Week 9 Part 1 - ABO Discrepancies and Transfusion in Transplantation

Question 1

ABO Grouping Discrepancies

Answer 1

An ABO discrepancy occurs when the forward and reverse grouping reactions don’t match
If blood is required before resolution of the discrepancy, issue Group O RBCs or AB plasma

Question 2

What can a patient produce an anti-reagent antibody against, causing an ABO discepancy?

Answer 2

Dyes in Anti-A or Anti-B
Preservatives in reagent antibodies
Preservatives in reagent RBC preps
To prevent this - wash patient/reagent cells and resuspend in saline

Question 3

B(A) Phenotype

Answer 3

Individuals produce high concentrations of B glycosyltransferase that catalyses the addition of D-Galactose AND N-acetyl-D- galactosamine
Mostly B antigen, with weak expression of A antigen, on RBCs
Produce an anti-A antibody that agglutinates A1 and A2 RBCs

Question 4

With what antibody can the B(A) phenotype be detected?

Answer 4

Only detected when the MHO4 anti-A monoclonal antibody is used for forward grouping reactions
Solution - use a different grouping reagent

Question 5

Results for B(A) Phenotype

Answer 5

Anti-A: 1+
Anti-B: 4+
A cells: 4+
B cells: 0

Question 6

Acquired B

Answer 6

Group A individuals with gut diseases (Colon Ca, septicaemia)
Bacterial deacetylases remove acetyl group from GalNAc
Some anti-B reagents bind to D-galactosamine → w+ rxn
Not a true B antigen
Solution:
- use a different anti-B reagent
- decrease pH

Question 7

Acquired B Results

Answer 7

Anti-A: 3+
Anti-B: 1+
A cells: 0
B cells: 4+

Question 8

cisAB

Answer 8

In cisAB individuals, a single allele expressing both A AND B glycosyltransferases are inherited from an AB parent, and a single allele (usually O) from the other parent
cisAB individuals have decreased glycosyltransferase production → ↓ ag expression → weak forward reactions
Usually also produce a weak anti-B antibody
- reacts with B cells but not cisAB cells
Solution - family studies

Question 9

cisAB Results

Answer 9

Anti-A: 2+
Anti-B: 2+
A cells: 0
B cells: 1+

Question 10

Chimerism

Answer 10

Patient has two different populations of RBCs present in their circulation
Can be natural or acquired

Question 11

Natural Examples of Chimerism

Answer 11

Multiple births (twins, triplets, etc)
Dispermy
Fetal-maternal bleed

Question 12

Acquired Examples of Chimerism

Answer 12

Out-of-group transfusions
Bone Marrow/Stem Cell Transplants
Exchange Transfusion

Question 13

Chimerism - Twin Chimerism

Answer 13

Placental blood vessels anastomose between twins
Blood flows between the twins
Haematopoietic cells engraft in the BM, → 2 sets of cells

Question 14

Chimerism - Dispermy

Answer 14

Two sperm fertilise two maternal nuclei, and the resulting zygotes fuse to grow one body

Question 15

Chimerism Results

Answer 15

Depends on the degree of the chimera
Solution:
- initially, patient history
- requires use of molecular methods to identify chimera

Question 16

Types of Transplant

Answer 16

Autologous
- cells from own body
- for those in disease remission
Allogeneic
- cells from someone else
- for patients who can’t donate their own cells (chemo, irradiation, BM disease)
Syngeneic
- cells from identical twin
- for those with identical siblings (twins, triplets, etc)
- no chance of graft rejection, GvHD

Question 17

Sources of Haematopoietic Progenitor Cells (HPCs)

Answer 17

Bone Marrow (BM)
Peripheral Blood
- collected via leukapheresis
- HPCs mobilised from BM using G-CSF (Filgrastim), Plerixafor, Chemo
Umbilical Cord Blood

Question 18

Sample Preparation

Answer 18

CD34 counts (flow)
CD34 is a marker for HPCs
BM filtered to remove fat, debris, bone fragments
Separate buffy coat from RBCs/Plasma
- cell separator or Ficoll density gradient
- can enrich for CD34+ cells (magnetic beads/FACS)

Question 19

ABO Incompatible Transplants - Major Mismatch

Answer 19

Foreign antigen on donor cells
Recipient produces antibody against donor cells
i.e. O recipient receives A cells
Recipient lyses donor RBCs, so they must be removed before transplantation

Question 20

ABO Incompatible Transplants - Minor Mismatch

Answer 20

Foreign antibody in donor sample
Donor produces antibody against recipient cells
i.e. A recipient receives O cells
Aby’s in residual donor plasma lyse recipient RBCs
Passenger lymphocyte syndrome
- donor lymphocytes are infused into recipient
- donor lymphocytes produce aby → haemolysis

Question 21

ABO Incompatible Transplants - Bi-Directional Mismatch

Answer 21

Major and minor mismatch (i.e. A recipient, B donor)

Question 22

What Happens After Transplantation - Engraftment

Answer 22

Early
- 9-30 days
- ↑ neutrophil count
Platelet engraftment
- 15+ days
RBC engraftment/reconstitution
- 90+ days

Question 23

How are RBCs and PLTs treated before being transplanted?

Answer 23

Leukoreduced and irradiated

Question 24

Example of Transfusion Support in a Major Mismatch

Answer 24

O recipient, A donor as an example
Recipient will continue to have circulating anti- A, -B, -A,B for a period of time
Donor HPCs engraft, A RBCs produced, but will be lysed until recipient aby’s are cleared, hence transfusion requirement
Gp O RBCs (recipient group) transfused until recipient aby clears
PLT/FFP contain ABO antibodies
- we don’t want to transfuse the recipient with product that will lyse donor cell
Gp A PLT/FFP (donor group) transfused

Question 25

Example of Transfusion Support in a Minor Mismatch

Answer 25

A recipient, O donor as an example
Donor HPCs engraft. Recipient RBCs eventually become group O
Gp O RBCs (donor group) transfused
PLT/FFP contain ABO antibodies
- we don’t want to transfuse the recipient with product that will lyse the recipient RBCs
Gp A PLT/FFP (recipient group) transfused

Question 26

Overview of Transfusion Support in a Major and Minor Mismatch

Answer 26

In major:
- RBCs - same group as recipient
- PLT/FFP/Plasma product - same group as donor
In minor:
- RBCs - same group as donor
- PLT/FFP/Plasma product - same group as recipient

Question 27

HSC Transplant Recipient - ABO Discrepancy with a Minor Mismatched Transplant

Answer 27

e.g. Group A recipient receives group O transplant

Question 28

HSC Transplant Recipient - ABO Discrepancy with a Major Mismatched Transplant

Answer 28

e.g. Group O recipient receives group A transplant

Question 29

Transfusion Support in ABO-Incompatible Solid Transplants

Answer 29

ABO-incompatible kidneys are transplanted
Largest concern is organ rejection due to a major mismatch
Recipient antibodies are reduced by plasmapheresis and immunosuppression
Aim in subsequent transfusions is to keep ABO antibody levels low
Blood products, particularly plasma (containing) products, must be ABO compatible with recipient AND graft for remainder of recipient’s life
Passenger lymphocyte syndrome can occur in minor mismatch recipients
- RBCs compatible with recipient and donor may be transfused to minimise this