Lecture 5- transplantation Flashcards
what is transplantation?
Replacing cells, tissues or organs from one to another.
what is rejection?
failure of grafting caused by the immune system identifying the transplant as foreign.
what is transfusion?
Transplantation of circulating blood cells or plasma from one to another.
what is the history of transplantation?
Nose (skin, autologous) transplantation by Hindu Surgeons (in 700 B.C.)
Attempts for allogeneic skin transplantations by Italian surgeons (in 1400s)
Skin grafting was quite common during late 1800s.
Teeth transplantation by Scottish surgeon John Hunter in England
‘Transplanted tissue needs good blood circulation to survive’
‘Diseases of tooth donor could be passed on to the recipients’
In 1900, Karl Landsteiner; distinguished the main blood groups (Nobel Prize, 1930)
what was the beginning of modern transplantation?
WW II - skin allografts for military pilots (unsuccessful most of the time)
Skin allografts between family members tended to survive for longer than those between unrelated individuals
A second graft from a given donor was rejected more rapidly and more vigorously than the first.
what are the common transplants in the UK?
Solid organ transplantations in UK 2023/2024
Kidney: 3355
Liver: 891
Cardiothoracic (heart or lung or combined heart/lung): 377
Pancreas: 177
Intestine: 22
Tissue transplantations
Cornea
Hematopoietic stem cell transplantation (HSCT), often called bone marrow transplantation
what are immune privileged sites?
Cornea: Allogeneic
Transplants at certain anatomical sites are generally accepted without any immune rejection (lack of vascularization)
what are vascularised solid organs?
Allogeneic
Kidney, Lung, Liver, Heart , Pancreas, Combined
what are Haematopoietic stem cell transplants?
Allogeneic & Autologous
Sources of stem cells
- Bone marrow
- Peripheral blood (enriched by cytokine administration)
- Cord blood
what are skin transplants?
Allogeneic & Autologous
what is autologous (autograft)?
same individual eg skin from a different area of the body
what is allogenic (allograft)?
same species eg kidney from mother to child
what is syngeneic (isograft)?
genetically identical eg identical twins
what is xenogeneic (xenograft)?
different species eg heart from pig to a human
what is Human Leukocyte Antigen class 1
On all nucleated cells
Presents antigen to CD8+ Tc
what is Human Leukocyte Antigen class 2
Restricted to professional antigen presenting cells (DC, B cells, Macrophages)
Presents antigen to CD4+ Th
what is the HLA haplotype?
In humans HLA complex is located on the short arm of chromosome 6
HLA is inherited as a “set” of HLA groups called “haplotypes”
what is HLA polymorphism?
HLA is the most polymorphic region of the human genome
Aim: Diversity – Immune response to pathogens varies between individuals so the population could survive.
Major cause of graft rejection
what is the importance of HLA matching?
The more alike the HLA types of the donor and recipient are the more likely a transplant will be successful.
what is HLA typing?
Determination of HLA antigens on donor and recipient leukocytes by either serologic or DNA typing methods
eg PCR-SSP (Sequence-Specific Primers) or PCR-SSO (Sequence-Specific Oligonucleotide)
what is direct recognition?
Recipient T cells recognise the intact foreign HLA on Donor APC
Donor APC (passenger leukocytes) can leave the graft and migrate to the draining lymph node
Appropriate TCRs can directly recognise intact allo-MHC as foreign (a mixed lymphocyte reaction; MLR)
T cells are strongly activated, and drive effector responses
Important early in response
what is chronic rejection?
Cause: Graft is a continuous source of HLA allo-antigens. It can induce a rejection response at any time post-transplant.
Slow and progressive, long-term loss of function, years
Mechanism:
DTH, antibodies, immune complexes, slow cellular reactions
what is indirect recognition?
Recipient T cells recognise the foreign HLA processed and presented by Recipient APC
Uptake of allogeneic antigen by host APC
Donor Antigen degraded into peptides and presented on recipient MHC as for any exogenous antigen
Activated T cells can provide help to effector cells (Macrophages, antigen specific B cells etc.)
what is acute rejection?
Cause: Activation of T cells – Cellular immunity
Can start about a week after transplant
If occurs, most often happens within the first year
Mechanism:
CD8 Tc directly destroy the graft cells
CD4 Th secrete cytokines that induce inflammation, activate other cells (B cells, macrophages)
what is accelerated acute rejection?
Cause: Sensitized T cells – Memory
(e.g. by previous pregnancy, blood transfusion, previous transplantation)
Within days
Mechanism:
Cytokines, activation of monocyte, macrophages,
Proliferation of cytotoxic T lymphocytes
what are calcineurin inhibitors?
Cyclosporine revolutionised kidney transplantation in 80s.
Tacrolimus (FK506) acts similarly
Both isolated from fungi
Complexes with Calcineurin to prevent NFAT de-phosphorylation
NFAT can’t induce IL-2 gene transcription
what are corticosteroids?
Powerful anti-inflammatory drugs (e.g. Prednisolone)
Derivatives of glucocorticoids, bind to steroid receptors in cell cytoplasm
Affect gene transcription
Prevent production of cytokines (IL-1, IL-3, IL-4, TNF, GM-CSF)
Block Prostaglandin production
Reduce cell migration/recruitment in inflammation
Promotes inflammatory cell apoptosis
what are cytokine action inhibitors?
Rapamycin (Sirolimus)
Blocks mTOR (mamalian target of rapamycin)
Prevents cell cycle G1->S
Prevents mTOR dependent cytokine production
IL-12/23, IL-10, IL-1b, type1 IFN
what are nucleotide synthesis inhibitors?
Azathioprine and Mycophenolate Mofetil (MPA)
Blocks adenine and guanine nucleotide synthesis (purines)
Inhibits DNA and RNA synthesis
Blocks lymphocyte division
Prevents IL-2 production and lymphocyte activation
Toxicity to other dividing cells
what are the side effects of all of these?
Corticosteroids
growth retardation, osteoporosis, hypertension, obesity, diabetes . .
Nucleotide synthesis inhibitors
Bone marrow suppression, hepatic dysfunction, hair loss, GI effects
Calcineurin inhibitors
nephrotoxicity, hirsutism, hepatotoxicity, diabetes, neurotoxicity
Antibodies
Cytokine release syndrome, reaction to foreign protein. . .
= Global Immunosuppression
what is specific immunosuppression?
The ideal immunosuppressant:
Antigen-specific
inhibiting the immune response to the alloantigens
Preserving the recipient’s ability to respond to other foreign antigens
Induce tolerance
Monoclonal antibodies or soluble ligands
what is hyper acute rejection?
Cause: Antibodies – Humoral immunity
(ABO system, presence of pre-existing antibodies)
In minutes, hours
Mechanism:
Complement activation
Secondary activation of coagulation cascade
how do we minimise graft rejection?
1- Donor Selection
HLA matching
Screening for pre-existing Ab
2- Immunosuppression
Generalize
Specific
Ultimate goal - Induction of graft tolerance
how can Pig to Human Xenotransplantation work?
(CRISPR)-Cas9 genome editing
Knock-outs
Antigenic sugars on the surface of pig cells as recognised as foreign
Galactose a-l,3-galactose (Gal)
Knock-ins
Anti-inflammatory genes
Genes that promote normal blood coagulation (prevents blood vessel damage)
Regulatory protein genes that help suppress the antibody responses
Immunosuppression
Blockade of the B7-CD28 and the CD40/CD154 pathways
what is the Co-stimulatory blockade?
CTLA4Ig fusion protein (abatacept, belatacept)
Preferentially binds and blocks CD80/CD86 (B7), can’t bind to CD28 therefore no signal 2, no activation
Monoclonal anti-CD40L
what are types of Biological Agents (antibodies and fusion proteins)?
Anti CD3 (OKT3)
disables CD3 receptor (but can cause activation and cytokine release (IFNg, TNF))
Anti IL-2 receptor (CD25)
Basiliximab, Daclizumab (humanised anti CD25)
complete CD25 blockade for 20-40 days
what does it mean when it says “clinical immunosuppression is a careful balance between too much and not enough”?
too little = rejection, recurrent disease
too much = infection, cancer
what is the Donor specific antibody / Panel reactive antibody?
Detect the presence of pre-existing antibodies against HLA antigens.
Microbeads or ELISA plates are coated with HLA antigens
If the recipient has pre-formed anti-HLA antibodies in the serum, they bind to HLA coated microbeads or plates
what is transplant rejection?
Genetic variations between host & donor
Blood Groups (ABO)
HLA (Human Leukocyte Antigen): MHC (Major Histocompatibility complex)
Others
Mi-HA: Minor Histocompatibility Antigens
what is the Screening of donor & recipient prior to transplantation?
- Identifying the genetic variations between donor and recipient
ABO blood group testing
HLA typing - Identifying the pre-existing antibodies (anti-HLA) against donor cells.
Cytotoxic cross matching
Donor specific antibody screening (panel reactive antibody)
what is cytotoxic cross matching?
To determine if the recipient has any pre-existing antibodies to the donor cells (typically to HLA)
- No antibody binding, cells are not killed by complement activation
- If there are pre-existing anti-HLA antibodies, cells are killed by complement activation
Add stain to distinguish live & dead cells
