HLA Matching

STEM CELL TRANSPLANTATIONAND HISTOCOMPATIBILITY

Dr. Ann Van de Velde, Haematologist

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Drawing Apparatus - Copyright: Robert Howsare

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From HLA typing to immunogenetic profiling

Goal3

Investigate structural differences between HLA allelesFind the best donor/recipient match for hematopoietic stem cell transplation

The Haematopoietic System4

A good match (1/2)5

Our immune system attacks things it doesn’t recognize, including cells and tissues.

Stem cell transplants can be rejected by the recipient's immune system.

Therefore, the transplanted stem cells must match the recipient closely enough that they won't be recognized as intruders.

A good match (2/2)6

To determine whether the donor is a good immunological match with the recipient, a tissue typing test is performed using blood samples from both individuals.

This test identifies certain proteins, called HLA antigens, which reside on the surfaces of specific immune cells.

If the donor and the recipient have identical HLA antigens, they are a good match.

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46 XY – 46 XX9

The beginnings10

DNA11

Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different to distinguish one individual from another, unless they are monozygotic twins.

Beyond the Double Helix12

Human Genome Project (HGP) 2004 There are approximately 23,000 genes

in human beings Understanding how these genes express

themselves will provide clues to how diseases are caused.

What is HLA?13

Human Leukocyte Antigens The proteins encoded by HLAs are those

on the outer part of body cells that are unique to that person.

Plays a key role in immune response More polymorphic than red blood groups

ABO system: 4 possible combinations (A, B, AB, O)

HLA system: > 1 million combinations

HLA antigens 14

=>antibody production ABO: natural antibodies HLA: not-natural antibodies:

as a result of an immunologic challenge of a foreign material containing non-self HLAs via

Pregnancy Blood transfusion Transplantation

Origins – Jean Dausset (F)Nobel Prize in Physiology and Medicine in 198015

1954: anti-leucocyte agglutinating substance 1958: isoantibody specific to leucocytes 1965: all leucocyte antigens = part of

complex 1968: renamed HLA 1980: Nobel Prize => made it feasible to publish the first genetic map

and, later on, the first physical map of the human genome.

Histocompatibility16

HLA typing Screening and identification of HLA

antibodies Polymorphism of HLA represents a major

barrier to hematopoietic stem cell (HSC) transplantation.

DNA profiling (°10/09/1984, UK)= DNA testing = DNA typing = genetic fingerprinting17

not = full genome sequencing repetitive ("repeat") sequences that are

highly variable variable number tandem repeats (VNTRs) short tandem repeats (STRs)

Siblings: VNTR loci are very similar

Unrelated individuals: VNTR loci are very different

Variations of VNTR allele lengths in 6 individuals18

HLA2 Classs: I and II

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Each class of HLA is represented by more than one locus (polygeny).

class I loci are HLA-A,-B and –C class II loci HLA-DR, -DQ and -DP. All the HLA genes map within a single

region of the chromosome (hence the term Complex).

Homologous chromosomes (diploid)

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Homologous chromosomes (diploid)

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Chromosome 622

The HLA complex is located within the

6p21.3 region on the short arm of human

chromosome 6 and contains more than

220 genes of diverse function.

Many of the genes encode proteins of the

immune system.

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Haplotypes25

Alleles different forms of a gene/genetic locus

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Allelic variation at a gene locus27

WHO Nomenclature Committee for Factors of the HLA System> 7000 alleles

Haplotypes28

All loci are expressed co-dominantly, that is to say both the set of alleles inherited from one's father and the set inherited from one's mother are expressed on each cell.

The set of linked alleles found on the same chromosome is called a haplotype.

Homozygous and heterozygous

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MHC class Ilocus #

Major AntigensHLA A 1,884HLA B 2,490HLA C 1,384

Minor AntigensHLA E 11HLA F 22HLA G 49

MHC class II

HLA -A1 -B1 -B3 to -B51 Theor. possible

locus # # #combination

s

DM- 7 13 91DO- 12 13 156DP- 34 155 5,270DQ- 47 165 7,755DR- 7 1,094 92 8,302

1DRB3, DRB4, DRB5 have variable presence in humans

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Nomenclature applied to HLA

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serological (antibody based) recognition e.g., HLA-B27 or, shortened, B27

"HLA" in conjunction with a letter * and four-or-more-digit number e.g., HLA-B*08:01, A*68:01, A*24:02:01N

N=Null)

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Αλληλους / Allelos / "each other”

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GVH en GVL (1/2)36

The most impressive impact of novel DNA typing methods concerns matching for allogeneic HSC transplantation because subtle serologically silent sequence differences between allelic subtypes are recognized by alloreactive T-cells with serious consequences for graft outcome.

GVH and GVL (2/2)37

Allogeneic stem cell transplantations have the therapeutic effect of eliminating leukemia cells, with the danger of developing graft versus host disease. When donor and patient are HLA-identical, these effects are due to minor histocompatibility antigens, which are expressed from polymorphic genes.Identifing which genes and which peptides cause the GvL effect, without the development of GvHD.

Now the HLA-matched donor is ready to have her stem cells collected38