Lecture 5- transplantation

Question 1

what is transplantation?

Answer 1

Replacing cells, tissues or organs from one to another.

Question 2

what is rejection?

Answer 2

failure of grafting caused by the immune system identifying the transplant as foreign.

Question 3

what is transfusion?

Answer 3

Transplantation of circulating blood cells or plasma from one to another.

Question 4

what is the history of transplantation?

Answer 4

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)

Question 5

what was the beginning of modern transplantation?

Answer 5

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.

Question 6

what are the common transplants in the UK?

Answer 6

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

Question 7

what are immune privileged sites?

Answer 7

Cornea: Allogeneic
Transplants at certain anatomical sites are generally accepted without any immune rejection (lack of vascularization)

Question 8

what are vascularised solid organs?

Answer 8

Allogeneic
Kidney, Lung, Liver, Heart , Pancreas, Combined

Question 9

what are Haematopoietic stem cell transplants?

Answer 9

Allogeneic & Autologous

Sources of stem cells 
- Bone marrow 
       - Peripheral blood (enriched by cytokine administration)
- Cord blood

Question 10

what are skin transplants?

Answer 10

Allogeneic & Autologous

Question 11

what is autologous (autograft)?

Answer 11

same individual eg skin from a different area of the body

Question 12

what is allogenic (allograft)?

Answer 12

same species eg kidney from mother to child

Question 13

what is syngeneic (isograft)?

Answer 13

genetically identical eg identical twins

Question 14

what is xenogeneic (xenograft)?

Answer 14

different species eg heart from pig to a human

Question 15

what is Human Leukocyte Antigen class 1

Answer 15

On all nucleated cells
Presents antigen to CD8+ Tc

Question 16

what is Human Leukocyte Antigen class 2

Answer 16

Restricted to professional antigen presenting cells (DC, B cells, Macrophages)
Presents antigen to CD4+ Th

Question 17

what is the HLA haplotype?

Answer 17

In humans HLA complex is located on the short arm of chromosome 6
HLA is inherited as a “set” of HLA groups called “haplotypes”

Question 18

what is HLA polymorphism?

Answer 18

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

Question 19

what is the importance of HLA matching?

Answer 19

The more alike the HLA types of the donor and recipient are the more likely a transplant will be successful.

Question 20

what is HLA typing?

Answer 20

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)

Question 21

what is direct recognition?

Answer 21

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

Question 22

what is chronic rejection?

Answer 22

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

Question 23

what is indirect recognition?

Answer 23

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.)

Question 24

what is acute rejection?

Answer 24

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)

Question 25

what is accelerated acute rejection?

Answer 25

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

Question 26

what are calcineurin inhibitors?

Answer 26

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

Question 27

what are corticosteroids?

Answer 27

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

Question 28

what are cytokine action inhibitors?

Answer 28

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

Question 29

what are nucleotide synthesis inhibitors?

Answer 29

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

Question 30

what are the side effects of all of these?

Answer 30

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

Question 31

what is specific immunosuppression?

Answer 31

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

Question 32

what is hyper acute rejection?

Answer 32

Cause: Antibodies – Humoral immunity (ABO system, presence of pre-existing antibodies) In minutes, hours Mechanism: Complement activation Secondary activation of coagulation cascade

Question 33

how do we minimise graft rejection?

Answer 33

1- Donor Selection HLA matching Screening for pre-existing Ab 2- Immunosuppression Generalize Specific Ultimate goal - Induction of graft tolerance

Question 34

how can Pig to Human Xenotransplantation work?

Answer 34

(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

Question 35

what is the Co-stimulatory blockade?

Answer 35

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

Question 36

what are types of Biological Agents (antibodies and fusion proteins)?

Answer 36

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

Question 37

what does it mean when it says "clinical immunosuppression is a careful balance between too much and not enough"?

Answer 37

too little = rejection, recurrent disease too much = infection, cancer

Question 38

what is the Donor specific antibody / Panel reactive antibody?

Answer 38

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

Question 39

what is transplant rejection?

Answer 39

Genetic variations between host & donor Blood Groups (ABO) HLA (Human Leukocyte Antigen): MHC (Major Histocompatibility complex) Others Mi-HA: Minor Histocompatibility Antigens

Question 40

what is the Screening of donor & recipient prior to transplantation?

Answer 40

1. Identifying the genetic variations between donor and recipient ABO blood group testing HLA typing 2. Identifying the pre-existing antibodies (anti-HLA) against donor cells. Cytotoxic cross matching Donor specific antibody screening (panel reactive antibody)

Question 41

what is cytotoxic cross matching?

Answer 41

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