Lecture 13 - Transplant Immunology II Flashcards
List the things taken into consideration in pre-transplant assessment
- ABO matching
- Tissue typing - HLA matching
• Assessment of risk of rejection
- Pre-existing Ab
• Pre-tx cross matching
Compare A1 and A2 bloodtypes
A1:
• 80-90% of A individuals are A1
• RBCs express high density of terminal residues on the oligosaccharides
A2: • 10-20% of A individuals • Low density of terminal sugars on RBC oligosaccharides • Fewer and less potent Ags • Behaves like group O
Describe what can occur in transplants when there is ABO group mismatch
Hyperacute rejection:
• Depending on blood group, an individual will have pre-formed IgM Abs against allogeneic RBCs
How can pre-formed Ab be reduced pre-transplant?
Removal:
• Plasma exchange
• Catheter in arm; blood cleared of Ab, blood flows back in through catheter in the other arm
Neutralisation:
• Intravenous Ig
Decreased Ab prod’n:
• Splenectomy
• Rituximab
Describe ‘tissue typing’ stage of pre-transplant assessment
Tissue type : HLA type
Donor and host tissues are typed for HLA Ags using:
- Serology
• CDC
• Panel of defined sera - Molecular analysis
• PCR based
Why is tissue typing important?
With increasing HLA mismatches between donor and recipient, there is greater risk of transplant rejection
Describe assessment for pre-formed Abs
Clinical history:
• Pregnancy
• Previous blood transfusion
• Previous transplant
Check serum sensitisation to HLA:
• Panel of donor Ags (PRA)
Most patients with pre-formed Abs have no clinical history of sensitisation
What is PRA?
Describe its use
What does it indicate?
Panel reactive Ab
Process:
1. Pre-made trays with live lymphocytes from 40-60 individuals
(represents widest range of HLA possible)
- Recipient’s serum added
- If there are pre-formed Abs against particular HLA in serum, the cells will die
- Dead cells stain red
Indications:
• Indirect indication of ‘transplantability’
• Determines probability of ‘crossmatch’ negative with a particular donor
• Can identify specific Ags to avoid
What happens if there is a high PRA result?
- Longer waiting time
- Increased rejection episodes
- Greater immunosuppression required
- Decreased graft survival
Describe the process of pre-transplant crossmatch
“Transplant in a test-tube”
- Blood samples taken from donor and recipient
- Donor cells and recipient serum plated out into wells
- Rabbit C’ added
- Membrane injury visualised using light microscope
List drugs that act through calcineurin inhibition
Describe the MOA and the immunological effects
Cyclosporin
• Inhibits IL-2 gene transcription in T cells
• T cells cannot proliferate after becoming activated
• Reduced T cell and granulocyte exocytosis of granule-associated serine esterases
• B cells have reduced proliferation
• B cells undergo apoptosis following activation
Tacrolimus
• Similar activation to cyclosporin
• Binds FK-binding protein which binds calcineurin
• Same immunological effects
What are the AE of cyclosporin?
Nephrotoxicity
5-10 after renal transplant, an individual will need another transplant due to the effects of cyclosporin on the kidney
What are the side effects of steroids?
- Fluid retention
- Hypertension
- Increased susceptibility to infection
List an important steroid drug
Prednisolone
Where is the steroid receptor?
In the cytoplasm
Describe the effects of steroids
Anti-inflammatory:
↓ circulating lymphocytes
↓ neutrophil enzyme release
↓ monocyte activity
Immunosuppressive:
↓ lymphocyte proliferation
↓ Ag presentation by monocytes
Describe the signalling of steroids
- Steroids cross plasma membrane and bind with receptor in cytoplasm
- Heat shock protein dissociates from steroid receptor
- Steroid-receptor complex moves into nucleus and binds regulatory regions on DNA
- Activation of gene transcription
Describe how anti-proliferative drugs act
List some
- Azathioprine
- Mycophenalate
- Rapamycin
MOA:
• Inhibit DNA and RNA synthesis
Effect:
• Blocks IL-2 production and lymphocyte expansion
Describe the rationale of the use of combined immunosuppressive drugs
Allows use of lower doses of individual drugs to minimise side effects
What things will we see in the future of transplantation?
- Better immunological matching
- More specific immunosuppression
- Xenotransplantation
- Induction of specific tolerance to transplanted organ
- Stem cell transplants
Give an overview of immunological tolerance
The removal, suppression or isolation of auto-reactive lymphocytes
Central and peripheral mechanisms
- Deletion
- Receptor editing
- Anergy
- Suppression w/ Tregs
- Ignorance
Describe approaches to donor specific tolerance
Interrupt signalling:
• Cyclosporine
Co-stimulation blockade:
• Ipilimumab (anti-CTLA4 Ab); blocks CD28
Donor haematopoietic chimerism
• BM transplant
Tregs
• Tregs inhibit aggressive T cells in their response against the graft
What is stem cell transplantation?
In vitro differentiation of human ESCs into specialised tissues and then transplantation into people
Prospects: Regeneration of whole tissues: • Lungs • Blood • Heart • Neurons • Pancreas
Use of scaffold to grow organ
What ethical considerations need to be taken into account with transplantation?
Donor supply is the limiting factor in the growth of transplantation
The various sources of organs raises ethical issues:
Status of donors: • Brain dead, receiving cardiac / lung support • Not in coma • Not in persistent vegetative state • Not in 'locked-in' state
Tourism transplantation
Executed prisoner donors
List other names for Hyperacute rejection
Antibody mediated rejection
/
Humoral rejection
Describe the protocol for ABO matching in organ transplantation
Organs are only transplanted across blood group lines
Exceptions:
• O to A2 individual
• Pre-transplant reduction of Ab
Which HLA loci are most important in terms of pre-transplant tissue typing
Differences and A, B and DR are far more important than differences at C, DP and DQ.
Outline the cocktail of immunosuppressive drugs used for transplants
- Calcineurin inhibitors
• Cyclosporin
• Tacrolimus - Anti-inflammatories
• Steroids - Anti-proliferatives
• Azathioprine
What is CD25?
The alpha subunit of the IL-2 receptor
