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HLA – Basics
(or how to recognize “self”)
Directors’ Affairs Committee plus others
(with our gratitude)
Overview
• Some Definitions
– MHC and HLA
– Class I and Class II
– Nomenclature
• Class II extended haplotypes
• HLA Typing Technology
• HLA Immunogenicity
• Solid Phase Antibody detection methods
• HLA and Disease Associations
• HLA and Pharmacogenetics
• Review
2
Polymorphism slide-new alleles each year
3
Human Leukocyte Antigens
Major Histocompatibility Complex (MHC)
• MHC in humans is named “Human Leukocyte Antigens”
(HLA) as they were first defined on the surface of
peripheral blood leukocytes
• HLA Class I in humans is found on virtually all nucleated
cells and platelets
• HLA Class II (constitutive expression) is restricted to
specialized cells of the immune system (macrophages, B
cells, etc.)
• HLA genes are highly polymorphic
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HLA Protein Structure
• Class I is heterodimeric with a
polymorphic alpha chain and a
common beta-2 microglobulin
– Alpha chain is composed of 3
extra-cellular domains (α1, α2,
and α3)
– α1 and α2 form a groove like
structure with a floor of βpleated sheets and ridges of αhelices
– presents peptides derived from
internal cellular proteins to the T
cell receptor of CD8 T cells.
– involved in the immune response
against intra-cellular parasites,
viruses and cancer
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β2m
α2 α1
α3
plasma membrane
cytosol
Antigen Presenting Cell
plasma membrane
cytosolCD8 Tcell
TCR
CD8β2m
α2 α1
α3
plasma membrane
cytosol
Antigen Presenting Cell
plasma membrane
cytosolCD8 Tcell
TCR
CD8
A view down the
groove of an HLA-A2
molecule
HLA Class I Molecule
αααα1
domainαααα2
domain
Influenza M1
peptide
αααα3
domain
ββββ2
microglobulin
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HLA Protein Structure (con’t)
• Class II is also heterodimeric with
a polymorphic beta chain and a
much less polymorphic alpha
chain
– both chains are composed of 2
extra-cellular domains (α1, α2,
and β1, β2)
– Together the two first domains
create a peptide binding groove
which presents processed
peptides, from extra cellular
proteins, to CD4+ T cells
– involved in the immune response
against extra cellular infectious
agents and non-self HLA
molecules
7
β2
β1
α2
α1
plasma membrane
cytosol
Antigen Presenting Cell
plasma membrane
cytosolCD4 Tcell
TCR
CD4 β2
β1
α2
α1
plasma membrane
cytosol
Antigen Presenting Cell
plasma membrane
cytosolCD4 Tcell
TCR
CD4
αααα chain
ββββ chain
HLA-A2 peptide
A view down the
groove of an HLA-
DR1 molecule
HLA Class II Molecule
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HLA PolymorphismSerologic methods resolve only a small fraction of all known alleles (est. 3%)
Molecular techniques have emerged as the method of choice for HLA typing,
since strategies have been developed that resolve most/all known alleles and
provide a tool for identification of new alleles.
CLASS I CLASS II
3,107 A alleles 1,726 DRB1 alleles
3,887 B alleles 95 DRB3,B4,B5 alleles
2,623 C alleles 54 DQA1 alleles
780 DQB1 alleles
39 DPA1 alleles
520 DPB1 alleles
(status April 2015)
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HLA Polymorphism
http://hla.alleles.org
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HLA Polymorphism
HLA sequences and a current list of known HLA alleles are
found at the IMGT/HLA database:
http://www.ebi.ac.uk/ipd/imgt/hla/
The IMGT/HLA Database provides a specialist database for sequences of
the human major histocompatibility complex (HLA) and includes the
official sequences for the WHO Nomenclature Committee For Factors
of the HLA System.
The IMGT/HLA Database is part of the international ImMunoGeneTics
project (IMGT).
Robinson J, Halliwell JA, Hayhurst JH, Flicek P, Parham P, Marsh SGE
The IPD and IMGT/HLA database: allele variant databases
Nucleic Acids Research (2015) 43:D423-431
HLA Nomenclature
• Assignments are made under the auspices of World Health
Organization (WHO) Nomenclature committee
• Aim is to provide unique identification for:
– Loci
– Alleles
– Haplotypes
• Therefore the system must be very conservative but
adaptable to change
– Must not serve personal or national vanity
– Nomenclature should optimize not maximize the amount of
information in the code
12
HLA Nomenclature (con’t)
• Haplotype
– The combination of alleles from two or more loci located on the same
chromosome
– Does NOT imply any linkage disequilibrium
• Genotype
– The combination of two haplotypes; one from each parent, inherited
by an individual
• Linkage Disequilibrium
– Presence of two alleles that are inherited together more frequently
than would be expected based on the gene frequencies
13
HLA Nomenclature (con’t)• Each allele is initially identified by a letter(s) indicating “locus” A, B, C, DR,
DQ, and DP
• Then identified by individual specificity e.g. A1, B27, DR8, etc. (numbered
in order of discovery)
– Specificities were initially defined by using antisera (antibodies)
• Historically these were sera obtained from multiparous women
• Initially HLA Labs maintained large banks of specific sera
– Patient cells were mixed with various sera, incubated and then Complement
and a vital dye were added.
• If a cell had the corresponding antigen, then the antibody would bind,
complement fixed and cell death ensued.
• Most sera were “cross reactive” such that a technologist had to interpret
results, e.g.,: One well had antibody reactive with A23, A24 (Pos); but
another well with anti-A2, A23 might be negative; thus suggesting a
patient typing of A24
14
HLA Nomenclature (con’t)• HLA specificities can also be determined by genetic analysis
by identifying the presence/absence of the gene encoding the
HLA protein.
• Techniques include direct DNA sequencing, PCR using
Sequence Specific Primers (SSP) and PCR using sequence
specific oligonucleotide probes (SSO)
– Technique specifics will be discussed later
• Again the initial identification is the locus letter(s): A, B, C, etc.
– To differentiate from serological identification we use an asterisk (*)
and a place marker, such as: A*01, B*27, etc.
15
HLA Nomenclature (con’t)
• Class II molecular specificities are identified at the level of the
gene encoding a particular chain, that is alpha or beta. But
remember most of the polymorphism for Class II is in the beta
chain thus common identification reflects that: DRB1*01,
DQB1*02, etc.
• The molecular two digit specificity is referred to as “Low
Resolution” typing e.g., A*01, B*27, etc.
• “High Resolution” typing are sub-specificities of the main
group e.g., A*01:01, A*01:02, B*27:01, B*27:100
– Each representing a change in at least one AA
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HLA Nomenclature (con’t)
Expanded Allele Nomenclature:
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LOCUS
Molecular Typing
Antigen Level or Allele Family
Allele Level
“Subtype”
Synonymous “Non-
Coding” Substitutions
Suffix to
denote
changes in Expression
eg N=Null
HLA-DRB4*01 03 01 02N: ::
Intron
Substitutions
Colon
Delimiters
“MHC”
http://hla.alleles.org/nomenclature/naming.html
HLA Nomenclature (con’t)
• Quiz Question - What does the “--” (Blank) in the following typing indicate?
A*01, --; B*08, --; DRB1*03, DRB1*15
• Most molecular and certainly all serological typing can NOT distinguish between a single versus a double presence of any particular allele
• Given that both A*01 and B*08 are common in the N. Amer. population it is highly likely that the “real” typing is as follows:
A*01, A*01; B*08, B*08; DRB1*03, DRB1*15
• Another but much, much less likely possibility is that the individual is carrying an allele that can not be detected by the specific molecular technique employed
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HLA Nomenclature (con’t)
PROBLEM:
• Many registry donors have been tested by serological
methods
– The vast majority of these do not have good documentation of which
antigens were tested for and which were not
• The majority of HPC transplant candidates have been tested
by molecular (DNA-based) methodologies
• The nomenclature of antigens (serology) and alleles (DNA) is
in some cases NOT concordant
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HLA Nomenclature (con’t)
• Quiz Question – Is this Donor/Recipient pair a good match from an HLA perspective?
Donor: A19, A10; B12, B62; DR5, DR2
Recipient: A*29, A*26; B*44, B*15; DRB1*11, DRB1*15
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• Answer: Maybe but possibly yes– A19 (serological) was split: A*29, *30, *31, *32, *33, *74
– A10 (serological) was split: A*25, *26, *34, *66
– B12 (serological) was split: B*44, *45
– All the others are also splits although the molecular B*15 includes
the very different serological specificities B62, 63, 70, 71, 72, 75, 76
and 77
DRB Haplotype Variations
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Almost always inherited as a predictable haplotype
DRB1
DRB1
DRB1
DRB1
DRB1 DRB6
DRB6
DRB6
DRB6
DRB2
DRB7
DRB3 (52)
DRB8 DRB4 (53)
DRB5 (51)
DRB9
DRB9
DRB9
DRB9
DRB9
DQB1DQA1DPB1DPA1 DRA
DR1, DR10
DR15,16, 51
DR11, 12, 13, 14, 3
(17,18), 52
DR4, 7*, 9, 53
DR8
Pseudo-genes
Expressed Genes
*about 1/3 of DR7
haplotypes lack an expressed
DRB4 (DR53) gene
How do we do HLA typing?
22
Historically, HLA typing has been done at the
protein level, microlymphocytoxicity test being the
standard method.
HLA typing at the DNA level has become the
method of choice for clinical laboratories. DNA
methods are more robust and reproducible and
provide more information.
5’UTR E1 E2 E3 E4 E5 E6 E7 E8 3’UTR
PCR
Hybridization with set of
oligonucleotide probes
corresponding to the
polymorphic sites
Sequencing
SSO SBTSSPSequence
Specific
PCR amplification
Genomic DNA: HLA-A, B or C locus
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PCR Amplification
The majority of molecular assays for HLA typing
require the amplification of the target sequence of
DNA via Polymerase Chain Reaction, or PCR. A
sample of the patient’s DNA, called the template, is
allowed to react with specific primers. The primers
bind to the template DNA just upstream of the
sequence of DNA that is intended for amplification.
PCR AmplificationLet’s say the DNA sequence below is located on the
Major Histocompatibility Complex on the short arm
of chromosome 6, at exon 2 of the –DRB1 gene. The
region we want to amplify is the sequence
‘GTTTAACGGCAT’. The primer would bind
immediately upstream of the target sequence.
Template DNA
3’ 5’
Target sequence
C A T G G C G T T T A A C G G C A T A C A G G G A C
PCR Amplification
3’ 5’
Template DNA
A DNA polymerase enzyme (most frequently Taq),
recognizes the primer bound to the template, and
begins to add nucleotides to the 3’ end. When it
reaches the end of the template, it adds a final
adenine to complete the reaction.
G T A C C G
Primer5’ 3’
C A A A T T G C C G T A T G T C C C T G A
Target sequence
Taq
C A T G G C G T T T A A C G G C A T A C A G G G A C
There are three major steps to PCR amplification. Once the
required buffers, templates, nucleotides, polymerase, and primers
have been added to a reaction tube, the temperature is raised to
about 94 degrees Celsius to denature the double stranded DNA.
This step is called ‘melting’.
Template DNA
Note: The template DNA shown above has been inverted. The 5’
– 3’ strand is on the bottom, and the 3’ – 5’ strand is on top.
PCR Amplification
27
Template DNA
Next, the temperature is reduced to 50-60 degrees to allow the bind-ing of the primers to the template DNA. Two primers are needed for amplification. One binds upstream to the target sequence on the sense strand of the template, and one binds upstream to the target sequence on the antisense strand. This step is called ‘annealing’.
After enough time to allow for the binding of the primers (roughly 30 seconds), the temperature is raised to 72 degrees to allow the DNA polymerase to extend the primer in the step called ‘extension’.
PCR Amplification
After extension, the temperature is ramped up once again to about 94 degrees, and melting occurs again.
28
The temperature is again reduced to 50-60 degrees to allow new
primers to anneal to both the original template DNA, and the newly
created DNA strands from the previous PCR cycle.
This is followed by another round of extension.
PCR Amplification
29
The third cycle of melting, annealing, and extension produces the “short product”, a
length of double stranded DNA that is the exact length of the target sequence
bordered by a primer on each side. With each subsequent cycle, the short product is
doubled.
Short Products
After 25 to 35 cycles are completed a single DNA template may generate over a billion
target DNA short products. It is these products that are utilized in molecular assays for
HLA typing.
PCR Amplification
30
HLA Typing using SSO(SSO = Sequence specific oligonucleotides)
• Using PCR and generic primers amplify large amounts of
virtually all alleles (versions) of, for e.g., HLA-A
• Then using heat to again separate the dsDNA into single
strands (ss)
31
• Allow these to interact with ss specific oligo-
nucleotide probes bound to a solid matrix
(microarray Beads)
• Based on the pattern of which probes were bound
deduce the HLA type of the specimen
PCR-SSO / Microarray Beads
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1. PCR amplification 2. Denaturation
4. Labeling / Detection3. Hybridization
HLA Typing using SSO
Interpretation
is based on
both negative
and positive
beads when
compared
against a panel
of control
beads
33
SSP: Sequence Specific Primers
• As suggested by the name, SSP, does NOT use
generic primers but rather “Sequence Specific
Primers”
• Therefore the only DNA that is amplified is that
which matches the primers
– However this technique is quite labor-intensive and
unlike SSO can not be used in a “batch” mode i.e.,
only one sample at a time
34
DNA SSP Gel Electrophoresis
35
None +
36
Based on well position of positive reactions
on the SSP gel, the type can be assigned
Sequence Based Typing
• Both alleles (one from each copy of chromo-some 6) are sequenced simultaneously
• Ambiguities arise when particular allele combinations are present due to sequences in common across multiple alleles. These cis/trans ambiguities can be resolved.
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Sequence Based Typing
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Polymorphism: Two different nucleotides at the same position
on the individual’s two different chromosomes
39
Polymorphisms
• R = A + G
• M = A + C
• W = A + T
• S = G + C
• K = G + T
• Y = C + T
Nucleotide Base Codes
A = Adenine
G = Guanine
C = Cytosine
T = Thymine
40
The MHC in Transplant
• Allogeneic cellular response
• Alloantibody response
• Long-term graft survival correlated to degree of HLA antigen mismatch for both solid organ and BMT
• Antigens consist of epitopes (T cell or B cell) that can trigger a cellular or humoral response
41
41
HLA-A+B+DR Mismatches
Deceased Donor, First Kidney Tx, 2000-2011
CTS Collaborative Transplant Study
42
Opelz G. Transplantation 2013; 95:4-7
Even a single nucleotide/amino acid
change can be immunogenic
43
43
44
HLA Matching & Immunogenicity
• T cell immunogenicity: A nascent science and almost non-
existent with regard to HLA antigens
– Likely to be the most important aspect of HLA immunogenicity in
BMTx
• Current knowledge is driven by vaccine development
– While T cell repertoire is important, most work is looking at HLA Class I
and II supertypes
– HLA is extremely polymorphic (concentrated in the peptide binding
region) with each variant believed to be capable of binding a unique
set of peptide ligands
– BUT most HLA molecules are clustered into groups (Supertypes - 12)
with overlapping peptide binding specificities
44
45
HLA Matching & Immunogenicity
• With all of the above it becomes almost impossible for a
transplant program to determine the best mismatch (from a
group of MM donors)
• Currently the best we can do is:
– List the number and kind of aa MM between various alleles
(within a single antigen group – See http://histocheck.org)
or
– Use known/suspected serological epitopes as an
approximation of T cell epitopes
• An important advancement in this area came with Dr. Rene Duquesnoy’s
MatchMaker program (www.hlamatchmaker.net)
• This program tallies the number of likely epitope (eplets - B cell)
differences between different antigens and alleles
45
46
Patient is A*02:07
No exact match but …
A*02:07 vs A*02:01
One aa difference
Total Dissimilarity: 1.83
A*02:07 vs A*02:03
Four aa difference
Total Dissimilarity: 5.81
46
http://www.mh-hannover.de/institute/transfusion/histocheck/
Knowing Structure of MHC
• Allows re-examination of the nature of the
allo-immune response
• Not an antigenic response
• But an epitope response
• If you cannot match antigens… can you match
epitopes?
47
47
HLA Matchmaker Concept
The HLA type of the antibody producer
determines what structural
components of an immunizing HLA
antigen can be “seen” as
non-self
48
Structural Basis of a HLA-B51 Mismatch
Polymorphic
Residues on B51
49
“Seen” by
A2, A68;
B27, B44
“Seen” by
A2, A68;
B35, B44
“Seen” by
A2, A24;
B7, B8
HLA Matchmaker Concept
Matching at the Epitope Level Provides
an Additional Assessment of HLA
Compatibility
50
PRA- Panel Reactive Antibody
- Percent Reactive Antibody
• PRA can be a qualitative and/or quantitative assessment of allo-immunization in transplant patients. PRA only reflects the breadth of the response. Optimally, PRA testing should identify the specificity of an antibody and provide the “transplantability” of a patient.
• More importantly, PRA testing should correlate with (i.e:, Predict) the final crossmatch.
51
Bead Based PRA
• Antibodies to HLA (actual not putative as in cell-based assay) are
detected by a panel of beads each with its own fluorometric
signature
• Commercially available beads with bound HLA molecules from
more than 50 different cell lines covering the range of typical N.
American donors
• Antibodies are detected using fluorescent labeled second
antibody
• Can now perform the equivalent of a 50 cell PRA for any
individual within one week
• Software can also assist in identifying antibody specificities
52
PRA – Bead Based
53
Sample Number: 08-151553 Session Number: 2008-02-29-I-ID
%PRA: 34 Lot ID: 111507-LMI
Draw Date: 2/26/2008 Expiration Date: 11/7/2008
Patient HLA Type: A26,30; B13,38 Negative Controls: 128, 95, 229.5, 142
Reviewer: ______________ Positive Control: 13558.5
Bead DonorID AdjVal1 AdjVal2 AdjVal3 AdjValC Assigned Raw Val Class I Antigens
148 432 45.82 60.22 23.17 33.02 Positive 6182 A2 A36 B7 B72 Bw6 Cw2 Cw7
142 372 43.26 57.06 21.79 30.69 Positive 5900 A2 A23 B35 B61 Bw6 Cw15 Cw4
154 633 42.52 55.66 21.06 29.74 Positive 5824 A2 A23 B63 B65 Bw4 Bw6 Cw16 Cw8
139 404 41.87 54.6 20.32 29.02 Positive 5778 A2 A24 B51 B52 Bw4 Cw1 Cw12
144 215 40.51 52.75 19.51 27.52 Positive 5586 A2 A3 B50 B57 Bw4 Bw6 Cw18 Cw6
161 587 37.54 49 18.37 25.92 Positive 5159 A68 A74 B42 B57 Bw4 Bw6 Cw17 Cw7
113 2BW 36.56 47.87 17.95 25.58 Positive 4998 A2 A3 B13 B56 Bw4 Bw6 Cw1 Cw6
166 850 35.22 45.88 16.7 24.03 Positive 4895 A2 A24 B27 B44 Bw4 Cw1 Cw5
136 44DFW 34.41 45 16.53 23.75 Positive 4776 A2 A25 B44 B47 Bw4 Cw16 Cw6
152 258 32.43 42.41 15.6 22.26 Positive 4519 A11 A68 B18 B38 Bw4 Bw6 Cw4 Cw6
157 765 31.98 41.64 15.36 21.7 Positive 4452 A24 A68 B39 B55 Bw6 Cw3 Cw7
155 79LB 31.08 40.44 14.84 21.2 Positive 4300 A2 A33 B49 B71 Bw4 Bw6 Cw3 Cw7
147 247 19.94 25.16 8.62 12.41 Positive 2896 A1 A69 B35 B8 Bw6 Cw12 Cw7
133 17LB 13.32 16.25 4.41 6.51 Positive 2087 A1 A6602 B52 B58 Bw4 Cw12 Cw7
162 480 3.66 3.61 -0.34 -0.46 Positive 819 A29 A3 B58 B7 Bw4 Bw6 Cw7
138 60LB 1.82 0.97 -1.74 -2.41 Positive 589 A33 B49 B58 Bw4 Cw7
129 397 1.31 0.48 -1.4 -2.22 Positive 506 A3 A34 B57 B71 Bw4 Bw6 Cw3 Cw7
128 103 -0.17 -2.44 -3.29 -4.59 Negative 376 A24 A29 B37 B7 Bw4 Bw6 Cw6 Cw7
149 416 -0.27 -1.74 -2.37 -3.92 Negative 332 A29 A33 B78 B81 Bw6 Cw16 Cw18
124 531 0.24 -1.2 -2.11 -2.76 Negative 320 A34 A80 B18 B53 Bw4 Bw6 Cw2 Cw6
114 109 -0.7 -2.77 -3.47 -4.57 Negative 303 A31 A33 B35 B46 Bw6 Cw1 Cw4
165 206 -0.82 -2.29 -2.9 -3.95 Negative 285 A3 A74 B45 B8 Bw6 Cw16 Cw7
PRA can be calculated automatically
Antibody identification is interpreted from the results
34%
Class I:
100% PRA
Specificity???
54
Single Antigen Bead Assay
Specificity:
A2,68,69
B8,13,15,18,35,37,39,40,41,42,44,45,47,51,52,53,54,58,
78,81,82
Include?:
B27,48,49,50,55, 57
How to Report
Allele Specific Antibodies?
55
Calculated PRA (cPRA)
• With Single Antigen Bead Testing we can identify the
antibodies a patient has, but we can no longer have a
measured PRA
• However if PRA is “Percent Reactive Antibody” with a panel
of cells (or beads) representative of the donor population to
give a measure of “transplantability” then:
• Knowing both the antibodies in a patient and the HLA typing
of actual donors locally, regionally, or even nationally then
we can Calculate the PRA by asking how many of these
previous donors would this patient have had antibodies to?
i.e. Calculated PRA
56
cPRA calculator
http://optn.transplant.hrsa.gov/resources/allocationcalculators.asp
Antigenic Structure of HLA
• Serologically defined epitopes that were originally thought to
occur on only one gene product such as HLA-A2 were
referred to as “Private Epitopes”
• Other anti-HLA antibodies that reacted with more than one
gene product, e.g., anti-HLA A2, A9, and A28, were thought
to detect a shared or cross reactive epitope, termed “Public
Epitope”
• Antibodies to public epitopes have been used to categorize
HLA molecules into major Cross Reactive Groups (CREG’s)
– Each CREG can contain more than one Public Epitope
57
Same Donor - Different Patients
2C CREG = A2; A9 (23, 24); A28 (68, 69); B17 (57, 58)
58
Immunizer Patient Antibody
A2, 2; B27, 27 A24, 28; B27, 57 A2
A1, 24; B27, 57 A2
A2, 28
A1, 3; B27, 51 A2
A2, 28
A2, 28, 24
A2, B57
“New” Issues in Antibody Nomenclature
• Reminder: Class II HLA antigens are comprised of
two different polypeptides – the alpha and beta
chains – each coded for by different polymorphic
genes
• Anti-HLA antibodies were thought to have been
directed to the more polymorphic beta chain were
named accordingly
• Thus anti-DQ2 antibodies are reactive with antigens
containing DQB1*02 proteins
59
“New” Issues in Antibody Nomenclature
(continued)
• BUT some antibodies are highly specific for the alpha chain
• So for example: Patient is:
DQB1*02:01 with DQA1*02:01
while the donor is:
DQB1*02:01 with DQA1*05:01
• And the patient has “anti-DQ2” antibodies but which are
reactive exclusively with the alpha “05:01”
• There is NO STANDARD Nomenclature with which to identify
such antibodies!
60
HLA Testing for other Clinical Purposes
• Disease Risk Assessment
• Pharmacogenomics
• Immunotherapy
• Infectious Disease Vaccines
• Tumor Vaccines
61
HLA Association with Disease Risk
Certain diseases have a strong association with certain HLA types. Examples include:
• HLA-B27: Ankylosing Spondylitis and Acute Anterior Uveitis
• HLA-A29: Birdshot Retinopathy• HLA-B51: Behçet's Disease• HLA-Cw6: Psoriasis• HLA-DQ2,8: Celiac Disease• HLA-DR15,DQ6: Narcolepsy• HLA-DR3,4-DQ2,8: Diabetes• HLA-DR4: Rheumatoid Arthritis
62
HLA Association with Narcolepsy
• Our knowledge evolving over the years:
• HLA-DR2-DQ1
• HLA-DR15-DQ6
• HLA-DRB1*15:01-DQB1*06:02
• HLA-DQA1*01:02-DQB1*06:02
63
HLA Association with Celiac Disease
Our knowledge evolving over the years:
• HLA-A1
• HLA-A1/B8/DR3
• HLA-DR3/DQ2
• HLA-DQ2 and DQ8
64
HLA Association with Celiac Disease
• Association with: HLA-DQ2 and HLA-DQ8
usually with the “DQ2 cis” heterodimer:
DQA1*05, DQB1*02 coded on a DRB1*03:01 (DR17) haplotype
but can be “trans”:
DQA1*05 coded on a DRB1*11, DRB1*12 or DRB1*13 haplotype
and the DQB1*02 coded on a DRB1*07 haplotype
• The risk with DQ8 haplotype is usually:
DQA1*03 with DQB1*03:02 coded on a DR4 haplotype
65
HLA and Pharmacogenetics
• Severe allergic or hypersensitivity reaction to drugs– Stevens-Johnson Syndrome (SJS)– Toxic Epidermal Necrolysis (TEN)
• Association between allergy or hypersensitivity to a medication and HLA type
• HLA typing allows risk stratification of the patients
66
Drugs Associated with
Hypersensitivity Reactions
• Antiepileptic agents: Carbamazepine, Phenytoin, Phenobarbital, Lamotrigine
• Allopurinol
• Nevirapine
• Anti-inflammatories in oxicam family
• Sulfonamides
67
HLA and Drug Adverse Reactions
• HLA-B*57:01 hypersensitivity to Abacavir
• HLA-B*15:02 carbamazepine induced SJS or TEN
• HLA-B*58:01 allopurinol induced SJS or TEN
• HLA-DRB1*01 hypersensitivity to nevirapine
• HLA-DRB1*07 ximelagatran induced hepatotoxicity
68
HLA and Vaccine Development
• Vaccines producing cellular immunity require
peptide HLA binding
• Cancer cells can express “tumor specific antigens”
• Infectious disease agents have immunogenic
peptides
• Vaccine trials use peptides binding to common HLA
alleles (e.g., A*02:01)
• After proof of principal, trials include peptides
binding to other HLA alleles
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Review and Conclusions
• MHC = Major Histocompatibility Complex which in humans is called the “human leukocyte antigens”
• Class I: A, B, and C; Class II: DR, DQ, and DP– Highly polymorphic and co-dominantly expressed
• Nomenclature: letter designating the locus and a number designating specificity– Low resolution: one field; High resolution: two or more
fields separated by colons– Differences in serological vs molecular designations
• Typing can be done serologically or molecularly• Antibody Identification is critical in the proper interpretation
of PRA• HLA typing to help diagnosis of certain diseases• HLA typing to help prevent adverse drug reactions
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