Immune Modulation Flashcards
What are ways of boosting the immune system?
Vaccination
Replacement of missing components
Blocking immune checkpoints
Cytokine therapy
What are features of the adaptive immune response?
Wide repertoire of antigen receptors: Receptor repertoire is not entirely genetically encoded. Genes for segments of receptors are rearranged and nucleic acids deleted/added at the sites of rearrangement almost randomly. Potential to create in order of 1011 to 1012 receptors. Autoreactive cells are likely to be generated. Mechanisms must exist to delete or tolerise these autoreactive cells.
Exquisite specificity: Able to discriminate between very small differences in molecular structure.
What are antigen presenting cells?
APCs are cells that can present peptides to T lymphocytes to initiate an acquired immune response.
These cells include:
- Dendritic cell
- Macrophage
- B lymphocyte
What are types of osteoclasts?
Langerhans cells
Mesangial cells
Kupffer cells
Osteoclasts
Microglia
What is clonal expansion after exposure to an antigen?
T cells with appropriate specificity will proliferate and differentiate into effector cells (cytokine secreting, cytotoxic).
B cells with appropriate specificity will proliferate and differentiate to T cell independent (IgM) (memory and) plasma cells undergo germinal centre reaction and differentiate to T cell dependent IgG/A/E(M) memory and plasma cells.
Plasma cells secrete high affinity specific antibodies.
What is immunological memory?
Pre-formed pool of high affinity specific antibodies.
Residual pool of specific T and B cells with enhanced capacity to respond if re-infection occurs.
What are features of T-cell memory?
Longevity: Memory T cells are maintained for a long time without antigen by continual low-level proliferation in response to cytokines.
Different pattern of expression of cell surface proteins involved in chemotaxis/cell adhesion: These allow memory cells to access non-lymphoid tissues, the sites of microbial entry.
Rapid, robust response to subsequent antigen exposure: There are more memory cells. These cells are more easily activated than naïve cells.
What are features of B-cell memory?
Pre-formed antibody: Circulating high affinity IgG antibodies.
Longevity: Long lived memory B cells and plasma cells.
Rapid, robust response to subsequent antigen exposure: Memory B cells are more easily and rapidly activated than naïve cells.
How do vaccines promote immunity against influenza?
For influenza although CD8 T cells control the virus load it is antibody which provides a protective response.
Hemagglutinin (HA) is the receptor-binding and membrane fusion glycoprotein of influenza virus and the target for infectivity-neutralizing antibodies.
There is a clear correlation between resistance to infection and levels of IgG antibody to haemagglutinin (HA).
How is the BCG effective at mounting a protective response?
Attenuated, strain of bovine tuberculosis
Some protection against primary infection
Some protection against progression to active TB
T cell response is important in protection
What is the test for immunity against TB?
Mantoux test
Inject 0.1 ml of 5 tuberculin units of liquid tuberculin intradermally. The tuberculin used in the Mantoux skin test is also known as purified protein derivative, or PPD.
The patient’s arm is examined 48 to 72 hours after the tuberculin is injected.
The reaction is an area of induration (swelling that can be felt) around the site of the injection.
What are the different types of vaccines?
- Live vaccines
- Inactivated/Component vaccines
(Conjugates + Adjuvants increase immunogenicity) - RNA vaccines
- Adenoviral vector vaccines
- Dendritic cell vaccines
What are examples of live attenuated vaccines?
MMR
BCG
Yellow fever
Typhoid (oral)
Polio (Sabin oral)
Influenza (Fluenz tetra for children 2-17 years)
What are advantages of live attenuated vaccinations?
Establishes infection: Ideally mild symptoms.
Raises broad immune response to multiple antigens: More likely to protect against different strains.
Activates all phases of immune system. T cells, B cells: With local IgA, humoral IgG.
May confer lifelong immunity, sometimes just after one dose.
What are disadvantages of live attenuated vaccines?
Possible reversion to virulence (recombination, mutation): Vaccine associated paralytic poliomyelitis (VAPP, ca.1:750,000 recipients).
Spread to contacts: Spread to immunosuppressed/immunodeficient patients.
Storage problems.
What are examples of inactivated viruses?
Influenza (inactivated quadrivalent)
Cholera
Bubonic plague
Polio (Salk)
Hepatitis A
Pertussis
Rabies
What are examples of component/subunit vaccines?
Hepatitis B (HbS antigen)
HPV (capsid)
Influenza (recombinant quadrivalent - less commonly used)
What are examples of toxoid (inactivated toxin) vaccines?
Diphtheria
Tetanus
What are the advantages of inactivated/component vaccines?
No risk of reversion to virulent form
Can be used with immunodeficient patients
Storage easier
Lower cost
What are the disadvantages of inactivated/component vaccines?
Often do not follow normal route of infection.
Some components have poor immunogenicity.
May need multiple injections.
May require modification to enhance immunogenicity.
- Conjugate to protein carrier
- Adjuvant
What are conjugate vaccines made of?
Conjugate vaccines (often used in children)
Polysaccharide plus protein carrier.
Polysaccharide alone induces a T cell independent B cell response – transient.
Addition of protein carrier promotes T cell immunity which enhances the B cell/antibody response.
What are examples of conjugate vaccines?
Haemophilus Influenzae B
Meningococcus
Pneumococcus (Prevenar)
(Remember NHS for polysaccharide encapsulated bacteria)
What is an adjuvant to a vaccine?
Adjuvant increases the immune response without altering its specificity.
Mimic action of PAMPs (pathogen associated molecular patterns) on TLR (toll-like receptors) and other PRR (pattern recognition receptors).
What are examples of adjuvants?
Aluminium salts (humans)
Lipids: Monophosphoryl lipid A (humans HPV)
Oils: Freund’s adjuvant (animals)
What is an example of a mRNA vaccine?
SARS-CoV
How are mRNA vaccines made?
Infect E coli with plasmids containing DNA for spike protein.
Harvest plasmids from the cultures.
Excise DNA and transcribe to mRNA.
Complex with lipids to create the vaccine.
How do mRNA vaccines work?
Inject mRNA/lipid complexes:
- Non-infectious
- Non-integrating
- Degraded within days
mRNA enters cells (e.g. muscle cells, endothelial cells, fibroblasts, dendritic cells).
mRNA translated and spike protein synthesised/expressed on surface.
Stimulates immune response including B cells/antibodies and T cells.
What are adenoviral vector vaccines?
DNA of relevant protein (Covid spike protein) inserted to viral vector to produce vaccine.
AZ Covid vaccine vector: ChAdOx1-S
Sputnik Covid vaccine vector: Adenovirus types 26 and 5
Infect cells in vivo
Transcription/translation to produce protein
Stimulates immune response including B cells/antibodies and T cells.
What are dendritic cell vaccines?
Acquired defects in DC maturation and function associated with some malignancy suggests a rationale for using ex vivo–generated DC pulsed with tumour antigens as vaccines.
Focus on tumour associated antigens or mutational antigen.
What is Sipuleucel-T Provenge vaccine?
Personalised immunotherapy for prostatic cancer.
Remove white cells from patient’s blood (leukaphoresis).
APCs are harvested and incubated with recombinant protein PAP-GMCSF (Prostatic acid phosphatase-granulocyte macrophage colony stimulating factor).
APCs infused back to patient.
Stimulates patient’s immune response.
How can missing components of immune systems be replaced?
Haematopoietic stem cell transplantation - donor or autologous.
Antibody replacement
What are indications for stem cell transplant?
Life-threatening primary immunodeficiencies:
- Severe combined immunodeficiency
- Leukocyte adhesion defect
Haematological malignancy:
- Offers potential for complete and permanent cure
What is antibody replacement?
Human normal immunoglobulin prepared from pools of >1000 donors. Contains preformed IgG antibody to a wide range of unspecified organisms.
Blood product:
- Donors screened for Hep B, Hep C and HIV
- Further treated to kill any live virus
Administration
IV or SC
What are indications for antibody replacement therapy?
Primary antibody deficiency:
- X linked agammaglobulinaemia
- X linked hyper IgM syndrome
- Common variable immune deficiency
Secondary antibody deficiency:
- Haematological malignancies
- Chronic lymphocytic leukaemia
- Multiple myeloma
What is specific immunoglobulin modulation?
Human immunoglobulin used for post-exposure prophylaxis (passive immunisation).
Derived from plasma donors with high titres of IgG antibodies to specific pathogens.