9. Immune modulating therapies I Flashcards
What are different approaches to boosting the immune system?
Vaccination; replacement of missing components (e.g. replacing immune cells); blocking immune checkpoints; cytokine therapy
Which epidemic lead to the understanding of protection offered by primary measles infection?
Epidemic on Faroe islands
What is immune memory?
The immune system is able to remember an infection that is has encountered in the past and provide protection thereafter. This is a feature of the adaptive immune response
What cells is the adaptive immune response comprised of ?
B and T cells
How do we have a variety of antigen receptors (as part of the adaptive immune response)?
Consist of a wide variety of antigen receptors. This is NOT entirely genetically encoded. Genes for segments of receptors are rearranged and nucleic acids are deleted/added at the sites of rearrangement almost randomly. This gives potential to produce up to 10^12 different types of receptor. Autoreactive cells are likely to be generated but there are mechanisms to delete or tolerate these autoreactive cells. The adaptive immune response has exquisite specificity - it can discriminate between very small differences in molecular structure
What happens when an adaptive immune cell is engaged with an antigen it recognises?
- You get massive clonal expansion.
- T cells with appropriate specificity will proliferate and differentiate into effector cells (cytokine secreting, cytotoxic).
- B cells with appropriate specificity will proliferate.
- They can then differentiate into T-cell independent IgM plasma cells.
- Or they can undergo a germinal centre reaction and differentiate to T cell-dependent IgG producing memory and plasma cells.
- Following infection, a residual pool of specific cells with enhanced capacity to respond if re-infection occurs will be left (memory cells).
What is the CD8+ and CD4+ T cell response to recognition of antigen?
Antigen presented by APC to a CD8 T cell. CD8+ T cells are activated and T helper cells provide help (cytokine growth factor) to CD8 T cells. This leads to clonal expansion. Then the T cells die by apoptosis or survive as memory cells. A less pronounced proliferation is seen in CD4+ T cells
What are antigen-presenting cells?
These are cells that can present antigens to T cells to initiate an acquired immune response
What do APCs include?
Dendritic cells, macrophages and B lymphocytes
APCs include macrophages. What are types of macrophages?
Langerhans cells, mesangial cells, kupffer cells, osteoclasts, microglia
What are three features of memory T cells?
- Longevity (persist by the continuous low level proliferation in response to cytokines). 2. Memory cells have a different pattern of expression of cell surface proteins involved in chemotaxis cell adhesion. This allows memory cells to rapidly access non-lymphoid tissues (where microbes enter). 3. Rapid, robust response to subsequent antigen exposure. Lower threshold of activation than naive cells
What are three features of memory B cells?
Memory B cells and plasma cells will last for a long time. Produce a rapid and robust response on subsequent antigen exposure. Circulating pre-formed high affinity IgG antibodies are present.
What are the aims of vaccines?
Generate protective, long-lasting immune response; no adverse reactions; single shot; easy storage
What is target for influenza vaccines?
CD8 T cells control the viral load but the antibody is responsible for providing a protective response. Haemaglutinin (HA) is the receptor-binding and membrane fusion glycoprotein of influenza virus. HA is the target for antibodies. These antibodies can be detected using a haemaglutinin inhibition assay.
How can antibodies to influenza be detected using haemaglutinin inhibition assay? And what suggests a greater level of antibodies?
- If you put normal red cells in a dish, they will clump at the bottom forming a red spot. 2. If you add the influenza virus to the red cells, the haemaglutinin will make the cells stick together and it will cause a diffuse coloration across the well. 3. If you add the serum of someone who has a lot of antibodies against HA with the virus and red cells, it will inhibit the HA from causing the above effect - this results in the cells clumping at the bottom as if the virus was not present. 3. This can be done on a large scale with lots of well containing blood and virus with dilutions of the patients serum put on top. The higher the dilution at which the inhibitory effect can be seen, the greater the level of antibodies the patient has against HA (e.g. Pt1 has high levels of antibodies, Pt5 has lower levels of antibodies). The higher the antibody level the lower the likelihood of infection.
When does a patient have protection after the influenza virus?
Antibody protection begins 7 days after vaccine and protection can last for around 6 months.
What vaccine is used for tuberculosis?
BCG is an attenuated strain of bovine tuberculosis.
What does the BCG vaccine provide protection against?
Provides some protection against primary infection. Mainly provides protection against progression to active TB.
What response is important in the BCG vaccine?
T cell response
What is the Mantoux test for?
The Mantoux test is a widely used test for latent TB
How is the Mantoux test done?
Inject a small amount of liquid tuberculin (aka purified protein derivativ (PPD)) intradermally. The area of injection is examined 48-72 hours after tuberculin injection
What suggests a positive Mantoux test?
Positive: The reaction is an area of swelling around the injection site. Negative test for TB has no bump.
How long does BCG vaccine protect against TB?
Protection usually lasts for 10-15 years
What are different types of vaccines?
- Live attenuated vaccines; 2. inactivated/component vaccines (including conjugates, adjuvants, toxoids, component/subunit); 3. DNA vaccines; 4. dendritic cell vaccines
What is a live attenuated vaccine?
The organism is modified to limit pathogenesis
What are examples of live attenuated vaccines?
MMR, BCG, Yellow fever, Typhoid, Polio (Sabin), Vaccinia
What are the advantages of live attenuated vaccines?
Establishes infections (ideally mild); raises broad immune response to multiple antigens (more likely to offer protection against different strains); activates all phases of immune system; often confer life-long immunity after one dose
What are disadvantages of live attenuated vaccines?
Storage problems, possible reversion to virulence, spread to contacts, spread to immunocompromised/ immunosuppressed.
How can we increase immunogenicity in inactivated/component vaccines?
Conjugates + adjuvants increase immunogenicity
What are examples of inactivated/component vaccines?
Influenza, cholera, polio (Salk), Hep A, Pertussis, Rabies
What are examples of toxoid vaccines (inactivated toxins)?
Diphtheria, tetanus
What are examples of component/subunit vaccines?
Hep B (HBsAg); HPV (capsid); influenza (HA, neuraminidase)
What are the advantages of inactivated/component vaccines?
No mutation or reversion, can be used in immunodeficient patients, can lead to elimination of wild-type virus from the community, easier storage, lower cost
What are disadvantages of inactivated/component vaccines?
Often do not follow normal route of infection; may have poor immunogenicity; may need multiple injections; may require conjugates or adjuvants
What does a conjugate vaccine consist of?
Polysaccharide + protein carrier
What does the polysaccharide in conjugate vaccines do?
The polysaccharide alone induces a T cell-independent B cell response (transient)
What does addition of protein carrier in conjugate vaccines do?
Addition of the protein carrier promotes T cell immunity which enhances the B cell/antibody response
What are examples of conjugate vaccines?
Haemophilus influenzae B; meningococcus; pneumococcus. NOTE: these are polysaccharide encapsulated bacteria
What is an adjuvant?
An adjuvant is a substance that is added to a vaccine to stimulate and enhance the magnitude and durability of the immune response. It increases the immune response without altering its specificity.
What do adjuvants mimic the action of?
These mimic the action of PAMPs on TLR and other PRRs
What are examples of adjuvants?
Aluminium salts; lipids - monophosphoryl lipid A; Freund’s adjuvant (in animals)
What is alum used for and why?
(Aluminium salts) - most commonly used adjuvants in humans. Safe and effective
What are the mechanisms of alum?
Mechanism is NOT fully understood. May allow antigens to be slowly released over time leading to prolonged antigenic stimulation. May induce a mild inflammatory reaction that promotes development of the adaptive immune response. May activate Gr1+ IL4+ eosinophils to help prime naïve B cells leading to an antibody response.
What are ISCOMs (experimental)?
These are immune-stimulating complexes. These are cage-like structures mixed with antigens to provide multimeric presentation with built-in adjuvant. Enhances cell-mediated immunity.
What is CpG (experimental)?
Stands for cytosine and guanosine separated by a phosphate. CpG motifs bind via PRRs (TLR9) and induce an immune response
What are DNA vaccines (experimental)?
Plasmid containing a gene of choice (from the pathogen) is inserted into a muscle cell. The plasmid does NOT replicate but the gene encodes protein that is presented at the cell surface. This mimics the normal action of a virally infected cell and it stimulates T cell responses
What is a disadvantage of DNA vaccines?
Plasmid may integrate into host DNA and the response to DNA could lead to autoimmune diseases such as SLE
What are dendritic cell vaccines?
They are used against tumours where dendritic cell function may be compromised. You take a patient’s dendritic cells and load them with a tumour antigen and reintroduce them to the patient to try and boost the immune response against the tumour antigens. This requires antigens that are specific to the tumour and distinct from normal cells.
What are types of vaccines that are adjuvants?
Alum, ISCOMs, CpG, DNA vaccines, dendritic cell vaccines
Which vaccines are adjuvants used in?
Hep A, Hep B, Hib
How can we replace missing components of the immune system?
This can be done by haematopoietic stem cell transplantation. Offers potential for complete and permanent cure
What are indications for haematopoietic stem cell transplantation (in order to replace missing components of the immune system)?
Life-threatening immunodeficiency (e.g. SCID, leucocyte adhesion defect); haematological malignancy
How can antibodies be give as replacement of missing components of the immune system?
Immunoglobulin can be replaced by giving human normal immunoglobulin. Prepared from pools of > 1000 donors. Contains pre-formed IgG to a variety of organisms. Needs to be screened because it is a blood product. Administration: IV or SC
What are indications for antibody replacement?
Primary immunodeficiency (e.g. X-linked agammaglobulinaemia, X-linked hyper-IgM syndrome, common variable immunodeficiency) and secondary antibody deficiency (haematological malignancies: CLL, multiple myeloma; after bone marrow transplantation)
What is specific immunoglobulin?
Given when there is not enough Ig in the immune system. Type of passive immunisation, where human Ig is used for post-exposure prophylaxis. It is derived from plasma donors with high titres of IgG antibodies to specific pathogens.
What are examples of specific immunoglobulin?
HepB Ig, tetanus ig, rabies Ig, varicella zoster Ig
How can T cells be replaced when missing in the immune system?
Adoptive Cell Transfer (ACT)
What are types of Adoptive Cell Transfer (ACT)?
Virus specific T cells; tumour infiltrating T cells (TIL - T cell therapy); T cell receptor T cells (TCR - T cell therapy); chimeric antigen receptor T cells (CAR - T cell therapy)
By what process are virus specific T cells given?
Adoptive cell transfer (ACT)
In which condition can virus specific T cells be given?
Can be used for EBV in people who are immunosuppressed to prevent the development of B cell lymphoproliferative disease
How are virus specific T cells given to immunosuppressed patients with EBV?
Immunosuppressed patients need need functional EBV-specific T cells to prevent development of B cell lymphoproliferative disease.
- Blood is taken from the patient or from a matched individual.
- The peripheral blood mononuclear cells are isolated.
- They are then stimulated with EBV peptides.
- This creates an expansion of EBV-specific T cells.
- They are then infused back into the patient.
How does tumour infiltration T cell therapy work?
The tumour is removed from the patient. The T cells are stimulated within the tumour with cytokines (e.g. IL-2) in the presence of the tumour so that they develop a response against the tumour. The tumour infiltrating lymphocytes are selected and expanded, then reinfused into the patient.
How does TCR (T cell receptor) therapy work?
T cells are taken from the patient and viral or non-viral vectors are used to insert fragments of genes into these T cells. These gene fragments encode receptors. For TCR therapy, you will insert a gene that encodes a specific TCR (e.g. against a tumour cell antigen). TCR gene-engineered T cells are expanded and cell infusion in patient occurs with IL-2. The patient is preconditioned with chemotherapy.
How does CAR therapy work?
T cells are taken from the patient and viral or non-viral vectors are used to insert fragments of genes into these T cells. These gene fragments encode receptors. In CAR therapy, the receptors are chimeric (it contains both B and T cell components).
The type of CAR therapy that has come into use is targeting CD19 (which is present on B cells). The receptors on the CAR cell has an immunoglobulin variable domain at the end and it is joined onto the remainder of the T cell receptor (CD28 + CD3). So, it signals through the usual TCR pathway but it recognises CD19 through an immunoglobulin domain. This recognises CD19 on B cells and harnesses the T cells to kill the B cells. These cells are expanded and infused with IL-2 into patient, who is preconditioned with chemotherapy.
In which conditions is TCR and CAR T cell therapy being used increasingly in?
This is increasingly being used in ALL and NHL
What is an antibody specific to CTLA4?
Ipilimumab
What are CTLA4 and CD28 expressed by and what do they recognise?
CTLA4 and CD28 are both expressed by T cells and they both recognise the same antigens on APCs (CD80 and CD86)
What happens when APCs interact with CD28 and CTLA4?
When the molecules on the APCs interact with CD28 they transmit a stimulatory signal. Whereas when they interact with CTLA4, they transmit an inhibitory signal.
How does Ipilimumab work?
CTLA4 and CD28 are both recognise the same antigens on APCs (CD80 and CD86). Ipilimumab will bind to CTLA4 (inhibitory) meaning that all of the interactions of CD80 and CD86 occur through CD28 (stimulatory) thereby boosting the T cell response (you get more active T cells)
How do pembrolizumab and nivolumab work?
PD-1 (prevent death 1) transmits an inhibitory signal to T cells. Its ligands, PDL-1 and PDL-2, are present on antigen-presenting cells and some tumour cells. When tumour cells express the PD ligands, it is, in effect, turning off the T cells. Antibodies binding to the PD-1 will prevent this inhibitory effect thereby activating the T cells.
What have Pembrolizumab and Nivolumab been used in?
This has been used in advanced melanoma
Antibody specific to CTLA4 (ipilimumab) and antibodies specific to PD-1 (pembrolizumab and nivolumab) can be used together to greater effect - true or false?
True
What are downsides to the approaches of antibody specific to CTLA4 (ipilimumab) and antibodies specific to PD-1 (pembrolizumab and nivolumab)?
As these approaches involve invigorating the immune response, the patients tend to develop autoimmune diseases (e.g. arthritis, thyroid disease, diabetes)
What is the aim of clinical use of recombinant cytokines?
The aim is to modify the immune response
What is interferon alpha (recombinant cytokine) used in?
Used as an adjunct in the treatment of Hep B, Hep C, Kaposi sarcoma, CML, multiple myeloma
What is interferon beta (recombinant cytokine) used in?
Behcet’s disease, relapsing multiple sclerosis (no longer in use)
What is interferon gamma (recombinant cytokine) used in?
Chronic granulomatous disease
