S4 L1 Monoclonal antibodies

Question 1

What is the history as to how monoclonal antibodies were found?

Answer 1

• Suggested cells produced chemical substances that -linked with specific toxins to neutralise them
• Chemical substance break away from the cells and circulate around the body

Question 2

Where do antibodies come from?

Answer 2

Antibodies are specialised immunoglobulins secreted by B cells - specifically plasma cells

Question 3

What is the structure of an antibody?

Answer 3

Fab region and Fc region
Fab → antibody binding fragment
→ recognises antigen - hypervariable region, enabling the Ab to recognise an unlimited number of antigens
Fc → fragment crystallise region
→ Interact with cell surface receptors on other immune cells to stimulate the immune response

Question 4

What is an antigen?

Answer 4

Foreign substance that stimulates antibody production

Question 5

What is a monoclonal antibody?

Answer 5

Monovalent

• Affinity for a single antigen or epitope
  1. Fab region interacts with antigen present on infected cell
  2. Fc region binds to phagocytic cells → phagocytosis of affected cell

Question 6

What are monoclonal antibodies used for in clinical practice?

Answer 6

Diagnostic
→ Monoclonal antibodies bind to specific targets
→ Can be used to tag cell surface markers
→ Add chemistry to the monoclonal antibody, binding can be visualised
- Emission of light signal → flow cytometry
- Interaction with enzyme causing colour reaction → immunohistochemistry
→ Used for Red blood cell groupings
→ Pregnancy testing - monoclonal antibody target B-hCG (pregnancy hormone)

Therapeutics
→ Huge impact in treatment of illness such as lymphoma

Question 7

How are monoclonal antibodies developed?

Answer 7

• Monovalent antibodies which bind to the same epitope and are produced from a single B-lymphocyte clone
• First generated using mice - hybridoma technique
  1- Immunisation a certain species against a specific epitope on an antigen→ animal injected with antigen generates an immune response - produces antibodies
  2 - B lymphocytes isolated from the spleen of the animal
  3- Fused with immortal myeloma cell line (cancer of plasma cells) which have been engineered so that they don’t produce Ab themselves
  4- Resulting hybridoma cells are then cultured in vitro so only the hybridomas (fusion between the primary B lymphocyte and myeloma cells) survive - Screen Ab produces and grow out the specific monoclonal Ab antigen of interest
  5- Selected hybridomas are found making a specific desired clonal antibody - Monoclonal Ab produced

Question 8

What is special about monoclonal antibodies?

Answer 8

• Specific
• Produced in large amount
• Can be targeted against almost any cell-surface receptor

Question 9

What are the different types of monoclonal antibodies that are produced?

Answer 9

1. Naked monoclonal antibodies
2. Conjugated monoclonal antibodies
3. Bispecific monoclonal antibodies

Question 10

What are naked monoclonal antibodies?

Answer 10

Monoclonal antibodies that have no drug or marker attached to them

• Murine (-omab) → 0% human, high potential for immunogenicity
• Chimeric (-ximab) → 65% human, combine mice and human→ Fc region humanised, Fab region mouse, still potential for immunogenicity but less
• Humanised (-zumab) → >90% human
• Fully human (-umab) → 100% human, low immunogenicity

Question 11

What is a conjugated monoclonal antibody?

Answer 11

• Monoclonal antibody linked to a potent drug to allow targeted delivery of drug to cancer cell
• Attached to drug via a linker
• Specific to antigen on target cell meaning less effect on surrounding cells

Question 12

What are bispecific monoclonal antibodies?

Answer 12

• Utilise two binding domains of Ab structure
• Bind to two different cell populations
• Redirect immune response against cancer cells by binding to malignant cell (often B cells) and T cells
• Get T cell receptor function against B cell → removal / cell death of B cell

Question 13

How do monoclonal antibodies work?

Answer 13

1- Binding with cell surface receptor to either activate or inhibit signalling within the cells
2- Binding to induce cell death- triggers apoptosis
3- Binding with cell surface receptors to activate
- Antibody dependent cell mediated cytotoxicity (ADCC) → Fc portion of MAb binds to immune effector cells e.g. macrophages - cell lysis or phagocytosis
- Complement dependent cytotoxicity (CDC) → activate complement- formation of membrane attack complex in cells membrane resulting in cell lysis
4- Internalisation for antibodies delivering toxins to the cancer cells (taken in by the cell)
5- Blocking inhibitory effects on T cells (checkpoints) thus activating T cells to help kill the cancer cells → physiological T cell - dysfunctional do not recognise cancer cells so do not kill then so if you inhibit it then other T cells will recognise it

Question 14

What are the clinical used of monoclonal antibodies?

Answer 14

Haematology

Lymphoma

Question 15

What is the cluster differentiation classification?

Answer 15

• Catalogue of cell surface receptors expressed on B and T cells and other immune cells
• Takes each unique cell surface receptor and gives it a number which allows identification of cell phenotypes
• Helps with diagnosis - specific cell surface receptors expressed on each one
• Monoclonal antibodies can then be directed to specific receptor types - few are fully unique to cancer cells only but should allow a degree of prediction

Question 16

What type of cancer is a lymphoma?

Answer 16

• Divided into B and T cell neoplasms- clonal proliferation of lymphoid cells
• Typically causes enlargement of the lymph nodes
• The spleen, bone marrow and other areas of the body such as the liver, skin, testes and bowel (extra-nodal) may also be involved
• People with lymphoma often complain of drenching night sweats, fevers and weight loss → some have non of these symptoms

Question 17

What are the different types of B cells lymphoma?

Answer 17

Follicular lymphoma → lymph node taken over by small clonal B lymphocytes
Diffuse large B cell lymphoma → Takes over the node in a diffuse pattern
B cells express CD20

Question 18

What are the different treatments available for lymphoma?

Answer 18

• Chemotherapy → combination of chemotherapies shown to be effective in B cells
• Radiotherapy → used in localised disease, or symptoms control in palliative care or larger cases
• Monoclonal antibody therapy
• Emerging new targeted therapy
• Stem cell transplantation → select cases, use own stem cells that have been taken out before chemotherapy, reinfuse to bone marrow or can receive them from someone else

Question 19

What is an example of a chemotherapy that works against the CD20 receptor?

Answer 19

Rituximab - monoclonal antibody

Only expressed on mature B cells - therefore bone marrow cells are spared

Question 20

Why should we use monoclonal antibodies?

Answer 20

• Significantly improves response rates

- Significant improves survival at 10 years

Question 21

What are the side effects of monoclonal antibodies?

Answer 21

• Some have no or mild symptoms e.g. mild fatigue
• Many have mild reaction to 1st infusion and then tolerate subsequent infusions
• Few people have severe infusion related reactions as their immune system reacts to the presence of a foreign protein

Question 22

Why do side effect occur?

Answer 22

Patients immune system responds to monoclonal antibodies that they have not seen before
Engagement of immune effector cells and cross reaction with cancer cells

Question 23

What can affect the side effect felt from monoclonal antibody treatment?

Answer 23

Rate of infusion
- Minimum rate patient might not feel anything
- Increased rate might feel something e.g. heaviness in chest, hypoventilation, N+V, shivering (rigor)
Infusion then stopped and restarted at original rate
Some patients won’t notice any difference with the rate change and therefore can have fast infusion

Question 24

How can infusion related reactions be managed?

Answer 24

• Patient education
  → explain to pt they may feel side effects even after premedication
  → should inform staff the moment of any change so staff can take immediate action
  → Instruct patients to omit their anti-hypertension medication for 12hours prior to their infusion
• Prevention with pre-medication - steroids, antihistamines, paracetamol
• Start at slow infusion rate, slowly increase if tolerated
• Drugs require to treat IRR should be prescribed prior to starting treatment

Question 25

What are the other uses of monoclonal antibodies?

Answer 25

Wide uses
- Solid cancer
→ Trastuzumab - inhibition of Her2 signalling
→ Bevacizumab - inhibition of VEG-F signalling
→ Nivolumumab - inhibition of CTLA-4 signalling
- Autoimmune
→ Infliximab and adlimumab - inhibition of TNF-alpha
- Cardiology
→ Abciximab - inhibition of platelet glycoprotein IIb/IIIa
- Endocrine
→ Denosumuab- inhibition of RANK ligand on osteoclasts