Transplants

Question 1

Why would you use transplants?

Answer 1

If someone is undergoing end stage organ failure. This includes organs such as the heart, liver, kidney etc.

Question 2

What are the challenges of transplant?

Answer 2

Not enough donors
Loss of organs because of immune attack (rejection).

Question 3

Describe the immune response to transplanted organs?

Answer 3

If the organ is not off the same HLA the body will recognise all graft cells as foreign and mount the innate and adaptive immune response to destroy these cells.

Also ischaemia reperfusion injury will also take place and is caused by the donor organ being in a low oxygen environment

Question 4

What happens to a kidney when it undergoes ischaemic reperfusion injury?

Answer 4

The lack of oxygen causes immune cell activation activating cytokines which begin to destroy cells. This happens in most transplanted organs and you have between 15 and 20 hours to get the donor organ into the recipient.

Question 5

How is the innate immunity response triggered in ischaemic reperfusion injury?

Answer 5

The lack of oxygen causes DAMPs to bind to their receptors resulting in the complement to activate and neutrophils, macrophages and NK cells

Question 6

What do DC cells do in the immune response against transplanted organs?

Answer 6

DC’s pick up antigen and migrate the the lymph node where they upregulate and activate T-cells. These T-cells then go back and destroy the kidney cells. The main target of this immune response is the HLA antigens or the recipient.

Question 7

What do grafts express high levels of which is recognised as foreign by the adaptive immune response?

Answer 7

ABO antigens (you need to get this right)
HLA antigens
Non-HLA antigens

Question 8

Why are HLA (MHC) important?

Answer 8

They help the body react to foreign tissues and activate T-cells
They are the main target for the immune response

Question 9

What are the subtypes in class 1 and class 2 HLA (MHC) and what are they expressed on?

Answer 9

Class 1 = HLA-A, HLA-B, HLA-C (expressed on all nucleated cells)

Class 2 = HLA-DR, HLA-DQ, HLA-DP (expressed only on DCs, B cells, Mac/Monocytes)

Question 10

How many HLA molecules does an individual have?

Answer 10

6 class 1 molecules on the cell surface

12 class 2 HLA on cell surface

Question 11

Do unrelated individuals have different HLA’s?

Answer 11

Yes

Question 12

What does the recipients immune response target?

Answer 12

They react against the HLA which are found on all cells, involved in T cell activation and are highly variable

Question 13

What would happen if you were exposed to foreign DNA?

Answer 13

T-cell activation = this would destroy the donated cell leading to graft rejection.

Anti-HLA antibodies could be produced through exposure to foreign HLA e.g during pregnancy, transplant, blood transfusion

Question 14

What are the different types of allorecognition and how do these work?

Answer 14

Direct - this is not normal and is when the Donor APC shows donor HLA directly to recipient T cell

Indirect - normal - donor HLA goes into vesicles and antigen goes into recipient HLA before being shown to recipient T-cell

Semidirect - donor HLA goes into vesicles before bieng shown to recipeint T cell

Question 15

Do B cells react differently than usual when shown a donor HLA, and if so, why?

Answer 15

No

Question 16

What are HLA antibodies, how do they develop and why might they be bad?

Answer 16

These develop from your body seeing foreign DNA whether through pregnancy of previous transplant. This means that any new transplant must not have the HLA type that you have antibodies to as these will instantly react and reject the graft.

You can test this through luminex

Question 17

How would you manage the immune response in transplantation?

Answer 17

Immunosuppressants - will always be on these

Getting the closest match possible between donor and recepient.

Question 18

How are deceased donor organs allocated?

Answer 18

They are typed for blood, HLA, proteins etc and put into a web bank. The ODT (organ donation and transplant) team will identify matches and further cross matching will be done at the recipients local centre. If negative = transplant goes ahead, if positive = transplant rejected or risk management takes place.

Question 19

How do you tissue type for HLA?

Answer 19

You use antibodies to look at the proteins on the cell surface, label the HLA’s using PCR, look at the nucleotide sequence and compare to other people. Next generation sequencing is normally used for this.

Question 20

Why HLA match?

Answer 20

Reduces the risk of early cellular rejection and stops the graft slowly loosing its function and being rejected.

Question 21

Can you have some HLA be wrong?

Answer 21

Yes = does not need to be 100% HLA match for the graft to work (this would be nearly impossible for all people).

Question 22

What are the 2 ways HLA antibodies can develop?

Answer 22

Pre-formed - occur due to foreign tissue being in body before and are present at time of transplant

De novo - they occur because your body is rejecting the graft

Question 23

How does luminex testing work?

Answer 23

Microbeads coated in HLA antigen is placed in recipients serum. Wash beads before incubating with PE conjugate anti-human IgG before washing once more. Run the beads on luminex assigning the assay reactivity and antibody specificities. You then see lots of red peaks on computer which means theres a reaction and therefore cannot get graft depending on how severe.

Question 24

What are the ways grafts can be rejected and what causes this rejection?

Answer 24

Hyperaccute = instantly = caused by preformed anti-donor ABO or lots of HLA antibodies

Accelerated = days = caused by low levels preformed HLA antibodies and the T cell response.

Acute = weeks/months = primary activation of T cells (treated by increasing immunosuppresants)

Chronic = months - De novo HLA antibodies and the immune complexes or reccurance of disease.

Question 25

What things can cause chronic rejection?

Answer 25

Chronic allograft vasculopathy
Transplant glomerulopathy (TG) associated with chronic antibody-mediated rejection

Question 26

Why might De novo HLA antibodies occur?

Answer 26

Patient non-compliance with medication or just random

Question 27

How would you evaluate the risk of a donor and recipient?

Answer 27

You would crossmatch for HLA. There is some cases where there is no way that recepient can get that donoated organ as the HLA antibodies are too high (red), In other cases its a near perfect match (green). In orange cases it is given to people especially if they’ve been waiting a while or they dont think they’ll get a better match.

Question 28

What is the 2 ways you can do cross matching?

Answer 28

Wet = adding donor and recipient blood into a serum with one another and see if any antibodies form

Virtual = use donor HLA data and the patient luminex HLA antibody to predict likelihood of positive crossmatch.

Question 29

Where are all the places to look for a correct HLA match for haematopoietic stem cells?

Answer 29

Siblings (1 in 4 chance)
Unrelated donor registers
Cord registers (this is expensive and you would need 2 for enough blood).

You can also do transplants if someone shares half their HLA alleles

Question 30

WHat would happen if you dont get the correct HLA match in HSCT?

Answer 30

You would get GvHD (grafts vs host disease) which is when the immune cells you have transplanted into the recipient view the recipient as foreign and starts attacking all their cells.

Question 31

When can GvHD be good?

Answer 31

Some cells target and kill heamatopoietic cells causing graft vs leukemia (GvL) which is good for killing off leukaemia.

Question 32

What is the effect of disease stage with HLA matching in HSCT?

Answer 32

The further on in the disease the more chance of rejection and less survival.