Organ Transplantation and the HLA system

• Understand what the HLA system is and what it means to be histocompatible.

• Have a basic understanding of the organisation and inheritance of the MHC.

•Give an overview of pre-transplantation tests and understand their significance.

•Demonstrate an understanding of the molecular principle behind SSP-PCR and its use in HLA typing.

• Allograft transplantation: transfer of an organ from one individual to another

• Most common transplanted organ is the kidney.

• Immune response dictates whether body will accept or reject a graft

What is Transplantation?

The HLA system• Human leukocyte antigens otherwise known as MHC molecules• Highly polymorphic Glycoprotein complexes• ~ 200 genes on chromosome 6• 3 clusters:

MHC class I – HLA-A, HLA-B, HLA-CMHC class II – HLA-DR, HLA-DP, HLA-DQMHC class III – Soluble components

HLA inheritance and familial matching

• We express two alleles at each loci: one inherited from either parent.•Co-dominant expression• <0.5% recombination frequency

Homozygous parents

Heterozygous children

HLA inheritance and familial matching

•‘Haplotype’: a combination of alleles at adjacent loci on a chromosome that are inherited together.

•Breeding between two heterozygous individuals results in children with 4 possible genotypes

•There is a 1 in 4 chance of a complete match between two siblings

DonorHLA type: A1, -, B8, 39, DR1, 3.Homozygous at the A locus for A1Heterozygous at the B locus for B8 and B39Heterozygous at the DR locus for DR1 and DR3

RecipientHLA type: A1, 24, B39, 44, DR1, 11.Heterozygous at each loci1 mismatches for the B locus1 mismatch for the DR locus

HLA typing and nomenclatureheterozygous

Pre-transplant tests

• %PRA: Recipient serum screened for antibodies towards HLA antigens

• ABO blood typing

• HLA tissue typing

• Serum cross-matching

%PRA

Polymerase Chain Reaction

One cycle consists of...

Step 1 – denature dsDNA at 98o

Step 2 – annealing of primers by reducing the temperature

Step 3 – extension of primers by heat stable DNA polymerase

Gel electrophoresis

•DNA can be stained using ethidium bromide

•DNA fragments separated by size.

•Negatively charged DNA moves through the gel towards the anode

HLA Tying using SSP-PCR

•Ideal scenario: 12 HLA match•Important HLA antigens for Kidney transplantation: HLA-A, HLA-B, HLA-DR

HLA Matching

Cross matching

Hyper-acute (immediate) rejection

Thank you!• Please take the time to fill out a short assessment.• Thank you for taking the time to volunteer, it is much

appreciated. To thank you for taking part, 3 volunteers will receive a cash reward of either £5, £10 or £15. Please keep an eye on your inbox!

• If you would like to register as an organ donor visit www.organdonation.nhs.uk to find out more