Transcript frans08efi - HLA Matchmaker

Acceptable mismatches based on structural
epitopes on HLA molecules
Toulouse, April 2, 2008
Highly sensitized patients
• Highly sensitized patients: antibodies against the HLA
antigens of more than 85% of the panel.
• Difficult to transplant because cross-match with most
donors is positive.
• Obvious solution: HLA identical or compatible donor but
only available for a small proportion of the patients.
How to find a suitable donor for these patients?
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Approaches to enhance transplantation of highly sensitized patients
• Do not accept that the patient is sensitized and try
to remove the antibodies by:
* plasmapheresis
* intravenous immunoglobulins (IVIg)
* anti-CD20 antibodies
• Accept that the patient is sensitized and try to
stimulate the allocation of cross-match negative donor
kidneys to these patients.
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Eurotransplant Kidney Allocation System.
Point system based on different parameters:
• HLA match
• Match prognostic index (extra points for sensitized patients)
• Waiting time
• Regional donor (cold ischemia time)
• Country balance.
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Still a low chance for a higly sensitized patient to be transplanted.
% patients transplanted
100
90
80
70
60
50
40
30
20
10
0
ET-KAS
0
3
6
9
12
15
Waiting time (months)
18
21
24
Need for an acceptable mismatch program
• Policy in Eurotransplant is the registration of the nonacceptable HLA mismatches for sensitized patients to
prevent selection of donors with HLA mismatches
towards which the patient has preformed antibodies.
• Problem: it is impossible to determine all antibody
specificities in highly sensitized patients
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Acceptable Mismatch Program
• Basis: definition of those HLA antigens toward which the
patient did never form antibodies and use this knowledge
for donor selection.
• Original method: look at HLA type of negative panel
donors in screening and extensive antibody screening
against a patient specific panel (donors with a single HLA-A
or –B mismatch), taking advantage of a pool of 20,000 HLA
typed blood donors.
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Antibody screening
• Serum of patient (HLA: A1, A2, B7, B8) is tested against a panel of
HLA typed blood donors.
positive
negative
PRA is 92%
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Antibody screening
• Serum of patient (HLA: A1, A2, B7, B8) is tested against a panel of
HLA typed blood donors.
positive
negative
PRA is 92%
HLA type: A1, A24, B7, B8
acceptable mismatch is A24
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Non-inherited maternal HLA antigens are often
acceptable mismatches.
Analysis of sera from highly
sensitized patients
NIMA
NIPA
Antibodies
46
72
A.M
43
6
P< 0.001
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Very difficult patients
• AM are difficult to determine for highly immunized
patients with rare HLA phenotypes.
• For these patients no suitable blood donors are available
to determine acceptable mismatches or cross-matches
with the few available donors are positive.
• Main problem: most target cells express several
mismatched HLA antigens.
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Difficult to identify acceptable mismatches
A2
B8
Cw6
A1
B7
Cw3
Is HLA-A2 an acceptable mismatch?
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SAL: Single antigen expressing cell line
A2
A2
A2
A2
A2
A2
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SALs validated and shown to be useful for determination of
acceptable mismatches.
HLA-A
HLA-B
HLA-C
A*0101
B*0702
B*4403
Cw*0102
A*0201
B*1402
B*4501
Cw*0303
A*0301
B* 1501
B*4601
Cw*0304
A*1101
B*2705
B*4901
Cw*0401
A*2402
B*3501
B*5501
Cw*0602
A*2601
B*3801
Cw*0801
A*3101
B*3901
Cw*1202
A*3201
B*4001
Cw*1402
A*3303
B*4002
Cw*1502
A*6901
B*4402
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Alternative approach
• Commercial assays including the use of single antigen beads
(Luminex) although the conformation of these molecules may be
different than that of membrane bound HLA molecules.
HLA-A1
HLA-A2
HLA-A3
HLA-B7
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Definition of acceptable mismatches is difficult and is often based on
trial and error because our interpretation of the humoral immune
response to HLA is too simple.
anti-HLA-A2
HLA-A1
HLA-A2
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Many polymorphic sites, some of them shared between HLA alleles.
HLA-A2
HLA-B35
HLA-A68
HLA-B51
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HLA-B27
HLA-B44
Structural Immunogenicity of HLA-B51
Polymorphic
Residues on B51
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Structural Immunogenicity of HLA-B51
Polymorphic
Residues on B51
This polymorphism should be
considered in the context of self HLA
epitopes of the antibody producer
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Structural Immunogenicity of HLA-B51
Polymorphic
Residues on B51
For
A2,A68;
B27,B44
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Structural Immunogenicity of HLA-B51
Polymorphic
Residues on B51
For
A2,A68;
B27,B44
For
A2,A68;
B35,B44
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Structural Immunogenicity of HLA-B51
Polymorphic
Residues on B51
For
A2,A68;
B27,B44
For
A2,A68;
B35,B44
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For
A2,A24;
B7,B8
HLAMatchmaker is based on this principle
a computer algorithm developed by René Duquesnoy
Donor HLA-A,B mismatches are defined by
triplets of amino acid residues (epitopes) on antibody
accessible sites of HLA molecules
HLA-A1
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HLA matching at the triplet level
Donor m.m
B18
Patient:
B7
Immune system of the recipient recognizes:
A single HLA mismatch or 11 triplet mismatches
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HLA matching at the triplet level
Donor m.m
B18
Patient:
B7
B52
A33
.
Immune system of the recipient recognizes:
No triplet mismatches!
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No foreign antibody epitopes on HLA-B18 mismatch
for patient, with HLA type HLA-A33, B51, B7.
a1
a1
a2
peptide
b2M
a2
a3
Top view
Side view
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The number of triplet mismatches predicts HLA
antibody production after renal allograft rejection
% of patients with donor specific
HLA antibodies
100
90
80
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
triplet mismatches
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8
9
10 11 12
Dankers et al. 2005
Validation of HLA matchmaker for the identification of
acceptable mismatches in highly sensitized patients.
Mismatch
zero-triplet
HLA-A
HLA-B
tested
AM
tested
AM
18
18
54
54
CDC cross-matches confirm theoretical approach
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Additional value of HLAMatchmaker
Also HLA antigens with triplet differences can be identified as
acceptable mismatches. This information can be used for
identification of additional acceptable mismatches.
A1
A2
B7
B8
Self-triplet mismatches on basis of own HLA type
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Additional value of HLAMatchmaker
Also HLA antigens with triplet differences can be identified as
acceptable mismatches. This information can be used for
identification of additional acceptable mismatches.
A1
A2
B7
B8
AM: A3
AM: B14
More self-triplet mismatches on basis of combination of
acceptable mismatches and own HLA type:
Consequence: more acceptable mismatches can be found
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Donor selection on basis of acceptable mismatches.
Patient: A24, A31, B27, B51, DR4 (highly sensitized)
AM:
Suitable donors:
A25, A26, B44
A25, A31; B27, B51; DR4
A26, A31; B27, B51; DR4
A24, A25; B27, B51; DR4
A24, A26; B27, B51; DR4
A24, A31; B44, B51; DR4
A24, A31; B27, B44; DR4
A25, A31; B44, B51; DR4
A26, A31; B44, B51; DR4
A25, A31; B27, B44; DR4
A26, A31; B27, B44; DR4
A24, A25; B44, B51; DR4
A24, A26; B44, B51; DR4
etc.
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If such donor becomes
available within
Eurotransplant: mandatory
shipment of the kidney to
this highly sensitized patient
Conclusions:
HLAMatchmaker is of benefit for the identification of acceptable
mismatches for highly sensitized patients.
• Increased chance to be transplanted:
100
90
80
70
60
50
40
30
20
10
0
% patients transplanted
AM
ET-KAS
0
3
6
9
12
15
18
21
24
• Excellent graft survival:
100
90
80
70
AM
<5% PRA
5-85% PRA
>85% PRA
60
50
0
32
6
12
18
24
Acknowledgements
Marian Witvliet
Ilias Doxiadis
Arend Mulder
Jon van Rood
Guido Persijn
Marlies Dankers
René Duquesnoy
and the Eurotransplant community.
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