Vaccines and Vaccine Development

Question 1

Define Immunisation

• different forms

Answer 1

an artificial process by which an individual is rendered immuneTerm includes:

– Passive immunisation – no immune response in the recipient

– Active immunisation (vaccination) – recipient develops a protective adaptive immune response

Question 2

What is Passive Immunisation?

Answer 2

• Immunity conferred without an active host response on behalf of recipient
• Passive vaccines are preparations of antibodies taken from hyper-immune donors, either human or animal
• protection is temporary

Question 3

Give examples of Passive Immunisation in vaccines

• effect

Answer 3

• Immunoglobulin replacement in antibody deficiency
  
  • taken from donors
• VZV prophylaxis eg during exposure during pregnancy
• Anti-toxin therapies eg snake anti-serum
• protection is temporary

Question 4

How would the following presentation of Vassilis zoster zirus (VZV) in pregnancy be managed

• Definite history of previous chickenpox
• No history of chickenpox or unsure
• No history of chickenpox, or unsure

Answer 4

• Definite history of previous chickenpox
  
  • not indicated in the blood after VZV serology
    
    • reassure patients
• No history of chickenpox or unsure
  
  • VZV IgG positive
    
    • reassure patient
• No history of chickenpox, or unsure
  
  • VZV IgG negative or equivocal
    
    • administer VZV immunoglobulin to protect against primary infection

Question 5

What is Activ Immunisation (vaccination)

Answer 5

• Immunity conferred in recipient following the generation of an adaptive immune response
• General principle is to stimulate an adaptive immune response without causing clinically apparent infection

Question 6

What are general principles of vaccines?

Answer 6

• adminstered to target cohorts in advance of exposure to pathogen
• enough people need to be vaccinated to reach heard immunity
• vaccines are given to healthy people so risk to benefit ratio requires vaccines to have high safety standards
• most vaccines work by generating a long-lasting, high-affinity IgG antibody response
  
  • strong CD4 T cell response is important for this
• ‘problem’ diseases are generally those where the immune system cannot eliminate infection or generate long-lasting protective immunity during natural infection
  
  • MTB, HIV,malaria

Question 7

What goes into vaccines?

(3)

Answer 7

• Antigen: To stimulate an antigen-specific T and B cell response
• Adjuvants: Immune potentiators to increase the immunogenicity of the vaccine
  
  • most act on toll-like receptors
• ‘Excipients’: Various diluents and additives required for vaccine integrity

Question 8

How are active vaccines classified in terms of the antigen?

Answer 8

Question 9

What are live attenuated vaccines?

• how are they formed?

Answer 9

• Live but attenuated organisms used
  
  • attenuated –> reduced
• Achieved by prolonged culture ex vivo in non-physiological conditions
• This selects variants that are adapted to live in a culture
• These variants are viable in vivo but are no longer able to cause disease in humans

Question 10

Give examples of Live-attenuated vaccines

(4/7)

Answer 10

• Measles, Mumps, Rubella (MMR)
• Polio (Sabin)
• BCG
• Cholera
• Zoster
• VZV (not routinely used for primary prevention in UK at present)
• Live influenza (not main product in UK at present)

Question 11

What are the Pros of live attenuated vaccines?

Answer 11

• Replication within-host, therefore produces highly effective and durable responses
• In the case of viral vaccine, intracellular infection leads to a good CD8 response
• Repeated boosting not required
• In some diseases, may get secondary protection of unvaccinated individuals, who are infected with the live-attenuated vaccine strain eg polio

Question 12

What are the Cons of live vaccines?

Answer 12

• Storage problems, short shelf-life
  
  • needs a cold chain
• May revert to wild type
  
  • Eg vaccine-associated poliomyelitis: around 1 in 750 000 recipients
• Immunocompromised recipients may develop clinical disease

Question 13

Give an overview of the Varicella-Zoster Virus

Answer 13

• Primary infection = chickenpox
• Cellular and humoral immunity provide lifelong protection, but viruses establish permanent infection of sensory ganglia –>
  
  • Viral reactivation=zoster
• Particularly elderly, fairly debilitating and may cause long-term neuropathic pain

Question 14

Give an overview of the Varicella-Zoster Vaccine

• how does it work
• efficacy in the UK

Answer 14

• Live-attenuated VZV, works by induction of anti-VZV antibodies
• 95% effective at preventing chickenpox
• Attenuated virus does establish the infection of sensory ganglia, but subsequent zoster is probably rare
• 3-5% mild post-vaccination varicella infection
• Not on UK schedule at present, because:
  
  • VZV is a fairly benign childhood infection
  • ?Schedule is already crowded and controversial
  • Safety concerns based on evidence from other countries
    
    • ‘Disease shift’ to unvaccinated adults, in whom VZV is less well tolerated
    • Increase in zoster – probably reduced immune-boosting in adults

Question 15

Give an overview of Zoster infection and age

Answer 15

• The incidence of zoster increases with age, in parallel with declining cell-mediated immune responses to zoster

Question 16

Explain the Zoster vaccination

• type of vaccine
• effect and use

Answer 16

• Similar VZV preparation to that used for primary disease, but much higher dose
• Aims to boost memory T cell responses to VZV
• In over 60s, 50% reduction in zoster incidence after vaccination compared to controls; reduced severity and complications amongst vaccinated cases

Question 17

What is Poliomyelitis

Answer 17

• Enterovirus establishes infection in oropharynx and GI tract (alimentary phase)
• Spreads to peyers patches then disseminated via lymphatics
• Haematogenous spread (viremia phase)
• 1% of patients develop neurological phase: replication in motor neurones in spinal cord, brainstem and motor cortex, leading to denervation and flaccid paralysis

Question 18

What are the two Polio vaccines?

• what type of vaccines are they
• efficacy?

Answer 18

• Sabin oral polio vaccine (OPV) = live-attenuated
  
  • Viable virus can be recovered from stool after immunisation
  • Highly effective, and also establishes some protection in the non-immunised population
  • 1 in 750 000 vaccine-associated paralytic polio
  • better suited to endemic areas where benefits of higher efficacy outweigh risk of vaccine-associated paralysis
• Salk injected polio vaccine (IPV) = inactivated
  
  • Effective, but herd immunity inferior
  • better suited in lower prevalence areas (UK switched in 2004)

Question 19

Explain the Tuberculosis infection

Answer 19

• During primary infection, MTB establishes infection within phagolysosomes of macrophages.
• Macrophages present TB antigen to MTB-specific CD4 T cells, which secrete IFN-g
  
  • this activates macrophages to encase TB in the granuloma.
• It may be visible as a calcified lesion on plain CXR (Ghon focus)
• Most TB thought to be re-activation of this primary infection

Question 20

What is the TB vaccination?

• type of vaccine
• administration
• efficacy

Answer 20

• Only licensed product is BCG (bacille Calmette-Guerin)
• Produced by repeat passage of a non-tuberculous mycobacterium: Mycobacterium Bovis
  
  • ​gives an attenuated vaccine
• Aims to increase Th1 (IFN-g) cell responses to M bovis, thereby conferring protection against MTB
• Given by intradermal injection –> scar
• 80% effective in preventing disseminated TB/ TB meningitis in children; little or no effect on pulmonary TB in adults

Question 21

What are Killed (Inactivated) vaccines?

• how are they formed
• action, overall efficacy

Answer 21

• Entire organism used, but physical or chemical methods used to destroy viability (eg formaldehyde)
  
  • also preserves the immunogenicity of the organism
• Stimulates B cells, and taken up by antigen-presenting cells to stimulate antigen-specific CD4 T cells
• Probably elicit minimal CD8 response, as the vaccine cannot undergo intracellular replication
• Responses less robust compared to live-attenuated vaccines

Question 22

What are examples of Killed vaccines?

Answer 22

• Hepatitis A
• Influenza (standard vaccine – live-attenuated also available but not routinely used)

Question 23

What are Pros of Killed vaccines?

Answer 23

• No potential for reversion
• Safe for immunocompromised
• Stable in storage (formaldehyde)

Question 24

What are Cons of Killed vaccines?

Answer 24

• Weaker responses compared to live vaccines, and no CD8 response, therefore
  
  • Responses less durable than live vaccines
    
    • Generally, boosters required
  • Higher uptake generally required to achieve herd immunity

Question 25

Give an overview of the Influenza virus

Answer 25

• Seasonal viral illness
• Protective antibody responses largely directed against haemagglutinin (H) and neuramidase (N) surface antigens
• Natural antigenic ‘drift’ each year means that protective immune response from previous years may not be protective
• Major antigenic ‘shift’ when virus recombines with animal influenza strain – eg ‘Spanish’ Influenza (1918), H1N1 (2009)

Question 26

What is the approach to producing Influenza vaccines?

Answer 26

• As immune responses are not durable, CDC attempts to predict likely dominant viruses for next season
• Candidate viruses grown in hens eggs and distributed to manufacturers
  
  • Killed vaccine is standard UK approach
  • Live vaccine also available (nasal spray)
• Success varies from year to year

Question 27

What are Subunit vaccines?

• different types (3)

Answer 27

• Uses only a critical part of the organism
• Components may be:
  
  • purified from the organism or
  • generated by recombinant techniques
• Protection depends on eliciting CD4 and antibody responses
• Toxoids, Polysaccharide capsules, Recombinant protein subunit vaccines

Question 28

What are Toxoid Subunit vaccines?

• examples
• how do they work

Answer 28

• Many examples relate to toxin-producing bacteria
  
  • Corynebacterium diphtheria
  • Clostridium tetani
  • Bordatella pertussis (whopping cough)
• Toxins are taken and chemically detoxified to ‘toxoids’
• Retain immunogenicity
• Work by stimulating antibody response; antibodies then neutralise the toxin

Question 29

What is the vaccine used for tetanus?

Answer 29

• Subunit toxoid vaccine
  
  • you can still get infected with tetanus but the effect neuromuscular effect isn’t there
• Pre-formed high-affinity IgG antibodies can neutralise the toxin molecules in the circulation;
  
  • the immune complexes are then removed via the spleen
• Anti-toxin can also be given in established cases (passive immunisation)

Question 30

What are Polysaccharide capsules Subunit vaccines?

• which two infections is this used in?

Answer 30

• Thick polysaccharide coats of Streptococcus pneumoniae and Neisseria meningitidis make them resistant to phagocytosis
• Vaccines for these organisms formed of purified polysaccharide coats
• Vaccines formed of purified polysaccharide coats; aim to induce IgG antibodies that improve opsonisation
• Suboptimal as polysaccharides are weakly immunogenic:
  
  • No protein/ peptide, so no T cell response
  • they can stimulate a small population of T-independent B cells
• Latest vaccines utilise vaccine conjugation to boost responses: protein carrier attached to polysaccharide antigen

Question 31

Explain Vaccine Conjugation

Answer 31

• Naive B cell expressing surface IgM recognises polysaccharide antigen.
• Antigen is internalised together with the protein conjugate
• Conjugate is processed in the class II pathway.
• Naive B cell presents peptides from the conjugate to a helper T cell with the correct receptor.
• T cell helps the B cell to perform affinity maturation, but antibody is specific for the polysaccharide and not for the protein conjugate

Question 32

What is Recombinant protein Subunit vaccines?

• vaccines produced?

Answer 32

• The key immunogenic protein is required
  
  • the protein is then expressed in lower organisms
  • then purified to produce the vaccine
• Hep B surface antigen
• HPV vaccine

Question 33

Explain the development Human Papillomavirus Vaccination

• what does the vaccine protect against?

Answer 33

• HPV subtypes 16 and 18 infection major causal factor in cervical carcinoma
  
  • vaccine protects against this
• Vaccine development problematic as HPV is difficult to culture so they used
• Subunit vaccines are ‘empty virus particles’ that prevent primary infection
  
  • viral particles which only have the capsid protein
• Quadrivalent vaccine covers additional HPV strains (genital warts, penile cancer)

Question 34

What are the Pros of Subunit vaccines?

Answer 34

• Extremely safe as only parts of the organism is present
• Work well where primary infection may be prevented by an antibody response
• Works when the virus cannot easily be cultured eg HPV and Hep B

Question 35

What are the cons of Subunit vaccines?

Answer 35

• Development requires detailed knowledge of virology, pathogenesis and immunology
• Specialised and expensive production
• Weaker immune responses – boosting often needed and response rate varies

Question 36

What are Adjuvants?

Answer 36

• Boost immune response to the antigen
• Eg alum, lipopolysaccharide
• Work by binding to pattern-recognition receptors on antigen-presenting cells
• This enhances co-stimulation and cytokine secretion, which ensures a robust T/ B cell response
• Important field for development in order to improve responses to subunit vaccines
• Novel adjuvants are toll-like receptor ligands eg CPG repeats

Question 37

Explain mRNA vaccines

• how are they formed
• how do they work

Answer 37

• For mRNA vaccines, they create a sequence generated which codes for critical pathogen antigens
• Delivered via vector
  
  • eg lipid nanoparticles OR
  • ex vivo (harvest circulating monocytes then return to the recipient)
• Sequence translated by host cells to produce encoded antigens, which then stimulates host immune response

Question 38

What are the technical challenges of mRNA vaccines?

• solutions?

Answer 38

• Preventing degradation of mRNA – solution was lipid nanoparticle delivery
  
  • polyethylene glycol (PEG)- used to encapsulate the mRNA and protect it against destruction
• Inflammatory response caused by mRNA – solution was modifying nucleosides to reduce the inflammatory potential but still being able to create the protein of intrest

Question 39

What are the Positives of mRNA vaccines?

Answer 39

• Potentially rapidly available and modifiable;
• Relatively quick and easy to produce and adapt once facility established

Question 40

Explain Viral vectors

• challenges

Answer 40

• Benign virus that can be easily grown in culture engineered to carry genes encoding immunogenic antigens
• Altered virus used as a live-attenuated vaccine or a non-replicating viral vaccine

Challenges

• Pre-existing immunity to viral vector
• Immune responses to viral vector may affect later use