18 - Antibodies in Immunotherapy - Partridge Flashcards
what are nanobodies, draw one and what animal can they be isolated from?
single domain Abs
isolated from camels (contain both types of Ab)
Describe the differences between normal Ab and a nanobody
CONVENTIONAL;
2H & 2L chains
- both chains required for antigen binding
- large size, low formatting flexibility
- administered through injection
NANOBODY;
H chain Ab
- one H chain V region required for binding antigen
- small (1/10th size of mAb)
- stable and robust allowing flexible formatting
- multiple administration routes
- ease of manufacture. single V region can be expressed in bacteria
name the first nano body drug that has recently been approved by th EU. what is it effective against?
Cablivi - inhibits von Willebrand factor (overactive in autoimmune blood clotting disorder)
Give the 3 main uses of Ab in therapy and describe each, giving examples
1) PASSIVE IMMUNISATION
- neutralise toxins eg anti-venom, anti-tetanus
- prevent/treat infection eg Ebola virus
2) CANCER; Abs as magic bullets which target tumour cells
- eg CAMPATH Abs. anti-CD52. CD52 expressed by nearly all WBCs. targets leucocytes and can also trigger complement and ADCC. therefore used to treat leukemias and lymphomas (cancer of lymphocytes)
- eg HERCEPTIN Abs. anti-Her2. Her2 receptors over expressed in around 25% cancer allowing proliferation. bind to these receptor tyr kinases therefore blocking proliferation. can also mediate ADCC through NK cells
3) MODULATION OF IMMUNE RESPONSES eg in cancer, non-infectious diseases.
- depletion of leucocytes in donor organs. Abs to CD53, CD3, CD4. therefore successful organ transplantation and preventing graft organ attacking host. also used in autoimmune diseases to deplete T cells
- binding of cytokines and their receptors (eg IL1,6,TNFa) prevention of inflammatory and autoimmune diseases. also helpful in allergy to IgE
- immune checkpoint inhibitors eg to CTLA-4/PD-1. cancer immunotherapy
What are some of the problems associated with using Abs in cancer therapy?
- need to find An antigen that is specific only to cancer cells
- some cancers may shed their antigens
- tumour cells may be inaccessible because buried below mass of other cells
- reactions to Ab eg HAMA (human anti-mouse Ab) responses. reaction to mouse monoclonal Ab
Describe how cancers induce immunosuppression
- produce cytokines (TGFB) that induce TREGs
- induce expression of PD-L on tumour cells. PD-1 transiently expressed on activated T cells and this interaction -> inhibition
- CTLA-4 expression induced on activated T cells. when binds B7 (w/ higher avidity than CD28) on APC then its activity Is inhibited
How can the induction of immunosuppression by cancer cells be targeted?
Draw a diagram
- Abs that target and block these inhibitory immune checkpoints can be effective as cancer therapies
- reverse immunosuppression and reactivate T cells
- deplete TREGs. because CTLA-4 constitutively expressed, Abs to CTLA-4 may cause downregulation and natural immune response can develop
What are the Abs that target the immune checkpoints effective against?
metastatic melanoma and other advanced cancers (because aggressive require them to be caught early)
How do Abs actual work for immunotherapy?
we exploit their natural effector functions. eg binding to Fc regions (CD16 = FcyRIII) on NK cells -> ADCC
Briefly state the main ways in which Abs can be improved for immunotherapy
- altering of the Fc regions for FcR and C1q binding
- labelling Ab with drug/toxin/radionuclide
- development of immunotoxins
- improving affinity of CDR regions
- increasing valency (di/triabodies)
- bispecific Abs recognising antigens. eg recognition of both CD19 (tumour cells) and effector cell protein (CD3)
Describe how Fc regions on Abs have been improved for C1q/FcR binding
- sites for C1q/FcR binding have been mapped to specific Fc region aa
- Ab engineering can improve half life (better binding to FcRn), improve effector functions (ADCC, complement activation)
- glycoengineering can remove the glycosylation sites found within IgG Fc regions. (IgG has 2 n-linked glycans - Asn297). removal of these fucose molecules improves interaction with FcyRIII and therefore ADCC
- FcR normally interacts with CH2 domains of the hinge regions and removing these glycosyalted sites improves interaction
Draw a diagram and explain how labelling an Ab with drug/toxin/radionuclide is effective?
- can use lower drug doses because delivered straight to the target cell
What are immunotoxins?
Describe them
- Fc region has been replaced with toxin eg Burkholderia lethal factor 1 (BLF1), ricin, diphtheria toxin
- antigen specificity retained !
How can we improve affinity of Ab CDR regions?
- site directed/random mutagenesis of CDR regions
- select for the higher affinity Abs
- express these Abs in a phage display
What type of Abs are more useful against tumours? Describe some examples
- Ab fragments because they are smaller and can better penetrate tumours
- eg Fv - paired VARIABLE regions
- eg scFv - single chain Fv
