Lecture 5 - Monoclonal Antibodies Flashcards
Why do monoclonal antibodies have great therapeutic potential?
1)
2)
3)
1) Very well tolerated
2) Long half-life
3) Very specific and selective
Original strategy for making monoclonal antibodies: 1) 2) 3) 4)
1) Take B cells from an animal that has been injected with antigen of interest
2) Fuse B cells with myeloma cells
3) This makes hybridomas, with fused nuclei of myeloma cells and plasma cells
4) Select hybridoma expressing antibody of interest
Issues with first generation of monoclonal antibodies
1) Made in mice, so rejected as foreign by human immune system
2) Short serum half-life, from being rejected
3) Lack some effector functions, as Fc region couldn’t bind to human Fc receptors
Partial solution to monoclonal antibodies being rejected in humans
Graft human heavy chain onto mouse light chains
Issues with chimeric human-mouse antibodies
Antigen-binding site still recognised as foreign
More sophisticated way of making human/murine chimeric antibodies
Graft mouse CDR1, CDR2 and CDR3 regions into human antibody
Way to create mouse producing human antibodies
Create transgenic mouse with human Ig genes.
Generic way to make human B cells make monoclonal antibodies
1)
2)
1) Take human B cell that have survived infection, are high affinity and are expressing IgG.
2) Infect B cells with EBV (EBV can make B cells immortal)
Drawbacks to immortalising human B cells
B cells will only produce antibodies against an antigen that the person has encountered (must have naturally encountered antigen. Infecting humans with antigens of interest is unethical
Advantages of immortalising human B cells
1) Very well-tolerated
2) Will proliferate monoclonal antibodies that were effective in protecting the donor against past infection
How can mAbs be used to deliver drugs?
Bind drug to antibody
Antibody has specificity to bind to an area where the drug is to be delivered
How can antibodies be used to bring together cells?
Create an antibody that has two specificities, one for each cell of interest (EG: target call and NK cell)
Possible actions of mAbs 1) 2) 3) 4)
1) Ligand blockade
2) Receptor blockage or downregulation
3) Target cell depletion
4) Target cell activation
Example of mAb ligand blockade
Infliximab
Anti-TNFa antibody
Used to treat rheumatoid arthritis, Crohn’s disease, psoriasis
If inflammatory cells don’t receive stimulation from TNFa, they become inert or die
Other examples of mAb ligand blocking
Anti-VEGFA agent
Blocks angiogenesis in cancers
Anti-RANKL antibody to prevent bone reabsorption in B cell lymphomas
Example of mAb receptor blocking
Anti-HER2
Trastuzumab
HER2 is a member of epidermal growth factor ligands. Is involved in some breast cancers
Ways that mAbs can lead to target cell depletion
1)
2)
3)
1) Complement activation
2) NK cell activation
3) Macrophage activation
All against target cell opsonised with mAb
Example of mAb target cell depletion
Anti-CD20
Rituximab
B cells (not plasma cells) express CD20 on cell surface
Used to treat B cell lymphomas
Type of immunosuppression caused by rituximab
Depletes B cells, but not plasma cells
Therefore patient will be able to produce antibodies against previously encountered antigens, but won’t be able to mount a humoral response against novel antigens
mAb target cell activation
Can crosslink TCR-CD3 complexes on T cells, resulting in activation without antigen
Example of mAb target cell activation
Ipilimumab
Anti-CTLA4 antibody
CTLA4 is a T cell negative receptor, expressed on a T cell when the T cell binds to an antigen
Ipilimumab prevents binding to CTLA4, and therefore suppression of T cell response
What is Ipilimumab used for?
Treating severe metastatic melanoma
Limitations of mAbs 1) 2) 3) 4) 5)
1) Unpredictable effects
2) Cardiotoxicity
3) Infections, when target is immune cells
4) Acute anaphylaxis
5) Production of anti-mAb antibodies
These effects aren’t necesarily the case with all mAbs. Most are specific to certain mAbs
Chimeric antigen receptor treatment
Grafting antibody specificity onto T cell activation molecules, and then inserting molecules into a T cell using a viral vector
Structure of a chimeric antigen receptor
Membrane-bound protein
1) Antibody binding site, specific to desired antigen. Expressed on cell surface
2) T cell activating molecules, expressed on cytosolic side of cell membrane
Aim of producing chimeric antigen receptors
Fuse the specificity and binding affinity of antibody receptors with CD8+ T cell cytotoxicity
Experimental use of chimeric antigen receptors
Expressing anti-CD19 receptors, fused to CD8 T cell surface
Killed B cells expressing CD19 (CD19 like CD20 - expressed on all B cells except plasma cells)
How did anti-CD19 chimeric antigen receptor therapy work?
1)
2)
3)
1) Take blood sample from patient, isolate T lymphocytes. Introduce chimeric antigen receptor gene into T cells.
2) Deplete patient’s lymphocytes with chemotherapy
3) Reinfuse lymphocytes expressing chimeric antigen receptor
Example of an ‘orphan drug’
Anti-IL-1b mAb
What is anti-IL-1b mAb used to treat?
Cryopyrin-associated periodic syndromes
Systemic, uncontrolled inflammation
