In APC, they will be presented using MHC class 1 (As made in cells themselves).
So both Apc loaded with antigens travel to lymph node. Present to CD8 / CD4+ t cells.
pDNA Vaccines: benefits and limitations
increasingly popular in modern vaccine development
Vaccines generally only produce a B cell response. This mimics true infection
mimics true infection – induces both cellular and humoral immunity
cheap to produce; does not require a cold chain
limited to protein immunogens
Adjuvants
Adjuvants help generate strong, long-lasting protective immune response
Advantages: Dose sparing, Reduce amount of doses, = less doses of antigens, brings cost down, More rapid immune response and antibody response broadening (may include related strains)
Adjuvants can be divided to immune-stimulants and delivery systems.
Immune stimulants interact with specific receptor to activate innate system. Eg. TLR agonists, derivatives of bacterial enterotoxin, cytokines and chemokines
Delivery systems - example is viral vector, which is considered an adjutant because it can induce an immune response
Methods for needle-free immunization
Traditional route = syringe.
Needle free = less professional training.
These include liquid injections, microneedle patches, powdered formula, creams etc.
Mucosal vaccines can be delivered orally nasal, eye drops etc.
